Ecotypic differentiation matters for latitudinal variation in energy metabolism and flight performance in a butterfly under climate change

The hydroperiod gradient drives species sorting in pace-of-life strategies but not in stressor sensitivity in Lestes damselfly larvae

Many species sort along environmental gradients, whereby species traits are predicted to shift as integrated sets of life-history, behavioural and physiological traits thereby making up a fast-to-slow pace-of-life continuum. This has also been predicted to cause species differences in stressor sensitivity along such gradients with a faster pace-of-life causing a higher sensitivity. We tested for predictable differences in pace-of-life and in stressor sensitivity for a set of four Lestes damselfly species that separate along the hydroperiod gradient. We reared in a common-garden experiment, larvae of two vernal pond specialists, L. dryas and L. barbarus, and two hydroperiod generalists, L. sponsa and L. virens, and exposed them to transient food deprivation and pesticide exposure, and monitored a set of life-history, behavioural and physiological traits both in the larvae and in the adults. Consistent with the time constraints imposed by the shorter hydroperiod of their habitat, the vernal pond specialists showed a faster pace-of-life (faster growth and development, and higher activity levels) than the hydroperiod generalists. Yet, in contrast with theory, this was not associated with a higher metabolic rate and a lower energy budget, neither with a higher oxidative damage to lipids. Both food deprivation and pesticide exposure were experienced as stressors, and species showed compensatory responses to cope with the transient food deprivation, including compensatory growth and delayed development. Nevertheless, the sensitivity to these stressors could not be predicted based on the difference in pace-of-life strategy between the vernal pond specialists and the hydroperiod generalists because of a decoupling of life-history and physiological traits. Our study indicates that while pace-of-life strategies change largely predictably along the hydroperiod gradient, these are not reliable predictors of species sensitivity to stressors. This highlights the need to consider also physiological traits to arrive at a generalizable predictive framework of species sensitivity to global change.

Enhanced dispersal capacity in edge population individuals of a rapidly expanding butterfly

Natural range shifts offer the opportunity to study the phenotypic and genetic changes contributing to colonization success. The recent range shift of the Southern small white butterfly (Pieris mannii) from the South to the North of Europe offers a prime example to examine a potential dispersal syndrome in range-expanding individuals. We compared butterflies from the core and edge populations using a multimodal approach addressing behavioral, physiological, and morphological traits related to dispersal capacity. Relative to individuals from the core range (France), individuals from the edge (Germany) showed a higher capacity and motivation to fly, and a higher flight metabolic rate. They were also smaller, which may enhance their flight maneuverability and help them cope with limited resource availability, thereby increasing their settlement success in novel environments. Altogether, the behavioral, physiological, and morphological differences observed between core and edge populations in P. mannii suggest the existence of a dispersal syndrome in range-expanding individuals. Whether these differences result from genetic and/or phenotypic responses remains, however, to be determined.

Irreversible impact of early thermal conditions: an integrative study of developmental plasticity linked to mobility in a butterfly species

Within populations, phenotypic plasticity may allow adaptive phenotypic variation in response to selection generated by environmental heterogeneity. For instance, in multivoltine species, seasonal changes between and within generations may trigger morphological and physiological variation enhancing fitness under different environmental conditions. These seasonal changes may irreversibly affect adult phenotypes when experienced during development. Yet, the irreversible effects of developmental plasticity on adult morphology have rarely been linked to life-history traits even though they may affect different fitness components such as reproduction, mobility and self-maintenance. To address this issue, we raised larvae of Pieris napi butterflies under warm or cool conditions to subsequently compare adult performance in terms of reproduction performance (as assessed through fecundity), displacement capacity (as assessed through flight propensity and endurance) and self-maintenance (as assessed through the measurement of oxidative markers). As expected in ectotherms, individuals developed faster under warm conditions and were smaller than individuals developing under cool conditions. They also had more slender wings and showed a higher wing surface ratio. These morphological differences were associated with changes in the reproductive and flight performances of adults, as individuals developing under warm conditions laid fewer eggs and flew larger distances. Accordingly, the examination of their oxidative status suggested that individuals developing under warm conditions invested more strongly into self-maintenance than individuals developing under cool conditions (possibly at the expense of reproduction). Overall, our results indicate that developmental conditions have long-term consequences on several adult traits in butterflies. This plasticity likely acts on life history strategies for each generation to keep pace with seasonal variations and may facilitate acclimation processes in the context of climate change.

Using natural laboratories to study evolution to global warming: contrasting altitudinal, latitudinal, and urbanization gradients

Demonstrating the likelihood of evolution in response to global warming is important, yet challenging. We discuss how three spatial thermal gradients (latitudinal, altitudinal, and urbanization) can be used as natural laboratories to inform about the gradual thermal evolution of populations by applying a space-for-time substitution (SFTS) approach. We compare thermal variables and confounding non-thermal abiotic variables, methodological approaches and evolutionary aspects associated with each type of gradient. On the basis of an overview of recent insect studies, we show that a key assumption of SFTS, local thermal adaptation along these gradients, is often but not always met, requiring explicit validation. To increase realism when applying SFTS, we highlight the importance of integrating daily temperature fluctuations, multiple stressors and multiple interacting species. Finally, comparative studies, especially across gradient types, are important to provide more robust inferences of evolution under gradual global warming. Integrating these research directions will further strengthen the still underused, yet powerful SFTS approach to infer gradual evolution under global warming.

The effects of insecticides on butterflies - A review

Pesticides, in particular insecticides, can be very beneficial but have also been found to have harmful side effects on non-target insects. Butterflies play an important role in ecosystems, are well monitored and are recognised as good indicators of environmental health. The amount of information already known about butterfly ecology and the increased availability of genomes make them a very valuable model for the study of non-target effects of pesticide usage. The effects of pesticides are not simply linear, but complex through their interactions with a large variety of biotic and abiotic factors. Furthermore, these effects manifest themselves at a variety of levels, from the molecular to metapopulation level. Research should therefore aim to dissect these complex effects at a number of levels, but as we discuss in this review, this is seldom if ever done in butterflies. We suggest that in order dissect the complex effects of pesticides on butterflies we need to integrate detailed molecular studies, including characterising sequence variability of relevant target genes, with more classical evolutionary ecology; from direct toxicity tests on individual larvae in the laboratory to field studies that consider the potentiation of pesticides by ecologically relevant environmental biotic and abiotic stressors. Such integration would better inform population-level responses across broad geographical scales and provide more in-depth information about the non-target impacts of pesticides.