Meeting Abstract
Chimerism, where two or more genetically distinct individuals are found within a single body, occurs across a wide variety of taxa. Botryllus schlosseri is one of the model organisms used to study the evolution of chimerism. However, natural rates of chimerism are still not well known. Field surveys in varying locations and population densities have established estimates of 10 to 20%. Lab fusions between pairs of siblings from a single clutch found a fusion frequency close to 50% (Scofield et al., 1982). A field monitoring study of Botrylloides violaceus found recruits in a single population fused at a rate of 73% (Westerman et al., 2009). Here, we report on a fusion rate experiment using gravid marina-fertilized B. schlosseri colonies that were redeployed in the field. In each of 3 replicates, we attached a single source colony to the center of 3 PVC plates tied together and hung from an exposed seawall in the San Francisco Bay. Recruits were monitored for over two months to track the total number of fusions between larval settlers from the experimental source colony. Genetic samples were taken before and after fusion and a subsample of fusions were confirmed using 6 microsatellite loci. Recruit numbers were high with between 80-100 recruits per plate. Mortality rates were low, approximately 20-25% of the recruits disappeared, primarily in the initial week. The mean fusion rate of 59% was comparable with field rates observed in Botrylloides and much higher than previous field survey rates for Botryllus. This study shows how local populations of botryllids may quickly build up closely related aggregations of conspecifics via high fusion rates and may easily dominate space given appropriate conditions.
