Dispersal potential impacts size clines of grasshoppers across an elevation gradient

Intraspecific variation of thermal tolerance along elevational gradients: the case of a widespread diving beetle (Coleoptera: Dytiscidae)

Species distributed across wide elevational gradients are likely to experience local thermal adaptation and exhibit high thermal plasticity, as these gradients are characterised by steep environmental changes over short geographic distances (i.e., strong selection differentials). The prevalence of adaptive intraspecific variation in thermal tolerance with elevation remains unclear, however, particularly in freshwater taxa. We explored variation in upper and lower thermal limits and acclimation capacity among Iberian populations of adults of the widespread water beetle Agabus bipustulatus (Dytiscidae) across a 2000 m elevational gradient, from lowland to alpine areas. Since mean and extreme temperatures decline with elevation, we predicted that populations at higher elevations will show lower heat tolerance and higher cold tolerance than lowland ones. We also explored whether acclimation capacity is positively related with climatic variability across elevations. We found significant variation in thermal limits between populations of A. bipustulatus, but no evidence of local adaptation to different thermal conditions across the altitudinal gradient, as relationships between thermal limits and elevation or climatic variables were largely nonsignificant. Furthermore, plasticities of both upper and lower thermal limits were consistently low in all populations. These results suggest thermal niche conservatism in this species, likely due to gene flow counteracting the effects of divergent selection, or adaptations in other traits that buffer exposure to climate extremes. The limited adaptive potential and plasticity of thermal tolerance observed in A. bipustulatus suggest that even generalist species, distributed across wide environmental gradients, may have limited resilience to global warming.

Variety is the spice: The role of morphological variation of Triatoma infestans (Hemiptera, Reduviidae) at a macro-scale

Chagas disease is caused by the protozoan parasite Trypanosoma cruzi (Chagas, 1909). One of the primary vectors of T. cruzi in South America is Triatoma infestans (Klug, 1834). This triatomine species is distributed across a huge latitudinal gradient, inhabiting domiciliary , peridomiciliary , and wild environments. Its wide geographic distribution provides an excellent opportunity to study the relationships between environmental gradients and intraspecific morphological variation. In this study, we investigated variations in wing size and shape in T. infestans across six ecoregions. We aimed to address the following questions: How do wing size and shape vary on a regional scale, does morphological variation follow specific patterns along an environmental or latitudinal gradient, and what environmental factors might contribute to wing variation? Geometric morphometric methods were applied to the wings of 162 females belonging to 21 T. infestans populations, 13 from Argentina (n = 105), 5 from Bolivia (n = 42), and 3 from Paraguay (n = 15). A comparison of wing centroid size across the 21 populations showed significant differences. Canonical Variate Analysis (CVA) revealed significant differences in wing shape between the populations from Argentina, Bolivia, and Paraguay, although there was a considerable overlap, especially among the Argentinian populations. Well-structured populations were observed for the Bolivian and Paraguayan groups. Two analyses were performed to assess the association between wing size and shape, geographic and climatic variables: multiple linear regression analysis (MRA) for size and Partial Least Squares (PLS) regression for shape. The MRA showed a significant general model fit. Six temperature-related variables, one precipitation-related variable, and the latitude showed significant associations with wing size. The PLS analysis revealed a significant correlation between wing shape with latitude, longitude, temperature-related, and rainfall-related variables. Wing size and shape in T. infestans populations varied across geographic distribution. Our findings demonstrate that geographic and climatic variables significantly influence T. infestans wing morphology.

Pattern of plant communities' influence to grasshopper abundance distribution in heterogeneous landscapes at the upper reaches of Heihe River, Qilian Mountains, China

Understanding the impact of the heterogeneity of the ecological environment on biodiversity is a key issue in ecology. Topographical heterogeneity was potentially important in grassland systems to create or change habitats for grasshopper settlement and foraging. Yet, there was little knowledge of how grasshopper communities respond to plant communities along the altitude gradient. We investigated the role of plant communities on grasshopper diversity with geostatistical methods to test the effects of heterogeneity in the natural grassland on the upper reaches of the Heihe River, Qilian Mountains. To aim the goal of the study, nonreturn experiments were used to collect the grasshoppers' diversity and populations, and the plant's community was sampled at the same location. The results showed that the semivariograms of grasshopper abundance and plant communities were both nonlinear models, while the grasshopper abundance typically produces heterogeneity with a larger range and nuggets than plant communities (except the plant coverage range in the model, range <1.5 m). The two communities presented the spatial distribution pattern of aggregated distribution, and the spatial trend is more intense in the northeast-southwest direction than in the northwest-southeast. The grasshopper species developed a good selection on microenvironment to habitat and the distribution consistent with plants, forming the horizontal distribution with a flaky and plaque distribution pattern. The relationship between grasshoppers and plants was highly dependent on the altitude, and grasshopper abundance has a positive correlation with plant richness (F = 0.68) and plant coverage (F = 0.32) and has a negative correlation with plant height (F = 0.13). In summary, the spatial distribution and correlation characteristics of plant communities and grasshoppers formed a plaque heterogeneity structure under the altitude gradients.

