title: Evolution of reproductive isolation in stickleback fish.
abstract: To understand how new species form and what causes their collapse, we examined how reproductive isolation evolves during the speciation process, considering species pairs with little to extensive divergence, including a recently collapsed pair. We estimated many reproductive barriers in each of five sets of stickleback fish species pairs using our own data and decades of previous work. We found that the types of barriers important early in the speciation process differ from those important late. Two premating barriers-habitat and sexual isolation-evolve early in divergence and remain two of the strongest barriers throughout speciation. Premating isolation evolves before postmating isolation, and extrinsic isolation is far stronger than intrinsic. Completing speciation, however, may require postmating intrinsic incompatibilities. Reverse speciation in one species pair was characterized by significant loss of sexual isolation. We present estimates of barrier strengths before and after collapse of a species pair; such detail regarding the loss of isolation has never before been documented. Additionally, despite significant asymmetries in individual barriers, which can limit speciation, total isolation was essentially symmetric between species. Our study provides important insight into the order of barrier evolution and the relative importance of isolating barriers during speciation and tests fundamental predictions of ecological speciation.
authors.affiliation: Department of Integrative Biology, Michigan State University, East Lansing, Michigan.|Ecology, Evolutionary Biology, and Behavior Program, Michigan State University, East Lansing, Michigan.|BEACON Center for the Study of Evolution in Action, Michigan State University, East Lansing, Michigan.|Department of Biological Sciences, Watershed Studies Institute, Murray State University, 2112 Biology Building, Murray, State University, Murray, Kentucky, 42071.
authors.forename: Alycia C R
authors.initials: AC
authors.lastname: Lackey
authors.affiliation: Department of Integrative Biology, Michigan State University, East Lansing, Michigan.|Ecology, Evolutionary Biology, and Behavior Program, Michigan State University, East Lansing, Michigan.|BEACON Center for the Study of Evolution in Action, Michigan State University, East Lansing, Michigan.
authors.forename: Janette W
authors.initials: JW
authors.lastname: Boughman
mesh_terms: D000818:Animals; D005260:Female; D049810:Genetic Speciation; D008297:Male; D060047:Reproductive Isolation; D012726:Sexual Behavior, Animal; D023701:Smegmamorpha / Q000235:genetics / Q000502:physiology*
keywords: Asymmetric isolation; incipient species; postmating isolation; premating isolation; reverse speciation