Environmental extremes at high altitudes drive clutch size patterns in a wide-ranging lizard

Latitudinal patterns in reproductive output such as clutch size are linked to resource abundance and seasonal climate variation across taxa. Understanding if these patterns hold across local altitudinal gradients and within species can provide insight into key drivers of life-history evolution across scales. In this study, we examined geographical variations in clutch size and climate conditions in a wide-ranging lizard. We collected clutch data from ten populations of E. argus of varying elevation in China from both field observation and from the literature. A total of 369 clutches were obtained and generalized linear mixed-effects models were used to test the relationship between clutch size with body mass, habitat type, elevation, and climate conditions. Body mass strongly correlated with clutch size across all populations. Females from populations at high altitudes with low mean annual temperature and variability, and drier conditions had smaller clutches, while females at lower altitudes with higher mean temperatures and rainfall had larger clutch sizes. Poor climate conditions at high altitudes suggest fewer resources for females to invest in larger clutch sizes, likely due to reduced foraging and activity times, and growth under unfavourable conditions. These constraints match macroecological patterns of clutch size diversity in egg-laying taxa, suggesting local climate constraints can translate across scales to explain the diversity of reproductive output.