Species Concept and Accomplishing Isolation Flashcards
morphological species concept
- based on phenotypic differences
- Linnaeus used morphology when defining taxonomic changes
- the only species concept that is applicable to extinct species
- can be used in absence of behavioral or population genetic data
biological species concept
- Ernst Mayr suggested that similar appearance is not enough to distinguish a species
- a species is a population that can interbreed -> individuals in a species can only reproduce with individuals of the same species
a species may be made up by different populations, so there is no real way to assess interbreeding ability
evolutionary species concept
- based on the BSC, but with the inclusion of an explicit historical component
- a species is a separately-evolving lineage -> incorporates information from phylogenies
- most widely accepted
speciation
- natural consequence of population subdivision
- as pairs of species diverge genetically, they become reproductively isolated
- reproductive isolation: the individuals of each species are unable to have viable offspring with the other species
- reproductive incompatibility develops gradually in many groups reflecting the slow base at which genes accumulate in each lineage
Dobzhanksy-Muller Model
- explains how population subdivision leads to reproductive isolation
- an ancestral population is divided by a barrier to gene flow and the two groups evolve independently
- in each lineage new alleles become fixed at different loci; the new and old alleles are incompatible (natural selection, genetic drift)
- if populations are separated for long enough, speciation is likely to occur even if selective pressures are the same
allele incompatability
- under the DH model, long-isolated populations may suffer deleterious effects of resuming gene flow due to incompatibility
- if the two populations come back together, they may still be able to interbreed
- but the hybrid offspring will be unviable and the combination of genes could be harmful
allopatric speciation
isolation that is caused by a geographic barrier, stopping gene flow between a single population
sympatric speciation
isolation that arises within a geographically contiguous population
dispersal
movement of individuals to a new area (allopatric)
moves individuals across a barrier over which they cannot return -> gene flow halts
ex: dispersal events across Hawaiian islands created 600 fly species via 45 founder events
ex: biodiversity on the Galapagos island is due to dispersal
vicariance
- occurs when a barrier forms, dividing a population
- appearance of a new barrier within the existing range of a population causes it to be divided
- when multiple species undergo speciation at the same time in the same area -> ex: fish populations during Pleoitoscene glaciation
sympatric speciation
occurs in the absence of a geographic barrier
can occur with disruptive selection if certain genotypes have a preference for more distinct microhabitats where mating takes place
host-switching
- apple-maggot flies only deposited eggs on Hawthorne trees until European immigrants brought over apple trees
- the species becomes isolated since they tend to reproduce with species that have been raised on the same fruit + apple pupae develop faster
- widespread amongst insects
polyploidy
- autopolyploidy (polyploidy within a species) can occur accidentally if two diploid gametes fertilize -> tetraploid
- tetraploids and diploids are quickly separated as their offspring are triploid and sterile
- tetraploids can self-fertilize or mate with another tetraploid - reproductive isolation occurs within two generations
plant polyploidy
important in plant populations
70% of flowering species and 95% of ferns
