Body Size Clines Research Articles

A synthesis of major environmental-body size clines of the sexes within arthropod species

Body size at maturity often varies with environmental conditions, as well as between males and females within a species [termed Sexual Size Dimorphism (SSD)]. Variation in body size clines between the sexes can determine the degree to which SSD varies across environmental gradients. We use a meta-analytic approach to investigate whether major biogeographical and temporal (intra-annually across seasons) body size clines differ systematically between the sexes in arthropods. We consider 329 intra-specific environmental gradients in adult body size across latitude, altitude and with seasonal temperature variation, representing 126 arthropod species from 16 taxonomic orders. On average, we observe greater variability in male than female body size across latitude, consistent with the hypothesis that, over evolutionary time, directional selection has acted more strongly on male than female size. In contrast, neither sex exhibits consistently greater proportional changes in body size than the other sex across altitudinal or seasonal gradients, akin to earlier findings for plastic temperature-size responses measured in the laboratory. Variation in the degree to which body size gradients differ between the sexes cannot be explained by a range of potentially influential factors, including environment type (aquatic vs. terrestrial), voltinism, mean species’ body size, degree of SSD, or gradient direction. Ultimately, if we are to make better sense of the patterns (or lack thereof) in SSD across environmental gradients, we require a more detailed understanding of the underlying selective pressures driving clines in body size. Such understanding will provide a more comprehensive hypothesis-driven approach to explaining biogeographical and temporal variation in SSD.

Altitudinal variation in life‐history traits in the lawn ground cricket, Polionemobius mikado

AbstractIt has been reported that the lawn ground cricket, Polionemobius mikado (Orthoptera: Trigonidiidae), shows variations in voltinism and life‐history traits along latitude in Japan, but whether it shows variations along altitude has not been examined. The present study aims to determine whether there is variation in voltinism, body size and the incidence of embryonic diapause among populations of P. mikado at different altitudes in Kyoto, Japan. Six populations collected from 70 to 800 m a.s.l. showed a positive relationship between the adult head width and the altitude of sampling locality. This body size cline is attributed to the increasing proportion of larger univoltine individuals from low to high altitude. The incidence of diapause of the strain from altitude 800 m was approximately 100% when reared under natural photoperiods and temperatures from spring to summer at an altitude of 70 m, and was significantly higher than that of the strain from 70 m. These differences in life‐history traits suggest that the population of P. mikado at a higher altitude has adapted to a shorter length of the season available for growth.

An interspecific test of Bergmann's rule reveals inconsistent body size patterns across several lineages of water beetles (Coleoptera: Dytiscidae)

1. Bergmann's rule sensu lato, the ecogeographic pattern relating animals' body size with environmental temperature (or latitude), has been shown to be inconsistent among insect taxa. Body size clines remain largely unexplored in aquatic insects, which may show contrasting patterns to those found in terrestrial groups because of the physiological or mechanical constraints of the aquatic environment.2. Bergmann's rule was tested using data on body size, phylogeny and distribution for 93 species belonging to four lineages of dytiscid water beetles. The relationship between size and latitude was explored at two taxonomic resolutions – within each independent lineage, and for the whole dataset – employing phylogenetic generalised least‐squares to control for phylogenetic inertia. The potential influence of habitat preference (lotic versus lentic) on body size clines was also considered.3. Within‐lineage analyses showed negative relationships (i.e. converse Bergmann's rule), but only in two lineages (specifically in those that included both lotic and lentic species). By contrast, no relationship was found between body size and latitude for the whole dataset.4. These results suggest that there may be no universal interspecific trends in latitudinal variation of body size in aquatic insects, even among closely related groups, and show the need to account for phylogenetic inertia. Furthermore, habitat preferences should be considered when exploring latitudinal clines in body size in aquatic taxa at the interspecific level.

