Thermal performance curves (TPCs) are intended to approximate the relationship between temperature and fitness, and are commonly integrated into species distributional models for understanding climate change responses. However, TPCs may vary across traits because selection and environmental sensitivity (plasticity) differ across traits or because the timing and duration of the temperature exposure, here termed time scale, may alter trait variation. Yet, the extent to which TPCs vary temporally and across traits is rarely considered in assessments of climate change responses. Using a common garden approach, we estimated TPCs for standard metabolic rate (SMR), and activity in Drosophila melanogaster at three test temperatures (16, 25 and 30°C), using flies from each of six developmental temperatures (16, 18, 20, 25, 28 and 30°C). We examined the effects of time scale of temperature exposure (minutes/ hours versus days/weeks) in altering TPC shape and position, and commonly used descriptors of the TPC: thermal optimum (T opt), thermal limits (T min and T max) and thermal breadth (T br). In addition, we collated previously published estimates of TPCs for fecundity and egg-to-adult viability in D. melanogaster. We found that the descriptors of the TPCs varied across traits (egg-to-adult viability, SMR, activity and fecundity), but variation in TPCs within these traits was small across studies when measured at the same time scales. The time scale at which traits were measured contributed to greater variation in TPCs than the observed variance across traits, although the relative importance of time scale differed depending on the trait (activity versus fecundity). Variation in the TPC across traits and time scales suggests that TPCs using single traits may not be an accurate predictor of fitness and thermal adaptation across environments.

How the diverse bacterial communities inhabiting desert soils maintain energy and carbon needs is much debated. Traditionally, most bacteria are thought to persist by using organic carbon synthesized by photoautotrophs following transient hydration events. Recent studies focused on Antarctic desert soils have revealed, however, that some bacteria use atmospheric trace gases, such as hydrogen (H2), to conserve energy and fix carbon independently of photosynthesis. In this study, we investigated whether atmospheric H2 oxidation occurs in four nonpolar desert soils and compared this process to photosynthesis. To do so, we first profiled the distribution, expression, and activities of hydrogenases and photosystems in surface soils collected from the South Australian desert over a simulated hydration-desiccation cycle. Hydrogenase-encoding sequences were abundant in the metagenomes and metatranscriptomes and were detected in actinobacterial, acidobacterial, and cyanobacterial metagenome-assembled genomes. Native dry soil samples mediated H2 oxidation, but rates increased 950-fold following wetting. Oxygenic and anoxygenic phototrophs were also detected in the community but at lower abundances. Hydration significantly stimulated rates of photosynthetic carbon fixation and, to a lesser extent, dark carbon assimilation. Hydrogenase genes were also widespread in samples from three other climatically distinct deserts, the Namib, Gobi, and Mojave, and atmospheric H2 oxidation was also greatly stimulated by hydration at these sites. Together, these findings highlight that H2 is an important, hitherto-overlooked energy source supporting bacterial communities in desert soils. Contrary to our previous hypotheses, however, H2 oxidation occurs simultaneously rather than alternately with photosynthesis in such ecosystems and may even be mediated by some photoautotrophs. IMPORTANCE Desert ecosystems, spanning a third of the earth’s surface, harbor remarkably diverse microbial life despite having a low potential for photosynthesis. In this work, we reveal that atmospheric hydrogen serves as a major previously overlooked energy source for a large proportion of desert bacteria. We show that both chemoheterotrophic and photoautotrophic bacteria have the potential to oxidize hydrogen across deserts sampled across four continents. Whereas hydrogen oxidation was slow in native dry deserts, it increased by three orders of magnitude together with photosynthesis following hydration. This study revealed that continual harvesting of atmospheric energy sources may be a major way that desert communities adapt to long periods of water and energy deprivation, with significant ecological and biogeochemical ramifications.

As global climates change, alien species are anticipated to have a growing advantage relative to their indigenous counterparts, mediated through consistent trait differences between the groups. These insights have largely been developed based on interspecific comparisons using multiple species examined from different locations. Whether such consistent physiological trait differences are present within assemblages is not well understood, especially for animals. Yet, it is at the assemblage level that interactions play out. Here, we examine whether physiological trait differences observed at the interspecific level are also applicable to assemblages. We focus on the Collembola, an important component of the soil fauna characterized by invasions globally, and five traits related to fitness: critical thermal maximum, minimum and range, desiccation resistance and egg development rate. We test the predictions that the alien component of a local assemblage has greater basal physiological tolerances or higher rates, and more pronounced phenotypic plasticity than the indigenous component. Basal critical thermal maximum, thermal tolerance range, desiccation resistance, optimum temperature for egg development, the rate of development at that optimum and the upper temperature limiting egg hatching success are all significantly higher, on average, for the alien than the indigenous components of the assemblage. Outcomes for critical thermal minimum are variable. No significant differences in phenotypic plasticity exist between the alien and indigenous components of the assemblage. These results are consistent with previous interspecific studies investigating basal thermal tolerance limits and development rates and their phenotypic plasticity, in arthropods, but are inconsistent with results from previous work on desiccation resistance. Thus, for the Collembola, the anticipated advantage of alien over indigenous species under warming and drying is likely to be manifest in local assemblages, globally.

