GENE FLOW AND INEFFECTIVE ANTIPREDATOR BEHAVIOR IN A STREAM-BREEDING SALAMANDER

Predators often feed on prey that show ineffective antipredator behavi or. Gene flow among populations may constrain evolution of effective a ntipredator ability in larvae of the streamside salamander, Ambystoma barbouri, a species that occupies distinctly different habitats with c onflicting selection pressures. Some streams are ephemeral, where larv ae should be active to feed and reach metamorphosis before stream dryi ng. in contrast, other streams are more permanent and contain pools wi th predatory fish, where larvae should remain inactive to avoid fish p redation. Feeding rates and predator escape behavior were assayed for laboratory-reared larvae from 15 populations. Larval survival was also compared among populations in artificial streams with natural predato rs. Five populations represented streams subjected to fish predation a long a gradient of genetic and geographic isolation from populations w ithout fish; the remaining 10 populations were ephemeral and without f ish. Individuals from populations with fish had significantly stronger behavioral responses to fish (i.e., decreased feeding rate associated with the presence of fish and increased escape response) than individ uals from fishless populations. Larvae from populations containing fis h that were more isolated from fishless populations showed stronger an tipredator responses than less isolated populations. Further, larvae f rom more isolated populations survived longer in the predation experim ent, indicating that the behaviors measured were related with survival . These results suggest that gene flow between populations with confli cting selection pressures limits local adaptation in some salamander p opulations with fish. While previous studies have typically focused on the role of gene flow in pairs of populations, the results of this st udy suggest that gene flow is acting to swamp local adaptation across several populations.