Speciation Flashcards
Define species
the smallest evolutionary independent unit
What are the 3 species concepts
- biological SC
- morphospecies C
- phylogenetic SC
Define the biological species concept
defining species as groups that can interbreed and produce viable offspring and are reproductively isolated from other groups
strength of BSC
strength = confirms lack of gene flow
limitations of BSC
- assumes sexual reproduction
- in allopatric populations
Define morphospecies concept
defining species based on morphological differences
what are strengths of morphospecies concept
- can be sex or asexual
- can be living or extinct
what are limitations of morphospecies concept (4)
- may consist of arbitrary designations, may have some disagreement
- fossils, the difference in colour and soft tissue
- does not work well for bacteria or archea (all small round species)
- cryptic species - that have no morphological difference, but cannot reproduce
Define phylogenetic species concept
defining species by identifying the smallest monophyletic group in a phylogeny of a closely related population/species
Strength of PSC
strengths = can be applied to many groups
limitation of PSC
varies if looking at gene tree vs. species tree
What are the 2 categories for the tempo of speciation
- gradualism model
- punctuated equilibrium model
define gradualism vs. punctuated equilibrium models
gradualism = small changes building over time leading to separation in speciation
punctuated = everything stays the same until sudden extreme changes occur and cause speciation
What are the 3 simple steps to forming a species
- populations become isolated
- traits diverge
- reproductive isolation (could not reproduce IF brought back together)
What are the 2 categories in which population isolation can occur
- allopatric model
- sympatric model
Define allopatric vs. sympatric model
and examples
allopatric = populations are physically isolated
ex. mountains
sympatric = populations are not physically isolated but reproductively isolated
ex. divergent selection - behaviour, polyploidy, sexual selection
explain the difference of isolation and divergence steps in allopatric vs. sympatric models
allopatric has isolation as the first step and then divergence
whereas sympatric has isolation and divergence occurring at the same time
what 3 factors cause populations to diverge
- genetic drift
- natural selection
- sexual selection
how does genetic drift cause populations to diverge
the random movement of a small groups of individuals to a new area can drive the affects of speciation (ex. founder effect)
how does natural selection cause populations to diverge
preferences are heritable and non-random mating occurs which can effect factors such as allele frequencies, genetic marking, timing, to cause sympatric speciation
how does sexual selection cause populations to diverge
it affects gene flow directly, speciation can result from nonrandom mating
What are the 3 reproductive isolating mechanisms and explain
- premating = never mate
- prezygotic = mate, but no zygote forms
- postzygotic = zygote forms but is not born
What are the 3 results of populations being brought back together after speciation
- reinforcement
- hybrid speciation
- stable hybrid zone
Explain reinforcement
populations stay isolated and hybrids are selected against
Explain hybrid speciation
form a 3rd hybrid species that is favoured for in areas that the parents aren’t found
Explain stable hybrid zone
3rd hybrid species forms that is selected for in hybrid zone but not in other areas, do not colonize new areas