26Evolutionary theory proposes that maternal inheritance of mitochondria will facilitate the 27 accumulation of mitochondrial DNA (mtDNA) mutations that are harmful to males but benign 28 or beneficial to females. Furthermore, mtDNA haplotypes sampled from across a given species 29 distribution are expected to differ in the number and identity of these "male-harming" 30 mutations they accumulate. Consequently, it is predicted that the genetic variation that 31 delineates distinct mtDNA haplotypes of a given species should confer larger phenotypic 32 effects on males than females (reflecting mtDNA mutations that are male-harming, but female-33 benign), or sexually antagonistic effects (reflecting mutations that are male-harming, but 34 female-benefitting). These predictions have received support from recent work examining 35 mitochondrial haplotypic effects on adult life history traits in Drosophila melanogaster. Here, 36 we explore whether similar signatures of male-bias or sexual antagonism extend to a key 37 physiological trait -metabolic rate. We measured the effects of mitochondrial haplotypes on 38 the amount of carbon dioxide produced by individual flies, controlling for mass and activity, 39 across 13 strains of D. melanogaster that differed only in their mtDNA haplotype. The effects 40 of mtDNA haplotype on metabolic rate were larger in males than females. Furthermore, we 41 observed a negative intersexual correlation across the haplotypes for metabolic rate. Finally, 42 we uncovered a male-specific negative correlation, across haplotypes, between metabolic rate 43 and longevity. These results are consistent with the hypothesis that maternal mitochondrial 44 inheritance has led to the accumulation of a sex-specific genetic load within the mitochondrial 45 genome, which affects metabolic rate and that may have consequences for the evolution of sex-46 differences in life history. 47 48 Keywords: mitochondrial DNA; pleiotropy; rate of living; sex specific selective sieve; sexual 49 conflict; sexually antagonistic selection 50 Background 51Mitochondrial genes encode products that are key to the regulation of oxidative 52 phosphorylation. Given the pivotal importance of oxidative phosphorylation in the conversion 53 of chemical energy in eukaryotes, it was traditionally assumed that intense purifying selection 54 would prevent the accumulation of non-neutral (i.e. functional) genetic variants within the 55 coding sequence of the mitochondrial DNA (mtDNA). This assumption has, however, been 56 challenged over the past two decades by studies harnessing experimental designs able to 57 partition mitochondrial from nuclear genetic contributions to phenotypic expression [1][2][3][4]. 58These studies have generally shown that mtDNA haplotypes routinely harbour functional 59 polymorphisms that affect the expression of physiological and life history traits [5, 6]. 60Furthermore, several studies have reported that levels of mitochondrial genetic variation 61 underpinning phenotypic expression are often sex-spec...

The structure of tubular transport networks is thought to underlie much of biological regularity, from individuals to ecosystems. A core assumption of transport network models is either area-preserving or area-increasing branching, such that the summed cross-sectional area of all child branches is equal to or greater than the cross-sectional area of their respective parent branch. For insects, the most diverse group of animals, the assumption of area-preserving branching of tracheae is, however, based on measurements of a single individual and an assumption of gas exchange by diffusion. Here we show that ants exhibit neither area-preserving nor area-increasing branching in their abdominal tracheal systems. We find for 20 species of ants that the sum of child tracheal cross-sectional areas is typically less than that of the parent branch (area-decreasing). The radius, rather than the area, of the parent branch is conserved across the sum of child branches. Interpretation of the tracheal system as one optimized for the release of carbon dioxide, while readily catering to oxygen demand, explains the branching pattern. Our results, together with widespread demonstration that gas exchange in insects includes, and is often dominated by, convection, indicate that for generality, network transport models must include consideration of systems with different architectures.

The rarity of parthenogenetic species is typically attributed to the reduced genetic variability that accompanies the absence of sex, yet natural parthenogens can be surprisingly successful. Ecological success is often proposed to derive from hybridization through enhanced genetic diversity from repetitive origins or enhanced phenotypic breadth from heterosis. Here, we tested and rejected both hypotheses in a classic parthenogen, the diploid grasshopper Warramaba virgo . Genetic data revealed a single hybrid mating origin at least 0.25 million years ago, and comparative analyses of 14 physiological and life history traits showed no evidence for altered fitness relative to its sexual progenitors. Our findings imply that the rarity of parthenogenesis is due to constraints on origin rather than to rapid extinction.

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