Biol 214 Exam 4

Front 1

epistasis

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many genes produce products that interact with other gene products or DNA itself

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polygenic

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multiple loci can determine a single phenotype

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Pleitropy

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when one gene influences multiple phenotypic traits

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Haplotype

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haploid genotype, multilocus genotype of a chromosome or gamete (gametic phase)

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Linkage disequilibrium

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the non-random association of alleles at two or more loci, not necessarily on the same chromosome. It is not the same as linkage, which describes the association of two or more loci on a chromosome with limited recombination between them

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Recombination

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the process by which a strand of genetic material is broken and then joined to another DNA molecule. This may happen during meiosis of a diploid organism that sexually reproduces or may be something like conjugation in bacteria where there is an exchange of DNA between two haploid individuals

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Homologous recombination

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a type of genetic recombination in which nucleotide sequences are exchanged between two similar or identical strands of DNA

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recombination rate=

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proportion of gametes that are recombinant. ranges from 0 to 0.5

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if on different chromosomes, then recombination rate is going to be

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0.5 (Mendel's 2nd Law)

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given an allele frequency of p at locus A in the population, that allele will have a frequency of ____ for any given allele at locus B

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p

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when in linkage equilibrium, the frequency of any haplotype can be calculated by

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multiplying frequencies of the constituent alleles

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when in linkage equilibrium D =

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0

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D=

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fAB*fab - fAb*faB

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when in population LD

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fAb does not equal ps, etc.

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What causes LD

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selection, mutation, population admixture (gene flow), aka hybridization

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what does NOT cause LD

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physical linkage (no matter how close)
Inbreeding
(these only slow the rate of decay of LD)

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reason that Genetic Drift more powerful for changing gamete frequencies relative to changing allele frequencies at a given locus

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as more loci are considered, the more unique haplotypes there will be. Thus, the frequency of any given haplotype will be rare. the rarer it is, the more subject it is to sampling error.

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Decline in LD due to Recombination D'=

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D'=D(1-r)
r= recombination rate (0-0.5)

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rate of decline in LD between a pair of loci is proportional to

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recombination rate between the two loci

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Linkage equilibrium is _____ after a single round of random mating even under free recombination

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not restored

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Under LD, if selection for one allele at one locus,

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it will drive an increase of another allele at another locus thats not being selected for

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In a population in linkage equilibrium, selection in favor of allele A effect on allele B?

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no effect on frequency of allele B.

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selection drives advantageous allele to higher frequency before

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recombination can break up associations (selective sweep; also reduces surrounding genetic diversity)

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costly to use sex as a mode of reproduction

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-energy demanding
-may need to find a mate if dioecious
-Lose 50% of genetic material every generation

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Muller's ratchet

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Asexual populations accumulate deleterious mutations

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genetic load

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burden imposed by accumulation of mildly deleterious alleles

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Quantitative genetics

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a field of evolutionary biology that examines the evolution of continuously variable traits that are influenced by the combined effects of genotype at >1 locus and the environment

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Quantitative traits

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characters with continuously distributed phenotypes (e.g., height, beak depth in finches)

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Edward East (1916)

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experiments with longflower tobacco. these planets do not have discrete phenotype for corolla length- it is continuous.

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Edward East 2 predictions

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1. unless measure many, many offspring in F2 do not expect to find parental phenotypes because frequency of that genotype is very low.
2. However, all alleles are still present from parents, so should be able to artificially select for parental phenotype (over multiple generations) out of F2 generation

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Quantitative traits are influenced by

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the environment as well as genotype

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Heritability

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fraction of the total phenotypic variation in a trait that is due to variation in genes

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phenotypic variation

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(Vp)= variation due to genetics (Vg) and to environment (Ve)
Vp=Vg+Ve

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Broad sense Heritability

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Vg/Vp = Vg / (Vg+Ve)

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Genetic Variation

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(Vg) = variation due to additive genetics (Va) and dominance (Vd)
Vg=Va+Vd

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Narrow Sense Heritability

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(h^2) = Va/Vp = Va / (Va+Vd+Ve)

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Heritability is a value between

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0 and 1

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The heritability estimate is specific to

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the population, generation, and environment you are analyzing

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The heritability estimate is a ____, not a _____ parameter

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population, not an individual parameter

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Heritability does not indicate the degree to which a trait is genetic, it

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measures the proportion of the phenotypic variance that is the result of genetic factors

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Heritability tells us nothing about

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the role of genes in determining traits (e.g., heritability of nose number is undefined Va/Vp = 0/0) obviously genes are important in determining how many noses we have

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Why do we measure heritability

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it allows us to predict whether selection on a trait will cause a population to evolve

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High heritability within populations tells us nothing about

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the cause of differences between populations! **

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The plants in the Stanford population are taller, on average, than the plants in the Mather population. Does this mean that the Stanford population is genetically superior to the Mather population?

