Honors College Theses

Publication Date



Biology (B.S.B.)

Document Type and Release Option

Thesis (open access)

Faculty Mentor

Dr. Risa Cohen


Pharmaceuticals, including hormones and antibiotics, are considered contaminants due to their widespread use and release into the environment. Hormones, like the synthetic estrogen used in oral contraceptives (17α-ethinylestradiol), are present in freshwater and marine systems, but with relatively unknown effects on the organisms that live there. Ethinylestradiol (EE2) accumulates in waterlogged soil (sediment) with potential to harm sediment-dwelling animals. For example, fiddler crabs (Uca pugilator) are vital members of salt marsh communities. Their burrowing adds oxygen to sediments and cycles nutrients, and they are an important food resource to birds and raccoons. Male fiddler crabs are territorial, aggressively defending their burrows from intruders. Given that synthetic estrogen reduces aggression in fish, I hypothesized that EE2 affects male fiddler crab aggression. Male crabs exposed to EE2 were expected to retreat from threats instead of attacking more often than untreated animals. Aggression was measured as responses to threats (fleeing, attacking, no response) after exposure to sediment without (control) or with added EE2 (0.5 mg L -1). There was a trend toward EE2 treated crabs fleeing from a fight more often than control crabs which could lend support to the previous prediction. Another trend observed was the EE2-treated males exhibiting no responses to the simulated foreign threats. None of the other responses differed between treatments. The lack of significant responses was likely due to the measured concentration of EE2 in the treated sediment being two orders of magnitude less than the nominal concentration. Therefore, while these findings indicate the possibility that EE2-exposed males may have difficulty protecting themselves, their burrows, or their mate from predators, higher EE2 concentrations with larger sample sizes need to be tested for verification.