Geographic variation of body size in New World anurans: energy and water in a balance

The validity of Bergmann's rule, perhaps the best known ecogeographical rule, has been questioned for ectothermic species. Here, we explore the interspecific version of the rule documenting body size gradients for anurans across the whole New World and evaluating which environmental variables best explain the observed patterns. We assembled a dataset of body sizes for 2761 anuran species of the Western Hemisphere and conducted assemblage‐based and cross‐species analyses that consider the spatial and phylogenetic structure in the data. In accordance with heat and water‐related explanations for body size clines, we found a consistent association of median body size and potential evapotranspiration across the New World. A relevant role of water availability also emerges, suggesting the joint importance of body size for thermoregulation and hydroregulation in anurans. Anurans do not follow a simple Bergmannian pattern of increasing size towards high latitudes. Consistent with previous regional findings, our Hemisphere‐wide analyses detect that the geographic variation in anuran body sizes is highly dependent on a trade‐off between heat and water balance. The observed size‐climate relationships possibly emerge from the interplay between thermoregulatory abilities and the benefits inherent to reduced surface‐to‐volume ratios in larger species, which decrease the rates of evaporative water loss and favour heat retention. Our results also show how temperature becomes important for species that are directly in contact with the substrate and water, like burrowing and terrestrial anurans, while arboreal species exhibit a body size cline linked with potential evapotranspiration.

Scale-dependence in geographic variation in a freshwater gastropod across the Palearctic

ABSTRACTThe reality of spatial clinal variation in morphological traits of freshwater pulmonate snails (Gastropoda: Pulmonata) has repeatedly been questioned or totally discounted. There is a lack of sound statistical evidence in the articles hitherto published on this subject supporting these claims. Here, by means of different analytical methods (analysis of spatial autocorrelation, linear regression analysis, canonical correlation analysis and others), we demonstrate that shell variation in the dwarf pond snail, Galba truncatula, is patterned in space throughout the northern and central Palearctic, with latitudinally-oriented clines in body size and in some shell proportions. Shell size in G. truncatula decreases with latitude and temperature, representing a special case of converse Bergmann cline. However, the temperature itself is hardly the main driver of shell size variation. It is argued that the shorter growing seasons at high latitudes may represent a better explanation for the observed trend. Shell proportions in the dwarf pond snails vary weakly at the macrogeographic scale, being spatially patterned at lower (mesogeographic) scales around 1200–1500 km. In general, spatial variation in G. truncatula shell size is decoupled from variation in shell shape, demonstrating clear scale-dependence similar to that found in different species of terrestrial (non-aquatic) pulmonate snails.

An inversion supergene in Drosophila underpins latitudinal clines in survival traits

Chromosomal inversions often contribute to local adaptation across latitudinal clines, but the underlying selective mechanisms remain poorly understood. We and others have previously shown that a clinal inversion polymorphism in Drosophila melanogaster, In(3R)Payne, underpins body size clines along the North American and Australian east coasts. Here, we ask whether this polymorphism also contributes to clinal variation in other fitness-related traits, namely survival traits (lifespan, survival upon starvation and survival upon cold shock). We generated homokaryon lines, either carrying the inverted or standard chromosomal arrangement, isolated from populations approximating the endpoints of the North American cline (Florida, Maine) and phenotyped the flies at two growth temperatures (18°C, 25°C). Across both temperatures, high-latitude flies from Maine lived longer and were more stress resistant than low-latitude flies from Florida, as previously observed. Interestingly, we find that this latitudinal pattern is partly explained by the clinal distribution of the In(3R)P polymorphism, which is at ~50% frequency in Florida but absent in Maine: inverted karyotypes tended to be shorter-lived and less stress resistant than uninverted karyotypes. We also detected an interaction between karyotype and temperature on survival traits. As In(3R)P influences body size and multiple survival traits, it can be viewed as a 'supergene', a cluster of tightly linked loci affecting multiple complex phenotypes. We conjecture that the inversion cline is maintained by fitness trade-offs and balancing selection across geography; elucidating the mechanisms whereby this inversion affects alternative, locally adapted phenotypes across the cline is an important task for future work.

Life history traits, but not body size, vary systematically along latitudinal gradients on three continents in the widespread yellow dung fly

Large‐scale clinal variation in body size and other life‐history traits is common enough to have stimulated the postulation of several eco‐geographical rules. Whereas some clinal patterns are clearly adaptive, the causes of others remain unclear. We present a comprehensive intraspecific population comparison for the cosmopolitan yellow dung fly Scathophaga stercoraria (Diptera: Scathophagidae) to check for consistent world‐wide patterns. Common garden assessment of various life history traits permitted continental comparison of (clinal) quantitative genetic differentiation (Qst) with putatively neutral genetic differentiation (Fst) derived from field‐caught flies. Latitudinal clines in fly development time, growth rate, and overwintering propensity were consistent among North American, European and Japanese populations. Increased winter dormancy incidence and duration at higher latitude, combined with a faster growth rate and shorter development time, suggest that flies are adaptated to season length more than to temperature. The resulting body size clines, in contrast, were not very consistent; importantly, they were not negative, as expected under seasonal constraints, but flat or even positive clines. Quantitative genetic differentiation QST exceeded neutral molecular variation FST for most traits, suggesting that natural selection plays a consistent role in mediating global dung fly life histories. We conclude that faster growth and development in response to shorter growing seasons at higher latitudes may indirectly counteract expected direct effects of temperature on body‐size, potentially resulting in flat or inconsistent body size clines in nature.