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No: these populations are genetically identical because were grown from cuttings of the same seven plants

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What does heritability tell us about the origin of differences? or if one population is "better" than another?

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Nothing!

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There are differences in the way plants respond to

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environment

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adaptation is relative to

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the environment you are in

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parent offspring regression measures

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h^2 (slope of regression)

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why might offspring look like parent, besides genetics?

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maternal effect, environment

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common environment can

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confound analysis

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Selection differential

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(S) difference between trait mens of breeders (t*) and trait mean of entire population (t)

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Selection Gradient

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(β) is slope of relative fitness to trait value

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each mouse's standardized fitness =

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absolute fitness/mean

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β =

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S/var(t)

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breeder's equation

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R= h^2 x S

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The response to selection (R) is

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just the difference between the mean of the parents before selection and the mean of the offspring

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Why is the bee population in the tundra larger than the timberline population

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there are other pollinators besides bees in the timberline area. Hypothesis- bees are selecting for larger flowers.

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lower heritability=

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less change from selection

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Directional selection

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Changes average value of trait (increases or decreases)
Variance gets a little smaller

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Stabilizing selection

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average value of trait does not change
Variance gets smaller

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Stabilizing selection on a gall marking fly

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wasps kill fly larvae inside small galls faster; birds kill fly larvae inside large galls faster = Fly larvae inside medium-sized galls survived at the highest rates

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Disruptive Selection

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Average value of trait does not change
Variance gets larger

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disruptive selection on bill size in the black-bellied seedcracker

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survivors were those individuals with bills that were either relatively large or relatively small

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Kin Selection

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the "actor" in any social interaction affects the recipient of the action as well as itself. The costs and benefits of interactions are measured in units of surviving offspring

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Recipient and Actor benefits

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Cooperative

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Recipient benefits/actor harmed

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Altruistic (hard for this gene to persist in population)

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Recipient harmed/actor benefits

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Selfish

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recipient harmed/actor harmed

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spiteful

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Coefficients of relatedness (r)

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probability that the homologous alleles in two individuals are identical by descent

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Hamilton's rule

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an allele for altruistic behavior will spread if Br-C>0

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r

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relatedness between actor and recipient

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B

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benefit to recipient, measured in units of surviving offspring

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C

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cost to the actor, measured in units of surviving offspring

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Altruism will spread if

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benefits to recipient great, cost to actor are low, and both are closely related

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Inclusive fitness

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direct fitness (own reproduction) + indirect fitness (reproduction from relatives)

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Bcause the actor is benefiting via inclusive fitness

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maybe should not call altruism

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What is an adaptation

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A trait (or group of traits) that increases the fitness of its possessor, relative to those without the trait

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A trait is an adaptation for some function if...

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it has become prevalent or is maintained in a population because of selection for that function

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a major goal in evolutionary biology is to demonstrate

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"adaptive significance" of traits

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How do you test if a trait is adaptive? (not easy)

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-Demonstrate the function of the trait
-Demonstrate that the trait is linked to fitness
However, there are several means to test for evidence of selection on traits

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Association between oxpeckers and large mammals

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An example of mutualism, which evolved through coadaptation

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Oxpeckers were observed

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picking at open wounds, eating cows' ear wax and eating dead skin cells, but rarely eating cow ectoparasites
-Cows were observed trying to avoid the birds one to two times per minute

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What was found when oxpeckers were taken away

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-wounds on cattle heal more slowly when birds are present
-Cattle exposed to birds have considerably less earwax
-Is the presence of oxpeckers really adaptive for cattle?

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Not everything that "looks" like an adaptation actually is an adaptation

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1. a trait may be a necessary consequence of physics or chemistry
2. The trait may have evolved by random genetic drift rather than by natural selection
3. The feature may have evolved not because it conferred an adaptive advantage, but because it was correlated with a trait that did.
4. The character state may be a consequence of phylogenetic history

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A trait may not be...

