Phenology and the physiological niche are co-adapted in a desert-dwelling lizard

A major goal of seasonal biology is to understand how selection on phenology and the physiological niche interact. In oviparous species, fitness variation across the growing season suggests that phenological shifts will alter selective environments experienced by embryos. We hypothesize that physiology could become co-adapted with phenology; such that embryos perform better in the environmental conditions they are adapted to compared to embryos adapted to other environments (temporal matching). Here, we tested for temporal matching to seasonal changes in the environmental temperatures with toad-headed lizard, Phrynocephalus przewalskii, which inhabits the temperate desert steppe of China. We used a split-clutch reciprocal experiment, by incubating eggs from early- and late-breeding females at rising and falling temperature regimes, respectively, to separate the influence of intrinsic (genetic and parental) vs. extrinsic factors (developmental plasticity or acclimatization) on the performance and fitness of offspring. Eggs from early-breeding females were with higher quality than those from late-breeding females, likely due to better maternal provisioning. Offspring from early-breeding females had higher selected body temperatures and metabolic rates than those from late-breeding females. Falling temperatures that may indicate the end of the growing season, reduced incubation duration and increased metabolic rates for both early and late eggs, compared to rising temperatures. Late hatchlings had higher growth rates when incubated at falling compared to rising temperatures, while growth rates of early hatchlings were not sensitive to incubation temperature. Thus, growth and survival rates of late embryos were similar to early embryos under falling temperatures, despite early embryos being of generally higher quality. Overall, our study confirms that "early is higher quality." Intrinsic factors dominate offspring performance and fitness, with a general advantage for early embryos throughout the season. We found some support for temporal matching, demonstrating that late embryos with lower quality have physiological strategies that are specialized to late-season environments, allowing them to attain similar fitness in late-season environments to that of early embryos. A is available for this article.