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Date of Award


Document Type


Degree Name

Master of Science (M.S.)


Biological Sciences

First Advisor

Ajna Rivera

First Committee Member

Ryan Hill

Second Committee Member

Eric Thomas


Sexual dimorphism is exhibited throughout various organisms and takes an extensive variety of forms, although rarely does it take the form of eye-reduction within a population. This poses the question of whether this dimorphism arises due to sexual selection in order to increase reproductive success or rather from ecological selection as a result of sex-specific niche partitioning. In this case, we study an organism that displays a drastic form of sexual dimorphism, in that the males have large complex lateral eyes whereas the females lack eyes and merely have rudimentary lateral eye-spots. Euphilomedes carcharodonta is a small crustacean native to the coast of California. Studies on the dimorphism between these individuals have mainly been related to genetics and embryology. However, minimal studies have been performed questioning the evolutionary driving force behind their dimorphism. One study suggests that this driving force is ecological selection, more specifically, predator evasion as a result of the reproductive role hypothesis. In this study, we focus on sexual selection as a driving force and ask whether the eyes play a role in the ability of males to find mates. We blinded and mock-blinded male individuals, placed them in tank settings with females in the absence of predators, and observed their behavior. If sexual selection is involved in the eye development of males, we expected to see changes in male and/or female behavior in response to obstructing the vision of the males. We did not see changes in behavior of the males or the females. This leads us to conclude that the development of complex eyes in male Euphilomedes carcharodonta arises from ecological selection rather than sexual selection. With the previous work on predator evasion, these experiments and findings are the first to experimentally test the reproductive role hypothesis and are the beginning steps for further behavioral studies of these organisms and in discovering more about the unique dimorphism exhibited by Euphilomedes carcharodonta.



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