Variable impacts on reproductive energetics may render oviparous squamates more vulnerable to climate warming than viviparous species

Squamate reptiles exhibit two reproductive modes: oviparity and viviparity. Existing large-scale studies suggest that viviparous species are more vulnerable to climate warming based on viviparous species occupying relatively colder environments, which are predicted to decline in availability under climate warming. However, oviparous and viviparous squamates are geographically widespread and their distributions often overlap. Are oviparous or viviparous squamates more vulnerable to climate warming when they inhabit similar thermal environments? We used Sceloporus lizards in North America as a model system to predict the impact of climate warming on oviparous and viviparous species in sympatric zones. We used mechanistic models to quantify the changes in maternal energy balance (MEB) and offspring energy balance (OEB) under a climate warming scenario. We then projected the fitness impacts of future climate warming based on estimates of MEB and OEB. Under a climate warming scenario (RCP8.5), oviparous females are predicted to increase reproductive frequency more than viviparous females, which restricts time for postpartum energy accumulation before the end of the season and decreases MEB. Under climate warming, OEB of oviparous species increased more than viviparous species, but the increases were less geographically widespread. Interestingly, the developmental success and OEB of oviparous species are predicted to decline at some sites under climate warming, which is not predicted to happen for viviparous species. Our results highlight that oviparous species will respond more variably to climate warming than viviparous species. More specifically, oviparous species in hot areas with high temperature variation may be especially vulnerable under climate warming compared to sympatric viviparous species.