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an adaptation! ***

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Methods for Recognizing Adaptations: Experiments

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An experiment can be used to show that a feature enhances survival, reproductive success, or some aspect of performance that we might expect to be related to fitness

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Methods for Recognizing Adaptations: Observational Studies: (reveal adaptive aspects of traits): complexity

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complex features are commonly products of natural selection, so complexity may suggest the presence of an adaptation

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Methods for Recognizing Adaptations: Observational Studies: (reveal adaptive aspects of traits): Design

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Structures that look "designed" for a specific function may be adaptations

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Methods for Recognizing Adaptations: The Comparative Method

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for those features that have evolved multiple times (convergence), we can assess whether the evolution of the feature is correlated with a particular selection pressure

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Example Experiment: fly and jumping spiders

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Do the wing markings and display of the tephritid fly Z. vittigera represent an adaptation to predation? is the adaptation specific to thwarting jumping spiders?

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Results from experiment with fly and jumping spiders

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The presence of the wing stripes and display do deter jumping spiders, but not other predator species
The wing stripes is something that has evolved in response to a common predator

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Observational studies when..

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experiments involving actual manipulation of variables are not feasible
ex. thermoregulation in reptiles

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Garter snakes have different options for behaviorally modifying their body temperature

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-stay at surface, moving between sun and shade
-Stay in a burrow, moving deeper or shallower
-Stay under a rock (rock thickness affects this strategy)

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what strategy kept snakes closest to their optimal body temp throughout day and night?

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rock strategy (using medium-thickness rocks), according to temp measurements under various scenarios

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if medium-thickness rocks are theoretically the best temp regulators for garter snakes, would we observe that snakes make an adaptive "choice" in nature

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yes

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The Comparative Method

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Do different lineages respond in the same adaptive way to similar, independent selective episodes?

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comparative method: test a hypothesis of

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convergent evolution
-Requires that the evolutionary relationships among the species of interest are known (A resolved phylogeny)

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"controlling for phylogeny"

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-Need to correct for trait similarity among groups caused by phylogenetic similarity

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Example: comparative method: testis size in male megabats

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is larger testis size an adaptation to living in larger groups? (sperm competition)

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How to correct for similarity due to recent common ancestry?

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using Felsenstein's method. Think of it as a way of "subtracting out" the phylogenetic effects

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Results megabats

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There is a significant relationship between the two contrast values, so larger group size is positively associated with larger testis size in megabats

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Phenotypic Plasticity

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-when the same genotype produces different phenotypes, depending on environmental circumstances
-Can be genetic variation for the extent to which a trait is phenotypically plastic (genotype-by-environment interaction)

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Selection can favor higher or lower phenotypic plasticity, depending on..

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how the ability to change one's phenotype affects fitness

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water fleas

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attraction to light is phenotypically plastic. The smell of predatory fish causes them to avoid light. In populations where predation is hight, phenotypic plasticity is extreme. In populations with few predators, there is minor or no response to the smell of fish

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The study of life history evolution focuses on

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the 'timing" of events during the life span of organisms, why theses events occur when they do, and what fitness tradeoffs are associated with different schedules

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Examples of life history questions in evolutionary biology:

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-Why do species differ in the age at which sexual maturity is reached?
-Why do individuals of some species only reproduce once?
-Why do some organisms live longer than others?
-Why is there an "optimal" rate of offspring production?
-Why do some species produce many, tiny eggs, while others produce fewer, larger eggs?

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Life history differences are driven by

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how energy is allocated to reproduction, metabolism, and growth

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Female Sand crickets

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Example of an energy allocation trade off

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short winged female

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allocate more energy to egg production and less energy to dispersal ability
-predict more in stable habitats with abundant resources

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Long winged female

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allocate more energy wings and muscles for dispersal, and less energy to egg production
-predict more in unstable environments where food scarcity is likely

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What is the optimal rate of offspring production? Important trade off

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as the number of offspring produced at one time increases, there are fewer resources available for each individual offspring. (resources can be biochemical investments or behavioral investments for rearing young)
-Should and individual produce many offspring that each get few resources, or a few offspring that each get many resources?

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Lacks hypothesis

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selection will favor the "clutch size" that produces the highest offspring survival

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the probability that any individual offspring will survive ___ with increasing clutch size

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decreases

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the total number of surviving offspring reaches a maximum at

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an intermediate clutch size

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Are studies of natural populations consistent with Lack's hypothesis?

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In general, no. Most studies have revealed that individuals actually produce fewer offspring than expected under lack's model

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Explanations for the discrepancy

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-lack's hypothesis assumes no trade off among reproductive efforts in different years
-Clutch size might affect not only offspring survival, but other aspects of offspring fitness
-Clutch size could be a phenotypically plastic trait. Individuals might be able to adjust optimum clutch size from year to year, depending on environmental conditions

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What is the optimal size of each offspring?

