CONICET | Buscador de Institutos y Recursos Humanos

Evolutionary transitions in life-history strategies, such as the shift from egg-layingto live birth (viviparity) are of great interest to evolutionary biologists. In squamatereptiles, several hypotheses have been proposed to explain viviparity including thecold climate hypothesis, maternal manipulation hypothesis, hypoxia hypothesis, andseveral others. We used two approaches: first we studied 45 species of Liolaemus,a genus where nearly 50% of species are viviparous, using a diverse ecophysiologicaldataset to examine the cold climate and maternal manipulation hypotheses. Wecollected environmental thermal data (accounting for elevational differences amongspecies), physiological traits including preferred body temperature and its coefficientof variation as an indicator of precision in thermoregulation. Additionally, wecollected standard metabolic rates for 23 of the 45 species. In one clade (the darwiniigroup of species) with both reproductive modes, we ran our second approach.We tested for differences in thermal physiology and metabolic rates between viviparousand oviparous species during pregnancy and non-pregnancy periods. Thecold climate hypothesis received strong support because viviparous species occur insites with colder air temperatures (including areas at both higher elevations and latitudes)compared with oviparous species. Our detailed analysis showed that thematernal manipulation hypothesis also is supported; pregnant viviparous femalesshow lower variation in their selected temperature. Our evidence suggests that theAndean orogeny is likely to have played a key role in the diversification of Liolaemuslizards and the evolution of viviparity in this clade may have been driven bya variety of physiological advantages accrued at different stages of embryogenesisand over evolutionary time. Thus, historical climate changes may have led to eggretention and may have been accompanied by other adaptations such as thermoregulationprecision.

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