SHERRARD, K.M.; University of Chicago: The biomechanics and ontogeny of fatal constipation in the brooding sea squirt Corella inflata

Corella inflata is a species of solitary ascidian which broods by retaining its buoyant embryos in an inflated region of tunic near the excurrent siphon. This novel morphology has a negative consequence, apparently unique among ascidians, in that individuals rapidly become fatally constipated in most orientations. Animals in the wild are found in a siphons-down position, although. initial settlement orientation is random and attachment is too rigid to permit rapid changes. Here I present biomechanical and scaling analyses of the consequences to fecal elimination of ontogenetic changes in excurrent flow patterns arising from the development of the brooding bulge. Elimination of fecal pellets from the excurrent siphon depends on a strong gravitational component in adults. However, juvenile C. inflata can eliminate fecal pellets from any orientation due to morphological, behavioral and performance differences. Juveniles reorient somewhat hapharzardly during the first two months to reach the adult orientation before retention of feces becomes a risk. The brooding habit of C. inflata probably enhances larval survival, while exacting a cost to adults living on shifting substrates, and perhaps to reorienting juveniles.