An experimental study of the gestation costs in a viviparous lizard: a hormonal manipulation

The trade-offs between reproduction and survival or future reproduction represent the costs of reproduction, which are central to the theory of life-history traits evolution. In particular, different stages of the reproductive cycle may be associated with different costs and thus explain the evolution of alternative reproductive strategies. Viviparity (live bearing) has evolved from oviparity (egg laying) several times independently in vertebrates. To better understand these transitions, we aimed to specifically investigate gestation costs in a squamate reptile with a new experimental procedure. We reduced litter size during gestation in the common lizard (Zootoca vivipara) with a hormonal injection of arginine vasotocin. This method is less invasive than a surgical method and does not reduce the number of offspring of future reproductive events. We monitored body mass change, immune response, endurance capacity, thermoregulatory behavior, offspring characteristic at birth, female and offspring survival, female body mass gain after parturition, and offspring growth rate after birth. Maternal treatment did not significantly change the offspring characteristics measured. Thus, litter size reduction did not change offspring development during gestation. For the females, there is evidence that endurance capacity during gestation is modified because of the physical burden of the litter and because of physiological changes. With respect to gestation costs, we did not observe a trade-off between the investment during gestation and females' resources postparturition (female body mass) or survival, but there was a facultative trade-off with the immune response. It will be interesting to replicate this study to increase the robustness of these results and to confirm the effects on the endurance capacity and the immune response. Gestation costs seem to be limited in this species, and they should be studied in more detail to evaluate their influence on the evolution of viviparity.