Selective predation of threespine stickleback by rainbow trout

Threespine stickleback (Gasterosteus aculeatus) with divergent pelvic phenotypes from Wallace Lake, Alaska, were exposed to rainbow trout (Oncorhynchus mykiss) to test for selective predation. Trout more often successfully preyed upon individuals with pelvic reduction, which supports the hypothesis that robust pelvic girdles are maintained in stickleback populations because of selection by fish predators. Stickleback with complete pelvic girdles experienced a higher incidence of wounds from unsuccessful predation attempts, although this finding was not statistically significant, possibly because of low frequencies of wounded individuals. Spines likely facilitate postcapture defence, although stickleback with spines may also be less targeted by trout. This study supports the hypothesis that stocked rainbow trout pose a conservation threat to pelvic-reduced stickleback populations.