Geographic Variation In Body Size Research Articles

Geographic Variation in Somatic Growth Rate of Wood Turtles (Glyptemys insculpta)

Life history traits, such as body size and age at maturity, display intraspecific variation across a species' geographic range. Previous studies that examined body size variation among conspecific populations of turtles found that body size generally increases with increasing latitude, with the exception of Wood Turtles (Glyptemys insculpta) and Spotted Turtles (Clemmys guttata), which follow a non-linear relationship with larger body sizes at the two range extremes. Similarly, growth rates are influenced by climatic variables and should display geographic patterns reflective of different environments. The objectives of our study were to a) quantify somatic growth in a northern population of Wood Turtles, and b) determine if the observed geographic variation in body size was the result of interpopulation variation in somatic growth rates. In the northern population, as turtles approached maturity, somatic growth increments varied between the sexes such that on average males grew to larger mean carapace le...

Morphometric differentiation and geographic variation among populations of Boana cordobae (Anura: Hylidae): effect to age

We estimated differences in body size and age structure of six populations of Boana cordobae living at different altitudes, 808-2 310 m.a.s.l. in Córdoba and San Luis provinces (Argentina). We measured 15 morphometric variables and used skeletochronology to age determination of 79 individuals. Morphometric variables showed significant differences between sexes, being females larger than males, even when the effect of age was taken into account. We found a significant relationship between age and most of the morphometric variables. When removing the effects of age, we found significant inter-population differences in body size. Males from the high-elevation populations were larger than individuals from low-elevation populations. These results suggest that a difference in age structure between populations is a main factor for the geographic variation in body size of this species.

Geographic variation in body size and its relationship with environmental gradients in the Oriental Garden Lizard, Calotes versicolor.

Patterns of geographic variation in body size are predicted to evolve as adaptations to local environmental gradients. However, many of these clinal patterns in body size, such as Bergmann's rule, are controversial and require further investigation into ectotherms such as reptiles on a regional scale. To examine the environmental variables (temperature, precipitation, topography and primary productivity) that shaped patterns of geographic variation in body size in the reptile Calotes versicolor, we sampled 180 adult specimens (91 males and 89 females) at 40 locations across the species range in China. The MANOVA results suggest significant sexual size dimorphism in C. versicolor (F 23,124 = 11.32, p < .001). Our results showed that C. versicolor failed to fit the Bergmann's rule. We found that the most important predictors of variation in body size of C. versicolor differed for males and females, but mechanisms related to heat balance and water availability hypotheses were involved in both sexes. Temperature seasonality, precipitation of the driest month, precipitation seasonality, and precipitation of the driest quarter were the most important predictors of variation in body size in males, whereas mean precipitation of the warmest quarter, mean temperature of the wettest quarter, precipitation seasonality, and precipitation of the wettest month were most important for body size variation in females. The discrepancy between patterns of association between the sexes suggested that different selection pressures may be acting in males and females.

Primary productivity explains size variation across the Pallid bat's western geographic range

Abstract Body size is associated with many aspects of the life history, ecology and physiology of animals. Within a species, body size can vary substantially across space and time, and the mechanisms generating these patterns have been the focus of evolutionary and ecology research. Bergmann’s rule predicts a negative relationship between body size and temperature across the geographic range of endothermic animals; larger animals have a lower surface to volume ratio, which would allow for greater heat conservation. Despite the broad support for this pattern, its underlying mechanisms are heavily debated. Numerous alternative explanations have been proposed to explain why larger animals are found in colder climates and vice versa, including heat dissipation, environmental seasonality and resource availability. We used the Pallid bat, Antrozous pallidus, as a model to evaluate Bergmannian size patterns and the relative support for major explanatory hypotheses of geographic body size variation. We tested the hypothesis that geographic size variation is predicted by productivity, as opposed to seasonality, heat conservation or dissipation, or some combination of these processes. Additionally, we investigated the potential ecomorphological consequences of size variation in Pallid bats by determining if skull shape (an indicator of bite performance) varies with size. Whereas we did find that Pallid bat populations in northern latitudes are composed of larger individuals, our results suggest that net primary productivity and, to a lesser extent heat conservation, best explain size variation throughout the western range of this species. We also found that skull shape in Pallid bats changes in tandem with skull size, with larger bats having cranial traits associated with greater bite force production. The results of our study indicate that variation in resource availability may be a key factor underlying spatial patterns in size, morphology and, possibly, feeding performance within wide‐ranging bat species. A plain language summary is available for this article.

