Evaporative water loss in Kuhl's pipistrelles declines along an environmental gradient, from mesic to hyperarid

Intraspecific variation in animal energy and water balances may play an important role in local adaptation of populations to specific habitats such as deserts. We examined Kuhl's pipistrelle (Pipistrellus kuhlii), a common bat in Israel that ranges in distribution from mesic Mediterranean to hyperarid desert habitats, for intraspecific differences in metabolic rate (MR) and evaporative water loss (EWL) among populations along a climatic gradient. We tested the prediction that EWL, especially at high ambient temperatures is lower in Kuhl's pipistrelles from desert habitats than from mesic habitats. We measured MR and total evaporative water loss (TEWL) at four ambient temperatures (10 °C, 20 °C, 30 °C and 35 °C) in three groups of bats using open-flow respirometry. We fitted the bats with a mask to separate cutaneous water loss (CWL) from respiratory water loss (RWL) at 35 °C. At 35 °C, mean TEWL in the southernmost group, from the hyperarid location, was significantly lower than in the other two groups, with no apparent difference in mean MR. The source of difference TEWL was that the southern group had significantly lower CWL than the other two groups; RWL did not differ among them. This suggests that there are mechanisms that reduce EWL from the skin of the bats; a likely candidate is modification of the lipids in the outer layer of the dermis that make the skin possibly less permeable to water as has been described in birds and a few other species of bat. Evaporative water loss in three sample groups of populations of Pipistrellus kuhlii along a climactic gradient from mesic Mediterranean, to desert, and hyperarid desert habitats were measured. Total evaporative water loss (TEWL) in the group from the hyperarid habitat was significantly lower than in the other two groups at high ambient temperatures. The differences observed in TEWL are due to differences in measured cutaneous evaporative water loss. [Display omitted] •Cutaneous evaporative water loss (CWL) is the main avenue of water loss in many bat species.•We measured total evaporative water loss (TEWL) in three groups of Pipistrellus kuhlii from mesic, desert, and hyperarid habitats.•TEWL in the hyperarid group was significantly lower than in the other two groups at high ambient temperature.•We attributed the differences in TEWL to CWL, and suggest that this may be due to modification of the lipids in the dermis.