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12,683 results for “tolerability”
Data from: Development of microsatellite markers for buffalograss (Buchloë dactyloides; Poaceae), a drought-tolerant turfgrass alternative
Premise of the study: Buchloë dactyloides is an important component of Great Plains prairies and a popular drought-tolerant turfgrass alternative in North America. This species comprises an autopolyploid series, and microsatellite primers were developed in order to understand the distribution of genetic variation among cytotypes and across its large geographic range. Methods and Results: Fifteen microsatellite loci were designed and successfully amplified in six B. dactyloides populations. Within-population genetic diversity was comparatively high, consistent with B. dactyloides' life history. Allelic variation at 13 loci was consistent with cytotype established in chromosome-counted samples. Conclusions: This variable, interpretable set of loci allows for the determination of multi-locus genotype in B. dactyloides individuals of varying cytotype. Data such as these from a range-wide sample set can provide important insights for germplasm conservation and crop improvement in this ecologically and economically important species.
Data from: Hydrological niche segregation defines forest structure and drought tolerance strategies in a seasonal Amazon forest
1) Understanding if and how trees coordinate rooting depth and aboveground hydraulic traits to define drought-resistance strategies in seasonal Amazon forests is a major gap to model parametrization aimed at predicting the effects of climate change in these ecosystems. 2) We assessed the rooting depth of 12 dominant tree species (representing ~ 42% of the forest basal area) in a seasonal Amazon forest, using the stable isotope ratios (δ18O and δ²H) of water collected from tree xylem and soils from a range of depths. We took advantage of a major ENSO-related drought in 2015/2016 that caused substantial evaporative isotope enrichment on soil. We measured the minimum dry-season leaf water potential both in a normal year (2014; Ψnon-ENSO) and in an extreme drought year (2015; ΨENSO). Furthermore, we measured xylem hydraulic traits that indicate the range of water potentials that trees tolerate without risking hydraulic failure (P50 and P88). 3) We demonstrate that coexisting trees are largely segregated along a single hydrological niche axis defined by root depth differences, access to light, and tolerance of low water potential. These differences in rooting depth were strongly related to tree size; diameter at breast height (DBH) explained 72% of the variation in the δ18Oxylem. Additionally, δ18Oxylem explained 49% of the variation in P50 and 70% of P88, with higher tolerance of low water potential in shallow-rooted species, while δ18O of xylem water explained 47% and 77% of the variation of minimum Ψnon-ENSO and ΨENSO. 4) We propose a new formulation to estimate an effective functional rooting depth, i.e., the likely soil depth from which roots can sustain water uptake for physiological functions, using DBH as predictor of root depth at this site. Based on these estimates, we conclude that a number of families, genera and species are restricted to drawing water from shallow to deep soil in a large area of the Tapajós forest. 5) Our results support the theory of hydrological niche segregation and its underlying trade-off related to drought resistance, which also affect the dominance structure of trees in this seasonal eastern Amazon forest.
Data from: Heat shock protein expression enhances heat tolerance of reptile and bird embryos
The role of heat shock proteins (HSPs) in heat tolerance has been demonstrated in cultured cells and animal tissues, but rarely in whole organisms because of methodological difficulties associated with gene manipulation. By comparing HSP70 expression patterns among representative species of reptiles and birds, and by determining the effect of HSP70 overexpression on embryonic development and hatchling traits, we have identified the role of HSP70 in the heat tolerance of amniote embryos. Consistent with their thermal environment, and high incubation temperatures and heat tolerance, the embryos of birds have higher onset and maximum temperatures for induced HSP70 than do reptiles, and turtles have higher onset and maximum temperatures than do lizards. Interestingly, the trade-off between benefits and costs of HSP70 overexpression occurred between life-history stages: when turtle embryos developed at extreme high temperatures, HSP70 overexpression generated benefits by enhancing embryo heat tolerance and hatching success, but subsequently imposed costs by decreasing heat tolerance of surviving hatchlings. Taken together, the correlative and causal links between HSP70 and heat tolerance provide, to our knowledge, the first unequivocal evidence that HSP70 promotes thermal tolerance of embryos in oviparous amniotes.
