title: Reproductive isolation among allopatric Drosophila montana populations.
abstract: An outstanding goal in speciation research is to trace the mode and tempo of the evolution of barriers to gene flow. Such research benefits from studying incipient speciation, in which speciation between populations has not yet occurred, but where multiple potential mechanisms of reproductive isolation (RI: i.e., premating, postmating-prezygotic (PMPZ), and postzygotic barriers) may act. We used such a system to investigate these barriers among allopatric populations of Drosophila montana. In all heteropopulation crosses we found premating (sexual) isolation, which was either symmetric or asymmetric depending on the population pair compared. Postmating isolation was particularly strong in crosses involving males from one of the study populations, and while sperm were successfully transferred, stored, and motile, we experimentally demonstrated that the majority of eggs produced were unfertilized. Thus, we identified the nature of a PMPZ incompatibility. There was no evidence of intrinsic postzygotic effects. Measures of absolute and relative strengths of pre- and postmating barriers showed that populations differed in the mode and magnitude of RI barriers. Our results indicate that incipient RI among populations can be driven by different contributions of both premating and PMPZ barriers occurring between different population pairs and without the evolution of postzygotic barriers.
authors.affiliation: Department of Biological and Environmental Science, University of Jyväskylä, P.O. Box 35, FI-40014, Jyväskylä, Finland; Current Address: Department of Biological Sciences, University of Arkansas, Fayetteville, Arkansas, 72701.
authors.forename: Jackson H
authors.initials: JH
authors.lastname: Jennings
authors.forename: Rhonda R
authors.initials: RR
authors.lastname: Snook
authors.forename: Anneli
authors.initials: A
authors.lastname: Hoikkala
mesh_terms: D000818:Animals; D004330:Drosophila / Q000145:classification* / Q000235:genetics*; D005260:Female; D049810:Genetic Speciation; D008297:Male; D060047:Reproductive Isolation
keywords: Gametic isolation; postmating-prezygotic isolation; sexual isolation; speciation; speciation phenotypes