The Cocoon of the Fossorial FrogCyclorana australisFunctions Primarily as a Barrier to Water Exchange with the Substrate

Abstract

Studies of evaporative water loss using streams of dry air in the laboratory have demonstrated reduced rates in various taxa of cocooned frogs. However, because the cocoon is formed in subterranean burrows with humid microclimates and no air flow, loss of water by evaporation is likely to be negligible. In contrast, although potentially important, the influence of the cocoon on water exchange with the soil surface has not been characterized. In dry soils, there is a sizable water potential gradient between the frog and the soil; hence, we hypothesized that cocoons would play a role in reducing liquid water loss to dry substrates. Individuals of the burrowing frog Cyclorana australis (Hylidae: Pelodryadinae) were induced to form cocoons in the laboratory. On semisolid agar-solute substrates across a range of water potentials, the hygroscopic cocoon absorbed small but similar amounts of moisture. With the cocoon removed, the frogs gained or lost water, depending on the direction of the frog-substrate water potential difference. Plasma osmolality of cocooned frogs was significantly higher than in hydrated frogs. Because cocooned frogs did not exchange significant amounts of water at either high (wet) or low (dry) substrate water potentials, we conclude that the cocoon of fossorial frogs acts as a physical barrier that breaks the continuity between frog and substrate. We contend that the primary function of the cocoon is to prevent liquid water loss to drying clay and loam soils, rather than to prevent subterranean evaporative water loss.

Big, Bad, and Beautiful: Phylogenetic Relationships of the Horned Frogs (Anura: Ceratophryidae)

“…The accumulation of the layers is accompanied by a rapid decrease in evaporative water loss in laboratory conditions, reaching a minimum after about a month (McClanahan et al, 1983). In natural conditions it has been believed that the cocoon functions by preventing water loss to the dry soil (Shoemaker et al, 1992), as recently demonstrated for Litoria australis (Reynolds et al, 2010).…”

Is cancer an intelligent species?

“…Naked mole-rats ( Heterocephalus glaber ) have the ability defined at point 2, changing metabolism to survive underground in low-oxygen environments [ 14 ]. Australian frogs ( Cyclorana australis ) belong to point 3, creating a new environment rich of mucus to prevent skin from drying out in the hot climate [ 15 ]. Other species, such as penguins in Antarctica, carry out the amazing collective adaptation of point 4, crowding together to share their warmth and survive glaciation.…”

Field record of aestivation with formation of cocoon in the frog Leptodactylus fuscus (Anura: Leptodactylidae) in a semiarid region of northeastern Brazil

“…The cocooned Leptodactyolus fuscus was discovered during the dry season when there had been successive days without rain. This cocoon seems to act as physical barrier preventing water loss (Reynolds et al 2010 (Cartledge et al 2006, Tracy et al 2007, and South America [ceratophryids Lepidobatrachus llanensis Reig andCei, 1963 andCeratophrys ornata (Bell, 1843)] (McClanahan et al 1976(McClanahan et al , 1983. Given the distant relationships of these lineages, it seems likely that ability to form such cocoon evolved independently in the various groups and may be more widespread among aestivating anurans than currently thought Hillman 1981, Faivovich et al 2014).…”

“…It follows that most anurans occurring in the seemingly unfavorable conditions of the Caatinga have mechanisms to protect themselves from desiccation in the surface soil (Prado 2003, Navas et al 2004. Anurans employ three main strategies to avoid drying effects of the surface soil; they can burrow deep in the soil, accumulate urea in body fluids, and form cocoons (Shoemaker et al 1969, Shoemaker 1988, Cartledge et al 2006, Reynolds et al 2010. Typically, most Caatinga anurans also have additional adaptations.…”