Biology subjects

Sgro, C. M.

Publications and source records attributed to Sgro, C. M..

12 recordsLinked to original sources

bioRxiv2025

Local adaptation in climate tolerance at a small geographic scale contrasts with broad latitudinal patterns

While climate adaptation is typically quantified across broad gradients, the potential for adaptation to the same environmental variables at small scales is rarely tested. If local-scale environmental heterogeneity can generate patterns of adaptation similar to broad gradients, then we currently underestimate adaptive capacity to global change. We quantified population variation in climate tolerance traits and their plasticity for five populations of Drosophila melanogaster from a 3000-km latitudinal gradient, which we contrasted with eight local populations from an environmentally heterogeneous 600x300km area. Population variation in stress tolerance at the local scale was comparable to that across latitude. Consistent with local adaptation, populations from warmer and drier environments showed greater heat and desiccation tolerance, and populations from more predictable environments showed greater plasticity. Climate adaptation at smaller geographic scales can therefore be comparable to adaptation across broad geographic scales. However, patterns of adaptation often changed across geography, which makes predicting responses to global change challenging.

evolutionary biology↗

bioRxiv2025

Variation in temperature but not diet determines the stability of latitudinal clines in tolerance traits and their plasticity

Latitudinal clines are routinely used as evidence of adaptation across broad climatic gradients. However, if environmental variation influences the strength of latitudinal clines, then clinal patterns will be unstable, and using patterns of adaptation to predict population responses to global change will be difficult. To test whether environmental variation influences latitudinal clines, we sampled five populations of Drosophila melanogaster spanning 3000-km of east coast Australia, and measured stress tolerance (heat, cold and desiccation) and body size on flies that developed in six combinations of temperature (13{degrees}C, 25{degrees}C and 29{degrees}C) and diet (standard and low-calorie) treatments. We found latitudinal clines where populations further from the equator had larger wings, higher cold tolerance and lower heat tolerance. For all traits, temperature determined the strength of latitudinal clines, whereas diet had little influence. Steeper clines often emerged in warmer treatments, created by latitudinal clines in plasticity. In the warmest temperature, higher latitude populations showed larger increases in heat tolerance, larger reductions in desiccation tolerance but smaller decreases in cold tolerance. Heat tolerance was the only trait that supported the climate variability hypothesis and a trade-off between plasticity and tolerance. Environment-dependent latitudinal clines are therefore likely to determine variation in population responses to global change.

evolutionary biology↗

bioRxiv2025

Dietary sterol depletion is associated with gut dysfunction in Drosophila melanogaster females

Recent findings have shown that dietary restriction (DR) may extend lifespan by improving late life gut health. Given that recent work has shown that micronutrients such as sterols can mediate the effects of macronutrient ratios on longevity, we decided to examine the effects of sterol limitation on gut health. We found that mothers fed low sterol diets both suffer from increased incidence of intestinal permeability and reduced lifespans. Moreover, epithelial cells in the anterior region of the guts of flies fed low sterol diets showed signs of dysfunction prematurely when compared to flies fed adequate sterols. These findings indicate that the relationship between gut dysfunction and death in D. melanogaster females is conditional on dietary sterol limitation and may point to different paths of physiological decline with ageing that depend on the precise nutritional composition of the diet.

evolutionary biology↗

bioRxiv2024

Experimental evolution under combined thermal-nutritional stress in Drosophila melanogaster results in evolved shifts in larval thermotolerance and thermal plasticity

