LEONARD, J.L.; PEARSE, J.S.*: Sex in banana slugs: Different clades do different things

Five clades of banana slugs of the genus Ariolimax occur along the west coast of North America: columbianus from SE Alaska to central California, stramineus from central California to Mexico, and brachyphallus, californicus, and dolichophallus from the northern, central, and southern portions of the San Francisco Peninsula. They differ primarily in genital morphology, and preliminary mtDNA analyses support the distinctness of the clades. We have found in the laboratory that the different species vary in egg size and growth rate. They are hermaphodites which sometimes perform apophallation whereby one or both slugs chew off the penis of their partner at the end of copulation. Individuals of dolichophallus generally have single, long-duration intromissions (typically greater than 1 h) that are simultaneously reciprocal, whereas those of californicus have short (typically 10-20 min), unilateral intromissions. Apophallation does not inhibit copulation, with apophallate animals acting as females. Further studies will examine variation among the other clades, and look at paternity in an attempt to understand the evolutionary basis of apophallation.