A Long-Term Study of Coachella Fringe-Toed Lizards, Uma inornata, Reveals Seasonal and Annual Variation in Size and Growth

Productivity of warm deserts is highly correlated with rainfall. We analyzed body size data from a 35-yr study of Coachella Fringe-Toed Lizards, Uma inornata, to reveal precipitation-related differences among years both in growth and in the length-mass relationship (LMR). The LMR is a linear function enabling comparison of regression coefficients among groups. Adult male U. inornata were significantly larger and their maximum size differed substantially from that of females. Comparing regression coefficients of LMR between sexes revealed equal slopes, although intercepts differed slightly but significantly. We treated the sexes independently to test for seasonal and rainfall differences. Comparing seasonal differences among adults revealed that slopes were not parallel. Regression coefficients predicted that individuals weighed more in spring than in fall, which we attribute to winter rainfall. This was corroborated by recapture data. LMR slopes for extreme dry, extreme wet, and typical rainfall years were parallel, but the elevation for typical years differed significantly from both dry and wet years: they were heavier in typical years. Growth was slower in dry years than in wet or typical years. Differences in growth rates affect time to maturity. We used the production relation model of juvenile growth to estimate time to minimum reproductive size. Time to maturity is doubled during dry years in comparison with wet years (542 vs. 288 d for females, 400 vs. 200 d for males). Together, delayed maturity and predicted future increases in drought frequency and intensity imply conservation concerns for this protected species.

Automated summary

Productivity of warm deserts is closely linked to rainfall. A 35-year study of Coachella Fringe-Toed Lizards, Uma inornata, revealed precipitation-related differences in growth and the length-mass relationship (LMR). Adult males were significantly larger than females, and their maximum size differed. Regression analysis showed equal slopes but slightly different intercepts between sexes. Seasonal and rainfall differences were also observed, with individuals weighing more in spring due to winter rainfall. Growth was slower in dry years compared to wet or typical years, affecting time to maturity. Delayed maturity, combined with predicted future droughts, raises conservation concerns for this protected species.