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Climate change and climatic extremes may affect species directly or indirectly. While direct climatic effects have been intensively studied, indirect effects, such as increasing hybridization risk, are poorly understood., The goal of our study was to analyse the impact of climate on population dynamics of a rare habitat specialist, Chorthippus montanus, as well as the fine-scale spatial overlap with a sympatric habitat generalist, Chorthippus parallelus and the dispersion of hybrids. We were particularly interested in the role of spatiotemporal overlap on heterospecific encounter frequencies., We conducted high-precision mark-recapture studies on two sites over 7 years and genotyped 702 individuals of two C. montanus generations to detect hybrids. We tested the performance of three programs ( structure, newhybrids and adegenet) and accepted only hybrids detected by the two best performing programs. We then tested for correlations between yearly population trends and climatic variables. Furthermore, we analysed the spatial dispersion of both taxa and the hybrids to calculate variation in spatial and temporal overlap and infer heterospecific encounter probabilities., Our results revealed that droughts during the egg phase and rainy weather during nymphal development were strongly correlated with population declines in the habitat specialist. The highest hybridization rate (19·6%) was found in the population with lowest population size. The combined effects of spatial and temporal niche overlap decreased heterospecific encounter probabilities to 4·2-7·6% compared to 20-28% and 11-19% calculated alone from phenology or spatial overlap respectively. Hybrids were detected in areas of higher heterospecific encounter probability, mainly at the edge of the specialists' occupied habitat in areas with intermediate soil moisture conditions compared to the parental species., This illustrates that the combination of spatial and temporal segregation provides an effective barrier to hybridization. However, the high hybridization rate in one of the populations suggests that this function may decrease with decreasing population size. This supports the hypothesis that climatic extremes threaten rare species directly by reducing reproductive success and may indirectly increase hybridization risk., A is available for this article. [ABSTRACT FROM AUTHOR]

The influence of thermal history on temperature-dependent flight performance was investigated in an invasive agricultural pest insect, Ceratitis capitata (Diptera: Tephritidae). Flies were exposed to one of four developmental acclimation temperatures (Tacc: 15, 20, 25, 30°C) during their pupal stage and tested at these temperatures (Ttest) as adults using a full-factorial study design. Major factors influencing flight performance included sex, body mass, Ttest, and the interaction between Ttest, and Tacc. Successful flight performance increased with increasing Test across all acclimation groups (from 10% at 15°C to 77% at 30°C). Although Tacc did not affect flight performance independently, it did have a significant interaction effect with r test. Multiple comparisons showed that flies which had been acclimated to 15°C and 20°C performed better than those acclimated to 25°C and 30°C when tested at cold temperatures, but warm-acclimated flies did not outperform cold-acclimated flies at warmer temperatures. This provides partial support for the 'colder is better' hypothesis. To explain these results, several flight-related traits were examined to determine whether Tacc influenced flight performance as a consequence of changes in body or wing morphology, whole-animal metabolic rate or cytochrome c oxidase enzyme activity. Although significant effects of Tacc could be detected in several of the traits examined, with an emphasis on sex-related differences, increased flight performance could not be explained solely on the basis of changes in any of these traits. Overall, these results are important for understanding dispersal physiology despite the fact that the mechanisms of acclimation-related changes in flight performance remain unresolved. [ABSTRACT FROM AUTHOR]

The evolution of metabolic rate-temperature (MR-T) reaction norms is of fundamental importance to physiological ecology. Metabolic cold adaptation (MCA) predicts that populations or species from cooler environments will have either a higher metabolic rate at a common temperature or steeper MR-T relationships, indicating greater sensitivity of respiratory metabolism to temperature. Support for MCA has been found in some insect species by comparing species or populations differing in latitude. However, the generality of these findings are contentious, with most studies either unable to account for phenotypic plasticity or the evolutionary relatedness of species or populations. Hence, the importance of MCA is vigorously debated from both evolutionary and ecological perspectives. Furthermore, few species, particularly from tropical environments, have been shown to differ in MR-T sensitivity along altitudinal temperature gradients. Here, using four populations of tsetse flies (Glossina pallidipes, Diptera: Glossinidae) from thermally distinct geographic regions, we test the hypothesis that there is evolved variation in MR-T relationships to cold climates. We found that a high-altitude equatorial population from a cool habitat has a steeper MR-T reaction norm. By contrast, other populations from warmer environments in East Africa do not differ with respect to their MR-T reaction norms. Squared-change parsimony analyses, based on the combined mitochondrial 16S rDNA ribosomal subunit and cytochrome c oxidase subunit I (COI), support the hypothesis of adaptive differentiation of MR-T reaction norms in the cool-climate population. Seasonal adjustments or laboratory-temperature-induced phenotypic plasticity changed the intercept of the reaction norm rather than the slope, and thus the observed intraspecific variation in slopes of MR-T reaction norms could not be accounted for by phenotypic plasticity. These results therefore suggest evolutionary adaptation of MR-T reaction norms to cool climates (<22°C) in tsetse and provide novel support for MCA within an insect species. [ABSTRACT FROM AUTHOR]