Toward a general explanation for latitudinal clines in body size among chelonians

Toward a general explanation for latitudinal clines in body size among chelonians

Largely flat latitudinal life history clines in the dung fly Sepsis fulgens across Europe (Diptera: Sepsidae).

Clinal variation in body size and related life history traits is common and has stimulated the postulation of several eco-geographical rules. Whereas some clinal patterns are clearly adaptive, the causes of others remain obscure. We investigated intra-specific body size, development time and female fecundity (egg size and number) clines across 13 European populations of the dung fly Sepsis fulgens spanning 20° latitude from southern Italy to Estonia in a genetic common garden approach. Despite very short generation times (ca. 2weeks at 24°C), we found a converse Bergmann cline (smaller size at higher latitudes). As development time did not change with latitude (flat cline), integral growth rate thus likely declines towards the pole. At the same time, early fecundity, but not egg size, increased with latitude. Rather than being mediated by seasonal time constraints, the body size reduction in the northernmost flies from Estonia could suggest that these are marginal, edge populations, as when omitting them the body size cline became flat as well. Most of the other sepsid species investigated to date also show flat body size clines, a pattern that strikingly differs from Drosophila. We conclude that S. fulgens life history traits appear to be shaped by similar environmental pressures and selective mechanisms across Europe, be they adaptive or not. This reiterates the suggestion that body size clines can result as a secondary consequence of selection pressures shaping an entire life history syndrome, rendering them inconsistent and unpredictable in general.

Perils of recovering the Mexican wolf outside of its historical range

The Mexican wolf (Canis lupus baileyi) was included in the 1973 Endangered Species Act listing of the gray wolf (C. lupus), but then listed separately as a subspecies in 2015. Early accounts of its range included the Sierra Madre Occidental of Mexico, southeastern Arizona, southwestern New Mexico, and sometimes western Texas, supported by ecological, biogeographic, and morphological data. There have been multiple unsuccessful attempts to revise the original 1982 recovery plan and identify areas suitable for Mexican wolf reintroduction. Despite the fact that 90% of its historical range is in Mexico and widespread suitable habitat exists there, previous draft recovery plans recommended recovery mostly outside of Mexico and well north of the subspecies' historical range. Planning recovery outside historical range of this subspecies is fraught with problems that may compromise, thwart, or impede successful recovery. Dispersal of Mexican wolves northward and continued movements southward by Northwestern wolves (C. l. occidentalis), along with allowing establishment of Mexican wolves north of their historical range before they are recovered, may lead to premature and detrimental intraspecific hybridization. Interbreeding of Northwestern wolves from Canadian sources and Mexican wolves does not represent the historical cline of body size and genetic diversity in the Southwest. If Northwestern wolves come to occupy Mexican wolf recovery areas, these physically larger wolves are likely to dominate smaller Mexican wolves and quickly occupy breeding positions, as will their hybrid offspring. Hybrid population(s) thus derived will not contribute towards recovery because they will significantly threaten integrity of the listed entity. Directing Mexican wolf recovery northward outside historical range threatens the genetic integrity and recovery of the subspecies, is inconsistent with the current 10(j) regulations under the ESA, is unnecessary because large tracts of suitable habitat exist within historical range, is inconsistent with the concepts of restoration ecology, and disregards unique characteristics for which the Mexican wolf remains listed.

