LIMITED DISPERSAL AND PROXIMITY-DEPENDENT MATING SUCCESS IN THE COLONIAL ASCIDIAN BOTRYLLUS SCHLOSSERI.

Although the propagules of many sessile organisms have the capacity to disperse over large distances, dispersal is often spatially restricted. In this paper, I document, using a combination of mark/recapture techniques and histocompatibility assays, dispersal distance of the planktonic larvae of the sessile, colonial sea squirt Botryllus schlosseri. Both of these methods indicate that most larvae remain within a meter of their birthplace. Such limited dispersal should lead to increased matings among relatives, and the potential for inbreeding depression. However, the success of: 1) fertilization, 2) embryogenesis, and 3) larval metamorphosis all decrease as distance between mated colonies increases. The spatial scale over which this decrease in mating success occurs is concordant with the estimates of dispersal distance based on the larval mark/recapture data and histocompatibility assays. Taken together, these results imply that inbreeding depression is not a necessary consequence of limited dispersal and consanguineous matings in B. schlosseri. © 1987 The Society for the Study of Evolution.