Data from: Historically browsed jewelweed populations exhibit greater tolerance to deer herbivory than historically protected populations
Browsing by overabundant white-tailed deer (Odocoileus virginianus) has altered ecological relationships in forest communities across eastern North America. Recent but limited work suggests that deer browsing also selects for particular plant defensive traits. We hypothesized that browsing by deer has imposed selection on defensive traits in an annual native wildflower, orange jewelweed (Impatiens capensis). To test this hypothesis, we collected individuals from 26 natural populations across a 5000 km2 area in New York State, USA. Half of these populations were historically protected from deer and half were exposed to heavy browsing. We planted individuals in common gardens subjected to natural deer browsing or no browsing. Individuals from historically browsed populations exhibited significantly higher tolerance than those from historically protected populations. Herbivory by deer reduced lifetime fruit production by only 20% in historically browsed populations, as opposed to 57% in historically protected populations. Two mechanisms were correlated with this increased tolerance: increased number of flowering days and increased fruits per flowering node. Synthesis The increased tolerance of historically browsed populations suggests that these populations evolved increased tolerance or that historically protected populations lost tolerance over time. Variation in tolerance traits in native plant species may allow them to persist in the face of rapid ecological change.
Data from: Higher incubation temperatures produce long-lasting upward shifts in cold tolerance, but not heat tolerance, of hatchling geckos
Heatwaves are a regular occurrence in Australia, and are predicted to increase in intensity and duration in the future. These changes may elevate temperatures inside lizard nests, shortening the incubation period, so that hatchlings are more likely to emerge during heatwaves. Potentially, developmental plasticity or heat hardening could buffer hatchings from future warming. For example, higher incubation temperatures could shift critical thermal maxima upwards, enabling lizards to withstand higher temperatures. To investigate whether developmental plasticity affects hatchling thermal tolerance, we incubated eggs of the velvet gecko Amalosia lesueurii under two fluctuating incubation treatments to mimic current warm (mean = 24.3°C, range 18.4 - 31.1°C) and future hot (mean = 28.9°C, range 19.1 - 38.1°C) nest temperatures. We maintained the hatchlings under identical conditions, and measured their thermal tolerance (CTmax) at age 14 d and 42 d. We then released hatchlings at field sites, and recaptured individually marked lizards at age six months, to determine whether incubation induced shifts in thermal tolerance were transitory or long-lasting. We found that at age 14 d, hatchlings from the future hot temperature incubation treatment had higher CTmax (mean = 39.96 ± 0.25°C) than hatchlings from the current warm incubation treatment (mean = 39.70 ± 0.36°C). Hatchlings from the warm-incubation treatment also had significantly higher heat hardening capacity (mean = 0.79 ± 0.37°C) than hatchlings from hot-temperature incubation treatment (mean = 0.47 ± 0.17°C). However, both of these incubation-induced effects did not persist into later life. By contrast, incubation treatment had significant and long-lasting effects on the cold tolerance of hatchlings. At age 14 d, warm-incubated hatchlings tolerated colder temperatures (CTmin = 11.24 ± 0.41°C) than hot-incubated hatchlings (CTmin = 14.11 ± 0.25°C). This significant difference in cold tolerance persisted into the juvenile life stage, and was present in 6 month old lizards that we recaptured from field sites. This finding indicates that upward shifts in cold tolerance caused by higher nest temperatures might impact negatively on overwinter survival of lizards, but field studies linking fitness to thermal tolerance are necessary to test this idea. Overall, our results suggest that developmental plasticity for heat tolerance is unlikely to buffer lizard populations from increasing temperatures.
Data from: Quantitative trait loci for cold tolerance in chickpea
Fall-sown chickpea (Cicer arietinum L.) yields are often double those of spring-sown chickpea in regions with Mediterranean climates that have mild winters. However, winter kill can limit the productivity of fall-sown chickpea. Developing cold-tolerant chickpea would allow the expansion of the current geographic range where chickpea is grown and also improve productivity. The objective of this study was to identify the quantitative trait loci (QTL) associated with cold tolerance in chickpea. An interspecific recombinant inbred line population of 129 lines derived from a cross between ICC 4958, a cold-sensitive desi type (C. arietinum), and PI 489777, a cold-tolerant wild relative (C. reticulatum Ladiz), was used in this study. The population was phenotyped for cold tolerance in the field over four field seasons (September 2011–March 2015) and under controlled conditions two times. The population was genotyped using genotyping-by-sequencing, and an interspecific genetic linkage map consisting of 747 single nucleotide polymorphism (SNP) markers, spanning a distance of 393.7 cM, was developed. Three significant QTL were found on linkage groups (LGs) 1B, 3, and 8. The QTL on LGs 3 and 8 were consistently detected in six environments with logarithm of odds score ranges of 5.16 to 15.11 and 5.68 to 23.96, respectively. The QTL CT Ca-3.1 explained 7.15 to 34.6% of the phenotypic variance in all environments, whereas QTL CT Ca-8.1 explained 11.5 to 48.4%. The QTL-associated SNP markers may become useful for breeding with further fine mapping for increasing cold tolerance in domestic chickpea.
