The interplay of cutaneous water loss, gas exchange and blood flow in the toad,Bufo woodhousei:adaptations in a terrestrially adapted amphibian

Abstract

Cutaneous gas exchange in amphibians, which accounts for approximately two thirds of total CO 2 excretion as well as significant O 2 uptake, occurs across a well-vascularized, relatively thin and lightly keratinized epidermis (see Feder and Burggren, 1985;Boutilier et al., 1992;Shoemaker et al., 1992, for reviews). While cutaneous gas exchange per se is relatively well understood in amphibians, the interplay between cutaneous gas exchange and transcutaneous water fluxes remains enigmatic. From a physico-chemical perspective, quite different sets of forces influence water and gas movements: gas movement in both directions depends on partial pressure gradients; dehydration involves a phase change from liquid to gas as water evaporates from the skin; and rehydration involves osmotic or bulk flow. Thus, one might anticipate complex, interrelated roles for skin perfusion in each of these processes. The role of the amphibian skin as a dynamic rather than merely passive barrier to both water loss and water uptake has been long studied. Adolph (1931) reported that dead, skinned aquatic frogs lost water by evaporation in air at rates similar to a free water surface, suggesting that adjustments in cutaneous blood flow are not likely to play a key role in regulating transcutaneous water loss in amphibians. This position has been advocated by several subsequent studies (see Shoemaker and Nagy, 1977;Shoemaker et al., 1992). However, a more recent study showed that the skin of the terrestrial toad Bufo marinus offers a significant resistance to Toads experiencing dehydrating conditions exhibit complex physiological and behavioral responses, some of which can potentially impact cutaneous gas exchange, an important component of total gas exchange. We measured the effect of dehydration on cutaneous gas exchange in the xeric-adapted toad Bufo woodhousei. First, two pharmacological agents were used to stimulate cutaneous blood flow -phentolamine (an α-blocker) and isoproterenol, a β-stimulant and powerful cardioaccelerator -to determine a relationship between cutaneous blood flow and water loss. Both drugs increased heart rate and blood pressure, and caused visually evident extensive vasodilation of the skin. Untreated toads in a dry air stream took an average of 10.1±0.7·h to dehydrate to 80% body mass, while animals treated with isoproterenol and phentolamine requires only 7.2±0.8·h and 7.4±0.9·h, respectively. Rehydration, which was more rapid than dehydration, was similarly accelerated in pharmacologically treated toads. 18 O during dehydration presumably results at least in part from decreased cutaneous blood flow, possibly in an attempt to reduce the transcutaneous water loss that would otherwise result during dehydrating conditions. Concurrently, cutaneous M CO ∑ is maintained under dehyrdating conditions by a greatly increased Pa CO ∑ diffusion gradient across the skin. Thus, Bufo woodhousei appears able to restrict cutaneous blood flow without compromising vital cutaneous CO 2 loss. Cutaneous gas exchange (M

The Role of Microhabitats in the Desiccation and Survival of Anurans in Recently Harvested Oak–Hickory Forest

“…Skin does not reduce evaporative water loss in most amphibian species, including the three study species (Tracy, 1976;Jorgensen, 1997). Small differences in evaporative water loss among species in laboratory experiments are attributed to differences in body shape (Thorson, 1955), characteristics of the blood (Burggren and Vitalis, 2005), and initial water content (Thorson, 1955). For example, terrestrial amphibian species increase their initial water content by storing water in the bladder, and thus prolong the time to desiccation by having more water to lose (Jorgensen, 1997).…”

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

“…However, the interactive effects of both of these factors on the partitioning of total evaporation (EWL Total ) between EWL Resp and EWL Skin remains uncertain. This evaluation is ecologically and functionally meaningful as these two routes of EWL involve different sets of constraints that may be differently affected by changes in temperature and hydration state (Hutchison et al, 1968;Geise and Linsemair, 1986;Rogowitz et al, 1999;Burggren and Vitalis, 2005). Accordingly, we examined the combined effects of temperature and hydration level on the partitioning of EWL between its cutaneous and respiratory components in the terrestrial toad Rhinella diptycha (Cope 1862).…”

Regulation of theRana sylvaticabrevinin-1SY antimicrobial peptide during development and in dorsal and ventral skin in response to freezing, anoxia, and dehydration

“…Even in the face of high water loss, the skin remains important for cutaneous CO 2 excretion (Boutilier et al, 1979;Burggren and Vitalis, 2005). During anoxia, breathing rate has been shown to progressively decrease until it eventually ceases in Rana pipiens and as lymph movement is dependent on lung ventilation in frogs, the physiological responses to anoxia may inadvertently lower immunity (Winmill et al, 2005;Hedrick et al, 2007) as the lymphatics, as well as the blood, carry immune cells.…”