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-given a finite pool of resources for offspring production, this pool can be divided up into many, small, pieces, or a few large pieces

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optimal size of offspring: important trade off

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An individual can produce many small offspring (few resources per offspring), or a few large offspring (many resources per offspring)

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Parental fitness for a given offspring size

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the product of the number of offspring able to be produced and the survival probability for an offspring.

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In hatchery-raised chinook salmon, optimal egg mass is

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intermediate

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1 conflicts between the sexes over life history traits

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the optimal number of offspring per mating bout might differ between males and females. In D melanogaster, it is optimal for males if their mate produces the maximal # of offspring. For the female, however, this is suboptimal considering future reproductive events

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2 Genetic variation for life history traits

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because life history traits are closely connected with fitness, we expect selection to have reduced genetic variation for these traits. Empirical studies, however, have shown substantial genetic variation for L.H. traits. Based on some examples, genetic variation can be maintained if different "morphs' display different L.H. strategies, and frequency-dependent selection results in the persistence of the different morphs. Other explanations also are possible and valid.

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3 Not all populations are at the theoretical optimum

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theoretical optima for life history traits, even when all the assumptions are correct, may not be observed in natural populations. this can be due to a lack of time or genetic variation required to evolve to the optimum.

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Sexual Selection

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selection that arises from differential reproductive success due to variation in mating success

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For a trait to evolve under sexual selection,

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the trait must be correlated with mating success and that mating success must be correlated with reproductive success

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1948 Bateman's experiment with Drosophila melanogaster

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-he placed small groups of males and females in milk bottles with food
-Parentage analysis: assigned offspring to their parents using phenotypic markers, whose inheritance could be tracked based on simple Mendelian principles

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results in Bateman's experiment

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# offspring increased as males got more mates
# offspring reaches an asymptote

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the Selection Gradient

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Describes the "steepness" of the relationship between trait values and fitness

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the Batmeman Gradient (or sexual selection gradient)

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-Describes a selection gradient for mating success.
-the steeper it is the greater the strength of sexual selection

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A positive relationship between mating success and fitness suggests

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that selection will favor traits that allow an organism to obtain more mates

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this positive relationship is the cause of

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sexual selection
How steep this relationship is determines how strong the selection is.

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The presence of sexual selection tends to ___ the variance in mating success and the variance of fitness in the population

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increase

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Bateman's principles

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1. A high variance in mating success is a sign of sexual selection
2. A high variance in reproductive success (fitness) is another sign of sexual selection
3. A positive relationship between mating success and reproductive success is the cause of sexual selection

Front 134

In Bateman's experiment, sexual selection was clearly stronger on males than females. But why?

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-the two sexes often have different reproductive potential, due to basic biological constraints.
-In D. melanogaster, females have a limited number of eggs, all of which can be fertilized by one or two males. Males have millions of sperm, so their fitness is limited only by how many females they can inseminate.

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In many animal species this is the case, simply due to

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the size and energy difference between eggs and sperm

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anisogamy

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a union between two gametes that differ in size or form; refers to the difference in size and energy between eggs and sperm

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Robert Trivers (influenced by Bateman's work)

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He generalized the role of anisogamy in sexual selection to include sex-differences in "parental investment"

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The sex that invests more in the production and rearing of offspring will likely experience...

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weker sexual selection, relative to the sex that invests less

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Syngathus typhle

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sex role reversed (pipefish)

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The fitness of the sex with a steeper Bateman gradient is more limited by

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the number of mates

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The fitness of the sex with the shallower Bateman gradient is more limited by

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the quality of mates

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Greater success in obtaining mates could be due to

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1) Traits that allow one to directly compete with members of the same sex for mating opportunities. "Intrasexual Selection"
2.) Traits that attract potential mates. "Intersexual Selection"
3.) Both

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Evolutionary outcomes of sexual selection?

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-Sexual Dimorphism
-Maladaptive traits

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Sexual Dimorphism: Secondary Sex traits

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-Differences between the sexes that do not directly participate in reproduction
-All differences between the sexes except for genitalia and gonads
-Usually involved in mating opportunity and mating success

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sexual Dimorphism

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-Morphology (such as body size)
-Physiology (such as hormonal differences)
-Behavior

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Not all sexual dimorphism observed in nature is due to sexual selection

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-Natural selection can result in the evolution of sexual dimorphism.
-Other evolutionary mechanisms could also theoretically cause the evolution of sexual dimorphism

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Maladaptive traits

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...

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possible mechanisms of sexual Selection

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-Scrambles
-Endurance rivalry
-contests
-Post-copulatory sexual selection
-Mate choice

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Mechanisms: Intrasexual Selection

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Scrambles, endurance rivalry, contests, sperm competition, etc.

