DEMAINTENON, MJ; University of Hawaii at Hilo: Evolution of small body size in columbellid gastropods (Gastropoda: Neogastropoda).

The evolution of small body size has important consequences in terms of organismal ecology and physiology, and is also closely associated with episodes of origination and diversification leading to many higher taxa. Most of the extant clades of gastropod molluscs are thought to have evolved from small ancestral forms. Evolutionary trends leading to molluscan miniaturization are not well documented however. Columbellids are an immensely successful group of marine neogastropods (most of 10 to 20 mm shell length) that includes several genera (mostly in the tropical west Pacific) whose members reach no more than 4 mm in shell length. The existence of several small genera suggests multiple origins of small body size in modern columbellids, however the morphological similarity and sympatry that characterize these genera suggest that they may comprise only one or a very few clades. Preliminary results from phylogenetic analyses combined with investigation of internal anatomy and cell sizes will be used to investigate three primary questions: 1) How many independent groups of small columbellids (those less than 5 mm adult size) have evolved? How (by miniaturization, reduction or loss of specific anatomical structures, or a combination of the two) has each group achieved small body size? And are there any predominant patterns of change that have occurred independently in two or more groups?