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47 Cards in this Set

  • Front
  • Back
Requirements mutational theory
Mutational theory has 2 requirements to overcome 50% cost
1. The rate of deleterious mutation: U > 1
2. Synergistic epistasis: fitness effect per mutation must get increasingly
greater as number of mutations increases
• Host-parasite dynamics
n coevolution, changes by one species (e.g., host)
could lead to extinction of the other (e.g., parasite)
and vice versa.
another example of red queen hypothesis
-Parasites castrate the most common asexual clones and
reduce their numbers –negative frequency dependence
-Sexual snails present a “moving target” of genetic diversity
that prevents the parasite from wiping them out
micro and macro evolution
evolution that occurs at or above the level of species, in contrast with microevolution,[citation needed] which refers to smaller evolutionary changes (typically described as changes in allele frequencies) within a species or population
• Linnaean classification (incl. categories)
Homo sapiens
• The trouble with the species concept
Many biologists argue that species are not “arbitrary” in this same sense
• Causes of variation within species
Complicated by variation withinspecies
and also by similarity betweenspecies
• Sibling species
Sibling species are closely related species
that appear similar or even identical
• Typological species concept
- A species is a group of organisms conforming to a common morphology
- Species are static, non-variable assemblages: essentialism
- Variation results from imperfect manifestations of the “idea” implicit in species
• Biological species concept
Species are groups of actually or potentially interbreeding natural populations
that are reproductively isolatedfrom other such groups (Ernst Mayr)
Pros: -Places taxonomy within the framework of population genetics
-Species are a gene pool through which there is gene flow
-Applicable to many real-world situations
Cons: -Iterbreedingcriterion does not apply to asexual organisms
-In practice, how do we assess reproductive isolation?
• Phylogenetic species concept
Species are the smallest aggregation of populations (sexual) or lineages
(asexual) diagnosable by a unique combination of character states
• Pre- and postzygotic barriers (incl. examples;

Ecological or habitat isolation
Populations occur in different habitats in the same geographic region
These closely-related Drosophila species occur together and feed and lay eggs
in the necrotic tissue of cacti, but they have speciated via ecological isolation

Temporal isolation
Differences in the timing of reproduction prevent species from interbreeding
Rana aurorabreeds January to March
Rana boylii breeds mid-March to June

Mechanical isolation
Reproduction prevented by differences in size or shape of reproductive structures
Two very different examples:
“Lock-and-key” genitalia in damselflies
Floral structure and pollinator size

How do animals recognize mates of the same
species and avoid mates of different species?
-Breeding calls
-Courtship rituals
-Color, morphology


Different # chromosomes:
Horse 2n= 64
Donkey 2n= 62

Despite sterility, they are very desirable hybrids
Mules thought to be smarter than horses or donkeys
• Hybrid sterility
-Hybridization produces viable offspring, but they are sterile genetic “dead ends”
-Domestic donkey(Equus asinus) and horse (Equus caballus) = different species

Different # chromosomes:
Horse 2n= 64
Donkey 2n= 62

Despite sterility, they are very desirable hybrids
Mules thought to be smarter than horses or donkeys
• Natural hybridization (incl. golden-winged/blue-winged warbler example
Natural hybridization can have important consequences
Northward expansion of Blue-winged (BW) warbler
Hybridizes with Golden-winged (GW) warbler
• Hybrid speciation (incl. mechanism)
Common in plants, also occurs in animals
Not only does hybridization occur, it can be a source of new species
Often (but not always), hybrids are viable because they are polyploid
Extra chromosomes avoids problem of homologue mismatching at meiosis
• Mechanism of introgression
• Anagenesis
known as "phyletic change," is the evolution of species involving a change in gene frequency in an entire population rather than a cladogenetic branching event. When enough mutations reach fixation in a population to significantly differentiate from an ancestral population, a new species name may be assigned. A key point is that the entire population is different from the ancestral population so that the ancestral population can be considered extinct. It is easy to see from the preceding definition how controversy can arise among taxonomists when the differences are significant enough to warrant a new species classification. Anagenesis may also be referred to as phyletic evolution or gradual evolution.
s an evolutionary splitting event in which each branch and its smaller branches forms a "clade", an evolutionary mechanism and a process of adaptive evolution that leads to the development of a greater variety of sister organisms. This event usually occurs when a few organisms end up in new, often distant areas or when environmental changes cause several extinctions, opening up ecological niches for the survivors. A great example of cladogenesis today is the Hawaiian archipelago, to which stray organisms traveled across the ocean via ocean currents and winds. Most of the species on the islands are not found anywhere else on Earth due to evolutionary divergence.
Allopatric speciation
One or more populations of a species become separated from otherpopulations
-Geographic barrier (mountain, river, glacier, lake dries into pools)
-Colonization of new area (e.g., new island, new lake during flood)
-Intermediate population in middle of range goes locally extinct
form of speciation, the formation of new species through evolution. In this form, new species are formed in isolated peripheral populations; this is similar to allopatric speciation in that populations are isolated and prevented from exchanging genes. However, peripatric speciation, unlike allopatric speciation, proposes that one of the populations is much smaller than the other.
is a form of speciation that occurs due to variations in mating frequency of a population within a continuous geographical area.

In this model, the parent species lives in a continuous habitat, in contrast with allopatric speciation where subpopulations become geographically isolated.