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Mechanisms: Intersexual selection

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Mate choice, cryptic choice (post-copulatory)

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Scramble competition

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Mating success may depend on a race to be the first to find and/or fertilize a mate

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Endurance Rivalry

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Mating success may depend on how long a male can stay at a breeding site, and selection will favor males that out compete rivals by enduring the costs of defending a breeding site

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Contests

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Mating success may depend on dominance, success in fights, or an ability to bypass fighting altogether

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Alternative mating strategies

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when combat isn't your thing (salmon too small)

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Post-copulatory Competition

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If females mate with multiple males, competition may continue after mating; lions kill offspring so females can give birth to his own offspring

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mate Choice

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mating success may depend on courtship displays, which are driven by mate preferences for particular traits (pretty feathers)

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Long tails in male red collared widowbirds

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longer tail-->more mates--> more offspring; but skinnier than shorter tails (driven by sexual selection, not natural selection)

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Reasons for Choosiness?

Back 158

-trying to get better genes for your offspring
-Mate directly benefits through acquisition of resources.
-non choosy sex is taking advantage of some preexisting sensory bias in the choosy sex
-Can be genetic correlations between trait in one sex and choice in the other

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Microevolution

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examines the change in allele/genotype frequencies within and among populations of a species

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species concepts: morphospecies

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species based on morphological differences/similarities

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advantages of morphospecies

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-can use on extant and extinct taxa
-often used as first means for identification
-easy to collect

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Disadvantages of morphospecies

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-what delineates a new species- how much difference?
-some organisms have limited morphology to work with (e.g., bacteria)
-cryptic species (morphologically indistinguishable, but genetically distinct)
-sexual dimorphism- need to define for males and females

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species concepts: Biological Species Concept (probably most popular)

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species are groups of interbreeding natural populations that are reproductively isolated from other such groups

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Advantages of Biological species concept

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-focuses on evolutionary mechanism- gene flow
-provides a more objective criterion than morphospecies concept

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Disadvantages of Biological Species concept

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-largely focuses on a single evolutionary mechanism- gene flow
-What about organisms with asexual reproduction?
-what about fossils where cannot test reproductive isolation?
-Reproductive compatibility is a plesiomorphic character (although reproductive compatibility does not have to equal reproductive isolation as isolation can occur by other means)

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species concepts: Phylogenetic Species Concept

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defines species as the smallest diagnosable monophyletic group; species are evolutionary independent long enough for "diagnostic" traits to appear

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Phylogenetic Species concept advantages

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-can use on extant and extinct taxa
-molecular data make it feasible to test in most if not all extant taxa
-can use regardless of reproductive mode

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Phylogenetic Species concept disadvantages

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-it may be that each population is actually a distinct species according to PSC (although not a problem with the concept, but how we handle the organization of so many possible "species")
-Need to be cautious of horizontal gene transfer (e.g., especially bacteria) because can create incorrect phylogeny

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Phyletic speciation

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gradual change through time within a lineage (similar to chronospecies)

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hybridization

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fusion of two species to form a new species

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Cladogenesis

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origin of new lineage- "splitting of lineages"

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Instantaneous cladogenesis

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e.g. polyploidy or other genetic events that prevent offspring from mating with parent population

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gradual cladogenesis

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divergence of lineages occurs over time
-allopatric, parapatric, sympatric

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allopatric

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physical isolation creates an effective barrier to gene flow- now other evolutionary mechanisms result in divergence
-can happen via dispersal and colonization of new habitats
-or vicariance events (a population is split into smaller units)

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vicariance

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a population is split into smaller units

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Parapatric

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habitat is continuous between the populations that are diverging into separate species
-ring species may be an example (some don't agree)
-May occur along a cline
-or an ecotone

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cline

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a gradual change in conditions which gives rise to slightly different characteristics predominating in the organisms that live along it

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Ecotone

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a transition area between two adjacent but different habitats

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Sympatric

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refers to the formation of two or more descendant species from a single ancestral species all occupying the same geographic location

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Sympatric cont'd

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-often cited examples of sympatric speciation are found in insects that become dependent on different host plants in the same area (table 16.1)
-however some have argued that the evidence of sympatric speciation are in fact examples of micro-allopatric speciation (what we perceive as sympatric may not be so in other organisms)

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host parasite example

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will describe how can be allopatric or sympatric

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sexual selection coupled with assortive mating could result in or reinforce

Back 182

sympatric speciation

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Example of sympatric divergence: three-spined sticklebacks

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-In each of 5 lakes have 2 different forms
-DNA data show how each lake was colonized independently, presumably by a marine ancestor, after the last ice age and that the two forms in each lake are more closely related to each other than they are to individuals in the other lakes
-Nevertheless, neither form mates with the other, but will mate with like form from another lake.

