Viviparity Advantages in the Lizard Liolaemus sarmientoi from the End of the World

Abstract

Two hypotheses have prevailed to explain the evolution of viviparity in reptiles: the first proposed that viviparity evolved in response to cold-climates because the possibility of pregnant females to thermoregulate at higher temperatures than embryos could experience in a nest in nature. The second hypothesis posits that the advantage of viviparity is based on the possibility of females to maintain stable body temperatures during development, enhancing offspring fitness. With the aim to contribute to understanding the origins of viviparity in reptiles, we experimentally subjected pregnant females of the austral lizard Liolaemus sarmientoi to two temperature treatments until parturition: one that simulated environmental temperatures for a potential nest (17–25 °C) and another that allowed females to thermoregulate at their preferred body temperature (17–45 °C). Then, we analysed newborn body conditions and their locomotor performance to estimate their fitness. In addition, we measured the body temperature in the field and the preferred temperature in the laboratory of pregnant and non-pregnant females. Pregnant females thermoregulated to achieve higher temperatures than the environmental temperatures, and also thermoregulated within a narrower range than non-pregnant females. This could have allowed embryos to develop in higher and more stable temperatures than they would experience in a nest in nature. Thus, offspring developed at the female preferred temperature showed greater fitness and were born earlier in the season than those developed at lower environmental temperatures. Herein, we show that results are in agreement with the two hypotheses of the origin of viviparity for one of the southernmost lizards of the world.