Dark pigmentation of adults resulting from cold exposure during development is ubiquitous among insects. Yet the costs associated with the developmental plasticity of melanisation have been explored only for a handful of species.We explored two hypotheses relating to colour plasticity of insects. First, if melanin pigments are costly to synthesise and require allocation of resources, increased melanisation should be negatively associated with performance traits (the cost hypothesis). Second, given the positive association between melanisation and immune responses or desiccation resistance in some species, melanisation and performance may co‐vary positively (the positive covariance hypothesis). Furthermore, given the typical differences in reproductive effort and activity between females and males, we expect these performance–melanisation relationships to differ between sexes.We assessed whether temperature‐induced melanisation of the globally invasive beetle Harmonia axyridis f. succinea (Pallas) (Coleoptera: Coccinellidae) was related to standard metabolic rate and flight performance while accounting for developmental temperature and family affiliation.Melanisation explained little variation in standard metabolic rate at most temperatures tested (15, 20, 25, 30 and 35°C). For flight performance and after the cold‐rearing regime, lighter coloured female beetles had increased flight speed compared with darker females, whereas the opposite was found in males. In addition, in warm‐reared beetles, darker individuals had lower mean flight speeds.The results suggest that at least some flight performance costs are associated with developmentally induced melanisation, supporting the cost hypothesis. Disparities in these relationships between males and females suggest that the drivers underlying variation in melanisation differ between sexes. Importantly, variation in melanisation was more acute for females reared in the warm regime compared with equally treated males and to cold‐reared individuals. We propose new directions to test hypotheses pertaining to the maintenance of colour variation and performance between sexes in nature. [ABSTRACT FROM AUTHOR]

Widespread species experience a variety of climates across their distribution, which can structure their thermal tolerance, and ultimately, responses to climate change. For ectotherms, activity is highly dependent on temperature, its variability and availability of favourable microclimates. Thermal exposure and tolerance may be structured by the availability and heterogeneity of microclimates for species living along temperature and/or precipitation gradients – but patterns and mechanisms underlying such gradients are poorly understood. We measured critical thermal limits (CTmax and CTmin) for five populations of two sympatric lizard species, a nocturnal gecko (Chondrodactylus bibronii) and a diurnal skink (Trachylepis variegata) and recorded hourly thermal variation for a year in three types of microclimate relevant to the activity of lizards (crevice, full sun and partial shade) for six sites across a precipitation gradient. Using a combination of physiological and modelling approaches, we derived warming tolerance for the present and the end of the century. In the present climate, we found an overall wider thermal tolerance for the nocturnal species relative to the diurnal species, and no variation in CTmax but variable CTmin along the precipitation gradient for both species. However, warming tolerances varied significantly over the course of the day, across months and microhabitats. The diurnal skink was most restricted in its daily activity in the three driest sites with up to six daily hours of restricted activity in the open (i.e. outside refugia) during the summer months, while the impacts for the nocturnal gecko were less severe, due to its higher CTmax and night activity. With climate change, lizards will experience more months where activity is restricted and increased exposure to high temperatures even within the more sheltered microhabitats. Together our results highlight the importance of considering the relevant spatiotemporal scale and habitat for understanding the thermal exposure of diurnal and nocturnal species. [ABSTRACT FROM AUTHOR]

A classic question in evolutionary biology is whether behavioral flexibility hastens or hinders evolutionary change. The latter idea, that behavior reduces the number of environmental states experienced by an organism and buffers that organism against selection, has been dubbed the "Bogert Effect" after Charles Bogert, the biologist who first popularized the phenomenon using data from lizards. The Bogert Effect is pervasive when traits like body temperature, which tend to be invariant across space in species that behaviorally thermoregulate, are considered. Nevertheless, behavioral thermoregulation decreases or stops when spatial variation in operative temperature is low. We compared environmental temperatures, thermoregulatory behavior, and a suite of physiological and morphological traits between two populations of the southern rock agama (Agama atra) in South Africa that experience different climatic regimes. Individuals from both populations thermoregulated efficiently, maintaining body temperatures within their preferred temperature range throughout most of their activity cycle. Nevertheless, they differed in the thermal sensitivity of resting metabolic rate at cooler body temperatures and in morphology. Our results support the common assertion that thermoregulatory behavior may prevent divergence in traits like field-active body temperature, which are measured during periods of high environmental heterogeneity. Nevertheless, we show that other traits may be free to diverge if they are under selection during times when environments are homogenous. We argue that the importance of the Bogert Effect is critically dependent on the nature of environmental heterogeneity and will therefore be relevant to some traits and irrelevant to others in many populations. [ABSTRACT FROM AUTHOR]

