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Publication Date


Document Type

Honors Project


Biological Sciences


Phenotypic plasticity, Littorina obtusata-Defenses, Littorina saxatilis-Defenses, Carcinus maenas, Biological invasions-Maine, Gulf of, Animal defenses, Maine, Gulf of, Predator induced defenses, Gulf of Maine, Crusing resistance, Littorina obtusata, Littorina saxatilis


In response to the invasion of the crab Carcinus maenas into the Gulf of Maine, a native intertidal snail, Littorina obtusata was observed to undergo a drastic morphological shift. It transitioned from a primarily high-spired, thin-shelled form to the present day low-spired, thick shelled form. Although initially attributed to rapid selection, further work has suggested that phenotypic plasticity could have played an important role in this shift. C. maenas has impacted other native snail species, such as the high-spired L. saxatilis. This study aimed to examine the impact of crab cue as well as food availability on shell morphology and strength of L. obtusata and L. saxatilis. I found that shell strength varied between species, with low-spired, L. obtusata being significantly stronger than similarly sized L. saxatilis. I also found strength differences between L. obtusata from high and low crab density sites, with snails from high-density sites being significantly stronger. In response to crab cue, shell thickness for both species increased. L. obtusata exhibited no significant responses to food availability, while L. saxatilis exhibited a variety of responses. For L. saxatilis, shell height was largest for snails not exposed to crab cue with high food availability, while aperture area responded only to crab cue, with smaller apertures resulting from exposure to crab cue. These results show that closely related species can exhibit different levels of phenotypic plasticity in response to a common predator, as well as showing that the responses can vary. They also point to phenotypic plasticity as a possible explanation for the historical shift in shell morphology of L. obtusata in response to the C. maenas invasion.




65 pages : illustrations (some color). Honors Project-Smith College, 2014. Includes bibliographical references (pages 41-44)