Speciation basics
This process produces new species through evolution of reproductive isolation
What is speciation
Schluter uses this term for reproductive isolation that evolves through adaptation to different environments or niches.
What is ecological speciation?
These fish evolved different body shapes in Bahamian blue holes with versus without predators.
What are mosquito fish, Gambusia hubbsi?
This experiment places each population in both its own habitat and the other population’s habitat to compare fitness.
What is a reciprocal transplant experiment?
Despite differences in terminology, both papers emphasize this evolutionary force as a major contributor to speciation.
What is natural selection?
This species concept groups interbreeding natural populations that are reproductively isolated from other groups.
What is the Biological Species concept
In this alternative mechanism, populations facing similar selection pressures fix different advantageous mutations.
What is mutation-order speciation
Coastal perennial and inland annual races of this monkeyflower have low fitness when transplanted into each other’s habitat.
What is Mimulus guttatus?
This form of isolation occurs when individuals entering another population’s habitat have low fitness there.
What is immigrant inviability?
Sobel and colleagues question the usefulness of dividing speciation into these two opposing labels.
What are ecological and nonecological speciation? They argue that ecological, selective, and stochastic factors can interact within a single speciation event.
When individuals preferentially mate with others of the same ecotype, they exhibit this mating pattern.
what is assortive mating
Mutation-order divergence includes chance, but differs from this process because the fixed mutations are favored by selection.
What is genetic drift?
Swapping alleles at the yup flower-color locus between monkeyflower species changed this animal-mediated component of reproductive isolation.
What is pollinator preference, or pollinator isolation? The experiment involved Mimulus cardinalis and M. lewisii.
In Schluter’s framework, researchers begin with traits under divergent selection, connect them to reproductive isolation, and then identify the genes. This is the named research approach.
What is the top-down approach? The bottom-up approach begins by genetically mapping reproductive isolation.
Sobel distinguishes actual spatial separation from this genetically based difference in geographic distribution caused by habitat adaptation.
What is ecogeographic isolation? Actual spatial separation is called effective geographic isolation and can also reflect historical factors.
These two broad classes of barriers act before versus after formation of a zygote.
What are prezygotic and postzygotic barriers?
A gene that benefits its own transmission spreads, followed by a gene that counters its effects. Schluter identifies this kind of conflict as a possible route to mutation-order speciation.
What is intragenomic conflict? Examples include meiotic drive and suppressor genes, or cytoplasmic male sterility and nuclear restorer genes.
In Schluter’s Figure 1A, mosquito fish from separate populations were more likely to mate when they shared this environmental feature.
What is the same predation environment? Fish from similar predation environments also had similar body shapes.
Repeated independent populations show greater reproductive isolation across contrasting habitats than across similar habitats. Schluter calls this a test of this phenomenon.
What is parallel speciation? Researchers must establish independent origins to help rule out a single origin followed by dispersal.
An early habitat barrier blocks 80% of potential gene flow. A later barrier blocks 80% of what remains. In this calculation adapted from Sobel’s example, the later barrier blocks this percentage of the original potential gene flow.
What is 16%? Only 20% remains after the first barrier, and 80% of that is 16%; together, the barriers block 96%.
Two populations look different after adapting to different habitats. This additional finding is needed to demonstrate speciation rather than adaptation alone.
What is reproductive isolation, or reduced gene flow due to biological differences?
Gene flow especially hinders mutation-order speciation for this reason, even though populations are adapting.
What is the spread of the same advantageous mutations between populations? This can prevent populations from following different genetic paths and developing reproductive isolation.
Sobel’s Figure 2 shows that a new polyploid may fail despite reproductive barriers if it shares its ancestor’s niche. Name the mating disadvantage it faces when rare and one ecological way to help it persist.
What are the minority cytotype disadvantage and adaptation to a different niche? Rare polyploids often mate with the common parental cytotype, producing low-fitness offspring; occupying a different niche can reduce those encounters and competition.
A reproductive-isolation gene shows a signature of positive selection. Before attributing speciation to that selection, Schluter says researchers must establish this timing.
What is fixation before complete reproductive isolation? If the mutation became fixed after speciation was complete, it cannot explain the original formation of the species barrier.
A researcher measures strong hybrid sterility in species that separated long ago. Sobel recommends focusing on these species pairs to identify barriers that actually contributed to speciation.
What are species pairs that have only recently achieved species status? Strong barriers in older species may have accumulated after speciation was already complete.