Insect temperature–body size trends common to laboratory, latitudinal and seasonal gradients are not found across altitudes

Abstract Body size affects rates of most biological and ecological processes, from individual performance to ecosystem function, and is fundamentally linked to organism fitness. Within species, size at maturity can vary systematically with environmental temperature in the laboratory and across seasons, as well as over latitudinal gradients. Recent meta‐analyses have revealed a close match in the magnitude and direction of these size gradients in various arthropod orders, suggesting that these size responses share common drivers. As with increasing latitude, temperature also decreases with increasing altitude. Although the general direction of body size clines along altitudinal gradients has been examined previously, to our knowledge altitude–body size (A–S) clines have never been synthesised quantitatively, nor compared with temperature–size (T–S) responses measured under controlled laboratory conditions. Here we quantitatively examine variation in intraspecific A–S clines among 121 insect species from 50 different global locations, representing 12 taxonomic orders. While some taxa were better represented in the literature than others, our analysis reveals extensive variation in the magnitude and direction of A–S clines. Following the assumption that temperature on average declines by 1°C per 150 m increase in altitude, order‐specific A–S clines in the field appear to deviate from laboratory T–S responses. Specifically, the magnitude of A–S clines and T–S responses are more closely matched in some taxonomic orders (e.g. Diptera) than others (e.g. Orthoptera). These findings contrast with the strong co‐variation observed between latitude‐size clines and T–S responses, and between laboratory and seasonal T–S responses. The lack of clear size relationships with elevation, and hence temperature, is likely due to the counteracting effects of other major drivers with altitude, including season length and oxygen partial pressure. Switches in voltinism within species across altitude, and the dispersal of individuals across different elevations, may also obscure trends. A plain language summary is available for this article.

Steep converse Bergmann's cline in a carrion beetle: between‐ and within‐population variation in body size along an elevational gradient

AbstractBody size is an integrative trait with substantial fitness consequences in animals. Geographical clines in body size have fascinated biologists because of their potential to provide insight into the mechanisms governing local adaptation and phenotypic plasticity. In this complex study, we focused on variation in body size of Silpha carinata (Coleoptera: Silphidae) along elevation gradients in Central Europe. Altitudinal clines were investigated separately for males and females as sex‐specific responses to environmental conditions are documented for a variety of insect species. To identify potential underlying mechanisms responsible for observed patterns, a common garden experiment and investigation of within‐population variation in body size were performed. Body size of S. carinata recorded in nature sharply decreased with increasing altitude in both genders, whereas sexual size dimorphism did not change with altitude. The degree of within‐population variation in body size recorded in nature did not change with altitude. Under standardized laboratory conditions, higher altitude females produced smaller eggs than those from lower altitude. This size difference persisted to the very end of the larval period. Unfortunately, only few offspring survived till adulthood in the laboratory and thus precise analysis of offspring adult sizes was unfeasible, but between‐population differences in body size seems to persist to adulthood. The observed converse Bergmann's cline in S. carinata fits well with what has been predicted for large, carnivorous, univoltine insect species. Until now, investigation of within‐population variation in body size is rare in insects, and future complementary studies focused on this issue are highly needed as within‐population variation could explain body size patterns observed at between‐population level.

Megacicadas show a temperature-mediated converse Bergmann cline in body size (larger in the warmer south) but no body size difference between 13- and 17-year species pairs

A recommendation of: Koyama T, Ito H, Kakishima S, Yoshimura J, Cooley JR, Simon C, Sota T Geographic body size variation in the periodical cicadas Magicicada: implications for life cycle divergence and local adaptation 10.1111/jeb.12653

Intra-specific Body Size Variation of Ground Beetles (Сoleoptera: Сarabidae) in Latitudinal Gradient

