Anuran life histories remain consistent across contrasting precipitation regimes in Northeastern Brazilian forests

Abstract

Amphibians are inherently dependent on water, and many species characteristics are influenced by this resource, particularly in ecoregions with contrasting precipitation regimes, such as the dry Caatinga and the moist Atlantic Forests of Northeastern Brazil. We compared these environments and hypothesized that anurans, regardless of the species, would be smaller in the Caatinga due to unpredictable duration of the rainy season, which accelerates metamorphosis, and the resulting fluctuations of resources, which limit energy reserves for growth. Furthermore, we anticipated that female reproductive strategies in the Caatinga would be more focused on quality rather than quantity, with small clutches and large oocytes. To test these hypotheses, we sampled areas of Caatinga and Atlantic Forest (two of each) in northeastern Brazil through 15-day consecutive campaigns conducted during the dry and rainy seasons. We combined active searches and pitfall traps to collect the anurans. We performed intraspecific comparisons using morphometric measurements and number and volume of oocytes. Contrary to our expectations, body size did not differ between forests for either sex. In moist environments, the extended reproductive period and the associated energetic demands may constrain growth, imposing costs similar to those in the semiarid environment, resulting in comparable body sizes. Similarly, few differences were observed in oocyte numbers and volumes. Leptodactylus macrosternum and Rhinella diptycha showed fewer and smaller oocytes, respectively, in the Caatinga. Biological factors such as lifespan and body size, and environmental factors such as the duration of the hydroperiod, predation, and insolation can influence oocyte size and numbers in different conditions. However, they likely interact in minimizing energy expenditure, resulting in similar reproductive strategies in contrasting environments.