Date Thesis Awarded
Bachelors of Science (BS)
Most marine invertebrates develop in the plankton, where microscopic offspring can avoid abundant benthic predators until settlement. However, at least four phyla of marine invertebrates (Annelida, Mollusca, Nemertea, and Platyhelminthes) deposit benthic egg capsules or masses. Often, these animals possess other means to protect their young, including chemical or morphological defenses or nonrandom selection of deposition sites. Egg capsule deposition is the dominant reproductive strategy among gastropod molluscs, including the abundant mud snail, Ilyanassa obsoleta. In intertidal and shallow subtidal habitats in Maine, the mud snail preferentially lays egg capsules on blades of eelgrass (Zostera marina) that stand upright in the water column. In a field and lab study, I examined deposition of Ilyanassa obsoleta eggs and found that mud snails lay their egg capsules on eelgrass at 6-8 cm off the benthos or higher. When exposed to egg capsule predators such as hermit crabs and periwinkles, mud snails increase the average lowest height of laying by 1-3 cm. In the presence of hermit crabs, capsules placed just 5 cm up a blade have survivorship as much as 4 times higher than capsules placed directly on the benthos. Placement of egg capsules off of the benthos may be an adaptive plastic response allowing mud snails to protect their embryos from benthic predators.
Harmon, Emily A., "Plasticity in egg placement in response to predator cues in the mud snail, Ilyanassa obsoleta" (2016). Undergraduate Honors Theses. Paper 940.
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