Amphibian life histories are closely tied to water availability, making them particularly sensitive to precipitation regimes and hydrological dynamics. Ecological theory suggests that different environmental conditions impose distinct selective pressures, potentially driving divergence in both morphology and reproductive strategies.

Traditionally, it has been proposed that stable, resource-rich environments favor the evolution of larger individuals and females that produce large clutches of eggs. In contrast, species in more unpredictable or harsher environments are expected to be smaller, producing fewer but larger eggs—emphasizing offspring quality over quantity to maximize survival under challenging conditions.

The dry Caatinga region and the moist Atlantic Forest of Brazil present a unique natural laboratory to test this hypothesis due to their starkly contrasting hydrological conditions. Amphibians from the Caatinga, characterized by seasonal droughts and limited water availability, are hypothesized to be smaller and to prioritize reproductive investment in fewer, higher-quality offspring compared to those from the more humid Atlantic Forest.

However, a recent study published in Acta Herpetologica challenges these assumptions. By measuring and comparing morphometric traits and reproductive output in amphibians across both ecoregions, the researchers found no significant differences in body size among four species shared between the two habitats. This unexpected result suggests that amphibians in drier regions may mitigate resource limitations through behavioral adaptations, such as estivation or using subterranean shelters, thereby maintaining growth.

Similarly, clutch size did not significantly differ between ecoregions in two of the three species for which reproductive data were available. A divergence in oocyte number was observed in one species, but not in a consistent or predictable pattern. These findings suggest that factors beyond precipitation—such as predation risk, which may be lower in ephemeral ponds—could influence reproductive strategies in ways that counteract the expected trade-offs.

In conclusion, the study highlights that precipitation regimes alone cannot fully explain morphological and reproductive patterns in amphibians across Brazil’s diverse ecosystems. The results call for further research into additional ecological stressors and adaptive strategies that may shape amphibian life histories.

Read the full paper in Acta Herpetologica for detailed insights.

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