@phdthesis{Dierks2012, author = {Anneke Dierks}, title = {Thermal adaptation in insects: Effects of inbreeding, environment and selection}, journal = {Thermal adaptation in insects: Effects of inbreeding, environment and selection}, url = {https://nbn-resolving.org/urn:nbn:de:gbv:9-001335-6}, year = {2012}, abstract = {The ability to withstand thermal stress is considered to be of crucial importance for individual fitness and species’ survival. Thus, organisms need to employ effective mechanisms to ensure survival under stressful thermal conditions. Responses to environmental challenges may occur quickly through phenotypic plasticity or through genetic adaptation needing longer periods of time. Beside thermal stress, other environmental factors might have a similar impact on temperature stress resistance. We first investigated phenotypic adjustment in temperature stress resistance following different environmental manipulations in the butterfly Bicyclus anynana. We found that temperature-induced plasticity quickly and strongly modulated temperature stress resistance and that such responses are readily reversible. Short time hardening responses revealed more complex patterns, with, e.g., cold stress resistance being highest at intermediate hardening temperatures. However, we found resistance traits also to be affected by food availability, age and light cycle. We further investigated whether temperature stress resistance is affected by photoperiod in the fly Protophormia terraenovae. Indeed, variation in temperature stress resistance can be triggered by photoperiod (and temperature), with shorter day lengths inducing more cold- and longer day lengths more heat-tolerant phenotypes. We suggest that short-term, photoperiod-mediated changes in insect thermal tolerance represent a mechanism of adaptive seasonal plasticity. In addition to temperature stress, inbreeding may negatively affect an organism’s ability to cope with changing conditions. This may additively contribute to the extinction risk of small populations in the coming decades for which the frequency and intensity of extreme weather events is predicted to strongly increase. We investigated the effects of inbreeding on egg hatching success, development and temperature stress tolerance in the tropical butterfly Bicyclus anynana using three levels of inbreeding (outbred control, one and two full-sib matings). Even comparatively low levels of inbreeding yield negative consequences for reproduction and development under beneficial conditions. Inbreeding also reduced cold tolerance in adult butterflies, while heat tolerance remained unaffected. We therefore conclude that acute stress tolerance may not be generally impaired by inbreeding. Reduced genetic diversity as a consequence of inbreeding or drift may also interfere with a population’s evolutionary potential. We investigated the consequences of inbreeding on evolutionary potential (the ability to increase cold resistance) using artificial selection starting from three different levels of inbreeding (outbred control, one and two full-sib matings). Although a negative impact of genetic erosion (e.g. through inbreeding) on evolutionary potential is predicted by theory, empirical evidence for such effects seems to be exceedingly scarce. Our study showed a clear response to selection on cold stress resistance, which was smaller in inbred compared to outbred populations. Correlated responses to selection in 10 different life history and stress resistance traits were essentially absent. Inbreeding depression was still measurable in some traits after the course of selection. Traits more closely related to fitness showed a clear fitness rebound, suggesting a trait-specific impact of purging. Importantly, we here experimentally demonstrated that increased levels of inbreeding indeed reduced evolutionary potential, and therefore the ability to cope with environmental change. Finally we tested whether selection on increased cold tolerance in the adult stage increases cold resistance throughout ontogeny. A significant response to selection was found in one day-old butterflies (the age at which selection took place). Older adults showed a very similar though weaker response. Nevertheless, cold resistance did not increase in either egg, larval or pupal stage in the selection lines, but was even lower compared to control lines for eggs and young larvae. These findings suggest a cost of increased adult cold tolerance, with the latter presumably reducing resource availability for offspring provisioning and thereby stress tolerance during development. This thesis emphasized the importance of considering genetic as well as environmental effects together, as both may interactively challenge an individual’s ability to respond to changing conditions. In times of a human-induced loss and fragmentation of natural habitats reducing population size and thereby presumably reducing genetic diversity, plus increased temperature stress due to climate change, the long-term persistence of any given species or population will depend on this ability.}, language = {de} }