Lecture 24 Flashcards
(25 cards)
what is the biological species concept?
species are groups of potentially interbreeding populations that are reprodctively isolated from other groups
this definition works well for sexuall reproducing animals, not asexual
how do we asses if populations are potentially interbreeding?
need to be able to produce viable offspring
what is the phylogenetic species concept?
smallest possible group descending from a common ancestor and recognizable by unique derived traits. useful for systemics and focuses on phylogentic history
what is the general lineage species concept?
- species are metapopulations that exchange alleles frequently enough to comprise the same gene pool
- a metapopulation is a group of spatially separated populations of the same species that interact at some level
- they exchange alleles just enough to comprise a gene pool but are often spatially separated that have rarely interacted
- species descrived in terms of genetic differences among populations (most common for asexual organisms)
how do we choose which definition of species to choose?
we choose the definition of species depending on the question and what information we want to know
what is speciation?
the process by which one genetically cohesive population splits into two or more reproductively isolated populations
what does speciation require?
requires the disruption of gene flow and the evolution of reproductive isolating mechanisms. This is what keeps the species apart.
what are the big 3 reproductive isolating mechanisms?
- prezygotic barriers (pre mating and post mating)
- postzygotic barriers
what are prezygotic barriers?
before fertilization barriers
what are the two types of prezygotic barriers? explain both.
Pre-mating barriers:
* the two organisms at this point are not even trying to mate
* different breeding times or places
* different mating behavior, so they meet, but won’t mate with each other
Post-mating barriers:
* copulation occurs, but gametes are not transferred
* gametes are transferred, but eggs are not fertilized
how can post mating barrier occur?
no fertilization would occur due to gametic incompatibility. Sperm or pollen from one species fails to penetrate and fertilize the egg of another species
what are the post zygotic barriers?
- after fertilization barriers
- hybrids are produced, but have low fitness
what are the two types of post-zygotic barriers?
Extrinsic
* The low fitness of the hybrid is not due to something about the hybrid itself but the external environment
* ecological inviability
* behavioral sterility
Intrinsic
* Some sort of genetic incompatibilities are the result in this hybrid. could be the chromosomes don’t work well together or could be sterile
* hybrid inviability
* hybrid sterility
What is meant by the post zygotic barrier, extrinsic barrier, ecological inviability?
- does not do well in the environment
- In the butterfly example, the hybrid butterflies (due to their unique color pattern) were attacked by birds signifigantly more frequently than those of either of the ‘normal’ parent
- so the hybrids would have lower survival than the parents
what is meant by the postzygotic intrinsic barrier hybrid sterility?
- the hybrid would be sterile
- the mule is an example of this
- hybrid sterility could be due to chromosomal sterility. For the mile, it has an odd number of chromosomes so it is unable to line up during meiosis, therefore unable to make sperm or eggs
what are the two isolating barriers that block gene flow (geographical barriers)?
- Allopatry: populations are in separate non-overlapping geographical areas- there are geographical barriers to gene flow
- Sympatry: populations are in the same geographic area, but according to most species concepts species must be able to remain distinct from each other even when they occur in sympatry
what are the three models of speciation?
- allopatric speciation
- sympatric speciation
- parapatric speciation
what is the allopatric speciation model of speciation?
- speciation with geographic isolation
- how most species form, but not always
- evolution of reproductive isolating mechanisms between populations that are geographically separated
- geographic separation is defined by spatial restriction of gene flow, not just physical distance (ex. could be separated on either side of a river)
what is the sympatric model of speciation?
- reproductive isolation evolves without geographic restriction to gene flow
- requires non random mating based on genetic or phenotypic factors
what is ecological speciation
- an example of sympatric speciation (can be apart of it)
- evolution of reproductive barriers due to adaptation to divergent environments
- adapting to different environments and as a consequence they don’t mate anymore
What are 3 key components of sympatric speciation?
- Reproductive isolation can arise even in sympatry because individuals in different subpopulations rarely interbreed
- reproductive isolation can occur as a by product of adaptation to divergent environments (ex. if disruptive selection happens for too long, leads to two different species, and the intermediate to be less fit)
- early stages can involve extrinsic reproductive barrier to gene flow
what is the connection between disruptive selection and speciation?
If disruptive selection happens for too long, leads to two different species happen
what is paraptric speciation?
when you have sympatric and allopatric speciation processes happening at the s)ame time (just know this, don’t need to know too much
what is the general order that results in speciation?
divergence, barrier to gene flow, and then reproductive isolation