Data from: Protein expression parallels thermal tolerance and ecologic changes in the diversification of a diving beetle species complex
Physiological changes associated with evolutionary and ecological processes such as diversification, range expansion or speciation are still incompletely understood, especially for non-model species. Here we study differences in protein expression in response to temperature in a western Mediterranean diving beetle species complex, using two-dimensional differential gel electrophoresis with one Moroccan and one Iberian population each of Agabus ramblae and Agabus brunneus. We identified proteins with significant expression differences after thermal treatments comparing them with a reference EST library generated from one of the species of the complex (A. ramblae). The colonisation during the Middle Pleistocene of the Iberian peninsula by A. ramblae, where maximum temperatures and seasonality are lower than in the ancestral north African range, was associated with changes in the response to 27 °C in proteins related to energy metabolism. The subsequent speciation of A. brunneus from within populations of Iberian A. ramblae was associated with changes in the expression of several stress-related proteins (mostly chaperons) when exposed to 4 °C. These changes are in agreement with the known tolerance to lower temperatures of A. brunneus, which occupies a larger geographical area with a wider range of climatic conditions. In both cases, protein expression changes paralleled the evolution of thermal tolerance and the climatic conditions experienced by the species. However, although the colonisation of the Iberian peninsula did not result in morphological change, the speciation process of A. brunneus within Iberia involved genetic isolation and substantial differences in male genitalia and body size and shape.
Local adaptation constrains drought tolerance in a tropical foundation tree
<p>1. Plant species with broad climatic ranges might be more vulnerable to climate change than previously appreciated due to intraspecific variation in climatic stress tolerance. In tropical forests, drought is increasingly frequent and severe, causing widespread declines and altering community dynamics. Yet, little is known about whether foundation tropical trees vary in drought tolerance throughout their distributions, and how intraspecific variation in drought tolerance might contribute to their vulnerability to climate change. 2. We tested for local adaptation in seedling emergence and establishment with a full-factorial reciprocal transplant experiment including 27 populations and 109,350 seeds along a 3500 mm precipitation gradient for a widespread tropical foundation tree, Metrosideros polymorpha, in Hawaii. To more precisely relate seedling performance to soil moisture, we conducted a complementary greenhouse experiment to test responses of the same focal populations to simulated drought. 3. In the reciprocal transplant experiment, we observed significant variation among populations and sites in germination and seedling establishment rates. Overall, there was a significant link between historical rainfall of populations and their performance under current rainfall at the study sites consistent with local adaptation. In particular, populations from historically wet sites demonstrated lower germination rates in currently dry sites compared to wet field sites, while populations from historically dry sites germinated well across all sites, with particularly high germination in dry sites. In the greenhouse, seedlings from wet populations survived fewer days without water, and succumbed at wetter soil conditions than populations from historically dry sites, corroborating results from the field experiment. 4. <em>Synthesis. </em>While climate change models project the greatest drying trends for historically dry areas in Hawaii, even moderate drying of wet sites could significantly reduce M. polymorpha recruitment given the sensitivity of seedlings to slight changes in water regimes. Thus, although M. polymorpha demonstrates high seedling drought tolerance in some populations, providing evidence of resilience at the species-scale, there are nonetheless vulnerable populations likely to decline under climate change. Our approach demonstrates that even trees with high dispersal can show significant clines in drought tolerance, and suggests that similar intraspecific variation might be an important consideration for other tropical tree species.</p>
Data from: Evolutionary potential of multiple measures of upper thermal tolerance in Drosophila melanogaster
Thermal tolerance influences the distribution and abundance of many species, but the adaptive capacity of species to increase upper thermal tolerance is poorly understood. Given that patterns of heat tolerance can strongly depend on assay method, it is crucial to get a better understanding of genetic variances and correlations among different heat tolerance components. This study tests for correlated responses in different heat tolerance assays in Drosophila melanogaster lines selected for increased heat tolerance following exposure to a static high temperature. Traits tested included heat tolerance measured under static (basal and hardened) and ramping assays (using different starting temperatures and ramping rates), with lines exposed to fluctuating conditions (3 days of a cycling temperature regime) and a variable food treatment. Selected lines had higher heat tolerance than control lines in all static and ramping assays. The upper thermal tolerance was up to 0·5 °C higher in the selected compared to control lines after ten generations of strong selection. Selection using a static assay therefore leads to correlated responses in other heat-resistant components, suggesting that traits are genetically correlated and not influenced strongly by assay conditions. While the D. melanogaster population we studied harboured additive genetic variation to evolve increased upper thermal tolerance, the level detected may be insufficient to keep up with temperature increases predicted under climate change.
