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47 Cards in this Set
- Front
- Back
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Requirements mutational theory
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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 |
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• Host-parasite dynamics
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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 |
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micro and macro evolution
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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
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• Linnaean classification (incl. categories)
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Kingdom
Animalia Phylum Chordata Class Mammalia Order Primates Family Hominidae Genus Homo Species Homo sapiens |
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• The trouble with the species concept
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Many biologists argue that species are not “arbitrary” in this same sense
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• Causes of variation within species
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Complicated by variation withinspecies
and also by similarity betweenspecies |
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• Sibling species
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Sibling species are closely related species
that appear similar or even identical |
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• Typological species concept
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- 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 |
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• Biological species concept
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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? |
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• Phylogenetic species concept
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Species are the smallest aggregation of populations (sexual) or lineages
(asexual) diagnosable by a unique combination of character states |
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• Pre- and postzygotic barriers (incl. examples;
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pre
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 -Pheromones post Different # chromosomes: Horse 2n= 64 Donkey 2n= 62 Despite sterility, they are very desirable hybrids Mules thought to be smarter than horses or donkeys |
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• Hybrid sterility
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-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 |
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• Natural hybridization (incl. golden-winged/blue-winged warbler example
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Natural hybridization can have important consequences
Northward expansion of Blue-winged (BW) warbler Hybridizes with Golden-winged (GW) warbler |
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• Hybrid speciation (incl. mechanism)
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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 |
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• Mechanism of introgression
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ntrogression
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• Anagenesis
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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.
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cladogenesis
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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.
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Allopatric speciation
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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 |
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peripatric
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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.
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parapatric
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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. |
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sympatric
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the genetic divergence of multiple populations (from a single parent species) inhabiting the same geographic region; such that those populations become different species.
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• The case of the African cichlids
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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.... |
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• Reinforcement
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Parapatric and sympatric speciation require reinforcement
Both assume populations without physical barrier to gene flow So selection against “hybrid” genotypes is required |
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• Assortative mating
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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 |
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• Principles of ring species
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ring species present an interesting problem for those who seek to divide the living world into discrete species.
S p a c e Ring species are a special case that is rare in nature, but informative for studying speciation Substitute geographic space for evolutionary time |
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• Causes of speciation in Drosophila experiment
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-Raised for many generations on different diets
-Then recombined and allowed to mate freely -Result: assortativemating (prezygoticisolation) |
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• Phylogeny
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Branching diagram showing relationships between species (or higher taxa)
based on their shared common ancestors |
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Terminal nodes, internal nodes
check the slide for more explanation |
Terminal nodes = contemporary taxa
Internal nodes = ancestral taxa |
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• Difference “simple” classification and phylogeny
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phylogeny-> divinding organism through time.
simple -> simple classification |
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• Mono-, para-, polyphyletic groups
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Monophyletic group->Includes an ancestor
all of its descendants para-> all of its descendants ncludes ancestor and some, but not all of its descendants poly-> Includes two convergent descendants but not their common ancestor |
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• The case of lizards and snakes
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“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 |
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• The case of birds and reptiles
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Paraphyly
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 |
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• Homoplasy
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Taxashare a character, but not by descent from a common ancestor
Equivalent to analogy, homoplasy is a product of convergent evolution |
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• Morphology vs. molecules
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Morphology
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 Nucleotides 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 PRO& CON |
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Biogeography
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Study of the geographic distribution of taxa in an attempt to explain the
factors that account for these distributional patterns |
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• Endemic,
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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. |
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disjunct
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Disjunct–distributed in more than one
region with a gap in between e.g., R. ariel |
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Cosmopolitan
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found on all (or most)
continents e.g., pigeons |
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• Fundamental vs. realized niche
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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 |
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• Palynology
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study of pollen: identify plants by fossil pollen and radiocarbon dating
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• The biogeographic regions and their origin
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Early biogeographers noted that many terrestrial animal taxa are distributed in
one of six major geographic regions of the world |
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• Wallace’s line
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line between New Guinea and
Phillipines |
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• Index of similarity
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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 |
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• Laurasia
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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.
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Gondwana
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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
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• Vicariance events
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Vicariance events–plate tectonics, glaciation, formation of rivers, mountains, etc.
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• Glacial refugia
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lands that animals took refuge, lands that were not covered with ice
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