MCGHEE, Katie/E; Florida State University, Tallahassee: Indiscriminate fusion of swimming sponge larvae

For sedentary marine invertebrates, allorecognition systems allow individuals to distinguish between genetically similar and distinct tissue they may encounter and are thought to reduce tissue fusion with individuals other than self or kin. However, the cost/benefit trade-offs associated with fusion at a sessile adult stage may be drastically different than those associated with fusion at a mobile larval stage where size may be critical and encounters can be avoided or pursued. The purple sponge, Haliclona sp. (Class Demospongiae), is a temperate encrusting sponge commonly found in the intertidal along the West Coast of Canada. It releases free-swimming larvae that are capable of fusing and forming swimming chimeric larvae without loss of metamorphic ability. Using these larvae, I investigated the effect of relatedness on larval fusion frequencies and whether larvae distinguish between siblings, larvae from sponges at the same site, and larvae from sponges on islands separated by over a kilometer. Larval fusion frequencies averaged 13.4% and did not differ significantly between larval treatments indicating that larvae are unable to distinguish between individuals of varying relatedness. Interestingly, adult sponges differed significantly in the propensity of their larvae to fuse, suggesting the presence of individual strategies influencing the behavior of their larvae. In addition, behaviors leading to aggregation and increased larval encounter rate were investigated by comparing the swimming patterns of single larvae and paired larvae. The results of this study indicate that contrary to the predictions of self- or kin-recognition theory, factors other than relatedness may be involved in determining the likelihood of larval fusion.