Dissertation Research: The Evolution and Consequences of Variation in Life Histories and Development of Marine Gastropods in the genus Crepidula

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9972555Chernoff and Collin The species diversity of groups of organisms is influenced by many different factors, both external (the environment) and internal (physiology, life history). One key factor in the extinction and diversification of marine organisms is thought to be dispersal ability. Marine invertebrates (including starfish, clams, and snails) typically develop from a free-floating planktonic larval stage, either feeding or nonfeeding in behavior. These larvae provide a means of dispersal for animals that are often sedentary during their adult life. However, some species develop without going through such a larval stage (direct development). Direct developers hatch as miniature adults in the place where the eggs were deposited, and have low potential for dispersal. Differences in dispersal ability between species with planktonic larvae and species with direct development are associated with differences in extinction rates and with the rates of origin of new species. Species with planktonic larvae have lower rates of extinction and are less likely to give rise to new species. Because dispersal ability may have a strong influence on taxonomic diversity, it is important to understand the causes of variation in dispersal ability. Graduate student Rachel Collin, mentored by adviser Dr. Barry Chernoff at the University of Chicago, is studying larval development modes and phylogenetic relationships in one such group of marine organisms. Crepidula, a genus of marine snails with about 50 species, contains some species with direct development and some species with planktonic larvae. The genus offers an ideal opportunity to test hypotheses about the causes of differences in development type. DNA sequences for three genes for each species will be analyzed in order to determine the genealogical relationships among the species and proposed close relatives. In addition, live animals will be observed in the field and their development will be described. These observations will be combined with a hypothesis of species relationships to determine if direct development is correlated with ecological factors like body size, habitat depth, and latitude. This research will determine if genetic differences are greater for species with direct development than for species with planktonic larvae, and if close relatives are more likely to have the same development type than more distant relatives. The results of this research will improve understanding of how changes in larval development affect the diversification or extinction of marine invertebrate groups.