Oxygen supply limits the heat tolerance of avian embryos
<p>Physiologists have primarily focused on two potential explanations for heat stress in animals—the classic model of molecular stability and a more recent model of oxygen limitation. Although the classic model has widespread support, the oxygen-supply model applies to many aquatic animals and some terrestrial ones. In particular, the embryonic stage of terrestrial animals seems most susceptible to oxygen limitation because embryos acquire oxygen from the atmosphere by diffusion rather than ventilation. We report experiments confirming the two conditions of the oxygen-supply model in Japanese quail embryos, Coturnix coturnix. Hypoxia (12% O2) greatly reduced the chance of survival at 47.5°C, and hyperoxia greatly improved the chance of survival at 48.5°C. This finding expands the scope of the oxygen-supply model to a terrestrial, endothermic species, suggesting that oxygen supply generally limits the heat tolerance of embryos.</p>
Data from: Patterns of genetic variation in desiccation tolerance in embryos of the terrestrial-breeding frog, Pseudophryne guentheri
Environmental change often requires evolutionary responses, and therefore understanding the genetic architecture of susceptible populations is essential for predicting their capacity to respond adaptively. However, quantitative genetic studies are rarely targeted at populations considered vulnerable to such environmental perturbations. Here, we assess the level of heritable variation in the ability of embryos to tolerate desiccation stress in Pseudophryne guentheri, a terrestrial-breeding frog that is currently experiencing a drying climate. We applied a North Carolina II breeding design to identify sources of genetic and environmental variance, and genotype-by-environment interactions (GEIs), underlying the expression of embryo survival, hatching times, hatchling mass, size and shape. Our analysis revealed highly significant effects of water potential and maternal effects on all measured traits, while additive genetic effects were significant for hatchling shape and non-additive effects were observed for embryo survival. Interestingly, GEIs, including for some traits complex three-way sire-by-dam-by-environment interactions, were significant, indicating that progeny from certain male-female crosses were more tolerant to water stress than others. These findings suggest a limited capacity of P. guentheri to respond to a drying climate, but also reveal that the detrimental effects of non-viable male-female crosses (i.e. genetic incompatibility) can be masked in benign environments.
Data from: Evolutionary potential of thermal preference and heat tolerance in Drosophila subobscura
Evolutionary change of thermal traits (i.e. heat tolerance and behavioral thermoregulation) is one of the most important mechanisms exhibited by organisms to respond to global warming. However, the evolutionary potential of heat tolerance, estimated as narrow-sense heritability, depends on the methodology employed. An alternative adaptive mechanism to buffer extreme temperatures is behavioral thermoregulation, although the association between heat tolerance and thermal preference is not clearly understood. We suspect that methodological effects associated with the duration of heat stress during thermal tolerance assays are responsible for missing this genetic association. To test this hypothesis, we estimated the heritabilities and genetic correlations for thermal traits in Drosophila subobscura, using high-temperature static and slow ramping assays. We found that heritability for heat tolerance was higher in static assays (h2 = 0.134) than in slow ramping assays (h2 = 0.084), suggesting that fast assays may provide a more precise estimation of the genetic variation of heat tolerance. In addition, thermal preference exhibited a low heritability (h2 = 0.066), suggesting a reduced evolutionary response for this trait. We also found that the different estimates of heat tolerance and thermal preference were not genetically correlated, regardless of how heat tolerance was estimated. In conclusion, our data suggest that these thermal traits can evolve independently in this species. In agreement with previous evidence, these results indicate that methodology may have an important impact on genetic estimates of heat tolerance and that fast assays are more likely to detect the genetic component of heat tolerance.
