Lecture 25 Flashcards
(29 cards)
if populations have diverged during a period when the groups have lived apart, what should their hybrid offspring experience?
- any hybrid offspring that are rpoduced should have markedly reduced fitness relative to individuals in each of the parental populations
- if they don’t experience reduced fitness, then the hyrbrids would continue to get reproduced until a new species forms
what does post zygotic isolation usually produce?
one cross would produce a viable offsprng and the other would produce a sterile offspring. there may even be a phenotypic difference in the offspring depending on what species is the father and which is the mother
what are epistatic interactions?
two loci and how they interact depends on the specific alleles combined
what are the incompatabilities in post zygotic isolation usually due to (like when they’re sterile)?
chromosomal differences or epistatic interactions among genes
what is the bateson-dobzhansky-muller incompatibilities?
- arise from negative interactions at two or more loci
- populations accumulate allelic differences att two or more loci, that cause genetic incompatabilities when combined in hybrids
what is the bateson muller dobzhansky model?
- populations become fixed for different alleles at two or more loci
- this model relies on negative interactions among genes
- go onto the slide and look at the model
what can happen to the F1 generation of hybrids if the alleles don’t work well together?
the F1 hybrid would have lower fitness, and this model (BMD model) doesn’t work well together
even when two populations are considered separate species, what can happen between them?
there still may be some gene flow between them and they can form hybrids
when species do interbreed and gene flow occurs, what are the four possible outcomes?
- incompatability, leading to selection against hybrids
- extrinsic inviability (the hybrid itself may be fine, but not a good fit for the environment)
- hyrbids favored due to novel traits, which can lead to a new species
- hyrbid zone in transitional habitats but they do not form a stable species
what should there be to prevent hybrid species?
there should be strong selection to prevent hybrid species
what is reinforcement?
- selection against hybrids
- if hybrids have reduced fitness compared to parents, then selection should favor traits that minimize the production of hybrids
- can occur if the fitness cost from lost mating opportunities is balanced by a fitness gain in offspring viability (so the hyrbrid has to have lower viability to prevent hybrids in the first place)
- so like selection for premating or prezygotic isolation
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Where can hybrids do better than their parents?
- hyrbids can do better in changing environments
- this is when they can do better than their environments
what is hybridization
the process of creating a hybrid
what is polyploidy?
full duplication of chromosome set
what can polyploidy lead to in terms of hybridization?
if there is polyploidy species that gets produced from a hybrid, this hybrid can no longer mate with the parental species, immediately making it its own species.
this is common and okay in plants that can self fertilize, since they don’t have to rely on there being another exact same hybrid
what are the two ways that the multiplication of the number of chromosomes can occur, polyploidy?
autopolyploidy: duplication of the chromsomes of a single species, nondisjunction during meiosis
allopolyploidy: duplication of a combination of chromsoomes from different species, which is more common
what can allopolyploidy lead to
- extremely rapid speciation
- two species hybridize, and a duplication event produces offspring with double the number of chromsomes. the new species is now reproductively isolated from either parent, and is effectively a new species
how can speciation by sexual selection occur?
- prezygotic isolating mechanisms often involve characters under sezual selection
- a species may have a specific trait that allows them to reckognize males of the same species, so that they only mate with specific males. this blocks the opportunity to produce hybrids with a different species, making it a prezygotic isolating mechanism
sexual selection + colonization of new islands can lead to…
speciation
what is the classic view of the speed of speciation?
- barrier to gene flow develops
- slow accumulation of genetic differences through mutation, drift, and natural seletion (slow accumulation of geneic differences at multiple loci and it happens over a long time)
- genetic divergence leads to reproductively isolating mechanisms (RIMs) as a by product
- perhaps secondary contact, with some level of hybridization possible
what is evidence of the classic view of speciation?
- look at the chart on the slidehow/graph
- accumulation of small differences over time (repersented by genetic difference on x axis) eventually leads to reproductive isolation (shown on y axis)
- in general, species pairs with greater genetic difference have greater reproductive isolation
- become more distantly related over time
- this graphing system allows us to measure their reproductive isolation
what is adaptive radiation?
the evolution of ecological and phenotypic diversity within a rapidly multiplying lineage
what does adaptive radiation involve?
the differentiation of a single ancestor into an array of species that inhabit a variety of environments and that differ in traits used to exploit those environments
what do islands provide an opportunity for?
dispersal and allopatric speciation