Variation of Body Size in Rice Water Weevil (Coleoptera: Curculionidae) and Its Associations with Population Biology

Life history characteristics help us to determine the ability of invasive species to establish and thrive in an exotic environment. However, so far, there have been very few reports concerning geographic variation in the body size of invasive insects and the associations between body size variation and population biology. In this study, we surveyed the geographic variation in body size of an invasive agricultural pest, the rice water weevil Lissorhoptrus oryzophilus Kuschel (Coleoptera: Curculionidae), in China. Its body size variation was found to follow Bergmann’s rule, a size cline related to latitude/altitude in which weevils tended to be larger in higher latitude/altitude localities. Moreover, using adults of different body size within populations, we also characterized the relationship between body size and some population traits of this weevil, including reproduction, food consumption, cold tolerance, and agility. The results showed that, large and mid-size adults (within populations) tended to consume more rice leaves, and larger adults also laid more and longer eggs, when compared with smaller adults. However, smaller adults appeared to have higher agility. In conclusion, body size of rice water weevil varies significantly with geography, and body size variation (within populations) may affect life history traits.

Temperature is the main correlate of the global biogeography of turtle body size

AbstractAimsGeographical gradients in body size have been extensively studied in endotherms, and general rules exist to describe body size variation in these animals. However, the existence of broad‐scale patterns in body size variation in ectotherms remains largely debated. Turtles (tortoises and freshwater turtles) are ectothermic organisms whose geographical variation in body size has not been examined widely. Here, we test a suite of hypotheses, proposed to explain body size patterns in other animals, for this group of reptiles.LocationGlobal.Time periodCurrent.Major taxa studiedTurtles.MethodsWe gathered distribution, phylogenetic and body size data for 235 species of turtles, which were distributed in a global equal area grid of 200 km × 200 km. We also obtained predictor variables [mean annual temperature, actual evapotranspiration, temperature variation since the Last Glacial Maximum (LGM) and human footprint] directly associated with the main hypotheses tested in body size studies. Our analyses followed a cross‐species and an assemblage‐based approach and were performed for all turtles and for terrestrial and aquatic species separately.ResultsMean annual temperature was the main correlate of body size for the whole group and for terrestrial turtles in both approaches, having a positive correlation with this trait. Body sizes of aquatic turtles were not influenced by any of the tested variables. In the cross‐species approach we also found that temperature variation since the LGM was an important positive correlate of body size in terrestrial turtles.Main conclusionsOur study reinforces the importance of environmental temperatures in explaining animal body size patterns. The heat balance hypothesis was not rejected by our data, whereas migration, productivity and human disturbance hypotheses were rejected. Finally, body size of terrestrial and aquatic turtles had different patterns, also suggesting that habitat is an important factor in understanding geographical variation in body size.

Factors Related to Altitudinal Body Size Variation in the Earthworm-Eating Ground Beetle Carabus japonicus

To understand geographic body size variation in an insect species, various factors including habitat temperature, correlation between life history traits, and food availability must be examined. Carabus (Ohomopterus) japonicus is univoltine, feeds exclusively on earthworms during its larval stage, and shows a clinal body size variation along the habitat temperature gradient in northern Kyushu, Japan. Carabus japonicus occurs at both high and low altitudes; at high altitudes it coexists with a larger species, C. (O.) dehaanii. At low altitudes, C. japonicus shows larger body sizes. We sought to determine whether this increase in body size is only an adaptation to high habitat temperatures in the absence of C. dehaanii, and examined the life history of C. japonicus and seasonal trends in prey earthworms at six sites between altitudes of 30 and 980 m. While high-altitude populations used the entire warm season for reproduction and larval development, low-altitude populations showed shorter periods of reproductive activity and larval incidence coincided with seasonal trends in earthworm abundance. Thus, C. japonicus attained larger body sizes at lower altitudes without a notable extension of their juvenile period. At lower altitudes, earthworms grew faster and reached sizes, which may be too large for predation by small carabid larvae. Large females had higher fecundity, and laid larger eggs, from which larger first instar larvae hatch. The large body size of C. japonicus in warm habitats may thus be an adaptation not only for high fecundity, but also for producing large first instar larvae to more efficiently prey on large earthworms.

