Meeting Abstract

2.2  Sunday, Jan. 4  Intraspecific Variation of Egg Size and Hatching Size in Crepidula : Effects of Temperature and Population Structure COLLIN, R; Smithsonian Tropical Research Institute collinr@si.edu

A single egg size and hatching size are often attributed to each species of marine invertebrate, and little attention is paid to intra-specific variation. For many species, however, several different egg sizes have been reported in the literature. Presumably, egg size can vary among females, among populations or among habitants. If differences are due to genetic variation, such differences may reflect location adaptation and indicate one of the first steps in the evolution of different modes of development. I examined the effects of temperature, population, and female on egg size and hatching size for two sympatric species of marine gastropods, Crepidula atrasolea and Crepidula ustulatulina. Both species show significant effects of temperature and female on egg size and hatching size. Egg size and hatching size are larger in the low temperature treatment than at high temperatures. Crepidula ustulatulina, the species with significant population structure, also shows a significant effect of population. Hatchling shape also differs among populations of C. ustulatulina. Overall most of the variation (60%) in both egg size and hatching size was due to variation among females. However, only a single brood was examined for each female. When multiple broods were examined, significant variation among broods from a single female were evident. The variation between broods from the same female and significant effects of temperature suggest that it may be difficult for selection to act directly on egg size or hatching size in these species.