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Evolution Exam 3: Species concept
Terms in this set (73)
What is a species?
Species are the fundamental units of natural diversity and evolution. They are the smallest evolutionarily independent lineages distinct from other lineages
What are observed patterns used for defining species?
Patterns used for defining species may be morphological similarity or distinct clades
What are processes that can be used in defining species?
Processes that can be used in defining species are reproductive isolation/compatibility, adaptive divergence
Why should we care about species concepts and what is an example?
Species concept is a key issue for biodiversity and conservation. Red wolves, for example, are a genetic hybrid between gray wolves and coyotes. They have been extinct in the wild since 1970s, but should we be spending money to maintain a captive breeding program?
What are the four species concepts?
Morphological/typological species concept, biological species concept, cohesion species concept, phylogenetic species concept
What should you keep in mind in regards to the four species concepts?
1. All are trying to objectively identify evolutionarily independent lineages 2. All have strengths and weaknesses 3. The species groupings they recognize are often the same 4. Differences occur when you run into messy biological realities
What is the Morphological/typological species concept?
The morphological/typological species concept is based on the platonic ideal of essentialism. Members of the same species should closely resemble the same ideal or "type". Species are defined based on careful morphological measurements. It is the simplest and most widely used species concept
What are the strengths of the morphological/typological species concept?
The strengths of the Morphological/typological species concept are that it can be applied to living or extinct species and it does not depend on complex genetic analysis. Example is anchura substriata from late Cretaceous period. All individuals of this species recognized by distinct horn feature
What are the weaknesses of the morphological/typological species concept?
The weaknesses of the morphological/typological species concept are that the choice of traits can be arbitrary and subject to revisions and homoplasy, can fail to recognize divergent lineages of their morphology is similar, and can split a single species of morphologically diverse.
What is an example of the morphological/typological species concept choosing arbitrary traits?
Example is cotoneaster species where the choice of three different traits can lead to three different species groupings
What is an example of the morphological/typological species failing to recognize divergent lineages if morphology is similar?
The chihuahuan Raven has a 4% mtDNA divergence from other ravens but looks exactly the same as the common raven
What is an example of the morphological/typological species concept splitting a single species if morphologically diverse?
Aphids have both winged and wingless, sexual and asexual forms which arise at different times of the aphid life cycle
What is polyphenism?
Multiple distinct phenotypes that arise from a given genotype
What is developmental plasticity?
changes in neural connections during development as a result of environmental interactions
What is the biological species concept?
Biological species concept defines species as groups of actually or potentially interbreeding natural populations which are reproductively isolated from other such groups. First to define species as independent evolutionary lineages.
What are the two main types of reproductive isolating barriers?
The two main types of reproductive isolating barriers are prezygotic and postzygotic
What are two types of prezygotic reproductive isolating barriers?
premating and postmating
What are two types of postzygotic reproductive isolating barriers?
Intrinsic and Extrinsic
What are the three types of premating prezygotic reproductive isolating barriers?
Temporal, Spatial, and Behavioral
What is an example of temporal premating prezygotic reproductive isolating barriers?
The flowering phenology of camassia quamash and camassia leichtlinii. C. quamash and C. leichtlinii flower at different times
What is phenology?
Phenology is the timing that biological things are happening over the seasons
What is an example of spatial premating prezygotc reproductive isolating barriers?
Helianthus annuus and Helianthus anomalus live in different habitats found geographically far from one another
What is an example of behavioral premating prezygotic reproductive isolating barriers?
In animals, sexually selected traits are behavioral premating prezygotic reproductive isolating barriers. In plants, types of pollinators. Aquilegia formosa is hummingbird pollinated during the day. Aquilegia pubescens is hawkmoth pollinated at night
What is a postmating prezygotic reproductive isolating barrier?
mechanical and gametic incompatibilities
What are three examples of postmating prezygotic reproductive isolating barriers?
1. Morphological incompatibility of genitalia in insects 2. Sea urchin sperm and egg, structure of the bindin protein on the sperm and proteins on the egg determine compatibility 3. Pollen and sperm precedence, germinating pollen from the same species grows faster and reaches ovaries first
What are intrinsic postzygotic reproductive isolating barriers?
Intrinsic postzygotic reproductive isolating barriers are hybrid inviability and sterility which reflect genetic make up
What are examples of intrinsic postzygotic reproductive isolating barriers?
Aborted embryos, malformed and inviable offspring. Mules are F1 hybrid of female horse and male donkey and are sterile
What are extrinsic postzygotic reproductive isolating barriers?
Extrinsic postzygotic reproductive isolating barriers are hybrids that have low viability or mating success in their environment
What are examples of extrinsic postzygotic reproductive isolating barriers?
Hybrid heliconius butterflies have low fitness because their warning coloration is not recognized by predators, low mating success due to intermediate sexually selected traits
What are the strengths of the biological species concept?
Based on the importance of gene flow within species and lack of gene flow between species, defines what a species is and how speciation occurs
How does speciation occur under the biological species concept?
Under the biological species concept, speciation occurs when a population becomes reproductively isolated from another population
What are the weaknesses of the biological species concept?
Too little gene flow and too much gene flow
What is an example of the biological species concept using too little gene flow?
Biological species depends on sexual reproduction and doesn't apply to asexual species. Most species are asexual
What is the cohesion species concept?
The cohesion species concept deems a species as the most inclusive population of individuals having the potential for phenotypic cohesion through intrinsic cohesion mechanisms
What are cohesion mechanisms?
Genetic exchangeability and Demographic exchangeability
What is genetic exchangeability?
