Temperature is a major factor affecting population abundance and individual performance. Net reproductive rate (R0) and intrinsic rate of increase (r) differ in their response to different temperature regimes, and much of the difference is mediated by generation time (Tg). Here, we evaluate the effects of thermal mean and variability on R0, r and Tg, at four population densities in Drosophila melanogaster. The results show that R0, r and Tg present differential responses to thermal variation. Although temperature effects on R0 and Tg are non-linear, r response was negligible. R0 and Tg comprise a generational time scale, while r is at a chronological time scale. Thus, we argue that individuals growing under different thermal environments perform similarly on a chronological scale, but differently on a generational scale.

Thermal performance curves have provided a common framework to study the impact of temperature in biological systems. However, few generalities have emerged to date. Here, we combine an experimental approach with theoretical analyses to demonstrate that performance curves are expected to vary predictably with the levels of biological organization. We measured rates of enzymatic reactions, organismal performance and population viability in Drosophila acclimated to different thermal conditions and show that performance curves become narrower with thermal optima shifting towards lower temperatures at higher levels or organization. We then explain these results on theoretical grounds, showing that this pattern reflects the cumulative impact of asymmetric thermal effects that piles up with complexity. These results and the proposed framework are important to understand how organisms, populations and ecological communities might respond to changing thermal conditions.

No abstract

The maintenance of sexuality is a puzzling phenomenon in evolutionary biology. Many universal hypotheses have been proposed to explain the prevalence of sex despite its costs, but it has been hypothesized that sex could be also retained by lineage‐specific mechanisms that would confer some short‐term advantage. Aphids are good models to study the maintenance of sex because they exhibit coexistence of both sexual and asexual populations within the same species and because they invade a large variety of ecosystems. Sex in aphids is thought to be maintained because only sexually produced eggs can persist in cold climates, but whether sex is obligate or facultative depending on climatic conditions remains to be elucidated. In this study, we have inferred the reproductive mode of introduced populations of the pea aphid Acyrthosiphon pisum in Chile along a climatic gradient using phenotypic assays and genetic‐based criteria to test the ecological short‐term advantage of sex in cold environments. Our results showed a latitudinal trend in the reproductive mode of Chilean pea aphid population from obligate parthenogenesis in the north to an intermediate life cycle producing both parthenogenetic and sexual progeny in the southernmost locality, where harsh winters are usual. These findings are congruent with the hypothesis of the ecological short‐term advantage of sex in aphids.

Defense against natural aggressors, such as bacterial infections, requires both energy and an immune-cellular response. However, the question as to how these two components are interconnected in small endotherms by means of the host diet remains only poorly understood. Here, we tested in laboratory mice whether dietary proteins and carbohydrates can modulate the interplay between energy expenditure, food intake and the innate and adaptive immune response when confronting a bacterial challenge (Bacillus Calmette-Guérin, BCG). We observed that mice fed with a high protein diet (HP) developed a better immune response associated to increased numbers of circulating monocytes. In addition, HP diet directly influenced the peripheral blood proportions of both T and B lymphocytes even before the BCG challenge. Interestingly, animals that developed this type of immune response after BCG challenge showed an increased rate of metabolism and food consumption before being challenged. Thus, HP diet induced in non-challenged animals a similar energy expenditure and food intake described by BCG-treated mice. These data suggest that a high amount of proteins in diet can modify the energetic and nutrient dynamic in the host causing a better immune reaction against a microbial challenge.

No abstract

Warming and ocean acidification are currently critical global change drivers for marine ecosystems due to their complex and irreversible effects on the ecology and evolution of marine communities. Changes in the chemistry and the temperature of the ocean impact the biological performance of marine resources by affecting their energy budget and thus imposing energetic restrictions and trade-offs on their survival, growth, and reproduction. In this study, we evaluated the interplaying effects of increased pCO2 levels and temperature on the economically relevant clam Ameghinomya antiqua, an infaunal bivalve inhabiting a wide distributional range along the coast of Chile. Juvenile clams collected from southern Chile were exposed to a 90-day experimental set-up emulating the current and a future scenario projeced to the end of the current century for both high pCO2/low-pH and temperature (10 and 15°C) projected for the Chilean coast. Clams showed physiological plasticity to different projected environmental scenarios without mortality. In addition, our results showed that the specimens under low-pH conditions were not able to meet the energetic requirements when increased temperature imposed high maintenance costs, consequently showing metabolic depression. Indeed, although the calcification rate was negative in the high-pCO2 scenario, it was the temperature that determined the amount of shell loss. These results indicate that the studied clam can face environmental changes for short-term periods modifying energetic allocation on maintenance and growth processes, but with possible long-term population costs, endangering the sustainability of an important benthic artisanal fisheries resource.