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

Abstract

Adaptations to aridity of the reedfrog Hyperolius viridiflavus nitidulus, living in different parts of the season-ally very dry and hot West African savanna, are investigated. 1. During the dry season mainly juveniles (weighing 200-600 mg) were found in the field. A very low rate of evaporative water loss (EWL; about 1.2% of the body weight/day under laboratory dry season conditions) enables the frogs to estivate unshaded on dry plants. There they are exposed to temperatures occasionally reaching 45° C and are to sustain high radiation loads. The EWL of wet season frogs (WSF) was on average 30 times higher. 2. In dry season frogs (DSF) a thin layer of desiccated mucus seals the body surface reducing water loss and securing tight attachment to the substrate. The DSF are not in a state of torpor but are able to become active at any moment. The highest tolerable water loss of DSF amounts to 50% of their initial body weight. Since uptake of water or food often is impossible for more than two months, the small DSF have to survive these harsh conditions with very limited reserves of energy and water. 3. The low EWL of DSF does not engender any cooling effects. Only above a certain high temperature limit, defined as the critical thermal maximum (CTM; 43-44°C) we found a steep increase of EWL-probably indicating evaporative cooling. The CTM is affected by the temperature during acclimatization. 4. In contrast to WSF cutaneous respiration is not found in DSF. All CO is delivered via the lungs by discontinuous ventilation. The simultaneous water loss via the respiratory tract makes up to 14.9+/-8.9% of the entire water loss. 5. A very fast water uptake (69.3+/-19.4%/h) via thin and vascular skin areas at the ventral flanks and the inner sides of the legs enables the frogs to use small quantities of water available for very short times only. This highly permeable skin is protected against desiccation by the typical squat resting position of the frogs. 6. DSF usually to neither urinate nor defecate; they are not proved to be uricotelic. Probably they store the nitrogenuous wastes as urea in the body fluids and as purines in the iridophores and connective tissues. It is suggested that there is no selective advantage for uricotelism in the small H. v. nitidulus.

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).…”

Reproductive Energetics of the African Reed Frogs, Hyperolius viridiflavus and Hyperolius marmoratus

“…(Taigen, Emerson, and Pough 1982;0.094 mL 02/g· h at 20°C), Hyperolius marmoratus verucosus (Withers et al 1982; 0.0671 mL 02/g· h at 20°C), and H. marmoratus taeniatus (Geise 1987;0.130 mL 02/g' h at 25°C). There are two possible reasons for this.…”

“…Maihak AG. ;Geise 1987) at 25°C and with an air-flow rate of 16 L/h. At 16 Llh sensitivity of the analyzer was 0.77 ppm per scale of 1 mm.…”

“…Eggs are laid on vegetation under water. Females produce multiple clutches during the course of the breeding season (Richards 1977;Geise 1987;Telford and Dyson 1990) that typically lasts several months (Telford 1985).…”

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.…”