High-Elevation Populations of Montane Grasshoppers Exhibit Greater Developmental Plasticity in Response to Seasonal Cues

Populations of insects can differ in how sensitive their development, growth, and performance are to environmental conditions such as temperature and daylength. The environmental sensitivity of development can alter phenology (seasonal timing) and ecology. Warming accelerates development of most populations. However, high-elevation and season-limited populations can exhibit developmental plasticity to either advance or prolong development depending on conditions. We examine how diurnal temperature variation and daylength interact to shape growth, development, and performance of several populations of the montane grasshopper, Melanoplus boulderensis, along an elevation gradient. We then compare these experimental results to observed patterns of development in the field. Although populations exhibited similar thermal sensitivities of development under long-day conditions, development of high-elevation populations was more sensitive to temperature under short-day conditions. This developmental plasticity resulted in rapid development of high elevation populations in short-day conditions with high temperature variability, consistent with their observed capacity for rapid development in the field when conditions are permissive early in the season. Notably, accelerated development generally did not decrease body size or alter body shape. Developmental conditions did not strongly influence thermal tolerance but altered the temperature dependence of performance in difficult-to-predict ways. In sum, the high-elevation and season-limited populations exhibited developmental plasticity that enables advancing or prolonging development consistent with field phenology. Our results suggest these patterns are driven by the thermal sensitivity of development increasing when days are short early in the season compared to when days are long later in the season. Developmental plasticity will shape phenological responses to climate change with potential implications for community and ecosystem structure.

Elevational Changes in Mormon Cricket Life Histories: Minimum Temperature for Nymphal Growth Declines With Elevation

As the mean temperature and the duration of the growing season decline with elevation, growth of immature insects should initiate at a lower temperature, but it should also be faster to complete development prior to season's end. Although flightless, Mormon crickets migrate in large aggregations across broad spatial and elevational distances that might limit adaptations to local environments. In addition, selection to be active at cooler temperatures might limit selection to maximize growth rate. I measured growth rate in controlled environments for nymphs from three populations that vary in altitude (87-2,688 m) but are similar in latitude (43.2-45.7°N). Growth rate increased significantly with mean rearing temperature between 22 and 30°C. The intercept of the regression of growth rate on temperature increased with elevation, whereas the slope did not change significantly. For any given rearing temperature, growth rate increased with elevation, which suggests that selection to initiate growth at cooler temperatures did not compromise growth rate. Body mass did not differ between the two lower elevations, whereas the highest elevation population had smaller hatchlings and adults. Critical thermal minimum (base temperature) declined with elevation (0.7°C per 1,000 m), and the degree days were 509 across all elevations. For pest management, a base temperature from midelevation of 15.3°C (60°F) and growing degree days of 509 (equivalent to 916 Fahrenheit-based degree days) are reasonable estimates for applications from sea level to 2,700 m.

Shrinking body sizes in response to warming: explanations for the temperature-size rule with special emphasis on the role of oxygen

Body size is central to ecology at levels ranging from organismal fecundity to the functioning of communities and ecosystems. Understanding temperature-induced variations in body size is therefore of fundamental and applied interest, yet thermal responses of body size remain poorly understood. Temperature-size (T-S) responses tend to be negative (e.g. smaller body size at maturity when reared under warmer conditions), which has been termed the temperature-size rule (TSR). Explanations emphasize either physiological mechanisms (e.g. limitation of oxygen or other resources and temperature-dependent resource allocation) or the adaptive value of either a large body size (e.g. to increase fecundity) or a short development time (e.g. in response to increased mortality in warm conditions). Oxygen limitation could act as a proximate factor, but we suggest it more likely constitutes a selective pressure to reduce body size in the warm: risks of oxygen limitation will be reduced as a consequence of evolution eliminating genotypes more prone to oxygen limitation. Thus, T-S responses can be explained by the 'Ghost of Oxygen-limitation Past', whereby the resulting (evolved) T-S responses safeguard sufficient oxygen provisioning under warmer conditions, reflecting the balance between oxygen supply and demands experienced by ancestors. T-S responses vary considerably across species, but some of this variation is predictable. Body-size reductions with warming are stronger in aquatic taxa than in terrestrial taxa. We discuss whether larger aquatic taxa may especially face greater risks of oxygen limitation as they grow, which may be manifested at the cellular level, the level of the gills and the whole-organism level. In contrast to aquatic species, terrestrial ectotherms may be less prone to oxygen limitation and prioritize early maturity over large size, likely because overwintering is more challenging, with concomitant stronger end-of season time constraints. Mechanisms related to time constraints and oxygen limitation are not mutually exclusive explanations for the TSR. Rather, these and other mechanisms may operate in tandem. But their relative importance may vary depending on the ecology and physiology of the species in question, explaining not only the general tendency of negative T-S responses but also variation in T-S responses among animals differing in mode of respiration (e.g. water breathers versus air breathers), genome size, voltinism and thermally associated behaviour (e.g. heliotherms).

