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

Abstract

The relationship between different degrees of intraspecific crowding of reedfrog tadpoles and their physiological responses to a deterioration of the natal pond water quality was examined under laboratory conditions. Tadpoles that were reared at a lower density metamorphosed significantly earlier than those raised at a higher density. As density increases, the average body length at metamorphosis decreases. However, at low tadpole density, a significantly higher diversity of body size classes among freshly metamorphosed froglets was observed than under more crowded conditions. Mortality increased during metamorphic climax and was inversely correlated with the tadpole density.In ephemeral ponds, an accumulation of nitrogenous wastes from metabolic processes and/or a concentration by evaporation in prolonged rainless periods can pose a considerable chemical stress to reedfrog tadpoles. Hyperolius viridiflavus ommatostictus responded to an increasing ammonia concentration with an activity increase of the ornithine cycle (intensified urea synthesis). hi contrast, Hyperolius marmoratus taeniatus exhibited a strong tolerance against high ammonia levels.A deterioration of the natal pond water quality caused H. v. ommatostictus and H. v. nitidulus tadpoles to adjust to harsher climatic conditions at the time of metamorphosis. This physiological preadjustment enabled the froglets to start feeding and growing immediately after metamorphosis even at low air humidity and rare precipitation events. In contrast, froglets that were raised in daily refreshed water exhibited high mortality rates if subjected to identical conditions. As one possible indicator of the actual climatic conditions prevailing in the surrounding terrestrial habitat, fluctuations in the water ammonia level are discussed.

Influence of developmental stage on sensitivity to ammonium nitrate of aquatic stages of amphibians

“…We also observed a smaller size in D. galganoi and P. cultripes tadpoles exposed to ammonium nitrate from earlier stages. A decrease in food ingestion as a result of lost activity or an excessive energetic investment in detoxifying mechanisms, such as the urea-ornithine cycle [27], would be some of the possible causes for the smaller size of exposed individuals. Thus, any of these mechanisms should have affected, in a greater way, individuals exposed from earlier developmental stages.…”

Impacts of selective logging on amphibians in a Bolivian tropical humid forest

“…In addition, many adult frogs are typically limited to microsites with high Forest Ecology and Management 191 (2004) [275][276][277][278][279][280][281][282] humidity, which are found in riparian areas bordering forested streams. Logging can increase the deterioration rate of temporary water sources (streams and pools) by increasing the drying rates and increasing the ammonia concentrations in these water sources, possibly to toxic levels (Schmuck et al, 1994). Many invertebrates also depend on these riparian water sources for egg and larval development.…”

The effects of kinship and density on growth and metamorphosis of the bronze frog (Rana temporalis) tadpoles

“…6 Distribution of body mass of R. temporalis tadpoles in different rearing conditions at metamorphic climax (stages 42-46). Non-identical labels (a,b,c) indicate significant differences from each other (χ 2 test) resources (Rugh 1934;Wilbur 1977a,b;Dash and Hota 1980;Hota and Dash 1981;Jasienski 1988;Schmuck et al 1994;Hokit and Blaustein 1997). These studies showed that generally growth rates, measured in terms of body mass, vary inversely with population density, and slowly growing individuals metamorphose at smaller sizes than their larger conspecifics.…”