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conclusion (three-spined sticklebacks)

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in each lake, competition for limited resources resulted in disruptive selection coupled with assortive mating

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disruptive selection: three spined sticklebacks

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competition favoring fishes at either extreme of body size and mouth size over those nearer the mean

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Assortive mating: three spined sticklebacks

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each size preferred mates like it- favored a divergence into two subpopulations exploiting different food in different parts of the lake

Front 187

stickleback example: the fact that this pattern of speciation occurred the same way on separate occasions suggest strongly that

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ecological factors in a sympatric population can cause speciation

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Within lakes have divergence of trait under selection, that leads to

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reproductive isolation (not necessarily incompatibility)- now each form can drift independently and get divergence across genome

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Allopatric lake populations are diverging across genome due to

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drift

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Important thing to remember in speciation

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(not calling something allopatric or sympatric etc.)
-To find the mechanism(s) that is (are) resulting in the divergence

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the patterns we observe (sympatric allopatric etc.)

Back 191

gives us clues to the mechanism

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selection important in driving speciation within lakes, but

Back 192

still have divergence between lakes due to drift as "neutral markers" still more similar within than between lakes
-so may have up to 10 species in 5 lakes
-also example of why do not use selected markers to infer phylogeny- want to use neutral markers (something not under selection, maybe due to genetic drift or migration)

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Hybridization

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mating between individuals of genetically distinct populations/species

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What happens when diverged populations come back into contact and there is still the potential to interbreed?

Back 194

1. Get complete homogenization such that 2 diverged units become 1 (hybrid equal fitness to parents)
2. Reinforcement to complete reproductive isolation
3. Maintenance of hybrids within a hybrid zone
4. Hybridization may lead to formation of new species

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reinforcement

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natural selection that results in a mechanism to prevent hybridization among individuals of diverged populations that are now in secondary contact (selection against hybridization because hybrid has less fitness)

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Reinforcement results in

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prezygotic isolation- mechanisms that prevent fertilization (behavioral physiological etc.)

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low fitness of hybrids may be due to postzygotic isolation

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ex. hybrid offspring are sterile or infertile

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Hybrid zone maintenance

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hybrids are maintained because they have higher fitness in zone of contact relative to parental populations
-such zones may allow the leakage (introgression) of alleles from one species to another

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New species formation may occur if

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hybrid occupies new habitat and is more fit that parental populations. also may get new species if hybridization results in a polyploid species.

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Speciation in the fossil record: If it is true (as we think it is) that most speciation involves populations that are geographically isolated (allopatric), then

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speciation should be difficult to document using the fossil record

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Speciation in the fossil record: speciation can only be detected if

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if at least two separate populations can be studied over the same temporal sequence
-in addition, the populations under study have to include the ones that lead to the separate species
-Nevertheless, there are few examples of what looks like speciation in the fossil record

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Speciation in Radiolarians

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Radiolarians, amoeboid planktonic protozoa that produce intricate mineral skeletons
-species A inhabited southern North Pacific
-later, appeared in norther part and soon started showing features of species B
-then, later, species B reinvaded souther waters
-After species B became sympatric with its parent species, it evolved larger size, while species A evolved smaller size

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Species A and B

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A= Eucytridium calvertense
B= Eucyrtidium matuyamai

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Mitochondrial DNA between human and chimps differ at

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~10%

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2 main points need to know about human ancestry

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-many hominid lineages have gone extinct
-some of these lineages coexisted at the same time and same place based on fossil records

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Human Ancestry: difficult to disentangle the different hypotheses without..

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more ancient DNA

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It is clear all present day people descended from

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african ancestors

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Current data suggest first model and maybe second one- either way present day differences among races must have arisen in

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last few hundred thousand years

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parasite

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organism that lives in or on another organism for all or part of its life and in doing takes resources away from the host without any return benefit to the host

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microparasites

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-bacteria, viruses, protozoa, fungi
-multiply within host (multiple generations)
-acute infections (host death or immunity)

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macroparasites

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-helminths (e.g., nematodes, flatworms), arthropods
-release eggs or larvae into external environment
-chronic infections (morbidity not mortality

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How common are parasites?

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Probably more species of parasites than free living organisms
ex. over 23,000 bony fish species
-each one has at least 1 species of flatworm-if not more!

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Are parasites Bad? No!