Data from: Can physiological engineering/programming increase multi-generational thermal tolerance to extreme temperature events?
Organisms increasingly encounter higher frequencies of extreme weather events as a consequence of global climate change. Currently, few strategies are available to mitigate climate change effects on animals arising from acute extreme high temperature events. We tested the capacity of physiological engineering to influence the intra- and multi-generational upper thermal tolerance capacity of a model organism Artemia, subjected to extreme high temperatures. Enhancement of specific physiological regulators during development could affect thermal tolerances or life-history attributes affecting subsequent fitness. Using experimental Artemia populations we exposed F0 individuals to one of four treatments; heat hardening (28 &[deg]C to 36 &[deg]C, 1 &[deg]C per 10 minutes), heat hardening plus serotonin (0.056 μg ml-1), heat hardening plus methionine (0.79 mg ml-1), and a control treatment. Regulator concentrations were based on previous literature. Serotonin may promote thermotolerance, acting upon metabolism and life-history. Methionine acts as a methylation agent across generations. For all groups, measurements were collected for three performance traits of individual thermal tolerance (upper sublethal thermal limit, lethal limit, and dysregulation range) over two generations. Results showed no treatment increased upper thermal limit during acute thermal stress, although serotonin-treated and methionine-treated individuals outperformed controls across multiple thermal performance traits. Additionally, some effects were evident across generations. Together these results suggest phenotypic engineering provides complex outcomes; and if implemented with heat hardening can further influence performance in multiple thermal tolerance traits, within and across generations. Potentially, such techniques could be up-scaled to provide resilience and stability in populations susceptible to extreme temperature events.
Data from: High tolerance of tropical sapling growth and gas exchange to moderate warming
The effects of global warming on tropical forest growth and carbon storage are uncertain. While observations on canopy trees indicate negative correlations between temperature and growth, some seedling studies suggest the opposite. These contrasting results may reflect ontogenetic differences in temperature responses, or differences between the performance of potted plants under controlled conditions and plants under more variable conditions in the field. To try to bridge the gap between highly-controlled experiments on small seedlings and field observations on canopy trees we conducted two sets of outdoor experiments on saplings up to 2.5 m tall; one set to study the effects of night warming, and another set on the effects of day warming. To test the hypothesis that night warming would reduce growth in tropical saplings through stimulation of respiration, we grew the early-successional species Ochroma pyramidale in large 380-liter soil containers under ambient nighttime temperature and ambient +4.5°C. To test the hypothesis that day warming would reduce growth by reducing photosynthesis we compared plants in multi-species and single-species mesocosms rooted in the ground under ambient and passively warmed daytime conditions. In all experiments we monitored growth and measured foliar physiology and plant biomass allocation. Neither night warming nor day warming significantly affected biomass accumulation and allocation. Height growth increased with night warming in Ochroma pyramidale, but decreased with day warming in late-successional species. Night warming resulted in acclimation of dark respiration. Day warming resulted in acclimation of photosynthesis in early-successional species, but warming decreased photosynthesis in late-successional tree species. The seedling-to-sapling transition is a critical stage in the life of trees. We found no evidence that in this juvenile growth phase moderate increases in mean temperature reduce the performance of tropical trees, although increases in peak daytime temperature may negatively impact photosynthesis, especially in late-successional species.
Data from: Recovery from bleaching is mediated by threshold densities of background thermo-tolerant symbiont types in a reef-building coral
Sensitive molecular analyses show that most corals host a complement of Symbiodinium genotypes that includes thermo-tolerant types in low abundance. While tolerant symbiont types are hypothesized to facilitate tolerance to temperature and recovery from bleaching, empirical data on their distribution and relative abundance in corals under ambient and stress conditions are still rare. We quantified visual bleaching and mortality of coral hosts, along with relative abundance of C- and D-type Symbiodinium cells in 82 Acropora millepora colonies from three locations on the Great Barrier Reef transplanted to a central inshore site over a 13 month period. Our analyses reveal dynamic change in symbiont associations within colonies and among populations over time. Coral bleaching and declines in C- but not D-type symbionts were observed in transplanted corals. Survival and recovery of 25% of corals from one population was associated with either initial D-dominance or an increase in D-type symbionts that could be predicted by a minimum pre-stress D : C ratio of 0.003. One-third of corals from this population became D dominated at the bleached stage despite no initial detection of this symbiont type, but failed to recover and died in mid to late summer. These results provide a predictive threshold minimum density of background D-type symbionts in A. millepora, above which survival following extreme thermal stress is increased.
