Geographic variation of resistance to water loss within two species of lungless salamanders: implications for activity

Abstract

Citation: Riddell, E. A., and M. W. Sears. 2015. Geographic variation of resistance to water loss within two species of lungless salamanders: implications for activity. Ecosphere 6(5):86. http://dx.doi.org/10.1890/ES14-00360.1Abstract. For many organisms, constraints on activity increase energetic costs, which ultimately reduce the suitability of a particular habitat. Mechanistic species distribution models often use estimates of activity to predict how organisms will respond to climate change. These models couple physiology and morphology with climatic data to estimate potential activity. In turn, the duration of activity is used to estimate the energetic balance of individuals at a given location. Whether individuals remain in positive net energetic balance determines if a given location is suitable for the species. However, because these models often assume that physiology does not vary across the species range, estimates of activity (and consequently energetics) are potentially misleading. To test the consequence of this assumption, we measured total resistance to water loss (R) within two species of lungless salamanders (Plethodon metcalfi and P. teyahalee) collected from locations along their elevational extent in southwestern North Carolina. Because hydration state constrains the activity of salamanders, increasing R would increase potential activity. Here, we leveraged the natural changes in environmental conditions along an elevational gradient to determine if salamanders modify R in different environments. We predicted that salamanders collected from low elevations would have higher R to compensate for the warmer, drier conditions at low elevations that may limit activity. We determined R in the laboratory using a flow-through system at two temperatures (128C, 188C) and at three vapor pressure deficits (0.2 kPa, 0.35 kPa, 0.5 kPa). For P. metcalfi, individuals collected from low elevations exhibited the highest R, suggesting either acclimatization or adaptation to local conditions. For P. teyahalee, individuals collected from high elevations exhibited the highest R, but these results may reflect alternative pressures due to differences in behavior. The results also suggest that salamanders might use temperature as a cue to increase R, but the capacity to do so depends upon the temperatures experienced in nature. Moreover, we show that variation in R has the potential to alter the duration of activity over the elevational ranges of these species, illustrating the importance of incorporating geographic variation of physiological traits for predicting a species' response to climate.

Cross-Life Stage Effects of Aquatic Larval Density and Terrestrial Moisture on Growth and Corticosterone in the Spotted Salamander

“…This is contrary to our prediction, as smaller salamanders are expected to have higher rates of water loss per unit area [23]. While studies have found evidence for geographic variation in desiccation resistance indicative of local adaptation based on gradients of environmental moisture e.g., [82,83] it is notable that we did not find evidence for plasticity in resistance to water loss based on our moisture treatments. This result has important implications for the ability of salamanders to respond to changes in environmental moisture.…”

Variation in field body temperature and total evaporative water loss along an environmental gradient in a diurnal ectotherm

“…A recent study on water loss rates in lungless salamanders found mixed results, with one species adapted to cope better with dehydration at lower altitudes and a second species better suited for higher altitudes (Riddell & Sears, ). The apparent contradiction between microclimatic and physiological measurements might be explained if we consider variation instead of the average values of microclimatic conditions.…”

Trade‐offs between water loss and gas exchange influence habitat suitability of a woodland salamander

“…reduction in rates of water loss) during acclimation to warm temperatures. We based our prediction upon previous experiments in which salamanders used warm temperatures as a cue to adjust water loss rates (Riddell & Sears ). However, if did not decline, we predicted that individuals might increase heart rates to promote oxygen delivery (Franklin et al., ).…”