Effects of embryo energy, egg size and larval food supply on the development of asteroid echinoderms

Organisms have limited resources available to invest in reproduction,
causing a tradeoff between the number and size of offspring. One
consequence of this tradeoff is the evolution of disparate egg sizes and,
by extension, developmental modes. In particular, echinoid echinoderms
(sea urchins and sand dollars) have been widely used to experimentally
manipulate how changes in egg size affect development. Here we test the
generality of the echinoid results by 1) using laser ablations of
blastomeres to experimentally reduce embryo energy in the asteroid
echinoderms (sea stars), Pisaster ochraceus and Asterias forbesi and 2)
comparing naturally produced, variably-sized eggs (1.7 fold volume
difference between large and small eggs) in A. forbesi. In P. ochraceus
and A. forbesi there were no significant differences between juveniles
from both experimentally reduced embryos and naturally produced eggs of
variable size. However, in both embryo reduction and egg size variation
experiments, simultaneous reductions in larval food had a significant and
large effect on larval and juvenile development. These results indicate
that 1) food levels are more important than embryo energy or egg size in
determining larval and juvenile quality in sea stars and 2) the relative
importance of embryo energy or egg size to fundamental life history
parameters (time-to and size-at metamorphosis), does not appear to be
consistent within echinoderms.