High developmental temperature leads to low reproduction despite adult temperature

Thermal Stress and Adult Fitness in a Drosophila suzukii Neotropical Propagule

Drosophila suzukii (Matsumura 1931) is a cosmopolitan horticultural pest originally from temperate East Asia; yet, its recent introduction in southeast and central Brazil raises the possibility it might expand into warmer climatic zones. In theoretical terms, the adaptive potential of invasive species can be impaired by the lack of genetic variation, but, on the other hand, phenotypic plasticity might play an important role in the adaptation to the new environment. In this context, we investigated the effects of temperature variation (18°C, 22°C, and 28°C) on fitness traits and size of male reproductive organs (accessory glands and testis) in a natural D. suzukii population recently introduced in the neotropical region. Development time decreased significantly with increasing temperature, but egg-to-adult survival was not affected, attaining rates around 50% for the three temperatures. Development at 28°C affected differentially adult male and female biological performance: males displayed higher mortality and severe and permanent reduction in offspring production, whereas females showed the same mortality as controls and a temporary decrease in offspring production, followed of a clear recovery. Finally, reproductive organs size in immature and mature males was affected by developmental temperature variation in the following ways. Testis length decreased with body size (i.e., at higher temperatures) and increased with maturation time after adult hatching, whereas for accessory glands there was no significant difference between different temperatures, resulting in proportionally larger glands for smaller body sizes. These results show differences in developmental dynamics of reproductive tract structures due to temperature variation.

Heat-induced female biased sex ratio during development is not mitigated after prolonged thermal selection

BACKGROUND

The negative impacts of climate change on biodiversity are consistently increasing. Developmental stages are particularly sensitive in many ectotherms. Moreover, sex-specific differences in how organisms cope with thermal stress can produce biased sex ratios upon emergence, with potentially major impacts on population persistence. This is an issue that needs investigation, particularly testing whether thermal selection can alleviate sex ratio distortions in the long-term is a critical but neglected issue. Here, we report an experiment analyzing the sex ratio patterns at different developmental temperatures in Drosophila subobscura populations subjected to long-term experimental evolution (~ 30 generations) under a warming environment.

RESULTS

We show that exposure to high developmental temperatures consistently promotes sex ratio imbalance upon emergence, with a higher number of female than male offspring. Furthermore, we found that thermal selection resulting from evolution in a warming environment did not alleviate such sex ratio distortions generated by heat stress.

CONCLUSIONS

We demonstrate that heat stress during development can lead to clear sex ratio deviations upon emergence likely because of differential survival between sexes. In face of these findings, it is likely that sex ratio deviations of this sort occur in natural populations when facing environmental perturbation. The inability of many insects to avoid thermal shifts during their (more) sessile developmental stages makes this finding particularly troublesome for population subsistence in face of climate warming events.

Slow and population specific evolutionary response to a warming environment

Adaptation to increasingly warmer environments may be critical to avoid extinction. Whether and how these adaptive responses can arise is under debate. Though several studies have tackled evolutionary responses under different thermal selective regimes, very few have specifically addressed the underlying patterns of thermal adaptation under scenarios of progressive warming conditions. Also, considering how much past history affects such evolutionary response is critical. Here, we report a long-term experimental evolution study addressing the adaptive response of Drosophila subobscura populations with distinct biogeographical history to two thermal regimes. Our results showed clear differences between the historically differentiated populations, with adaptation to the warming conditions only evident in the low latitude populations. Furthermore, this adaptation was only detected after more than 30 generations of thermal evolution. Our findings show some evolutionary potential of Drosophila populations to respond to a warming environment, but the response was slow and population specific, emphasizing limitations to the ability of ectotherms to adapt to rapid thermal shifts.

Developmental temperature alters the thermal sensitivity of courtship activity and signal-preference relationships, but not mating rates

Mating behaviors are sensitive to novel or stressful thermal conditions, particularly for ectothermic organisms. An organism's sensitivity to temperature, which may manifest in altered mating outcomes, can be shaped in part by temperatures experienced during development. Here, we tested how developmental temperature shapes the expression of adult mating-related behaviors across different ambient conditions, with a focus on courtship behavior, mating rates, and mating signals and preferences. To do so, we reared treehoppers under two temperature regimes and then tested the expression of male and female mating behaviors across a range of ambient temperatures. We found that developmental temperature affects the thermal sensitivity of courtship behavior and mating signals for males. However, developmental temperature did not affect the thermal sensitivity of courtship or mate preferences in females. This sex-specific plasticity did not alter the likelihood of mating across ambient temperatures, but it did disrupt how closely mating signals and preferences matched each other at higher ambient temperatures. As a result, developmental temperature could alter sexual selection through signal-preference de-coupling. We further discuss how adult age may drive sex-specific results, and the potential for mismatches between developmental and mating thermal environments under future climate change predictions.

Past history shapes evolution of reproductive success in a global warming scenario

Adaptive evolution is critical for animal populations to thrive in the fast-changing natural environments. Ectotherms are particularly vulnerable to global warming and, although their limited coping ability has been suggested, few real-time evolution experiments have directly accessed their evolutionary potential. Here, we report a long-term experimental evolution study addressing the evolution of Drosophila thermal reaction norms, after ∼30 generations under different dynamic thermal regimes: fluctuating (daily variation between 15 and 21 °C) or warming (daily fluctuation with increases in both thermal mean and variance across generations). We analyzed the evolutionary dynamics of Drosophila subobscura populations as a function of the thermally variable environments in which they evolved and their distinct background. Our results showed clear differences between the historically differentiated populations: high latitude D. subobscura populations responded to selection, improving their reproductive success at higher temperatures whereas their low latitude counterparts did not. This suggests population variation in the amount of genetic variation available for thermal adaptation, an aspect that needs to be considered to allow for better predictions of future climate change responses. Our results highlight the complex nature of thermal responses in face of environmental heterogeneity and emphasize the importance of considering inter-population variation in thermal evolution studies.

