Climate change impacts on fitness depend on nesting habitat in lizards

1. Through nest-site selection, mothers exert control over the incubation environment to which eggs are exposed, which in turn can affect offspring fitness. The strong relationship between offspring quality and incubation temperature in many ectotherms suggests that contemporary climate change could modify the fitness benefits gained from such behaviour. 2. We used life-history data from a tropical lizard (the long-tailed skink, Eutropis longicaudata) to show that a natural dichotomy in nesting habitat directly influences fitness, but that higher ambient temperatures in recent years are having a disproportionate impact on 'optimal' nest sites. 3. Gravid lizards either lay eggs beneath rocks in natural habitat or inside a concrete wall in human-modified habitat, where incubation temperatures are higher. Consequently, females using artificial habitat produced larger hatchlings that matured earlier and had higher rates of survival than conspecifics using natural habitat. 4. Ambient temperatures have impacted artificial habitats disproportionately over the last decade by increasing nest temperatures in artificial habitat three times that of natural habitat (1.5 vs. 0.5 degrees C, respectively). This has reversed nest-site quality by lowering offspring viability of artificial nest sites, but has increased offspring viability of natural nest sites. 5. Climate change has overridden the fitness benefits derived from nesting in artificial habitats, but has caused a resultant increase in the fitness benefits derived from nesting in natural habitats. Laboratory incubation experiments confirm that these patterns are attributed to temperature. 6. Our study highlights the interactive effects of disparate human environmental impacts on fauna; by creating the concrete wall, human habitat modification initially conferred fitness benefits by increasing incubation temperatures, but human-induced climate change has raised nest temperatures above the point at which fitness is reduced. 7. Contemporary climate change is altering the location and availability of 'optimal' nesting habitat, thereby changing the ability of nesting females to adaptively manipulate the phenotypes of their offspring. Consequently, human-induced climate change can lead to some habitats becoming ecological traps.