Temperature and dehydration effects on metabolism, water uptake, and the partitioning between respiratory and cutaneous evaporative water loss in a terrestrial toad

Abstract

Terrestrial anurans often experience fluctuations in body temperature and hydration state, which are known to influence evaporative water loss through the skin (EWL Skin ) and lungs (EWL Resp ). These effects arise from associated changes in skin permeability, metabolism and lung ventilation. Herein, we determined the rates of EWL Skin and EWL Resp in the terrestrial toad Rhinella diptycha at different temperatures and hydration states. We measured oxygen uptake rates to verify whether alterations in the partitioning between EWL Skin and EWL Resp were associated with metabolism-induced changes in pulmonary gas exchange. We also measured the influence of hydration and temperature on water uptake (WU) through the skin. Finally, as estimates of skin resistance to evaporation (R s ) are usually inferred from total evaporative water loss (EWL Total ), under the assumption of negligible EWL Resp , we calculated the potential error in accepting this assumption for different temperature and hydration states. EWL Skin and EWL Resp increased with temperature, but this response was greater for EWL Resp , which was attributed to the temperature-induced elevation in metabolism and lung ventilation. Dehydration caused a decrease in the relative contribution of EWL Skin to EWL Total , mirrored by the concurrent increase in the contribution of EWL Resp , at all temperatures. Thus, R s increased with dehydration. WU rates were dictated by dehydration with little influence of temperature. The partitioning between EWL Skin and EWL Resp was affected by both temperature and hydration state and, under some conditions, considering EWL Resp as negligible led to significant errors in the assessment of skin resistance to evaporation.

Acclimation to Water Restriction Implies Different Paces for Behavioral and Physiological Responses in a Lizard Species

“…Other studies that have tested for plastic changes in cutaneous water loss rates generally found that lizards or snakes acclimated to drier environments or water restricted environments can adjust cutaneous water loss rates within days or weeks of exposure (Kobayashi et al 1983;Kattan and Lillywhite 1989;Moen et al 2005but see Neilson 2002Gunderson et al 2011). Reduction of cutaneous water loss rates is also well documented in anurans exposed to chronic water deprivation Senzano and Andrade 2018). It is generally accepted that the skin resistance to water loss depends mainly on the intracellular lipid content and ultrastructure of the mesos layer of the epidermis (reviewed by Lillywhite 2006).…”

“…Ectotherms may also respond to water restriction by thermal depression, that is, the lowering of their preferred set temperature (Ladyman and Bradshaw 2003;Köhler et al 2011; Andrade 2017). This is because higher body temperatures are associated with stronger respiratory and cutaneous water loss rates during activity (e.g., Oufiero and Van Sant 2018;Senzano and Andrade 2018). Previous studies focused mostly on one of these acclimation mechanisms, and their prevalence or pace has been little investigated so far, especially in dry skinned ectotherms.…”

A worldwide and annotated database of evaporative water loss rates in squamate reptiles

“…Therefore, for those cases in which the information could be recovered, we collected and reported all the components necessary for calculating R s , even though we have not added it as a separate variable in the dataset (Kearney & Porter, 2020). Note that there are potential caveats with respect to this approach because of unknowns in the regional variation of skin and body temperatures (Barroso et al, 2016), difficulties in partitioning sub‐components of EWL (Senzano & Andrade, 2018), and further study or species‐specific features that make it difficult to calculate Rs (Mautz, 1982).…”

Host defense or parasite cue: Skin secretions mediate interactions between amphibians and their parasites

“…Thus, for example, a highly effective immune response to pathogens that enter the body might relax selection for barriers on the skin. Additionally, it is important to remember that the skin has many other functions, such as respiration, regulating water flow and as the location of toxin‐excreting glands (Blennerhassett et al, 2019; Huang et al, 2016; Kosmala et al, 2020; Senzano & Andrade, 2018).…”