Adaptations of the reed frog Hyperolius viridiflavus (Amphibia: Anura: Hyperoliidae) to its arid environment

Abstract

Hyperolius viridiflavus possesses one complete layer of iridophores in the stratum spongiosum of its skin at about 8 days after metamorphosis. The high reflectance of this thin layer is almost certainly the result of multilayer interference reflection. In order to reflect a mean of about 35% of the incident radiation across a spectrum of 300-2900 nm only 30 layers of well-arranged crystals are required, resulting in a layer 10.5 microns thick. These theoretical values are in good agreement with the actual mean diameter of single iridophores (15.0 +/- 3.0 microns), the number of stacked platelets (40-100) and the measured reflectance of one complete layer of these cells (32.2 +/- 2.3%). Iridescence colours typical of multilayer interference reflectors were seen after severe dehydration. The skin colour turned from white (0-10% weight loss) through a copper-like iridescence (10-25% weight loss) to green iridescence (25-42%). In dry season state, H. viridiflavus needs a much higher reflectance to cope with the problems of high solar radiation load during long periods with severe dehydration stress. Dry-adapted skin contains about 4-6 layers of iridophores. The measured reflectance (up to 60% across the solar spectrum) of this thick layer (over 60 microns) is not in keeping with the results obtained by applying the multilayer interference theory. Light, scattered independently of wavelength from disordered crystals, superimposes on the multilayer-induced spectral reflectance. The initial parallel shift of the multilayer curves with increasing thickness and the almost constant ("white") reflectance of layers exceeding 60 microns clearly point to a changing physical basis with increasing layer thickness.

Lipid-reduced evaporative water loss in two arboreal hylid frogs

“…In nearly every case, the species is arboreal. In some xeric, arboreal species, such as those of the genera Chiromantis (Drewes et al, 1977;Withers et al,1984), Hyperolius (Geise and Linsenmair, 1986;Kobelt and Linsenmair, 1986;Withers et al, 1982a,b) and Phyllomedusa (McClanahan et al, 1978;Shoemaker et al, 1972;Shoemaker and McClanahan, 1975), the rate of water loss is very low, equivalent to that of desert reptiles. These species have been termed the "water-proof" frogs (Withers et al, 1984).…”

“…In contrast to other frogs, they do not actively avoid the hot, dry conditions of their habitats. Consequently, there is considerable potential for over-heating, which appears to be offset either by an increase in the rate of cutaneous water loss at higher temperatures, by `sweating' from mucous glands (Shoemaker et al, 1987) or as a consequence of the `melting' of waterproofing skin lipids (Blaylock et al, 1976), or reflectance of heat by guanine rich iridophores (Kobelt and Linsenmair, 1986;.…”

“…Phyllomedusa sauvageii (Shoemaker et al, 1987) and Litoria caerulea (Christian et al, 1988) have been reported to wipe the secretions of specialized lipid glands over their bodies to retard water loss, but no other species has had its mechanism so fully elucidated. Suggestions have included a mucopolysaccharide skin layer reportedly found in terrestrial Anura only (Elkan, 1976), specialized guanine-rich chromatophores found in species of Chiromantis and Hyperolius (Kobelt and Linsenmair, 1986) and intercellular epidermal lipids (Withers et al, 1984).…”

Life Cycle Strategies and Physiological Adjustments of Reedfrog Tadpoles (Amphibia, Anura, Hyperoliidae) in Relation to Environmental Conditions

“…Juveniles have developed a series of spectacular physiological adaptations which allow them to survive even under the especially demanding conditions of the strongly and rather unpredictably fluctuating savannah habitats (Geise and Linsenmair, 1988;Kobelt and Linsenmair, 1992;Schmuck et aI., 1988). These Hyperolius species start spawning during periods of high precipitation and continue until well into the transitional season which is usually characterized by, at most, very casual and light rain but generally a regular nightly dewfall (assumed for H. v. ommatostictus, H. m.…”

Balanço híbrido e desempenho locomotor em esécies de anuros de mata atlântica e cerrado

“…Destas secreções, o muco e os lipídeos vêm sendo funcionalmente associadas ao balanço hídrico. Alguns estudos conjecturaram uma possível função da secreção mucosa na redução da perda de água por evaporação, seja selando os espaços extracelulares do stratum corneum (Toledo & Jared 1993), seja selando pequenas fendas entre o corpo e os membros de alguns anuros (Geise & Linsenmair 1986;Kobelt & Linsenmair 1986), porém a composição desta secreção mucosa não foi determinada, de forma que seu conteúdo de lipídeos permanece não conhecido (Lillywhite 2006). Em algumas espécies de anfíbios, assim como nos demais tetrápodes, os lipídeos secretados parecem ser o principal fator controlador do movimento transepitelial de água.…”