Meeting Abstract

101.7  Wednesday, Jan. 7  Predator-induced changes in maternal investment in an intertidal snail ALLEN, JD; Randolph-Macon College jonathanallen@rmc.edu

Marine invertebrate animals frequently exhibit inducible morphological defenses in the presence of predators. However, few studies have investigated how adults modify reproductive behavior in the presence of predators in order to reduce mortality rates on their offspring. In this study I tested how an intertidal snail, Ilyanassa obsoleta, adjusts its investment in eggs and egg capsules in response to a common predatory crab, Carcinus maenas. This is a useful system for testing the effects of predators on reproduction because of the readiness with which Ilyanassa will lay in the lab, their abundance on mud flats on both coasts of North America and their short time to hatching (~ 2 weeks). Adult Ilyanassa have been shown to respond behaviorally to chemical cues from Carcinus but the effects of this response on their reproduction has not been assessed. Carcinus preys on both adult and embryonic Ilyanassa and I therefore predicted that adults would respond to this common predator by adjusting investment in their embryos to reduce intracapsular development time. The mixed development (intracapsular development followed by a feeding larval stage) of Ilyanassa was predicted to allow a reduction in one phase of the developmental period (intracapsular development) in favor of an extension of a second phase (a feeding veliger larva) when predation rates are high on the benthos (i.e. when crabs are present). In the presence of chemical cues from predatory crabs, adult Ilyanassa laid similar numbers of egg capsules but significantly more eggs per capsule and slightly larger eggs per capsule. Egg capsule size, time to laying and time to hatching were also measured in these experiments and the effects of predatory crabs on these metrics will also be discussed.