Descrição, ecologia reprodutiva, variações nos níveis hormonais e nas descargas elétricas de Microsternarchus javieri (Gymnotiformes, Hypopomidae)

Abstract

Reproduction is the process by which all species maintain themselves, transferring all genetic variations to its offspring. To maximize the allocation of resources necessary towards reproduction, species can present different reproductive tactics over their lifetime. The reproductive events in fish species depend on both proximate factors or ultimate factors. Electric fishes of the order Gymnotiformes produce electric organ discharges (EODs) important for communication and navigation in often turbid and structurally complex environments. They can communicate species identity, sex, size and/or reproductive stage using one or more parameters in the EODs. These electric signals can carry information about circulating sex hormones that might be relevant to conspecifics to assess the motivation and physiological state of the signaler. Thus, the information embedded in these signals may contribute to a greater reproductive success, reinforcing the honesty of the EODs as a proxy of fishes’ physical condition. In this thesis, first, we described an electric fish as a new species, Microsternarchus javieri, from streams in the Negro and Branco River basin. We found that M. javieri presented a combination of morphological characters different from its congeners, M. bilineatus and M. brevis. It had a greater interspecific than intraspecific genetic distance, and a different EOD waveform compared to that of M. brevis. We further investigated its reproductive ecology for a one-year period in natural conditions. We observed that this electric fish exhibits a small size, negative allometric growth, bimodal reproductive period, fast growth, seasonal batch spawning, and terminal post-reproductive mortality in males. Suggesting this species is semelparous with a seasonal reproductive strategy. Finally, we assessed the relationship between the sex hormone levels and the EODs during the one-year study. We concluded that mature males had higher 11-ketotestosterone than immature and maturing males. Also, the EOD waveform differed between sexes during the reproductive period, were males had a slower repetition rate, and a more elongated second phase than females. These differences were negatively correlated with testosterone levels. Thus, testosterone levels are mediating the broadening of the EOD pulse in M. javieri individuals during the breeding season.