Sex Ratio and Body Condition in Female Uca pugnax Fiddler Crabs Along the Eastern Coast of the United States



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The fiddler crab Uca pugnax is a semi-terrestrial estuarine crab that lives in salt marshes along the Eastern coast of North America from northern Florida to New Hampshire (Sanford et al. 2006). Uca pugnax is an important study organism because it impacts the surrounding ecosystem, as fiddler crabs can maintain Spartina growth, are a major staple in the diet of many fish species and other predators, and eat many of the meiofaunal organisms present in the surrounding Spartina. There is an interest in studying these crabs in particular because their coastal range is expanding north, and this expansion could lead to a modification in the structure of the surrounding ecosystem. The farthest north scientists previously found these crabs was in Cape Cod, MA, but in recent years climate change has caused a northern range expansion of both the species and of fiddler crabs as a whole (Sanford et al. 2006). In the northern part of Uca pugnax’s range, water temperature is the limiting factor, and therefore explains the range expansion north due to the increasing global temperatures. In fiddler crabs, fat is mobilized for reproduction, and since fitness means the ability to survive and reproduce, fitness equals fatness, or body condition. It is hypothesized that latitude is correlated with Uca pugnax body condition, and that there is also some seasonal variation in body condition along the range. When four different locations along the range were sampled, no differences in body condition were found between sites. This is interesting because in the northern end of the range, adult fiddler crabs spend nearly half of the year underground, and thus have a much shorter feeding season than southern fiddler crabs. However, a significant difference was found between seasons for fall 2012 and the interaction of season and location. The number of ovigerous females was lowest in the fall throughout all locations, and a male-skewed sex ratio was seen in Georgia. These results are preliminary, but suggest that crabs in all locations share a similar body condition despite the varying global temperatures. There is also a seasonal difference, which may be more prominent at the southern end of the range.



Uca pugnax, fiddler crab, body condition, climate change, sex ratio