Mate choice in the face of both inbreeding and outbreeding depression in the intertidal copepod Tigriopus californicus

In species vulnerable to both inbreeding and outbreeding depression, indivi duals might be expected to choose mates at intermediate levels of genetic r elatedness. Previous work on the intertidal copepod Tigriopus californicus has repeatedly shown that crosses between populations result in either no e ffect or hybrid vigor in the first generation, and hybrid breakdown in the second generation. Previous work also shows that mating between full siblin gs results in inbreeding depression. The present study again found inbreedi ng depression, with full sibling mating causing significant fitness decline s in two of the three populations assayed. In the mate choice assays, a sin gle female was combined with two males. Despite the costs of both inbreedin g and outbreeding, mate choice showed clear inbreeding avoidance but no cle ar pattern of outbreeding avoidance. This lack of outbreeding avoidance may be attributed either to the temporary increase in fitness in the F-1 gener ation or to the absence of selection for premating isolation in wholly allo patric populations with infrequent migration. If this inability to avoid un wise matings is common to other taxa, it may contribute to the problem of o utbreeding depression when allopatric populations are mixed together.