A global analysis of viviparity in squamates highlights its prevalence in cold climates

Abstract

Aim: Viviparity has evolved more times in squamates than in any other vertebrate group; therefore, squamates offer an excellent model system in which to study the patterns, drivers and implications of reproductive mode evolution. Based on current species distributions, we examined three selective forces hypothesized to drive the evolution of squamate viviparity (cold climate, variable climate and hypoxic conditions) and tested whether viviparity is associated with larger body size.Location: Global. Time period: Present day.Taxon: Squamata. Methods:We compiled a dataset of 9061 squamate species, including their distributions, elevation, climate, body mass and reproductive modes. We applied species-level and assemblage-level approaches for predicting reproductive mode, both globally and within biogeographical realms. We tested the relationships of temperature, interannual and intra-annual climatic variation, elevation (as a proxy for hypoxic conditions) and body mass with reproductive mode, using path analyses to account for correlations among the environmental predictors.Results: Viviparity was strongly associated with cold climates at both species and assemblage levels, despite the prevalence of viviparity in some warm climates. Viviparity was not clearly correlated with climatic variability or elevation. The probability of being viviparous exhibited a weak positive correlation with body size. Conclusions:Although phylogenetic history is important, potentially explaining the occurrence of viviparous species in regions that are warm at present, current global squamate distribution is characterized by a higher relative abundance of viviparity in cold environments, supporting the prediction of the "cold-climate" hypothesis.The roles of climatic variation and hypoxia are less important and not straightforward. Elevation probably exerts various selective pressures and influences the prevalence of viviparity primarily through its effect on temperature rather than on oxygen concentration.

Inferring the extinction risk of Data Deficient and Not Evaluated Australian squamates

“…less frequent reproduction) and has been weakly linked to threatened extinction risk in Australian squamates (Senior et al., 2021). Additionally, viviparity is posited to be a cold climate adaptation (Zimin et al., 2022) and thus species often have a restricted, high elevation range and inhabit areas where climate change is having a rapid impact (Senior et al., 2021; Sinervo et al., 2010). Cold climates are often subjected to a sizable human footprint in Australia which negatively impacts species due to an association with habitat loss, overexploitation and invasive species (Senior et al., 2021).…”

Altitudinal gradients and body size variation among Chinese lizards in different terrains

“…widespread species, Horváthová et al, 2013; Liang et al, 2018; Liang & Shi, 2017; Pincheira‐Donoso & Meiri, 2013) and further affect interspecific variation of body size at different altitudes. Besides, life‐history traits could influence body size, for example, viviparity is associated with large body size but always existed in cold regions (Zimin et al, 2022). At the high‐altitude stage of this study, viviparous Phrynocephalus lizards were found to inhabit extremely high regions with enlarged size, which could buffer the overall trends of body size variation along altitudes.…”

Severe fire regimes decrease ectothermic populations’ resilience

“…2016). In reptiles, viviparity developed as an adaptation to increase reproduction success in cold climates (Zimin et al . 2022), and might also confer species with the ability to buffer populations against environmental stochasticity, including resilience to disturbances.…”

“…Recently reported links between demographic buffering and transient dynamics after disturbances (demographic resilience) (Capdevila et al 2020) may explain these patterns (Stott et al 2010;McDonald et al 2016). In reptiles, viviparity developed as an adaptation to increase reproduction success in cold climates (Zimin et al 2022), and might also confer species with the ability to buffer populations against environmental stochasticity, including resilience to disturbances. Therefore, demographically buffering species may outcompete others in the most extreme fire regimes (total absence of fire vs. frequent and severe fires), as we show here.…”