Meeting Abstract

S3-1.2  Wednesday, Jan. 4  What Can “Intermediates” Tell Us About Evolutionary Transitions Between Modes of Invertebrate Development? COLLIN, R; Smithsonian Tropical Research Institute collinr@si.edu

Mode of development in marine invertebrates has been largely viewed as a dichotomy between small eggs that develop into free-living planktotrophic larvae and large eggs that bypass the larval stage and develop directly into juveniles. Modes of development viewed as intermediate between these two extremes include facultative feeding larvae, non-feeding lecithotrophic larvae, and poecilogony where nutritional mode varies within a species. Available phylogenies, however, do not usually show these forms in positions intermediate between planktotrophs and direct developers, and recent optimality modeling efforts have also shown that “intermediate” nutritional modes may be more evolutionary stable than previously believed. Are these forms truly transitional or intermediate, in evolutionary terms? Do evolutionary transitions between modes of development necessarily involve these forms? Does the evolutionary potential of poecilogonous forms differ from that of other “intermediate” forms of development? And how could natural selection act on existing genetic variation to drive evolutionary changes between developmental forms? To get at these questions we need to move away from the legacy of the bimodal view of egg size and development modes and not fall into the trap of viewing all “intermediates” as equal.