Abstract
Anuran embryos and tadpoles are daily exposed to wide thermal variations in their ponds, with maximum temperatures at midday. The aim of this research was to study the impact of three daily variable thermal environments (with maximum experimental temperatures between 10:00 and 16:00 hours), on the survival, developmental time and body size of metamorphs of four tropical anuran species from lowland habitats in Colombia. A total of 50 embryos (Gosner stage ten) to metamorphosis (Gosner stage 46) of Rhinella humboldti, Hypsiboas crepitans and Engystomops pustulosus were exposed to each one of the three daily variable temperature treatments: high temperature (mean = 27.5 °C; maximum temperature = 34 ± 1 °C; range = 23-35 °C), medium temperature (25.5 °C; 29 ± 1 °C; 23-30 °C), and low temperature (24 °C; 24 ± 1 °C; 23-25 °C). For the other species, Espadarana prosoblepon, 40 embryos to metamorphosis were exposed to each one of the following thermal treatments: high temperature (mean = 22 °C; maximum temperature = 25 ± 1 °C; range = 18-26 °C), medium temperature (20.5 °C; 22 ± 1 °C; 18-23 °C), and low temperature (19 °C; 19 ± 1 °C; 18-20 °C). For all species, the thermal variable environment with the highest temperature showed the greatest accumulated survival, reduced significantly the developmental time from embryos to metamorphs, and the snout-vent-length of metamorphs. Therefore, under field conditions where ponds are exposed to thermally variable environments, the highest temperatures may promote a decrease in the period of time to metamorphosis, and a positive increase for the anuran survival; nevertheless, extreme temperatures were also found in the microhabitat of the species studied, higher than their upper thermal limits reported, which suggest a vulnerable situation for them and other tropical anurans from similar habitats.
Highlights
The effect of constant temperatures on life-history traits in amphibians has been long known, but less so under variable temperature environments
H. crepitans E. prosoblepon E. pustulosus R. humboldti embryos to metamorphs (LM: F = 26.85, P = 0.00), which was observed in all species (Fig. 3)
On the contrary, when exposed to lower experimental temperatures, metamorphs were larger, and tadpoles showed a slower growth, which is a typical response in amphibian larvae (Berven, & Gill, 1983; Smith-Gill, & Berven, 1979)
Summary
The effect of constant temperatures on life-history traits in amphibians has been long known, but less so under variable temperature environments. We examined the effect of three daily variable temperatures on the expression of several lifehistory traits in four tropical anuran species from Colombia, Rhinella humboldti, Hypsiboas crepitans, Engystomops pustulosus and Espadarana prosoblepon, that inhabit water bodies susceptible to large daily variations in the thermal environment. We studied these species as they are typical of the tropical dry forest, which is one of the most threatened ecosystems in the study region, the Tolima department, in Colombia and the Neotropics (Pizano, Cabrera, & Garcia, 2014; PortilloQuintero, & Sánchez-Azofeifa, 2010). We were interested in knowing whether the high temperatures, in the daily variable thermal environments, would have a greater effect on the life-history traits assessed, than the medium and low experimental temperatures
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