Animals commonly face combinations of thermal and nutritional stress in nature, which will intensify under climate change. While genetic adaptation is necessary to buffer long-term stress, its unclear whether adaptation to combined stress can occur without compromising viability and thermal plasticity. We tested larval thermotolerance and thermal plasticity in Drosophila melanogaster selected under different temperatures (18{degrees}C, 25{degrees}C, and 28{degrees}C) and diets (standard, diluted, and low-protein:high-carbohydrate [P:C]). Basal larval cold tolerance was affected by both protein concentration and temperature; larvae evolved higher basal cold tolerance on the diluted and low P:C diets at 18{degrees}C and 28{degrees}C. Hardening increased cold tolerance for most lines, except those selected at 18{degrees}C and 28{degrees}C on low P:C diets and at 25{degrees}C on standard diets. Basal larval heat tolerance was affected by selection temperature; selection at 25{degrees}C increased heat tolerance. An interaction between selection temperature, selection diet, and hardening treatment affected larval heat tolerance; hardening reduced heat tolerance in most lines, except those selected at 25{degrees}C on low P:C diets and at 28{degrees}C on standard diets. Our results suggest that adaptation to combined stress allows basal cold tolerance and its plasticity to co-evolve, but not heat tolerance, highlighting ectotherms vulnerability to long-term climate change.

evolutionary biology↗

bioRxiv2023

Fluctuating temperatures exacerbate nutritional stress during development in Drosophila melanogaster

Recent studies suggest that elevated temperatures interact with nutrition to exacerbate the negative effects of poor nutrition. Furthermore, populations adapted to distinct environments differ in their sensitivity to combined thermal and nutritional stress. However, most studies have tested these effects using constant temperatures, even though animals in the wild experience daily and seasonal thermal fluctuations. Here, we used two locally-adapted populations of D. melanogaster from the east coast of Australia (a tropical and a temperate population) to ask whether temperature fluctuations interact with nutrition in the same manner as constant temperature conditions to shape life history traits, and how this differs across populations. We found that fluctuating temperatures exacerbate the negative effects of a poor diet when compared to constant temperatures. Moreover, the negative effects of nutritional stress were significantly greater in the tropical population. In contrast, we found that the temperate population was able to utilize nutrition in unique ways to maintain optimal viability under warmer temperatures. Our findings reveal the ways in which temperature and nutrition interact to impact key life history traits in geographically distinct populations, while also highlighting the importance of using temperature assays representative of natural diel cycles when examining insect responses to climate change.

evolutionary biology↗

bioRxiv2023

Variation in plasticity in response to combined thermal-nutritional stress is genetically independent between sexes and across traits

Phenotypic plasticity helps animals to buffer the effects of increasing thermal and nutritional stress created by climate change. Plastic responses to single and combined stressors can vary among genetically diverged populations. However, less is known about how plasticity in response to combined stress varies among individuals within a population or whether such variation changes across life-history traits. This is important because individual variation within populations shapes population-level responses to environmental change. Here, we used isogenic lines of Drosophila melanogaster to assess plasticity of egg-to-adult viability and sex-specific body size for combinations of two temperatures (25{degrees}C or 28{degrees}C) and three diets (standard diet, low caloric diet, or low protein:carbohydrate ratio diet). Our results reveal substantial within-population genetic variation in plasticity for egg-to-adult viability and wing size in response to combined thermal-nutritional stress. This genetic variation in plasticity was a result of cross-environment genetic correlations that were often < 1 for both traits, as well as changes in the expression of genetic variation across environments for egg-to-adult viability. Cross-sex genetic correlations for body size were weaker when the sexes were reared in different conditions, suggesting that the genetic basis of traits may change with the environment. Further, our results suggest that plasticity in egg-to-adult viability is genetically independent from plasticity in body size. Importantly, plasticity in response to diet and temperature individually differed from plastic shifts in response to diet and temperature in combination. By quantifying plasticity and the expression of genetic variance in response to combined stress across traits, our study reveals the complexity of animal responses to environmental change, and the need for a more nuanced understanding of the potential for populations to adapt to ongoing climate change.

evolutionary biology↗

bioRxiv2023

Identifying the proximate mechanisms that generate variation in nutritional plasticity for fecundity in Drosophila melanogaster