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-represent an significant amount of biodiversity
-many applied uses (toxicology, ecosystem health)
-interesting ecology and evolution (unique adaptations)!
-Population regulators

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Can parasites affect host health?

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Yes!
- > 5million deaths/year caused by parasites
- ~3 billion dollars spent on anti-helminthic drugs in livestock
-mostly in developing countries or tropical areas
-how much do you spend on your dog or cat?

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Virulence not a property of the parasite

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-Often defined in relation to some aspect of parasite-induced reductions in host fitness
-However, this is a host-centric evolutionary point of view. Different hosts may respond differently to the same parasite strain
-The host is a resource the parasite uses to maximize its fitness.
-The way a parasite exploits a host will depend on the strategies that maximize its fitness irrespective of the welfare of the host.
-Remember selection is not forward thinking, so no reason a less pathogenic parasite will evolve to ensure hosts are around for future infections.
-In parasites, *selection acts on rates of host exploitation irrespective of effects on host fitness*

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Kingdom Protozoa: Phylum Sarcomastigophora

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amoeba and flagellates

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Kingdom Protozoa: Phylum Apicomplexa

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malaria, etc.

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Entamoeba histolytica (Phylum Sarcomastigophora Subphylum Sarcodina)

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-Worldwide distribution
-*fecal contamination*
-amebic dysentary
-asexual reproduction in gut (binary fission)
-cysts in feces
-effective treatments
Other species of Enatmoeba not pathogenic but important to know for diagnosis

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Giardia intestinalis (lamblia) (Phylum Sarcomastigophora subphylum Mastigophora)

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-Worlidwide distribution
-fecal contamination
-asymptomatic to severe diarrhea and malabsorption
-asexual reproduction in gut (binary fission)
-cysts in feces
-effective treatments

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parasites belong to the kingdom

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Protozoa

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Trypanosoma brucei spp.

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African sleeping sickness
-there are drugs for treatment, but need to treat quickly
*transmitted by Tsetse fly*
In human host- reproduction
humans intermediate host*

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T.b. gambiense

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west/central africa
-chronic disease starts in blood get fever, chills, then lymph then CNS

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T.B. rhodesiense

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East/southeast Africa
-acute disease can die in blood stage of infection

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Trypanosoma cruzi

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Chagas disease
-Assassin/Kissing bugs- parasite in bug feces by site of the bit wound- scratch in parasite
-Americas- southern US to Argentina (because of behavior of bugs)
-Chronic Disease: fever, anorexia, mild hepatosplenomegaly
-chronic Chagas disease and its complications can be fatal
-drugs for treatment, but better to treat in acute phase

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Cutaneous leishmaniasis

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old and new world tropical; once get become immune
there are treatments

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Visceral leishmaniasis

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mostly middle east, but in S. Am.
-fever, weight loss, swelling of spleen and liver, and anemia
-if untreated host dies b/c immune system breaks down

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Mucocutaneous leishmaniasis

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central and south America
can become visceral if not treated

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Toxoplasma gondii (Kingdom Protozoa)

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-Felids are final host
-sexual and asexual reproduction in cats
-asexual in all other hosts
-transplacental transmission in humans
-fetus can develop neurological problems
-about 20-70% of people exposed
(pregnant women shouldn't clean litter box)
-Worldwide- immunocompetent people- generally an asymptomatic infection

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KIngdom Animalia: Phylum Platyhelminthes

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flatworms, contains free living species; almost all hermaphroditic; parasitic groups: cestodes, digeneans, monogeneans

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Kingdom Animalia: Phylum Nematoda

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roundworms; free living, plant parasites, and animal parasites; more than one origin of animal parasitism

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Kingdom Animalia
Phylum Platyhelminthes
Class Trematoda
Subclass Digenea

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~6000 species usually, two suckers
-usually 3 host life cycle and snail first host*
-widespread parasites of all classes of vertebrates inhabit (as adult or juvenile worms) nearly every organ of their hosts
-several species infect humans

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Schistosoma mansoni transmission (a species of ^)

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200 million infected
(2 host life cycle instead of 3)
-S. mansoni (Africa, S. Am.)
-S. Japonicum (Asia)
-S. haematobium (Africa)
Dioecious
Many species of bird schistosomes (swimmer's itch)

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Phylum Platyhelminthes
Class Digenea (trematodes)
Fascioloides magna

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-deer liver fluke
-4 to 10 cm in length
Life cycle
-freshwater snails from family Lymnaeidae
-Cercarie emerge from the snail host and swim in water for up to two hours before encysting (metacercaria) on vegeation
-Final host (eg deer) eats vegetation with parasite- excysts and penetrates gut wall and migrates to liver