The combinations of trait values that occur within individual animals are often constrained, forming syndromes. The pace-of-life syndrome (POLS) theory proposes that physiological, behavioural and life history traits covary in a predictable way, with metabolic rate acting as the underlying driver of phenotypic variation along a 'slow–fast' axis. However, in many taxa, support for the association among traits predicted by POLS is either weak or absent. Interindividual variation in thermal sensitivities across traits might explain the lack of support for POLS. Indeed, several studies have found that populations contain 'thermal types', with traits falling along a cold–hot continuum, a pattern termed the thermal–behavioural syndrome. Here, we examine the role of temperature in mediating the covariation between physiology, locomotor performance and behaviour in an African lizard, the southern rock agama, Agama atra. First, we tested whether individuals vary in suites of behavioural traits (i.e. have behavioural types) and whether these differences persist across temperature. We then explored the relationship between behavioural type and thermal physiology. Lastly, we tested the fundamental prediction of POLS, whether resting metabolic rate underlies variation in behavioural types and thermal performance. We uncovered the presence of behavioural types in rock agamas, and behaviour was predicted by lizard thermal type. However, the direction of the association between these traits was mediated by body size. In large individuals, 'hot' and fast lizards were bold, whereas in smaller individuals, hot and fast lizards were shy. Despite theoretical predictions, resting metabolic rate did not drive variation in behavioural type in these lizards but did predict thermal type (i.e. thermal optimum). A general theory of pace of life will likely have to consider relationships between thermal physiology, body size and behaviour independently of the role of resting metabolism. • Lizards showed consistent differences in behaviour across time and temperatures. • Behavioural traits were grouped into behavioural types. • Behaviour was predicted by thermal performance, but this was mediated by body mass. • Resting metabolic rate did not predict behaviour at either of the tested temperatures. [ABSTRACT FROM AUTHOR]

Nest care and brooding in sunbirds (Nectariniidae) is thought to be performed exclusively by females. Here, we provide the first evidence that male sunbirds might help with brooding. During a ringing session in Hoekwil, South Africa, we observed one male Amethyst Sunbird (Chalcomitra amethystina) with a brood patch. Its sex was confirmed using molecular methods, and our observation suggests that nest care in sunbirds may at least in some cases be biparental. [ABSTRACT FROM AUTHOR]

Birds exhibit wide variation in their use of aquatic environments, on a spectrum from entirely terrestrial, through amphibious, to highly aquatic. Although there are limited empirical data on hearing sensitivity of birds underwater, mounting evidence indicates that diving birds detect and respond to sound underwater, suggesting that some modifications of the ear may assist foraging or other behaviors below the surface. In air, the tympanic middle ear acts as an impedance matcher that increases sound pressure and decreases sound vibration velocity between the outside air and the inner ear. Underwater, the impedance-matching task is reversed and the ear is exposed to high hydrostatic pressures. Using micro- and nano-CT (computerized tomography) scans of bird ears in 127 species across 26 taxonomic orders, we measured a suite of morphological traits of importance to aerial and aquatic hearing to test predictions relating to impedance-matching in birds with distinct aquatic lifestyles, while accounting for allometry and phylogeny. Birds that engage in underwater pursuit and deep diving showed the greatest differences in ear structure relative to terrestrial species. In these heavily modified ears, the size of the input areas of both the tympanic membrane and the columella footplate of the middle ear were reduced. Underwater pursuit and diving birds also typically had a shorter extrastapedius, a reduced cranial air volume and connectivity and several modifications in line with reversals of low-to-high impedance-matching. The results confirm adaptations of the middle ear to aquatic lifestyles in multiple independent bird lineages, likely facilitating hearing underwater and baroprotection, while potentially constraining the sensitivity of aerial hearing. [ABSTRACT FROM AUTHOR]

Although the impacts of climate change and invasive species are typically studied in isolation, they likely interact to reduce the viability of plant and animal populations. Indeed, invasive species, by definition, have succeeded in areas outside of their native range and may therefore have higher adaptive capacity relative to native species. Nevertheless, the genetic architecture of the thermal niche, which sets a limit to the potential for populations to evolve rapidly under climate change, has never been measured in an invasive species in its introduced range. Here, we estimate the genetic architecture of thermal performance in the harlequin beetle (Harmonia axyridis), a Central Asian species that has invaded four continents. We measured thermal performance curves in more than 400 third‐generation offspring from a paternal half‐sib breeding experiment and analyzed the genetic variance–covariance matrix. We show that while the critical thermal limits in this species have an additive genetic basis, most components of the thermal performance curve have low heritability. Moreover, we found evidence that genetic correlations may constrain the evolution of beetles under climate change. Our results suggest that some invasive species may have limited evolutionary capacity under climate change, despite their initial success in colonizing novel environments. [ABSTRACT FROM AUTHOR]