Genetic exchangeability are factors that define the spread of genetic variants through gene flow (including reproductive isolation)
What is demographic exchangeability?
Demographic exchangeability are factors that define the fundamental niche through drift and natural selection
What are the strengths of the cohesion species concept?
Works well for asexual and sexual species, even those that hybridize
What are the weaknesses of the cohesion species concept?
The cohesion species concept requires detailed knowledge of population genetics, past history, and ecology of species
What is the phylogenetic species concept?
The phylogenetic species concept deems a species as the smallest exclusive monophyletic group of common ancestry. Usually defines more species than other concepts. Focused on the history of each group or pattern rather than the processes
What are the strengths of phylogenetic species concept?
The phylogenetic species concept reflects the evolutionary history of an organism and seems to clearly define what species are
What are the weaknesses of phylogenetic species concept?
Phylogenetic species concept depends on monophyly and cannot recognize paraphyletic species
What is the general lineage concept?
The general lineage concept is an attempt to unify species concepts. States that different species criteria are met at different times, the order of which is not constant
What are the three geographic modes of speciation?
Allopatric, Parapatric, Sympatric
What are two types of allopatric speciation?
Vicariance and Peripatric
What is vicariance allopatric speciation?
Vicariance is the splitting of one continuous population into two or more large groups that are geographically isolated from each other
What are three signs of allopatric speciation?
1. Disjoint geographical distributions of different species within a genus 2. Haplotype divergence among geographically distinct populations of a species 3. Incipient reproductive isolation between geographically isolated populations of a species
What is an example of geographical distributions of different species within a genus, sign of allopatric speciation?
Earless lizard species in southest US and northern mexico. Species clades correspond to distinct geographical regions
What is an example of haplotype divergence among geographically distinct populations of a species, sign of allopatric speciation?
The yellow pine chipmunk shows up to 7.5% sequence divergence between geographically distinct populations
What is an example of incipient reproductive isolation between geographically isolated populations, sign of allopatric speciation?
The dusky salamander in southern appalachians. Greater geographical isolation corresponds to decreased mating success and greater genetic distance
What is peripatric allopatric speciation?
Peripatric allopatric speciation is a founder event from widespread species into new habitat which then diverges in isolation. Subject to both natural selection and genetic drift
What is a possible example of peripatric allopatric speciation?
Side blotched lizards are thought to have speciated from peripatric allopatric speciation
What is secondary contact?
When two geographically separated populations come back into contact
What are the three choices a population has after secondary contact
1. Interbreed with no consequences (single cohesive species) 2. Create hybrids with lower fitness "two species w/out NS" 3. Reinforcement (two species w/NS)
What is reinforcement?
The enhancement of prezygotic isolation in sympatry by natural selection
What are Dobzhansky/Muller Interactions?
Dobzhansky/Muller interactions are epistatic interactions leading to loss in fitness in hybrids after secondary contact
In drosophila, what is the deleterious interaction in hybrids?
What is Parapatric speciation?
Parapatric speciation is when neighboring populations, between which there is moderate gene flow, diverge and become reproductively isolated
In parapatric speciation, what is stronger natural selection or gene flow?
Natural selection overrides diluting effects of gene flow in parapatric speciation
What is the difficulty with parapatric speciation?
It is difficult to distinguish from allopatric speciation followed by secondary contact
What is an example of parapatric speciation?
Metal tolerant grass and metal intolerant grass have incurred a change in flowering time. Self fertilization has led to reproductive isolation
What will cause speciation to occur over adaptive divergence?
1. Low ratio of gene flow to natural selection 2. Selection on trait that leads to reproductive isolation or linkage between selected trait and reproductive isolation gene
What is sympatric speciation?
Sympatric speciation is the evolution of reproductive isolating barriers within a single, initially random mating population. Requires evolution of reproductive isolation without spatial isolation
What are two ways that sympatric speciation can occur?
1. Genome doubling 2. assortative mating by resource use
How can sympatric speciation occur by assortative mating by resource use?
If natural selection is favoring divergence in resource use and if mate choice is directly correlated with resource use then disruptive selection will lead to assortative mating by resource
What is ecological speciation?
Divergent selection for resource use that leads to assortative mating and speciation
What is possible example of sympatric speciation?
Apple maggot flies lay their eggs inside of fruit. Their native host plant is the hawthorn plan. When apples were introduced 300 years ago, apple maggots began to use apple trees. This preference is heritable. Apples develop 3-4 weeks before hawthorns forcing reproductive isolation in the maggot flies.
what are the four criteria for sympatric speciation?
1. Current species must be sympatric 2. Species must have substantial reproductive isolation based on genetic differences 3. Taxa must be sister species 4. Biogeographical and evolutionary history must make allopatric speciation unlikely
How can you test for sympatry vs allopatry?
In allopatric speciation, range overlap as a function of genetic distance should have a positive slope. In sympatric speciation, range overlap as a function of genetic distance should have a level or negative slope
What is polypoidization?
Polyploidization is instant sympatric speciation that involves genome doubling, formed from an unreduced diploid gamete
Can polyploids reproduce with diploids?
No, polyploids are reproductively isolated from Diploids. Tetraploid mating with diploid creates triploid (infertile from improper pairing of homologs during meiosis)
What allows for polyploid divergence?
Polyploids are often phenotypically distinct (larger flower size, different pollinators, shifts in flowering time, shifts to asexual reproduction)
Did lungless salamanders speciate allopatrically or sympatrically?
Lungless salamanders speciated allopatrically due to a positive slope correlating range overlap and genetic divergence or time
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