Breakdown in postmating isolation and the collapse of a species pair through hybridization.
Species that evolved through ecological speciation and that lack intrinsic genetic incompatibilities may nonetheless be maintained by extrinsic postmating isolating barriers that impose selection against hybrids. These species, however, may be vulnerable to a breakdown in postmating isolation. Here, we investigate a model system for ecological speciation: sympatric limnetic-benthic pairs of threespine sticklebacks. Recently, stickleback hybrid abundance in Enos Lake has increased. Given that ecological selection against hybrids was historically an important component of total reproductive isolation, we tested whether ecologically dependent postmating isolation is still functioning. We compared body shape, diet, growth, and survival in present-day Enos fish with trait data in the undisturbed Paxton Lake species pair and with historical Enos Lake data. In both Paxton and historical Enos data, we found a strong correlation between body shape and diet; however, in present-day Enos fish, this correlation was absent. Using fitness estimates based on growth rates and survival, we found no evidence of selection against intermediate morphologies. It appears that postmating isolation has broken down, allowing hybrids to persist and contributing to the collapse of the species pair.
Behm
Jocelyn E
JE
Department of Zoology, University of Wisconsin, Madison, Wisconsin 53706, USA. jebehm@wisc.edu
Ives
Anthony R
AR
Boughman
Janette W
JW
D000818:Animals; D049628:Body Size; D002247:Carbon Isotopes; D004032:Diet; D005260:Female; D049810:Genetic Speciation; D006824:Hybridization, Genetic; D008297:Male; D011157:Population Dynamics; D012726:Sexual Behavior, Animal; D023701:Smegmamorpha / Q000033:anatomy & histology / Q000235:genetics / Q000502:physiology*; D012934:Social Isolation
D002247:Carbon Isotopes