We study the charismatic threespine stickleback (Gasterosteus aculeatus complex), focusing our work on species pairs from several lakes in coastal British Columbia. Threespine sticklebacks offer an unparalleled opportunity to address questions about the role of sexual and natural selection in speciation. This is because they have speciated extremely rapidly, and repeatedly. These pairs evolved following separate colonization of each lake by the marine threespine stickleback (Gasterosteus aculeatus) following the retreat of the glaciers at the end of the Pleistocene 10,000-12,000 years ago. Each is directly descended from the marine ancestor and the species within a lake are not sister taxa.
Species pairs occur in seven lakes and all consist of a limnetic and benthic type. Pairs in at least four lakes have evolved independently from those in other lakes. In each lake the two species are highly differentiated ecologically, morphologically, and in mating behavior. They exploit alternate foraging niches: the limnetic feeds primarily on zooplankton in the open water and the benthic on invertebrates in the littoral zone. Differences in antipredator adaptations indicate they are also exposed to different suites of predators and parasites. Differences in the complexity of habitat has even led to differences in spatial learning (Odling-Smee, Boughman & Braithwaite 2008).
Benthics nest in vegetation while limnetics nest in the open. These breeding microhabitats differ in light regime (Boughman in prep), which affects nuptial color and color preference. All limnetics share a common environment distinct from that of benthics. Habitat differences may affect predation risk, male density, light environment, intensity of male territorial competition, encounter rates with females, mating success, courtship interruption, costs of choice for females, and parental care.
Limnetic male stickleback
Sticklebacks have long been a model system for sexual selection research. Some of Tinbergen’s earliest work explored color and courtship behavior in sticklebacks and a huge body of work has been devoted to sexual selection in sticklebacks. Sticklebacks are a model system for exploring the causes of speciation. They developed as a model system for studying the genetics of adaptation and speciation.
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