Genetic and environmental contributions to the morphology of lake and stream stickleback: implications for gene flow and reproductive isolation

Question: Do the morphological differences between wild lake and stream stickleback have a genetic basis? Organisms: Wild-caught and laboratory-reared threespine stickleback (Gasterosteus aculeatus) from Misty Lake, and from its inlet and outlet streams. Methods: A common-garden experiment was used to examine the genetic and environmental components of morphological variation. Morphology was quantified through multivariate body shape (geometric morphometrics) and through a suite of linear measurements. Conclusions: The most striking morphological differences between the inlet and lake populations have a genetic basis, whereas those between the outlet and lake populations do not. Most notably, inlet fish have genetically deeper bodies, shorter pelvic and dorsal spines, and deeper caudal peduncles than do lake or outlet fish. All traits showed substantial plasticity; however, the relative differences between ecotypes were similar in the wild and the laboratory. These genetically based morphological differences may contribute to several ecologically dependent reproductive barriers between lake and inlet stickleback.