Experimental Manipulation of Parental Investment in Echinoid Echinoderms

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Abstract
SYNOPSIS. In free spawning species, maternal investment is limited to the contents of the egg. Striking correlations between egg size and larval characteristics, such as development rate, larval size, body form, feeding capability, nutritional requirements, and size at metamorphosis, have been observed in many taxa of marine invertebrates, in spite of tremendous morphological and ecological diversity. Analysis of these relationships has historically been based on comparative observations or quantitative modeling. Advances in our understanding of life history ecology in marine organisms require combining evolutionary theory with functional analyses of larvae as pelagic organisms. I believe that development will prove to be an important integrative link between these fields. In taxa with regulative development {e.g., echinoid echinoderms), it is possible to experimentally manipulate the amount of material that is available for larval morphogenesis. This provides a powerful tool for elucidating the developmental consequences of changes in maternal investment. Here, I will examine the rationale and methodology underlying this experimental approach and review the conclusions and some outstanding questions concerning the influence of maternal investment on the morphology, function, growth, and development of larvae. The four main effects of an experimental reduction of egg size (blastomere isolation) are: 1) smaller larval size, 2) simpler larval form, and 3) slower development in the early-stage larvae, but 4) regulation of size, shape, and development rate in late-stage larvae.

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