Differences in Body Size and Water Balance Strategies between North Carolina and Florida Populations of the Sand Fiddler Crab, Uca Pugilator

Abstract

A B S T R A C TSand fiddler crabs, Uca pugilator, from North Carolina (NC) are two-times smaller than ones from Florida (FL). A water balance study was conducted to examine this size difference in relation to possible changes in habitat suitability. Like most crabs, U. pugilator are classified as hydrophilic, which is consistent with their preference for humid environments. In contrast to the North Carolina population, U. pugilator-FL loses water less rapidly and has higher percentage body water content, a water balance strategy that emphasizes retention. Conversely, the amount of body water required is less for U. pugilator-NC, enabling it to maintain water balance despite having a higher water loss rate. Both tolerated only about 1/4 loss of body water before succumbing to desiccation. Neither experienced a critical transition temperature, CTT. We concluded that water balance profiles of these two populations are complementary, representing trade-offs that permit survival in a moisture-rich habitat. Lower body water content, however, overlaps with features of arthropods that thrive at low temperature, suggesting that U. pugilator-NC may be more cold tolerant.

Comparative biology of the crab Goniopsis cruentata: geographic variation of body size, sexual maturity, and allometric growth

“…This would be particularly important in extremely hot, dry environments where the rate of water loss is more pronounced (Gardner et al 2011), which seems to occur more frequently on a temporal scale in Ceará because of recurring harsh droughts (Folhes et al 2009;Araújo et al 2012; also see maximum temperatures in Table 2). Such findings corroborate those of Yoder et al (2007), who experimentally demonstrated that individuals of Uca pugilator are larger, and consequently less susceptible to desiccation, in a drier environment. However, the drier location in their study was southwards (Florida, USA), whereas the humid location was northwards (North Carolina, USA), the opposite trend of what we observed in the present study.…”

Size-dependent temperature and desiccation constraints on performance capacity: Implications for sexual selection in a fiddler crab

“…The treadmill was held motionless during this time. A preliminary study found that crabs typically lost 4-10% of their body mass over the 2 h period, depending upon their starting size and presumably representing water loss due to evaporation and respiration (Weinstein, 1998;Yoder et al, 2005Yoder et al, , 2007. The order in which crabs were run was randomized with respect to body size and drying time (n =49 'no drying', 36 '2 h drying').…”

“…Presumably, small males are either quickly evicted from the breeding area by larger individuals (Jennions and Backwell, 1996;Pratt et al, 2003), run out of energy faster (Backwell et al, 1995;Jennions and Backwell, 1998;Kim and Choe, 2003;Pratt and McLain, 2002), or abandon the area after having little success in attracting a mate (Jennions and Backwell, 1998). In general, small organisms also have lower thermal inertia and higher mass-specific water loss rates than do large ones (Herreid, 1969;Stevenson, 1985;Yoder et al, 2007). Mating activity by U. pugilator occurs in mid-summer and previous work has shown that both thermal and desiccation stresses to surface-active crabs are potentially high at that time (Allen, 2007), suggesting an additional hypothesis to explain the skewed size distribution of males in the breeding area: small males are more susceptible to thermal and hydration stresses than large males and may therefore spend less time active on the march surface.…”

Are crabs stressed for water on a hot sand flat? Water loss and field water state of two species of intertidal fiddler crabs

“…Crabs do not replenish water from the atmosphere so water loss can only be compensated by direct contact with moist sediment or water (Yoder et al, 2005). The rate of water loss is inversely related to body size (Allen et al, 2012;Herreid, 1969), which varies over the geographic range of U. pugilator (Munguia et al, 2013;Yoder et al, 2007). The degree of carapace permeability also differs at different sites (Yoder et al, 2007).…”

“…The rate of water loss is inversely related to body size (Allen et al, 2012;Herreid, 1969), which varies over the geographic range of U. pugilator (Munguia et al, 2013;Yoder et al, 2007). The degree of carapace permeability also differs at different sites (Yoder et al, 2007). In general, species living farther from predictable immersion tend to be less permeable to water loss (Edney, 1961;Smith and Miller, 1973), but other factors may make it difficult to make a simple ordering among species (Thurman, 1998).…”