Effects of developmental and adult environments on ageing

Developmental and adult environments can interact in complex ways to influence the fitness of individuals. Most studies investigating effects of the environment on fitness focus on environments experienced and traits expressed at a single point in an organism's life. However, environments vary with time, so the effects of the environments that organisms experience at different ages may interact to affect how traits change throughout life. Here, we test whether thermal stress experienced during development leads individuals to cope better with thermal stress as adults. We manipulated temperature during both development and adulthood and measured a range of life-history traits, including senescence, in male and female seed beetles (Callosobruchus maculatus). We found that thermal stress during development reduced adult reproductive performance of females. In contrast, life span and age-dependent mortality were affected more by adult than developmental environments, with high adult temperatures decreasing longevity and increasing age-dependent mortality. Aside from an interaction between developmental and adult environments to affect age-dependent changes in male weight, we did not find any evidence of a beneficial acclimation response to developmental thermal stress. Overall, our results show that effects of developmental and adult environments can be both sex and trait specific, and that a full understanding of how environments interact to affect fitness and ageing requires the integrated study of conditions experienced during different stages of ontogeny.

Effect of developmental temperatures on Aphidius colemani host-foraging behavior at high temperature

Temperatures experienced by insects during their adult life often differ from developmental temperatures. Yet, developmental thermal acclimation can play an important role in shaping physiological, morphological, and behavioral traits at the adult stage. We explored how three rearing temperatures (10, 20, and 28 °C) affected host-foraging behaviors and associated traits under warm conditions in the parasitoid Aphidius colemani, a key model in behavioral ecology and an important natural enemy of aphids. Developmental time was longer at lower temperatures, resulting in bigger emerging parasitoids, with higher egg-loads. Parasitism rates, emergence rates, and parasitoid survival (once placed at high temperature) were the highest for parasitoids developed at 20 °C. When exposed to 28 °C, the expression of all behavioral items (time spent walking searching for hosts, number of antennal and ovipositor contacts with hosts) was higher for parasitoids reared at 20 °C, followed by those reared at 10 °C, then those reared at 28 °C. Finally, we showed that parasitoid residence time on aphid patches was determined by both developmental temperatures and the number of host encounter without oviposition, representative of the resource quality. We revealed that developing at 28 °C did not lead to increased adult performance at this temperature, probably because of complex interactions and trade-offs between developmental costs at high temperature and optimal foraging behaviors (e.g., parasitoid size and host-handling capacities). Our results strengthen the idea that thermal developmental plasticity may play an important role in insect behavioral responses to varying temperatures, and is important to consider in the context of climate change.

No evidence for short-term evolutionary response to a warming environment in Drosophila

Adaptive evolution is key in mediating responses to global warming and may sometimes be the only solution for species to survive. Such evolution will expectedly lead to changes in the populations' thermal reaction norm and improve their ability to cope with stressful conditions. Conversely, evolutionary constraints might limit the adaptive response. Here, we test these expectations by performing a real-time evolution experiment in historically differentiated Drosophila subobscura populations. We address the phenotypic change after nine generations of evolution in a daily fluctuating environment with average constant temperature, or in a warming environment with increasing average and amplitude temperature across generations. Our results showed that (1) evolution under a global warming scenario does not lead to a noticeable change in the thermal response; (2) historical background appears to be affecting responses under the warming environment, particularly at higher temperatures; and (3) thermal reaction norms are trait dependent: although lifelong exposure to low temperature decreases fecundity and productivity but not viability, high temperature causes negative transgenerational effects on productivity and viability, even with high fecundity. These findings in such an emblematic organism for thermal adaptation studies raise concerns about the short-term efficiency of adaptive responses to the current rising temperatures.

Developmental Temperature Affects Life-History Traits and Heat Tolerance in the Aphid Parasitoid Aphidius colemani

Developmental temperature plays important roles in the expression of insect traits through thermal developmental plasticity. We exposed the aphid parasitoid Aphidius colemani to different temperature regimes (10, 20, or 28 °C) throughout larval development and studied the expression of morphological and physiological traits indicator of fitness and heat tolerance in the adult. We showed that the mass decreased and the surface to volume ratio of parasitoids increased with the development temperature. Water content was not affected by rearing temperature, but parasitoids accumulated more lipids when reared at 20 °C. Egg content was not affected by developmental temperature, but adult survival was better for parasitoids reared at 20 °C. Finally, parasitoids developed at 20 °C showed the highest heat stupor threshold, whereas parasitoids developed at 28 °C showed the highest heat coma threshold (better heat tolerance CTmax1 and CTmax2, respectively), therefore only partly supporting the beneficial acclimation hypothesis. From a fundamental point of view, our study highlights the role of thermal plasticity (adaptive or not) on the expression of different life history traits in insects and the possible correlations that exist between these traits. From an applied perspective, these results are important in the context of biological control through mass release techniques of parasitoids in hot environments.