Determining responses of organisms to changing temperatures is a research priority as global warming threatens populations and ecosystems worldwide. Upper thermal limits are frequently measured as the critical thermal maximum (CTmax), a quick bioassay where organisms are exposed to increasing temperatures until motor functions stop. Here we propose that a better approach to assess organism responses to global warming is to estimate changes of fitness when organisms are exposed to current and future temperatures. To determine if high-elevation tropical insects are less tolerant to high temperatures than lowland insect species, we selected two communities of rolled-leaf beetles (genus Cephaloleia ) distributed along the Barva and Talamanca cordilleras in Costa Rica (Central America) After identifying cryptic species using DNA barcodes, we estimated CTmax for 1,252 individual beetles representing 56 populations and 46 species. To determine the effect of changing temperatures on insect fitness, we are performing life table analyses rearing 2973 rolled-leaf beetles from four different species at temperatures between 10 to 25°C (current temperatures along elevational gradients in Costa Rica) and 30°C (temperature in 100 y in the lowlands). Here we estimate for each insect species expected survivorship (lx), fecundity (mx) and fitness (r) at current and future temperatures.
Results/Conclusions
DNA barcodes (CO1) and CTmax analyses demonstrate that insect species previously thought to have broad elevational distributions and phenotypically plastic thermal tolerances actually comprise cryptic species complexes. These cryptic species occupy discrete elevational ranges, and their thermal tolerances seem to be locally adapted to temperatures in their life zones. Preliminary demographic analyses show that in some insect species larval and adult stages display different thermal tolerances. Our preliminary results suggest that a small increase of 1-5°C in ambient temperature will reduce insect survival, fecundity, fitness and generate population decline.