• Scaling of ear morphology with increasing head size may have implications for hearing performance. • In birds, most structures maintain equal proportions, but the columella becomes hyper-elongated. • The dimensions of several ear structures predict sensitivity and frequency hearing limits. • Unlike mammals, head size and ossicle mass in birds do not appear to constrain high frequency hearing. The dimensions of auditory structures among animals of varying body size can have implications for hearing performance. Larger animals often have a hearing range focused on lower frequencies than smaller animals, which may be explained by several anatomical mechanisms in the ear and their scaling relationships. While the effect of size on ear morphology and hearing performance has been explored in some mammals, anurans and lizards, much less is known about the scaling relationships for the single-ossicle, internally-coupled ears of birds. Using micro- and nano-CT scans of the tympanic middle and inner ears of 127 ecologically and phylogenetically diverse bird species, spanning more than 400-fold in head mass (2.3 to 950 g), we undertook phylogenetically-informed scaling analyses to test whether 12 morphological traits, of functional importance to hearing, maintain their relative proportions with increasing head mass. We then extended our analysis by regressing these morphological traits with measures of hearing sensitivity and range to better understand morphological underpinnings of hearing performance. We find that most auditory structures scale together in equal proportions, whereas columella length increases disproportionately. We also find that the size of several auditory structures is associated with increased hearing sensitivity and frequency hearing limits, while head mass did not explain these measures. Although both birds and mammals demonstrate proportional scaling between auditory structures, the consequences for hearing in each group may diverge due to unique morphological predictors of auditory performance. [ABSTRACT FROM AUTHOR]

Understanding how temperature determines the distribution of life is necessary to assess species' sensitivities to contemporary climate change. Here, we test the importance of temperature in limiting the geographic ranges of ectotherms by comparing the temperatures and areas that species occupy to the temperatures and areas species could potentially occupy on the basis of their physiological thermal tolerances. We find that marine species across all latitudes and terrestrial species from the tropics occupy temperatures that closely match their thermal tolerances. However, terrestrial species from temperate and polar latitudes are absent from warm, thermally tolerable areas that they could potentially occupy beyond their equatorward range limits, indicating that extreme temperature is often not the factor limiting their distributions at lower latitudes. This matches predictions from the hypothesis that adaptation to cold environments that facilitates survival in temperate and polar regions is associated with a performance trade-off that reduces species' abilities to contend in the tropics, possibly due to biotic exclusion. Our findings predict more direct responses to climate warming of marine ranges and cool range edges of terrestrial species., (© 2023. The Author(s).)

To forecast climate change impacts across habitats or taxa, thermal vulnerability indices (e.g., safety margins and warming tolerances) are growing in popularity. Here, we present their history, context, formulation, and current applications. We highlight discrepancies in terminology and usage, and we draw attention to key assumptions underpinning the main indices and to their ecological and evolutionary relevance. In the process, we flag biases influencing these indices that are not always evaluated. These biases affect both components of index formulations, namely: (i) the characterisation of the thermal environment; and (ii) an organism's physiological and behavioural responses to more frequent and severe warming. Presently, many outstanding questions weaken a thermal vulnerability index approach. We describe ways to validate vulnerability index applications and outline issues to be considered in further developing these indices., Competing Interests: Declaration of interests None declared by authors., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

A full-factorial study of the effects of rates of temperature change and start temperatures was undertaken for both upper and lower critical thermal limits (CTLs) using the tsetse fly, Glossina pallidipes. Results show that rates of temperature change and start temperatures have highly significant effects on CTLs, although the duration of the experiment also has a major effect. Contrary to a widely held expectation, slower rates of temperature change (i.e. longer experimental duration) resulted in poorer thermal tolerance at both high and low temperatures. Thus, across treatments, a negative relationship existed between duration and upper CTL while a positive relationship existed between duration and lower CTL. Most importantly, for predicting tsetse distribution, G. pallidipes suffer loss of function at less severe temperatures under the most ecologically relevant experimental conditions for upper (0.06 degrees C min(-1); 35 degrees C start temperature) and lower CTL (0.06 degrees C min(-1); 24 degrees C start temperature). This suggests that the functional thermal range of G. pallidipes in the wild may be much narrower than previously suspected, approximately 20-40 degrees C, and highlights their sensitivity to even moderate temperature variation. These effects are explained by limited plasticity of CTLs in this species over short time scales. The results of the present study have broad implications for understanding temperature tolerance in these and other terrestrial arthropods.