Niches in this habitat can differ along a environmental gradient, hampering gene flow, and thus creating a cline.

An example[1] of this is the grass Anthoxanthum, which has been known to undergo parapatric speciation in such cases as mine contamination of an area. Selection for resistance/tolerance to certain metals occurs. Flowering time generally changes (in an attempt at character displacement—strong selection against interbreeding—as the hybrids are generally ill-suited to the environment) and often plants will become self-pollinating.

Another example is ring species.
the genetic divergence of multiple populations (from a single parent species) inhabiting the same geographic region; such that those populations become different species.
• The case of the African cichlids
Cichlids400-500 species of cichlid can occur in a single African great lake!
Mode of speciationIs speciation allopatric or sympatric in African cichlids?
Speciation occurred in the past....
• Reinforcement
Parapatric and sympatric speciation require reinforcement
Both assume populations without physical barrier to gene flow
So selection against “hybrid” genotypes is required
• Assortative mating
Assortative mating: like mates with like. they mate with mate that are like them.
Natural selection cannot favor post-zygotic istolation= reduced hybrid fitness
There has to be some inherent genetic inferiority of hybrids, orsome inherent
reason why hybrid phenotypes do not perform as well in the environment
Pre-zygotic isolation could then evolve to “reinforce” selection against hybrids
• Principles of ring species
ring species present an interesting problem for those who seek to divide the living world into discrete species.

Ring species are a special case that is rare in
nature, but informative for studying speciation
Substitute geographic space for evolutionary time
• Causes of speciation in Drosophila experiment
-Raised for many generations on different diets
-Then recombined and allowed to mate freely
-Result: assortativemating (prezygoticisolation)
• Phylogeny
Branching diagram showing relationships between species (or higher taxa)
based on their shared common ancestors
Terminal nodes, internal nodes
check the slide for more explanation
Terminal nodes = contemporary taxa
Internal nodes = ancestral taxa
• Difference “simple” classification and phylogeny
phylogeny-> divinding organism through time.
simple -> simple classification
• Mono-, para-, polyphyletic groups
Monophyletic group->Includes an ancestor
all of its descendants
para-> all of its descendants
ncludes ancestor and
some, but not all of its

Includes two convergent
descendants but not their
common ancestor
• The case of lizards and snakes
“Lizards” (Sauria) are
paraphyleticwith respect
to snakes (Serpentes)
Serpentesis a monophyletic
cladewithin lizards
Squamata (lizards + snakes)
is a monophyleticclade
sister to sphenodontida
Snakes are just derived,
limbless lizards
• The case of birds and reptiles
Birds are more closely related
to crocodilians than to other
extant vertebrates
Archosauria = Birds + Crocs
We think of reptiles as turtles,
lizards, snakes, and crocodiles
But Reptilia is a paraphyletic
group unless it includes Aves
• Homoplasy
Taxashare a character, but not by descent from a common ancestor
Equivalent to analogy, homoplasy is a product of convergent evolution
• Morphology vs. molecules

Homoplasycan be assessed from
structure, development, etc. PRO

Characters may be subject to selection
= convergence = homoplasy CON

Takes lots of time to identify and code
characters for analysis CON

Onlysomeone familiar with taxon can
identify good characters PRO& CON


Homoplasycan’t be assessed directly
(an “A”is an“A”) CON

Characters may or may not be subject
to selection –depends on the site ?

Sequencing yields lots of characters
if gene is sufficiently variable PRO

Anyidiot can get sequence data
Study of the geographic distribution of taxa in an attempt to explain the
factors that account for these distributional patterns
• Endemic,
mited to a certain area*
e.g., R. culminatusand R. vitellinus
* A relative term –endemic to an island,
a country, a region, a continent, etc.
Disjunct–distributed in more than one
region with a gap in between
e.g., R. ariel
found on all (or most)
e.g., pigeons
• Fundamental vs. realized niche
Fundamental niche–range of conditions under which a species can survive
and reproduce (temperature, light level, humidity, etc.)
Realized niche–actual range of conditions under which a species does survive
and reproduce in the presence of competing species
• Palynology
study of pollen: identify plants by fossil pollen and radiocarbon dating
• The biogeographic regions and their origin
Early biogeographers noted that many terrestrial animal taxa are distributed in
one of six major geographic regions of the world
• Wallace’s line
line between New Guinea and
• Index of similarity
Index of similarity –how similar are the taxa in two different regions?

Index = C/N1
C = number of shared taxa
N1= number of taxa in region with
fewer taxa
N2= number of taxa in region with
more taxa
• Laurasia
was a supercontinent that most recently existed as a part of the split of the Pangaean supercontinent in the late Mesozoic era. It included most of the landmasses which make up today's continents of the northern hemisphere, chiefly Laurentia (most of modern North America), Baltica, Siberia, Kazakhstania, and the North China and East China Cratons.
The southern supercontinent Gondwana (originally Gondwanaland) included most of the landmasses in today's southern hemisphere, including Antarctica, South America, Africa, Madagascar, Australia-New Guinea, and New Zealand, as well as Arabia and the Indian subcontinent, which are in the Northern Hemisphere. The name is derived from the Gondwana region of central northern India
• Vicariance events
Vicariance events–plate tectonics, glaciation, formation of rivers, mountains, etc.
• Glacial refugia
lands that animals took refuge, lands that were not covered with ice