Inter- and intraspecific geographic variation of body size in South American redbelly toads of the genus Melanophryniscus Gallardo, 1961 (Anura: Bufonidae)

CLAUDIO J. BIDAU, DARDO A. MARTI & DIEGO BALDO

JOURNAL OF HERPETOLOGY

SOC STUDY AMPHIBIANS REPTILES

Lugar: Salt Lake City; Año: 2011 vol. 45 p. 66 - 74

0022-1511

Amphibians show strong dependence on environmental variables such as water balance and temperature. However, interactions affecting the geographic distribution of body size are poorly known. We present an analysis of body size within and between all species of an anuran genus using a climatic approach. We studied geographic body size distribution in both sexes of 24 species (129 populations) of South American redbelly toads (Melanophryniscus) spanning 16° latitude, 22° longitude, and 2400 m altitude. Body size was analyzed in relation to climatic parameters including temperature, precipitation, seasonality, evapotranspiration, and water balance at interspecific, interpopulational (all populations irrespective of species), and intraspecific (populations within species) levels. logSVL was regressed against climatic principal components scores with preset geographic coordinate variables using simultaneous autoregression. Interspecifically and interpopulationally, temperature and precipitation are the main factors behind the observed size clines, larger body sizes being associated with decreasing maximum ambient temperature and water availability. Intraspecific results for two species suggested body-size trends comparable to the interspecific ones. That temperature is affecting the size clines of Melanophryniscus is reinforced by the observation that logSVL is strongly positively correlated with mean altitude. Also, since anurans are strongly dependent on water for survival and reproduction, it is reasonable that besides temperature, larger body size is favored in drier environments and this is supported by the correlation between body size and the coefficient of variation of annual rainfall: lower surface/volume ratios in larger species would help conserve water in unpredictable environments. Also, Melanophryniscus species have reproductive peculiarities associated with ephemeral aquatic environments: explosive breeding synchronized with rainfall, eggs deposited in several clutches, and rapid tadpole development which suggest a strong relationship between life history and water balance.