Meeting Abstract
Organisms have a limited amount of resources available to produce offspring, leading to a tradeoff between the size and number of offspring they can produce. In the extreme, differences in per-offspring maternal investment can lead to disparate modes of development, even among closely related species. Echinoid echinoderms have long been used as a model system to investigate the consequences of changes in maternal investment for offspring development, but responses in echinoids may not apply to other taxa. To expand the taxonomic coverage of the effects of changes in maternal investment, we tested how experimental reductions in egg size affected larval and juvenile development in the seastar, Pisaster ochraceus. We manipulated maternal investment by killing one of the blastomeres of two-cell stage embryos with a laser, to effectively halve the amount of maternal investment in the egg. In control embryos (whole), no cells were killed and the initial investment was retained. The larvae from whole and half sized embryos were reared to metamorphosis in beakers with 20 embryos of a single treatment per beaker (N = 5). We measured time to metamorphosis, spine length at metamorphosis, and disk area at metamorphosis. Whole embryos developed into juveniles with three percent larger disk area and 10 percent more spines than half sized embryos. Whole embryos also reached metamorphosis on average 14 percent earlier than half sized embryos. These results were in the same direction as our predictions based on the effects of egg size manipulation in echinoids, but effect sizes were smaller than anticipated. We are currently tracking juveniles post-metamorphosis to test for latent effects of changes in maternal investment.
