Living in a predictable environment: Intraspecific variation in tadpole size and shape of the Sierra's treefrog

Abstract

Within the breeding sites of anurans, factors at the microhabitat scale can exhibit variations over the years, resulting in temporal fluctuations within these sites. These fluctuations may lead to modifications in “normal larval development” and observable phenotypic changes. These developmental alterations appear to have evolved as shared strategies for achieving reproductive success and ensuring the survival of offspring. In a population of Boana cordobae inhabiting the Central Pampean Sierras (Córdoba, Argentina), the coexistence of pre- and prometamorphic tadpoles throughout the year, coupled with variations in size and shape within the same developmental stage, has led us to question about the duration of the larval period, variations in the timing of developmental events, and the possible existence of distinct larval morphs for this species. Utilizing data collected over four consecutive years from various locations, we described the development, growth, and larval morphology using both linear and geometric morphometrics during the pre- and prometamorphic stages. Our aim was to comprehend how anuran larvae in predictable environments synchronize the timing of their phenotypic transformations with external conditions. We identified two distinct cohorts: spring–summer and autumn–spring, each exhibiting distinct rates of growth and development until metamorphosis, resulting in size discrepancies. Moreover, the physical attributes of the breeding sites influenced the size of the tadpoles. However, the observed variation in shape was not related to the ontogenetic period, cohort, or developmental site. Ultimately, the observed variations had no impact on the morphology at metamorphosis. The comprehensive data gathered from our observations in B. cordobae yield valuable insights that contribute to a deeper comprehension of anuran larval development under natural conditions where changes are predictable and follow a regular pattern throughout the year, ultimately maximizing reproductive success.