Viviparity (i.e. live-bearing) has evolved many times from oviparity (i.e. egg-laying), especially in squamates (i.e. lizards and snakes). This group is the one that has undergone the highest number of independent evolution of viviparity. Moreover, squamates have evolved viviparity in geologically-recent times and at low taxonomic levels. The common lizard is one of the rare species that exhibits both viviparity and oviparity. I thus used this species for my study on the costs and benefits of viviparity. I first studied adjustments of reproductive investment and gestation costs. I observed the absence of post-ovulatory adjustments of litter size, litter mass and offspring mass. However, I observed that females can adjust these parameters in response to the environmental conditions during vitellogenesis, to their body condition and to their parturition date of the previous year. Then, in order to study gestation costs, I used experimental approaches based on a manipulation of mating opportunity, on two manipulations of litter size, and on a comparison between oviparous and viviparous females. These studies highlighted context-dependent effects of gestation on the immune system, on the thermoregulatory behavior, on the endurance capacity and on the loss of mass of females; however, no effect on survival after parturition was observed. The comparative study showed that reproductive costs were higher for oviparous females than viviparous females before gestation. Furthermore, gestation is a period associated not only with costs but also with maternal effects. I have shown that offspring growth after birth depends on litter size during gestation. However, as often, the underlying mechanism of this maternal effect is not known. To investigate the underlying factors of maternal effects, I have developed an experimental approach based on the in vitro incubation of viviparous lizard embryos. Preliminary results are promising as I have managed to obtain live juveniles by this process. Finally, I have shown effects of grand-maternal age in viviparous lizards. This study gives the first evidence of grand-maternal age effects in a wild population.