Weather variation affects the dispersal of grasshoppers beyond their elevational ranges

Understanding how abiotic conditions influence dispersal patterns of organisms is important for understanding the degree to which species can track and persist in the face of changing climate.The goal of this study was to understand how weather conditions influence the dispersal pattern of multiple nonmigratory grasshopper species from lower elevation grassland habitats in which they complete their life-cycles to higher elevations that extend beyond their range limits.Using over a decade of weekly spring to late-summer field survey data along an elevational gradient, we explored how abundance and richness of dispersing grasshoppers were influenced by temperature, precipitation, and wind speed and direction. We also examined how changes in population sizes at lower elevations might influence these patterns.We observed that the abundance of dispersing grasshoppers along the gradient declined 4-fold from the foothills to the subalpine and increased with warmer conditions and when wind flow patterns were mild or in the downslope direction. Thirty-eight unique grasshopper species from lowland sites were detected as dispersers across the survey years, and warmer years and weak upslope wind conditions also increased the richness of these grasshoppers. The pattern of grasshoppers along the gradient was not sex biased. The positive effect of temperature on dispersal rates was likely explained by an increase in dispersal propensity rather than by an increase in the density of grasshoppers at low elevation sites.The results of this study support the hypothesis that the dispersal patterns of organisms are influenced by changing climatic conditions themselves and as such, that this context-dependent dispersal response should be considered when modeling and forecasting the ability of species to respond to climate change.

Adaptation to elevation but limited local adaptation in an amphibian

We performed a reciprocal transplant experiment to estimate "parallel" adaptation to elevation and "unique" adaptation to local sites at the same elevation, using the frog Rana temporaria in the Swiss Alps. It is important to distinguish these two processes because they have different implications for population structure and ecological specialization. Larvae were reared from hatching to metamorphosis within enclosures installed in their pond of origin, in three foreign ponds at the same elevation, and in four ponds at different elevation (1500-2000 m higher or lower). There were two source populations from each elevation, and adults were held in a common environment for 1 year before they were crossed to produce offspring for the experiment. Fitness was a measure that integrated larval survival, development rate, and body size. Parallel adaptation to elevation was indicated by an advantage at the home elevation (11.5% fitness difference at low elevation and 47% at high elevation). This effect was stronger than that observed in most other studies, according to a survey of previous transplant experiments across elevation (N = 8 animal species and 71 plants). Unique local adaptation within elevational zones was only 0.3-0.7 times as strong as parallel adaptation, probably because gene flow is comparatively high among nearby wetlands at the same elevation. The home-elevation advantage may reduce gene flow across the elevational gradient and enable the evolution of habitat races specialized on elevation.

Do different rates of gene flow underlie variation in phenotypic and phenological clines in a montane grasshopper community?

Species responses to environmental change are likely to depend on existing genetic and phenotypic variation, as well as evolutionary potential. A key challenge is to determine whether gene flow might facilitate or impede genomic divergence among populations responding to environmental change, and if emergent phenotypic variation is dependent on gene flow rates. A general expectation is that patterns of genetic differentiation in a set of codistributed species reflect differences in dispersal ability. In less dispersive species, we predict greater genetic divergence and reduced gene flow. This could lead to covariation in life-history traits due to local adaptation, although plasticity or drift could mirror these patterns. We compare genome-wide patterns of genetic structure in four phenotypically variable grasshopper species along a steep elevation gradient near Boulder, Colorado, and test the hypothesis that genomic differentiation is greater in short-winged grasshopper species, and statistically associated with variation in growth, reproductive, and physiological traits along this gradient. In addition, we estimate rates of gene flow under competing demographic models, as well as potential gene flow through surveys of phenological overlap among populations within a species. All species exhibit genetic structure along the elevation gradient and limited gene flow. The most pronounced genetic divergence appears in short-winged (less dispersive) species, which also exhibit less phenological overlap among populations. A high-elevation population of the most widespread species, Melanoplus sanguinipes, appears to be a sink population derived from low elevation populations. While dispersal ability has a clear connection to the genetic structure in different species, genetic distance does not predict growth, reproductive, or physiological trait variation in any species, requiring further investigation to clearly link phenotypic divergence to local adaptation.

