Effect of exposure to extreme temperatures on fertility of males of the eurythermic lizard Barisia imbricata.

Extreme temperatures can compromise reproduction in viviparous reptiles. We evaluated whether thermal stress affects male reproductive traits in Barisia imbricata, a eurythermic and cryophilic high-elevation lizard. Males were exposed for 12 h per day during 7 days to low (10 °C) or high (35 °C) temperatures, and testicular histology, gonadosomatic and epididymosomatic indices, circulating testosterone concentrations, and sperm performance were assessed. Sperm progressive motility was additionally evaluated over a 12-h incubation period at five temperatures (5, 10, 26, 35, and 38 °C). Both low and high treatments reduced gonadosomatic and epididymosomatic indices. Histological analyses revealed largely preserved seminiferous tubule organization, with mild epithelial alterations at low temperature and greater disorganization at high temperature, but without complete structural damage. Testosterone concentrations decreased under low-temperature exposure but remained similar to controls at high temperature. Sperm progressive motility remained detectable throughout the 12-h experimental period at low temperatures (5 to 10 °C), whereas exposure to warmer temperatures (26 to 38 °C) caused a rapid decline in sperm motility, with complete immobility occurring fastest at 38 °C. These results indicate that B. imbricata shows considerable reproductive tolerance to thermal extremes, although warmer temperatures constrain sperm performance. Our findings partially support the proposed hypothesis by demonstrating that short-term thermal sensitivity varies among reproductive traits, with testicular structure remaining largely preserved despite mild histological alterations, whereas sperm performance showed greater vulnerability to warming. These findings highlight the importance of reproductive thermal physiology in understanding reptile vulnerability under climate warming.