Multiple paths to cold tolerance: the role of environmental cues, morphological traits and the circadian clock gene vrille
<p><strong>Background</strong>: Tracing the association between insect cold tolerance and latitudinally and locally varying environmental conditions, as well as key morphological traits and molecular mechanisms, is essential for understanding the processes involved in adaptation. We explored these issues in two closely-related species, Drosophila montana and Drosophila flavomontana, originating from diverse climatic locations across several latitudes on the coastal and mountainous regions of North America. We also investigated the association between sequence variation in one of the key circadian clock genes, vrille, and cold tolerance in both species. Finally, we studied the impact of vrille on fly cold tolerance and cold acclimation ability by silencing it with RNA interference in D. montana.</p> <p><strong>Results</strong>: We performed a principal component analysis (PCA) on variables representing bioclimatic conditions on the study sites and used latitude as a proxy of photoperiod. PC1 separated the mountainous continental sites from the coastal ones based on temperature variability and precipitation, while PC2 arranged the sites based on summer and annual mean temperatures. Cold tolerance tests showed D. montana to be more cold-tolerant than D. flavomontana and chill coma resistance (CT<sub>min</sub>) of this species showed an association with PC2. Chill coma recovery time (CCRT) of both species improved towards northern latitudes, and in D. flavomontana this trait was also associated with PC1. D. flavomontana flies were darkest in the coast and in the northern mountainous populations, but coloration showed no linkage with cold tolerance. Body size decreased towards cold environments in both species, but only within D. montana populations largest flies showed fastest recovery from cold. Finally, both the sequence analysis and RNAi study on vrille suggested this gene to play an essential role in D. montana cold resistance and acclimation, but not in recovery time.</p> <p><strong>Conclusions</strong>: Our study demonstrates the complexity of insect cold tolerance and emphasizes the need to trace its association with multiple environmental variables and morphological traits to identify potential agents of natural selection. It also shows that a circadian clock gene vrille is essential both for short- and long-term cold acclimation, potentially elucidating the connection between circadian clock system and cold tolerance.</p> <p> </p>
Data from: Climate, physiological tolerance, and sex-biased dispersal shape genetic structure of Neotropical orchid bees
Understanding the impact of past climatic events on the demographic history of extant species is critical for predicting species' responses to future climate change. Paleoclimatic instability is a major mechanism of lineage diversification in taxa with low dispersal and small geographic ranges in tropical ecosystems. However, the impact of these climatic events remains questionable for the diversification of species with high levels of gene flow and large geographic distributions. In this study, we investigate the impact of Pleistocene climate change on three Neotropical orchid bee species (Eulaema bombiformis, E. meriana and E. cingulata) with transcontinental distributions and different physiological tolerances. We first generated ecological niche models to identify species-specific climatically stable areas during Pleistocene climatic oscillations. Using a combination of mitochondrial and nuclear markers, we inferred calibrated phylogenies and estimated historical demographic parameters to reconstruct the phylogeographic history of each species. Our results indicate species with narrower physiological tolerance experienced less suitable habitat during glaciations and currently exhibit strong population structure in the mitochondrial genome. However, nuclear markers with low and high mutation rates show lack of association with geography. These results combined with lower migration rate estimates from the mitochondrial than the nuclear genome suggest male-biased dispersal. We conclude that despite large effective population sizes and capacity for long-distance dispersal, climatic instability is an important mechanism of maternal lineage diversification in orchid bees. Thus, these Neotropical pollinators are susceptible to disruption of genetic connectivity in the event of large-scale climatic changes.
