Testing the viviparity hypotheses in a lizard from the end of the world: how temperature affect pregnant females and their offspring fitness?

FERNANDEZ, JIMENA BEATRIZ; KUBISCH, ERIKA; IBARGÜENGOYTÍA N. R

Congreso; 8th World Congress of Herpetology; 2016

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. 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. We test the two viviparity hypotheses in the viviparous lizard Liolaemus sarmientoi, who inhabit a cold harsh climate in the austral Patagonian steppe of Argentina, South America. For pregnant and non-pregnant females, we measured the body temperature during capture and the preferred body temperature in the laboratory. In addition, pregnant females were subjected to two temperature treatments until parturition: one that simulated environmental temperatures for a potential nest of an oviparous Liolaemus species (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 at the two mean preferred body temperatures of females of both treatments (21 and 30°C) to estimate their fitness. Pregnant females thermoregulated to achieve higher temperatures than the environmental temperatures, and also thermoregulated within a narrower range than non-pregnant females. This 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 body temperature showed greater fitness and were born earlier in the season than those developed at low environmental temperatures. Herein, we show that the two hypotheses of the origin of viviparity are confirmed and are also complementary in one of the southernmost lizards of the world.