Background. Large-scale patterns of body size variation have occupied biologists for over a century, yet the causes of some of these patterns remain elusive. Bergmann’s rule is a classical eco-geographic rule that relates body size of homoiothermal animals with environmental temperature (or latitude). Contemporary data indicate that latitudinal clines in body size, predicted by Bergmann’s rule also exist in ectothermic organisms and in some groups appear to be fairly common. Despite plenty of data from literature on latitudinal intraspecific body size variation in insects are scarce and in Ground Beetles are absent at all. The aim of this research was to: (i) model the effect of the region of habitation into the body size variation in widespread carabid species; (ii) describe body size variation of mentioned species in latitudinal gradient. Materials and methods. The design of our study was organized as follows: (1) we study the intraspecific variation of body size in carabids, bearing in mind that closely related species could act very differently, each individual species following or countering Bergmann's Rule in its own way; (2) in all studied species the same six traits were measured; (3) we used linear models to isolate concretely latitude effects (but not another environmental factors) to traits variation; (4) beetles were sampled in the same space over the vast regions covering their ranges. Six carabid species from different regions of Russia were analyzed. Linear models were applied to quantify contribution of region’s latitude where beetles had been sampled into that variation. We applied voice-counting method to reveal trends of traits size variation in latitude gradient and relative warp analysis (a principal component analysis of the weight matrix) when analyzing effect of latitude on body shape shifts in studied species of carabids. Results. Different traits of certain species varied in differing ways under the influence of the same environmental factor. Contribution of latitude into the traits variation was not similar in studied species. The compiled data over the all six traits variation in latitude gradient in each species showed that C. granulatus followed Bergmann's rule, P. cupreus – converse Bergmann's rule, in C. cancellatus, C. hortensis and P. melanarius the number of cases which followed direct Bergmann's clines, converse ones and non-significant shifts were equal, P. niger - didn't show any clines at all. Nevertheless the separate analysis of the only elytra length variation showed that in three Carabus species and P. niger elytra length decreased towards the high latitudes, P. melanarius demonstrated saw-tooth elytra length variation in latitude gradient and Poec. cupreus – the counter-gradient one. Conclusion . Explanation that takes into account the natural history, climatic correlations and sexual size dimorphism is needed to assess the observed contrasting geographic patterns and differences between species, morphometric traits and sexes, since size clines (e.g. Bergmannian clines) may obey to multiple selection pressures that are not only dependent on temperature constraints but also on other climatic and biotic factors that could influence body size. Key words: carabids, environmental factors, voice-counting method, converse Bergman clines, saw-tooth variation, counter-gradient variation, linear models.

地理的変異の近接的機構としての表現型可塑性 : 外温動物の体サイズ・クライン

地理的変異の近接的機構としての表現型可塑性 : 外温動物の体サイズ・クライン

Geographical clines of body size in terrestrial amphibians: water conservation hypothesis revisited

AbstractAimFaced with the dispute regarding spatial gradients of body size in ectotherms, we build upon their long‐known allometric relationship with water economy, which scales with thermal and hydric regimes, to revisit and refine the water conservation hypothesis (WCH). We provide a brief description of the WCH, including its physiological basis and geographical predictions for body size clines in terrestrial amphibians, and test it against heat‐based hypotheses in four amphibian clades.LocationThe Americas.MethodsWe employ phylogenetic comparative analyses to examine relationships between body size and both temperature, as a descriptor of the effect of heat alone, and potential evapotranspiration, which describes the water constraint along evaporative gradients. We assess these relationships in four amphibian clades: the subfamily of leaf frogs (Phyllomedusinae), genera of gladiator frogs (Hypsiboas), salamanders (Plethodon) and the family of glass frogs (Centrolenidae).ResultsThree clades did not show phylogenetic signals in body size variation. In addition, three clades showed a positive relationship with potential evapotranspiration as predicted, and all of them were unrelated to temperature. When present, however, the explanatory power of evaporative energy on body size variation was relatively weak.Main conclusionsThe conservation of water across evaporative gradients is both a more comprehensive explanation and a more pervasive driver of spatial clines in body size among terrestrial amphibians than is the balance of heat alone. However, the relatively low predictive ability of evaporative energy and its dependence on specific climatic configurations both emphasize and elucidate the non‐universality of the phenomenon.

Inter- and intraspecific variation in body- and genome size in calanoid copepods from temperate and arctic waters.

SummaryThe tendency of ectotherms to get larger in the cold (Bergmann clines) has potentially great implications for individual performance and food web dynamics. The mechanistic drivers of this trend are not well understood, however. One fundamental question is to which extent variation in body size is attributed to variation in cell size, which again is related to genome size. In this study, we analyzed body and genome size in four species of marine calanoid copepods, Calanus finmarchicus, C. glacialis, C. hyperboreus and Paraeuchaeta norvegica, with populations from both south Norwegian fjords and the High Arctic. The Calanus species showed typical interspecific Bergmann clines, and we assessed whether they also displayed similar intraspecific variations—and if correlation between genome size and body size differed between species. There were considerable inter‐ as well as intraspecific variations in body size and genome size, with the northernmost populations having the largest values of both variables within each species. Positive intraspecific relationships suggest a functional link between body and genome size, although its adaptiveness has not been settled. Impact of additional drivers like phylogeny or specific adaptations, however, was suggested by striking divergences in body size – genome size ratios among species. Thus, C. glacialis and C. hyperboreus, had fairly similar genome size despite very different body size, while P. norvegica, of similar body size as C. hyperboreus, had the largest genome sizes ever recorded from copepods. The inter‐ and intraspecific latitudinal body size clines suggest that climate change may have major impact on body size composition of keystone species in marine planktonic food webs.

