Genetically based differences in nest characteristics between lake, inlet, and hybrid threespine stickleback from the Misty system, British Columbia, Canada

Hypotheses: Adaptation to different environments can drive the evolution of mating isolation and thereby contribute to ecological speciation. Adaptive divergence in nest characteristics, which could be one avenue to mating isolation, has received little attention. For it to be important, populations adapted to different environments should show genetic differences in nest characteristics. Organisms: Second-generation, laboratory-reared stocks of threespine stickleback (Gasterosteus aculeatus L.) from the Misty system, British Columbia, Canada. Experimental fish included pure lake fish, pure inlet fish, and lake–inlet hybrids. Methods: Males of different types (lake, inlet, and hybrid) were paired in aquaria, allowed to build nests, and then exposed to females of all three types (individually and on separate days). The resulting nests were photographed, collected, weighed, and dissected. Results: Lake nests were bulkier than inlet nests, and less often placed on gravel substrate than sand. Hybrid males tended to build intermediate nests but showed very high variation. Some hybrids built lake-like nests and others built inlet-like nests. Conclusions: Nest characteristics show genetic differences between lake and inlet stickleback, and might therefore contribute to any mating isolation.