Positive genetic covariance and limited thermal tolerance constrain tropical insect responses to global warming

Tropical ectotherms are particularly vulnerable to global warming because their physiologies are assumed to be adapted to narrow temperature ranges. This study explores three mechanisms potentially constraining thermal adaptation to global warming in tropical insects: 1. tradeoffs in genotypic performance at different temperatures (the jack-of-all-trades hypothesis) 2. positive genetic covariance in performance, with some genotypes performing better than others at viable temperatures (the ‘winner and ‘loser genotypes hypothesis) or 3. limited genetic variation as the potential result of relaxed selection and the loss of genes associated with responses to extreme temperatures (the gene decay hypothesis). We estimated changes in growth and survival rates at multiple temperatures for three tropical rain forest insect herbivores (Cephaloleia rolled-leaf beetles, Chrysomelidae). We reared 2746 individuals in a full-sibling experimental design, at temperatures known to be experienced by this ...