Little evidence for Bergmann's rule body size clines in passerines along tropical elevational gradients

AbstractAimTo test whether intra‐ and interspecific patterns in body mass along elevational gradients follow Bergmann's rule for a subset of tropical montane passerines.LocationTropical elevational gradients in New Guinea, Borneo, Peru and Costa Rica.MethodsI used linear regressions to assess intraspecific patterns in body mass along elevational gradients in common New Guinean passerines (2697 mist‐netted individuals of 21 species). I then evaluated interspecific patterns using two data sets. First, I investigated differences in body mass in species pairs of elevational replacements, closely related species with minimal overlap along elevational gradients (species pairs; New Guinea: n = 45, Borneo: n = 22, Peru: n = 58 and Costa Rica: n = 30). Second, I used a comparative phylogenetic approach to test whether species’ mid‐point elevations predicted their masses within entire passerine avifaunas found along single elevational gradients (species; New Guinea: n = 184, Peru: n = 529 and Costa Rica: n = 220).ResultsNew Guinean passerines exhibited minimal intraspecific variation in mass along elevational gradients. In two species, lower elevation individuals had significantly larger masses than upper elevation conspecifics. In species pairs of elevational replacements, there was no trend for upper elevation species to have larger masses than lower elevation species. Overall, species pairs tended to have positive mass disparities (mass of upper elevation species/mass of lower elevation species). However, contrary to predictions of Bergmann's rule, mass disparity was unrelated to elevational overlap. When considering entire passerine avifaunas along single elevational gradients, species’ masses were uncorrelated with their mid‐point elevational distributions.Main conclusionsI found little evidence that tropical montane passerines have larger body masses at higher elevations where temperatures are colder. This lack of pattern was consistent across evolutionarily independent avifaunas of different biogeographical regions. These results suggest mean temperature is not a generally important driver of body size evolution in tropical montane passerines.

Reevaluating geographic variation in life‐history traits of a widespread Nearctic amphibian

AbstractAnimals from cold environments are usually larger than animals from warm environments, which often produce clines in body size. Because variation in body size can lead to trade‐offs between growth and reproduction, life‐history traits should also vary across climatic gradients. To determine if life‐history traits of wood frogs Rana sylvatica vary with climate, we examined female and male body length, clutch size, and ovum size from 37 locations across an unprecedented 32° of latitude. In conflict with recent research, body size, and ovum size decreased in cold climates and at higher latitudes. Clutch size did not vary with climate or latitude, but reproductive effort (clutch size:female size) did, suggesting selection for a life‐history traits that favors maximizing propagule number over propagule size in cold climates. With accelerating climate change that will expose populations to novel environmental conditions, it is important to identify the limits of adaptation, which can be informed by greater understanding of variation in life‐history traits.

A large‐scale latitudinal pattern of life‐history traits in a strictly univoltine damselfly

1. Variation in thermal conditions and season length along latitudinal gradients affect body size‐related traits over different life stages. Selection is expected to optimise these size traits in response to the costs and benefits.2. Egg, hatchling, larval and adult size in males and females were estimated along a latitudinal gradient of 2730 km across Europe in the univoltine damselfly Lestes sponsa, using a combination of field‐collection and laboratory‐rearing experiments. In the laboratory, individuals were grown in temperatures and photoperiod simulating those at the latitude of origin, and in common‐garden conditions.3. The size of adults sampled in nature was negatively correlated with latitude. In all populations the females were larger than the males. Results from simulated and common‐garden rearing experiments supported this pattern of size difference across latitudes and between sexes, suggesting a genetic component for the latitudinal size trend and female‐biased size dimorphism. In contrast, hatchling size showed a positive relationship with latitude, but egg size, although differing between latitudes, showed no such relationship.4. The results support a converse Bergmann cline, i.e. a negative body size cline towards the north. This negative cline in body size is probably driven by progressively stronger seasonal time and temperature constraints towards the higher latitudes and by the obligate univoltine life cycle of L. sponsa. As egg size showed no relationship with latitude, other environmental factors besides temperature, such as desiccation risk, probably affect this trait.