Not only big bulls - Correlation between morphometry, reproductive success, and testosterone level in a flooded savannah population of the Spectacled Caiman (Caiman crocodilus)

Testosterone is a steroid hormone involved in the expression of many morphological, physiological, and behavioral traits that arguably affect reproductive success. The evidence for that link is, however, incomplete or absent in the research on crocodilian species. Testosterone levels are also known to change throughout the breeding season, often on an hourly basis, which may further complicate studying their relationship with breeding success. We tested here whether baseline testosterone levels, measured out of the breeding season, are correlated with morphometry and reproductive success in Spectacled Caiman (Caiman crocodilus (Linnaeus, 1758)). Paternity tests, based on the amplification and genotyping of eight fluorochrome labeled microsatellites, failed to support a continuous relationship between these variables. Although adult males of all sizes contribute to reproduction, paternity was overrepresented in a few males with high values of maleness index (bigger males), supporting a despotic or pyramidal hierarchy among males. Maternity assignments supported the existence of multiple paternity, a phenomenon previously attributed in this species to the lack of large males caused by human hunting. The idea of larger males having more offspring is widespread in crocodilians, but to our knowledge, this is the first investigation that prove this dogma.