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Fasciola hepatica

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related parasite (sheep liver fluke) can be costly for sheep production

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Phylum platyhelminthes
class Monogenea

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-typically (often economically important) ectoparasites of the skin and/or gills of fish
-some species become endoparasitic by inhabiting the nose, the pharynx, cloaca bladder of amphibians, reptiles also in cetaceans and cephalopods
-attached to the host's surface by a characteristic haptor which is species-specific and provided with hooks and hooklets
-usually have a simple life cycle involving hermaphroditic adults, eggs and larvae

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Phylum Platyhelminthes
Class Cestoda

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-Typically, adults inhabit the intestines of their hosts, being anchored to the intestinal via a scolex, followed by a series of repeated reproductive segments called proglottids
-Sharks, rays, marine fish have large diversity of tapeworms (also maybe birds)
-some species infect man

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Phylum Platyhelminthes
Class Cestoda
Taenia solium

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-If ingest eggs can get cysticercosis (can affect your brain)
-humans can be both final and intermediate host

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Phylum Platyhelminthes
Class Cestoda
Echinococcus granulosus

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Canids final host
If humans get then larvae can migrate to most tissues and form hydatid cyst (asexual reproduction in cyst)
-hydatid disease

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Phylum Nematoda

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-between 16,000-20,000 described species
- ~5,800 parasitic in vertebrates (likely multiple origins)
-typically dioescious
-body covered by cuticle
-extremely diverse in life cycle patterns

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Phylum Nematoda: Ascaris lumbricoides

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human roundworm in gut (15-35 cm)
Worldwide distribution (over billion infected
-Highest prevalence in tropical and subtropical regions, and areas with inadequate sanitation
-large burdens may cause abdominal pains and affect growth in children, pulmonary symptoms in migratory phase
>200,000 eggs per day, persist in environment

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Ascaris Suum

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(may be same species as above) infects pigs (costly to swine production)
Effective treatments

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Phylum Nematoda: Hookworms

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Ancyclostoma duodenale, Necator americanus
-penetrate host
-2nd most common human helminthic infection (after ascariasis)
- ~25,000 eggs per day
-Iron deficiency anemia (adults feed on blood)
-cutaneous larval migrans, A. caninum (dogs), A. braziliense
-larvae cannot mature further in the human host, and migrate aimlessly within the epidermis, sometimes as much as several centimeters a day.

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Phylum Nematoda: Trichinella spiralis (uncooked pork)

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found worldwide in many carnivorous and omnivorous animals
-infections may be asymptomatic intestine by the time notice infected, larvae already in muscles
-facial edema, fever, rashes
-occasional life-threatening manifestations

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Phylum Nematoda: Filarial nematodes

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infective larvae are transmitted by infected biting arthropods during a blood meal
-Dirofilaria immitis- dog heartworm
-Wuchereria bancrofti- (elephantiasis) tropical areas worldwide, lymphatic infection
-Onchocerca volvuls- (river blindness) mainly in Africa; nodules in subcutaneous tissues

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Phylum Acanthocephala

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Spiny headed worms (proboscis with spines)
-Dioecious intestinal parasites with no intestine
-Vertebrate final hosts, arthropod intermediate hosts

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Phylum Pentastomida

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-Adults in lungs and respiratory systems of land-living carnivorous vertebrates
-Mostly found in reptiles
-Dioecious with complete digestive system
-Related to arthropods

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Transmission and host behavior Dicrocoelium dendriticum

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produce slime balls that ants eat. alters ants behavior- ant latches onto grass blades and then cows eat them

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Prevalence

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percent hosts infected

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mean abundance

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mean number of parasites per host examined

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mean intensity

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mena number of parasites per infected host

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infrapopulation

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all the parasites of a species within a host individual

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Component population

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all the parasites of a species within a host population

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Parasite Ecology- Distributions among hosts

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-Macroparasites tend to be aggregated – most hosts have no or few parasites and few hosts have many parasites
-May be produced by temporal or spatial heterogeneity in rates of exposure
-Or heterogeneity in host susceptibility to infection
-May affect parasite mating dynamics, sex ratio, risk of extinction, host health.

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Parasite Ecology- Applications beyond host health

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-Toxicology indicators – some parasites can accumulate heavy metals to concentrations orders of magnitude higher than those in the host tissues or the environment.
-Biotags – using parasites to indentify host origins, migrations, or stocks
-Food web dynamics – indicators of host diet – “ghosts of food items”
-Indicators of ecosystem health – many parasites have complex life cycles, so presence of parasite indicates presence of all hosts need for life cycle