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Date Permissions Signed


Date of Award

Winter 2022

Document Type

Masters Thesis

Department or Program Affiliation

Marine and Estuarine Science Program - Biology

Degree Name

Master of Science (MS)



First Advisor

Miner, Benjamin G., 1972-

Second Advisor

Lund, John Andrew

Third Advisor

Bingham, Brian L., 1960-

Fourth Advisor

Arellano, Shawn M.


Many organisms have complex life cycles that include ontogenetic niche shifts, or changes to morphology, physiology, diet, predators, and habitat. Natural selection favors individuals that choose the optimal time to undergo ontogenetic niche shifts that avoids unnecessary losses to fitness, and niche shift timing is therefore considered a plastic trait. Hatching is a common niche shift within animals, and modifications to hatch timing can mediate the costs and benefits of hatching sooner or later, depending on varying predation risk, resource availability, or habitat conditions. Predator-induced hatching plasticity in particular is well-documented within amphibians as well as other terrestrial vertebrates and arthropods, but few cases have been documented in the marine environment. This is likely due to the difficulty of making observations of hatching activity, as many marine invertebrates hatch as near-microscopic larvae. The purpose of this study was to develop hatching detectors that improve the ease and frequency of observations of hatching and then demonstrate their utility in investigations of hatching plasticity of two nudibranch species. The hatching detectors, comprised of an array of paired infrared emitters and phototransistors, measure fluctuations in absorbed infrared light to detect hatching. Coupled with wireless transmissions of hatching data, these sensors allowed quasi-real-time monitoring of hatching activity and high-temporal resolution estimates of hatch timing with minimal disturbance to developing embryos. Using these hatching detectors, I wanted to examine whether the nudibranchs H. crassicornis and O. bilamellata exhibit hatch timing plasticity. Given their benthic development within embryo masses and planktonic development after hatching, I hypothesized that both species would accelerate hatch timing when their embryo masses were presented with predation cues from benthic predators. I first investigated hatching plasticity in the aeolid H. crassicornis in response to a simulated predator attack (disruption of the embryo mass outer envelope at age 7 d) and to chemical cues from the embryo predator Heptacarpus brevirostris and the non-predator Petrolisthes eriomerus in a fully-crossed experimental design. There was an apparent interaction between the mechanical cue and embryo mass batch where the simulated predator attack had no effect on the first batch of embryo masses but reduced time-to-hatching in the second batch of embryo masses. The chemical cue had no significant effect on hatch timing. I performed another experiment with the dorid O. bilamellata to determine if they modify hatch timing in response to chemical cues from the embryo predator H. brevirostris or the non-predator Nucella lamellosa, but also found no significant effect. Although this study did not find clear evidence of predator-induced hatching plasticity in these two nudibranchs species, the hatching detectors functioned as intended and provide a means to facilitate future examinations of hatching plasticity in animals with similar life histories.




Hatching plasticity, Hermissenda crassicornis, Onchidoris bilamellata, infrared, ontogenetic niche shift


Western Washington University

OCLC Number


Subject – LCSH

Nudibranchia--North Pacific Ocean--Reproduction; Nudibranchia--Effect of predation on--North Pacific Ocean; Phenotypic plasticity--North Pacific Ocean

Geographic Coverage

North Pacific Ocean




masters theses




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