Speciation Flashcards
what is the morphological species concept
The Morphological Species Concept - distinguished by visible phenotype
what is the Ecological Species Concept
Ecological Species Concept - distinguished by ecological niche
what is the Biological Species Concept
Biological Species Concept (BSC) - distinguished by reproductive isolation; groups that do not interbreed are considered different species.
what are the 3 main species concepts
Morphological
Ecological
biological
what does Allopatry refer to
Allopatry refers to populations which are geographically separated
what is allopatric speciation
Allopatric speciation: local adaptation (Natural selection), mutation, and genetic drift, results in initially indentical populations diverging phenotypically and genetically.
Overtime, incompatibilities (genetic, behavioural, etc) accumulate, such that even if they ‘meet’ again (secondary contact) they no longer interbreed
what is Sympatric Speciation
Sympatry refers to populations which co-occur geographically
Sympatric speciation: thought to be less common than allopatric speciation, but possible if there is fine scale separation in space or time
how does Geneflow play into speciation
The key in both models is reproductive isolation, the reduction or absence of gene flow.
Gene flow counteracts the formation of species and, in general works against local adaptation.
what is the expectation regarding hybrid when the cause of initial divergence is local adaptation
If the cause of initial divergence is local adaptation, the one expectation is that hybrid offspring suffer low relative fitness compared to offspring of ‘pure’ crosses
i.e. natural selection against hybrid phenotypes (post-zygotic barriers)
what can species evolve to reinforce speciation
But species can also evolve mechanisms of ‘reinforcement’ potentially reducing the likelihood of making hybrids at all.
e.g. if mating preferences (pre-zygotic) evolved to minimize the risk/costs or producing unfit offspring (postzygotic)
what is microevolution
The forces of evolution explain changes along each branch aka “microevolution”
what is Macroevolution
Where do new species come from?
The emergence of new species is “Macroevolution”
what is speciation
Speciation is a reduction of gene flow which leads to new species.
Speciation preserves the history of microevolution. The shape of the Tree of life is determined by speciation and extinction.
what do Phylogenetic trees allow estimation of
Phylogenetic trees allows the estimation of diversification rates (net number of species)
how long are the intervals between speciation ‘events’
intervals between speciation ‘events’ can range from 4,000 years to 40 million years in various taxa.
The average is 6.5 million years.
how many genes are involved in speciation
Speciation can involve many or few genes
what is the difference between Allopatric and Sympatric speciation
Allopatric speciation involves geographic barriers while sympatric does not
what prevents speciation
Gene flow counteracts the formation of species and in general works against local adaptation.
So for speciation to occur, Gene flow must reduce.
what are 8 barriers to gene flow
There are ~8 types of barriers which can prevent gene flow:
- Habitat Isolation
- Temporal Isolation
- Behavioural Isolation
mating
- Mechanical Isolation
- Gametric Isolation
fertilization
- Reduced Hybrid viability
- Reduced Hybrid fertility
- Hybrid Breakdown (breakdown of hybrids in later generations)
1-5 are Prezygotic
6-8 are Postzygotic
describe incomplete reproductive isolation
Depending on the strength of the barrier (including selection against hybrids) and the amount of gene flow, Speciation can still proceed despite Hybridization
Incomplete reproductive Isolation is quite common in natural population
what are the 3 possible outcomes from Hybridization between 2 lineages:
There are 3 possible outcomes from Hybridization between 2 lineages:
- Reinforcement: the hybrids are less fit and speciation is reinforced
- Fusion: the hybrids are more fit and two lineages merge back together
- Stability, both species and hybrids co-exist
what is evolutionary stasis
Long periods of slow / no phenotypic evolution is referred to as evolutionary “stasis”
Can be caused by stabalizing selection
can Genetic drift actually change stuff
Genetic drift can generate a substantial amount of evolutionary change.
In some ways there seems to be much less evolution observed than would be expected from genetic drift.
what are the 3 key points from BIOL184
- All organisms ever are connected by a common ancestor.
- No species is inherently more “advanced”, superior, better, etc than others. The diversity reflects many different ways of adapting and persisting, despite the ever-changing conditions of Earth.
- All living species are different from their long gone ancestors and by definition the descendants of winners.
