Intragonadal incubation of progeny in three viviparous asterinid sea stars that differ in offspring provisioning, lecithotrophy vs matrotrophy

Abstract

In marine invertebrates that care for their young, the number of offspring is often correlated with adult size. The number, size, and mass of progeny relative to parent size were investigated in three asterinid sea star species that incubate their young in the gonads. Cryptasterina hystera has intragonadal planktonic-type lecithotrophic larvae with development supported by large eggs (440-µm diameter) and the juveniles are similar in size (655-µm diameter; coefficient of variation, CV = 6.89%). By contrast, Parvulastra vivipara and P. parvivipara have small vestigial larvae and small eggs (135–150-µm diameter) with offspring development supported by sibling cannibalism (matrotrophy). The juveniles in the gonads vary in size (500–5000-µm diameter, CV = 63.87 and 53.27%, respectively). All three species show a positive relationship between parent size and the number and size of juveniles. The allometry of brooding hypothesis that the number of progeny that can be cared for is (paradoxically) constrained in large adults due to space limitation was tested. In all species, the number of progeny increased with adult size, indicating that there are no allometric constraints on offspring incubation. To compare parental investment across the two modes of provisioning, the juvenile weight of C. hystera was used as a pro rata progeny unit. The matrotrophs had a higher reproductive output than similarly sized C. hystera. Of the hypotheses proposed to explain the evolution of parental care in marine invertebrates, none are broadly applicable to the viviparous asterinids because of the marked differences in their reproductive strategies.