Nutrition is an important determinant of an animals survival and fitness. Phenotypic plasticity allows a genotype to adjust life history traits to changes in its nutritional environment, and it varies among individuals. To understand how variation in plasticity is achieved, we made use of a Drosophila melanogaster isogenic panel to characterize nutritional plasticity for fecundity by feeding flies diets differing in their yeast content and counting the number of eggs produced. We then identified lines with the highest and lowest plastic responses to diet and dissected the potential proximate mechanisms responsible for these differences in plasticity, including morphology, behaviour, and physiology. Our results suggest that genetic variation in plasticity is not due to differences in ovariole number, but due to both increased food intake, and higher efficiency at converting food into eggs. Our results show that, in this population of D. melanogaster, variation in behaviour and physiology, but not morphology, underlies differences in plasticity for fecundity. Further, they set the stage for future studies aiming to understand how the proximate mechanisms that generate genetic variation in plasticity contribute to a populations persistence when faced with environmental changes.

evolutionary biology↗

bioRxiv2023

Anticipating change: the impact of simulated seasonal heterogeneity on heat tolerances along a latitudinal cline.

An understanding of thermal limits and variation across geographic regions is central to predicting how any population may respond to scenarios of global change. Latitudinal clines, in particular, have been used in demonstrating that populations can be locally adapted to their own thermal environment and, as a result, not all populations will be equally impacted by an increase in temperature. But how robust are these signals of thermal adaptation to the other ecological challenges that animals commonly face in the wild? Seasonal changes in population density, food availability, or photoperiod are common ecological challenges that could disrupt patterns of thermal tolerance along a cline if each population differentially used these signals to anticipate future temperatures and adjust their thermal tolerances accordingly. In this study, we aimed to test the robustness of a cline in thermal tolerance to simulated signals of seasonal heterogeneity. Experimental animals were derived from clones of the Australian water flea, Daphnia carinata, sampled from nine populations along a latitudinal transect in eastern Australia. We then factorially combined summer (18h light, 6h dark) and winter (6h light, 18h dark) photoperiods with high (5 million algal cells individual-1 day-1) and low (1 million algal cells individual-1 day-1) food availabilities, before performing static heat shock assays and recording knockdown times as a measure of thermal tolerance. In general, higher food availably led to an increase in thermal tolerances, with the magnitude of increase varying by clone. In contrast, summer photoperiods led to rank order changes in thermal tolerances, with heat resistance increasing for some clones, and other decreasing for others. Heat resistance, however, still declined along the latitudinal cline, irrespective of the manipulation of seasonal signals, with northern clones always showing greater thermal resistance, and that this was most likely driven by adaptation to winter thermal conditions. While photoperiod and food availability can clearly shape thermal tolerances for specific clones or populations, they are unlikely to be used to anticipate future temperatures, and thus observed clines in heat resistance will remained robust to these forms of seasonal heterogeneity.

evolutionary biology↗

bioRxiv2022

Thermal acclimation to warmer temperatures can protect host populations from both further heat stress and the potential invasion of pathogens

Phenotypic plasticity in response to shifts in temperature, known as thermal acclimation, is an essential component of the ability of a species to cope with environmental change. Not only does this process potentially improve an individuals thermal tolerance, it will also act simultaneously on various fitness related traits that determine whether a population increases or decreases in size. In light of global change, thermal acclimation therefore has consequences for population persistence that extend beyond simply coping with heat stress. This particularly important when we consider the additional threat of parasitism associated with global change, as the ability of a pathogen to invade a host population depends on both its capacity to proliferate within a host and spread between hosts, and thus the supply of new susceptible hosts in a population. Here, we use the host Daphnia magna and its bacterial pathogen Pasteuria ramosa to investigate how thermal acclimation may impact various aspects of host and pathogen performance at the scale of both an individual and the population. We independently test the effect of maternal thermal acclimation and direct thermal acclimation on host thermal tolerance, measured as knockdown times, as well as host fecundity and lifespan, and pathogen infection success and spore production. We find that direct thermal acclimation enhances host thermal tolerance and intrinsic rates of population growth, despite a decline observed for host fecundity and lifespan. Pathogens, on the other hand, faired consistently worse at warmer temperatures at the within-host scale, and also in their potential to invade a host population. Our results suggest that hosts could benefit more from warming than their pathogens, but highlight that considering both within- and between-host thermal performance, including thermal tolerance and fitness traits, is needed to fully appreciate how increasing thermal variability will impact host and pathogen populations.

