Date Thesis Awarded

5-2020

Document Type

Honors Thesis

Degree Name

Bachelors of Science (BS)

Department

Biology

Advisor

Jonathan Allen

Committee Members

Orissa Moulton

Rowan Lockwood

Abstract

Marine invertebrates exhibit complex life cycles featuring life history transitions that coincide with habitat changes from 1) benthic adults to planktonic embryos and larvae and then 2) a return to the benthos as a juvenile. After returning to the benthos, juvenile invertebrates experience high mortality due to predation. Juvenile invertebrates may have the ability, like other organisms, to respond to predator cues using inducible morphological defenses, a form of phenotypic plasticity. However, if the cues are only detected after settlement, time-lags inherent to phenotypic plasticity may delay production of defenses until after the period of highest vulnerability. It would, therefore, be beneficial for planktonic larvae to detect and phenotypically respond to predator cues before entering the benthos. Echinoderms are excellent models for trans-habitat phenotypic plasticity since larvae build their juvenile bodies while in the water column. As echinoderm larvae approach settlement, waterborne cues from the benthos may provide information about the future juvenile habitat, inducing expression of juvenile phenotypes that may improve post-metamorphic survival. I tested whether cues from benthic predators applied to planktonic echinoderm larvae result in modified juvenile phenotypes at settlement. Green urchin (Strongylocentrotus droebachiensis) and sand dollar (Dendraster excentricus) larvae were exposed to predatory crab cues once juvenile rudiment formation began. Green urchin larvae exposed to crab cues had significantly more juvenile spines at settlement. Sand dollar larvae exhibited earlier settlement, larger bodies, fewer spines, and shorter spines when exposed to benthic crab cues. Sand dollar larvae exposed to planktonic predator cues from crab larvae settled sooner and larger, with even fewer spines and shorter spines than those exposed to the benthic predator cue. These results suggest that echinoderm larvae alter their juvenile phenotypes in response to predator cues, but those responses vary between species and planktonic threats may be prioritized over benthic ones.

Available for download on Sunday, May 08, 2022

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