Relação alométrica entre massa corporal e massa dos testículos: em estudo sobre o investimento reprodutivo em uma população de Gracilinanus agilis (Burmeister, 1854) (Didelphimorphia: Didelphidae)

Abstract

Allometry refers to the relative growth of a part of the body as a function of the size of the organism and can be positive when larger individuals have larger structures or negative when the studied structure is disproportionately larger in smaller individuals. The study of allometry aims to describe such relationships, understand the mechanisms and processes that generate them, and their impact on the ecology and evolution of organisms. Within this contextwe aimed to test the occurrence of an allometric relationship between body mass and testis mass in Gracilinanus agilis, a semelparous species inhabiting the Cerrado biome. Based on the short lifetime of this species and the expected intense competition for access to females during a short, synchronized and unique breeding event, we expected to find a positive allometry between testes mass and body mass among males of G. agilis, so that larger individuals present greater investment in testes mass. Thus, we presumed a variation in 2) allometric coefficients between reproductive stages, with larger allometric coefficient during the breeding period and a decrease in these numbers during post-mating periods. We sampled G. agilis individuals at the Panga Ecological Station (Uberlândia; MG) between January 2011 and January 2020. Individuals were sampled monthly in a capture-markrecapture study using Sherman traps arranged in a grid. To evaluate the allometric relationship between variables, only adult and reproductive individuals had their body mass and testis mass estimated. Our results showed a negative allometric relationship in all regressions performed (OLS, RMA, and SMA), corroborating the hypothesis that there is allometry between the variables, but refuting the hypothesis that predicted positive allometry between the variables. We also found a positive allometric coefficient during the copulation phase, but negative during the following phases, following the expected pattern of decay in the coefficient throughout the reproductive period. Such results are strongly related to the high reproductive investment and sperm competition between males, due to a semelparous reproductive strategy. Therefore, smaller males will have an increase in testis mass to compensate their size.