MILES, Cecelia M.; WAYNE, Marta L.; University of Florida; University of Florida: Artificial selection on egg size in the polychaete worm Hydroides elegans

Life histories in marine invertebrates are very diverse, and the topic of the transition between obligate feeding larvae and non-feeding larval forms has been a recurrent theme. One theory regarding the transition to lecithotrophy is that as egg size increased, the larva would no longer have to feed to reach metamorphic competence. A complex trait such as egg size does not evolve in isolation, and changes in a trait so closely associated with fitness would likely involve tradeoffs not only in larval characters, but across the life history of an individual. In order to address the question of genetic correlations between related traits and egg size, a population of Hydroides elegans was established from worms collected at Pearl Harbor, HI in November 2002. Artificial selection based on egg size was performed for five generations creating three lines selected for large eggs and three control lines. A suite of fitness-related characters including fecundity, maternal dry weight, total egg energy, larval growth, and juvenile growth were measured after selection had occurred. Both egg size (diameter) and total energy per egg were significantly larger in the selected lines relative to the control lines. The large-egg mothers produced significantly larger numbers of eggs, though there was no detectable difference in dry weights between the two lines. No significant difference was observed between lines in size of the larva at 18-20h post-fertilization, but competent (5d) larvae were significantly larger in the large-egg lines. Possible implications of these results are discussed within the framework of the biology and life history of Hydroides elegans.