ecology↗

bioRxiv2021

Target of Rapamycin drives unequal responses to essential amino acid depletion in egg laying

Nutrition shapes a broad range of life history traits, ultimately impacting animal fitness. A key fitness-related trait, female fecundity is well known to change as a function of diet. In particular, the availability of dietary protein is one of the main drivers of egg production, and in the absence of essential amino acids egg laying declines. However, it is unclear whether all essential amino acids have the same impact on phenotypes like fecundity. Using a holidic diet, we fed adult female D. melanogaster diets that contain all necessary nutrients except one of the 10 essential amino acids and assessed the effects on egg production. For most essential amino acids, depleting a single amino acid induced as rapid a decline in egg production as when there were no amino acids in the diet. However, when either methionine or histidine were excluded from the diet, egg production declined more slowly. Next, we tested whether GCN2 and TOR were involved in this difference in response across amino acids. While mutations in GCN2 did not eliminate the differences in the rates of decline in egg laying among amino acid drop-out diets, we found that inhibiting TOR signalling caused egg laying to decline rapidly for all drop-out diets. TOR signalling does this by regulating the yolk-forming stages of egg chamber development. Our results suggest that amino acids differ in their ability to induce signalling via the TOR pathway. This is important because if phenotypes differ in sensitivity to individual amino acids, this generates the potential for mismatches between the output of a pathway and the animals true nutritional status.

developmental biology↗

bioRxiv2020

A dietary sterol trade off determines lifespan responses to dietary restriction in Drosophila melanogaster

Diet plays a significant role in maintaining lifelong health. In particular, lowering the dietary protein : carbohydrate ratio can improve lifespan. This has been interpreted as a direct effect of these macronutrients on physiology. Using Drosophila melanogaster, we show that the role of protein and carbohydrate on lifespan is indirect, acting by altering the partitioning of limiting amounts of dietary sterols between reproduction and lifespan. Shorter lifespans in flies fed on high protein : carbohydrate diets can be rescued by supplementing their food with cholesterol. Not only does this fundamentally alter the way we interpret the mechanisms of lifespan extension by dietary restriction, these data highlight the important principle that life histories can be affected by nutrient-dependent trade-offs that are indirect and independent of the nutrients (often macronutrients) that are the focus of study. This brings us closer to understanding the mechanistic basis of dietary restriction.

evolutionary biology↗

bioRxiv2017

Experimental evidence that thermal selection has shaped the latitudinal distribution of mitochondrial haplotypes in Australian fruit flies

Cellular metabolism is regulated by enzyme complexes within the mitochondrion, the function of which are sensitive to the prevailing temperature. Such thermal sensitivity, coupled with the observation that population frequencies of mitochondrial haplotypes tend to associate with latitude, altitude or climatic regions across species distributions, led to the hypothesis that thermal selection has played a role in shaping standing variation in the mitochondrial DNA (mtDNA) sequence. This hypothesis, however, remains controversial, and requires evidence that the distribution of haplotypes observed in nature corresponds with the capacity of these haplotypes to confer differences in thermal tolerance. Specifically, haplotypes predominating in tropical climates are predicted to encode increased tolerance to heat stress, but decreased tolerance to cold stress. We present direct evidence for these predictions, using mtDNA haplotypes sampled from the Australian distribution of Drosophila melanogaster. We show that the ability of flies to tolerate extreme thermal challenges is affected by sequence variation across mtDNA haplotypes, and that the thermal performance associated with each haplotype corresponds with its latitudinal prevalence. The haplotype that predominates at low (subtropical) latitudes confers greater resilience to heat stress, but lower resilience to cold stress, than haplotypes predominating at higher (temperate) latitudes. We explore molecular mechanisms that might underlie these responses, presenting evidence that the effects are in part regulated by SNPs that do not change the protein sequence. Our findings suggest that standing variation in the mitochondrial genome can be shaped by thermal selection, and could therefore contribute to evolutionary adaptation under climatic stress.

evolutionary biology↗