Data from: Elevational and microclimatic drivers of thermal tolerance in Andean Pristimantis frogs
Aim: We analysed elevational and microclimatic drivers of thermal tolerance diversity in a tropical mountain frog clade to test three macrophysiological predictions: less spatial variation in upper than lower thermal limits (Bretts' heat invariant hypothesis); narrower thermal tolerance ranges in habitats with less variation in temperature (Janzen´s climatic variability hypothesis); and higher level of heat impacts at lower altitudes. Location: Forest and open habitats through a 4230 m elevational gradient across the tropical Andes of Ecuador. Method: We examined variability in critical thermal limits (CTmax, and CTmin), and thermal breadth (CTmax-CTmin) in 21 species of Pristimantis frogs. Additionally, we monitored maximum and minimum temperatures at the local-scale (tmax, tmin), and estimated vulnerability to acute thermal stress from heat (CTmax-tmax) and cold (tmin – CTmin), by partitioning thermal diversity into elevational and microclimatic variation. Results: Our results were consistent with Brett's hypothesis: altitude promotes more variation in CTmin and tmin than in CTmax and tmax. Frogs inhabiting thermally variable open habitats have higher CTmax and tmax and greater thermal breadths than species restricted to forest habitats, which show less climatic overlap across the elevational gradient (Janzen´s hypothesis). Vulnerability to heat stress was higher in open than forest habitats and did not vary with altitude. Main conclusions: We suggest a mechanistic explanation of thermal tolerance diversity in elevational gradients by including microclimatic thermal variation. We propose that the unfeasibility to buffer minimum temperatures locally may explain the rapid increase in cold tolerance (lower CTmin) with elevation. In contrast, the relative invariability in heat tolerance (CTmax) with elevation may revolve around the organisms' habitat selection of open and canopy buffered habitats. Secondly, on the basis of microclimatic estimates, lowland and upland species may be equally vulnerable to temperature increase, which is contrary to the pattern inferred from regional interpolated climate estimators.
Data from: Microhabitat and body size effects on heat tolerance: implications for responses to climate change (army ants: Formicidae, Ecitoninae)
1. Models that predict organismal and population responses to climate change may be improved by considering ecological factors that affect species thermal tolerance. Species differences in microhabitat use can expose animals to diverse thermal selective environments at a given site and may cause sympatric species to evolve different thermal tolerances. 2. We tested the hypothesis that species differences in body size and microhabitat use (above- vs. below-ground activity) would correspond to differences in thermal tolerance (maximum critical temperatures: CTmax). Thermal buffering effects of soil can reduce exposure to extreme high temperatures for below-ground active species. We predicted larger-bodied individuals and species would have higher CTmax and that species mean CTmax would covary positively with degree of above-ground activity. We used Neotropical army ants (Formicidae: Ecitoninae) as models. Army ants vary in microhabitat use from largely subterranean to largely above-ground active species and are highly size polymorphic. 3. We collected data on above- and below-ground temperatures in habitats used by army ants to test for microhabitat temperature differences, and we conducted CTmax assays for army ant species with varying degrees of surface activity and with different body sizes within and between species. We then tested whether microhabitat use was associated with species differences in CTmax and whether microhabitat was a better predictor of CTmax than body size for species that overlapped in size. 4. Microhabitat use was a highly significant predictor of species' upper thermal tolerance limits, both for raw data and after accounting for the effects of phylogeny. Below-ground species were more thermally sensitive, with lower maximum critical temperatures (CTmax). The smallest workers within each species were the least heat tolerant, but the magnitude of CTmax change with body size was greater in below-ground species. Species-typical microhabitat was a stronger predictor of CTmax than body size for species that overlapped in size. Compared to the soil surface, 10-cm subsoil was a significantly moderated thermal environment for below-ground army ants, while maximum surface raid temperatures sometimes exceeded CTmax for the most thermally sensitive army ant castes. 5. We conclude sympatric species differences in thermal physiology correspond to microhabitat use. These patterns should be accounted for in models of species and community responses to thermal variation and climate change.
Data from: Genomic determinants of coral heat tolerance across latitudes
As global warming continues, reef-building corals could avoid local population declines through "genetic rescue" involving exchange of heat-tolerant genotypes across latitudes, but only if latitudinal variation in thermal tolerance is heritable. Here, we show an up–to–10-fold increase in odds of survival of coral larvae under heat stress when their parents come from a warmer lower-latitude location. Elevated thermal tolerance was associated with heritable differences in expression of oxidative, extracellular, transport, and mitochondrial functions that indicated a lack of prior stress. Moreover, two genomic regions strongly responded to selection for thermal tolerance in interlatitudinal crosses. These results demonstrate that variation in coral thermal tolerance across latitudes has a strong genetic basis and could serve as raw material for natural selection.
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