Changes in the Body Size of Carabid Beetles Along Elevational Gradients: A Multispecies Study of Between- and Within-Population Variation

Geographic variation in body size has fascinated biologists since the 19th century as it can provide insight into the evolution of the body size of various organisms. In this study, we investigated body size variation in eight carabid species/subspecies (Coleoptera: Carabidae) along elevational gradients in six Central European mountain ranges. First, we examined elevational variation in body size and whether female and male body sizes differed in their responses to elevation. Second, we examined intrapopulation variation in body size along an elevational gradient, and we compared the degrees of intrapopulation variation between males and females. The investigated species either followed a converse Bergmann's cline (Carabus auronitens auronitens Fabricius 1792; Carabus linnei Panzer 1810; Pterostichus melanarius (Illiger, 1798); Pterostichus pilosus (Host, 1789)) or their size was unaffected by elevation (Carabus auronitens escheri Palliardi, 1825; Carabus sylvestris sylvestris Panzer, 1796; Carabus sylvestris transsylvanicus Dejean, 1826; Pterostichus burmeisteri Heer, 1838). Females were the larger sex in all the investigated species, but the degree of sexual size dimorphism differed between species. In general, the degree of sexual size dimorphism showed no change with elevation. The degree of intrapopulation variation in body size slightly increased with elevation in C. sylvestris sylvestris and P. pilosus. Overall, the intrapopulation variation in body size significantly differed among the investigated carabid species. The existing literature on intrapopulation variation in the body size of insects is limited, but further investigation of this issue could provide a better understanding of the mechanisms that generate geographical clines.

Does wing reduction influence the relationship between altitude and insect body size? A case study using New Zealand's diverse stonefly fauna

Researchers have long been intrigued by evolutionary processes that explain biological diversity. Numerous studies have reported strong associations between animal body size and altitude, but insect analyses have often yielded equivocal results. Here, we analyze a collection database of New Zealand's diverse endemic stonefly fauna (106 species across 21 genera) to test for relationships between altitude and plecopteran body size. This insect assemblage includes a variety of wing-reduced (26 spp) and fully winged (80 spp) taxa and covers a broad range of altitudes (0-2,000 m). We detected significant relationships between altitude and body size for wing-reduced, but not fully winged, stonefly taxa. These results suggest that, while the maintenance of flight apparatus might place a constraint on body size in some fully winged species, the loss of flight may free insects from this evolutionary constraint. We suggest that rapid switches in insect dispersal ability may facilitate rapid evolutionary shifts across a number of biological attributes and may explain the inconsistent results from previous macroecological analyses of insect assemblages.

Geographic variation in wing size and shape of the grasshopper Trilophidia annulata (Orthoptera: Oedipodidae): morphological trait variations follow an ecogeographical rule

A quantitative analysis of wing variation in grasshoppers can help us to understand how environmental heterogeneity affects the phenotypic patterns of insects. In this study, geometric morphometric methods were used to measure the differences in wing shape and size of Trilophidia annulata among 39 geographical populations in China, and a regression analysis was applied to identify the major environmental factors contributing to the observed morphological variations. The results showed that the size of the forewing and hindwing were significantly different among populations; the shape of the forewing among populations can be divided into geographical groups, however hindwing shape are geographical overlapped, and populations cannot be divided into geographical groups. Environmental PCA and thin-plate spline analysis suggested that smaller individuals with shorter and blunter-tip forewings were mainly distributed in the lower latitudes and mountainous areas, where they have higher temperatures and more precipitation. Correspondingly, the larger-bodied grasshoppers, those that have longer forewings with a longer radial sector, are distributed in contrary circumstances. We conclude that the size variations in body, forewing and hindwing of T. annulata apparently follow the Bergmann clines. The importance of climatic variables in influencing morphological variation among populations, forewing shape of T. annulata varies along an environmental gradient.

Elevational differences in developmental plasticity determine phenological responses of grasshoppers to recent climate warming

Annual species may increase reproduction by increasing adult body size through extended development, but risk being unable to complete development in seasonally limited environments. Synthetic reviews indicate that most, but not all, species have responded to recent climate warming by advancing the seasonal timing of adult emergence or reproduction. Here, we show that 50 years of climate change have delayed development in high-elevation, season-limited grasshopper populations, but advanced development in populations at lower elevations. Developmental delays are most pronounced for early-season species, which might benefit most from delaying development when released from seasonal time constraints. Rearing experiments confirm that population, elevation and temperature interact to determine development time. Population differences in developmental plasticity may account for variability in phenological shifts among adults. An integrated consideration of the full life cycle that considers local adaptation and plasticity may be essential for understanding and predicting responses to climate change.