by Anna Alquitela
Ectotherms are organisms that rely on environmental heat sources to maintain their body temperatures. The timing of reproduction in these organisms has much to do with their available thermal time windows. According to Van Dyck et al. (2015), the warming climate could cause an increase in the annual number of generations of ectotherms, but this response is potentially maladaptive, leading to a developmental trap; if an organism reproduces at the end of its reproductive season, there is a good chance that the new generation will die and the energy used to produce that generation would have been in vain.
Van Dyck et al. performed field experiments with the wall brown butterfly, Lasiommata megera, an ectotherm, to show that regional warming could be affecting their late summer suspended development. These butterflies always produce two generations per year, but during warm summers a third generation may also be produced. Van Dyck et al. introduced 253 young caterpillars into four Belgian sites, two inland and two coastal. They found that all of the caterpillars in the inland sites, where the native populations have disappeared, survived to the adult stage, whereas only 42.5% of the caterpillars in the coastal sites developed to the adult stage even though native populations persist there. During the experiment, both the mean ambient temperature and the mean temperature at host-plant height were recorded. The mean ambient temperature was 0.5ºC higher and the mean temperature at host-plant level, where the caterpillars are located, was 1.2ºC higher at the inland sites than the coastal sites, respectively. The change in thermal conditions of the inland populations has caused a mismatch between seasonal cues and suspended development of L. megera.
Van Dyck et al. argue that the ectotherms that are most likely affected by climate change are those that “use photoperiod as an important cue for life-cycle regulation.” They stress the importance of emphasizing cue-response systems in the field of ecology and phenological evolution to better understand the impacts of climate change.
Van Dyck, H., Bonte, D., Puls, R., Gotthard, K., & Maes, D. 2015. The lost generation hypothesis: could climate change drive ectotherms into a developmental trap? Oikos 124, 54-61.