Increased cave dwelling reduces the ability of cave crickets to resist dehydration

Abstract

Differential strategies for maintaining water balance are reported for female adults of three cave crickets Hadenoecus cumberlandicus, H. opilionoides and H. jonesi, a species replacement series along the Cumberland Plateau in the southeastern United States. The distribution of H. cumberlandicus is much broader than the range of H. opilionoides, which is much smaller in body size, and that of H. jonesi, which possesses enhanced troglomorphic (cave dwelling) characteristics. Due to high net transpiration (water loss) rates and increased activation energies, H. jonesi and H. opilionoides are more susceptible to dehydration than H. cumberlandicus. To avoid dehydration, H. opilionoides and H. jonesi require more moisture than H. cumberlandicus to counter their higher rates of water loss. The heightened reliance on moisture likely indicates that the more troglomorphic H. jonesi and smaller H. opilionoides are required to spend more time in the moist cave region. Reliance on the cave for H. cumberlandicus is presumably less, allowing them to function in epigean habitats for longer periods and disperse to nearby caves, likely accounting for the more expansive distribution of this cricket. While in the cave habitat, cave crickets are exposed to water-saturated conditions, reducing the pressure of dehydration stress the longer a species remains in this wet environment. This reduced pressure leads to higher water loss rates as cave confinement increases. We conclude that increasing water loss rates associated with increasing troglomorphic adaptation in cave crickets is a side effect of extended residence in stable moist cave environments.

Day–night and seasonal variations of a subterranean invertebrate community in the twilight zone

“…A reduced relative humidity in particular, is a well-known limiting factor for the presence of the subterranean fauna (Howarth 1980, 1983, Sharratt et al 2000. Pronounced sensitivity to saturation deficit was experimentally demonstrated in subterranean beetles (Boyer-Lefèvre 1971), crickets (Yoder et al 2011) and spiders (Howarth 1980, Hadley et al 1981. The fact that subterranean species are preferentially associated with humid microhabitats (Howarth 1980(Howarth , 1983, indirectly implies that, at night, the twilight zone should represent a more suitable habitat for the subterranean fauna due to the higher levels of relative humidity -at least in winter and spring.…”

Complex Interactions between Temperature and Relative Humidity on Water Balance of Adult Tsetse (Glossinidae, Diptera): Implications for Climate Change

“…However, for each species an environment-specific transition temperature may exist beyond which cuticular lipids melt, resulting in rapidly increased cuticular permeability and, ultimately, accelerated water loss (Benoit, 2010; Gibbs, 2011). Second, insects increase the quantity of water available in their bodies to resist dehydration by (i) ingestion of free standing water or nectar, (ii) absorbing water from the ambient environment, (iii) the conversion of metabolic water, or (iv) increasing body size over evolutionary time-scales (reviewed in Hadley, 1994; Benoit and Denlinger, 2010; Chown et al, 2011; Yoder et al, 2011). Higher carbohydrate content can increase bound water reserves and has been associated with desiccation resistance in some insects (see, e.g., Gibbs et al, 1997; Marron et al, 2003).…”

“…However, insects from stable mesic environments might experience lower dehydration stress, resulting in an increased water loss rate (WLR) when exposed to xeric conditions (e.g., Yoder et al, 2011). Water balance traits can drive evolutionary processes, especially in insects associated with xeric environments, resulting in physiological diversification among individuals, populations, or species (Gibbs et al, 1997; Hoffmann and Harshman, 1999; Woods and Harrison, 2001; Chown and Terblanche, 2007; Gefen and Gibbs, 2009; Kleynhans and Terblanche, 2009; Matzkin et al, 2009; Simard et al, 2009; Benoit and Denlinger, 2010).…”

Cave cricket exit counts: environmental influences and duration of surveys

“…Beginning at sunset on evenings when the surface temperature is at least 5 uC, two surveyors count cave crickets for two hours as they emerge from a cave entrance. Environmental conditions that might influence cave cricket emergence are the amount of moonlight and the temperature and relative humidity on the surface (Campbell, 1976;Poulson et al, 1995;Yoder et al, 2011). Surface activity of cave crickets is reported to be lower when there is more moonlight, during cool or hot nighttime temperatures, and when relative humidity is lower.…”

“…But how these environmental variables actually affect the number of cave crickets that emerge from caves has not been examined. Furthermore, cave crickets are rarely active and foraging on the surface during daylight hours (Campbell, 1976;Yoder et al, 2011). In Carlsbad Caverns National Park, Campbell (1976) noted that as many as 50% of the cave crickets that emerged on summer nights did so between one and two hours after sunset.…”