The effect of seed traits on geographic variation in body size and sexual size dimorphism of the seed-feeding beetle Acanthoscelides macrophthalmus.

Explaining large‐scale patterns of variation in body size has been considered a central question in ecology and evolutionary biology because several life‐history traits are directly linked to body size. For ectothermic organisms, little is known about what processes influence geographic variation in body size. Changes in body size and sexual size dimorphism (SSD) have been associated with environmental variables, particularly for Bruchinae insects, which feed exclusively on seeds during the larval stage. However, the effect of important seed traits on body size variation has rarely been investigated, and whether SSD varies substantially among populations within bruchine species is poorly known. Using the seed‐feeding beetle Acanthoscelides macrophthalmus infesting its host plant Leucaena leucocephala, we investigated whether specific seed traits (hardness, size, water content, carbon/nitrogen ratio, and phenolic content) were determinant in generating geographic variation in body size and SSD of A. macrophthalmus. We also examined the relationships between body size and SSD with latitude and altitude. The body size of both sexes combined was not related to latitude, altitude, and any of the physical and chemical seed traits. However, the female body size tended to vary more in size than the males, generating significant variation in SSD in relation to latitude and altitude. The females were the larger sex at higher latitudes and at lower altitudes, precisely where seed water content was greater. Therefore, our results suggest that water content was the most important seed trait, most severely affecting the females, promoting geographic variation in SSD of A. macrophthalmus.

Geographical variation of body size in sigmodontine rodents depends on both environment and phylogenetic composition of communities

AbstractAimBody size variation in animal assemblages is a widely addressed pattern in biogeographical studies, and is affected by both environmental gradients and phylogenetic constraints. However, no study has yet explored to what extent the association between body size variation and environmental gradients across broad spatial scales is influenced by the biogeographical distribution of different phylogenetic lineages. In this study, we discriminate the influences of environmental variables and phylogenetic community composition on body size variation in South American sigmodontine rodents.LocationSouth America.MethodsWe computed the mean body mass of sigmodontine species co‐occurring in 1 × 1° cells across South America. For each cell we recorded mean values for three environmental variables. We characterized the phylogenetic composition of sigmodontine assemblages within each cell using phylogenetic fuzzy‐weighting and principal coordinates of phylogenetic structure (PCPS). We then partitioned out the influence of environmental factors and the phylogenetic community composition on mean body size.ResultsMean body size variation was mostly explained by shared influence of phylogenetic community composition (PCPS) and environmental factors (68%), while exclusive influence of PCPS was low (19%), and of environment was even lower (0.47%). Increases in body size were related to increases in annual mean temperature, and the influence of environment on body size was mediated by the distribution of sigmodontine lineages across South America.Main conclusionsEnvironment alone was not sufficient to explain body size variation in sigmodontine assemblages. Rather, environmental gradients interacted with historical processes to determine body size variation in the Neotropical assemblages. These results have implications for the way we think of body size gradients across species assemblages, because any gradient in a trait may be a result of differences in the biogeographical distribution of lineages across space, which should be considered in an explicit context.

Geographic body size variation in ectotherms: effects of seasonality on an anuran from the southern temperate forest.

BackgroundBody size variation has played a central role in biogeographical research, however, most studies have aimed to describe trends rather than search for underlying mechanisms. In order to provide a more comprehensive understanding of the causes of intra-specific body size variation in ectotherms, we evaluated eight hypotheses proposed in the literature to account for geographical body size variation using the Darwin’s frog (Rhinoderma darwinii), an anuran species widely distributed in the temperate forests of South America. Each of the evaluated hypotheses predicted a specific relationship between body size and environmental variables. The level of support for each of these hypotheses was assessed using an information-theoretic approach and based on data from 1015 adult frogs obtained from 14 sites across the entire distributional range of the species.ResultsThere was strong evidence favouring a single model comprising temperature seasonality as the predictor variable. Larger body sizes were found in areas of greater seasonality, giving support to the “starvation resistance” hypothesis. Considering the known role of temperature on ectothermic metabolism, however, we formulated a new, non-exclusive hypothesis, termed “hibernation hypothesis”: greater seasonality is expected to drive larger body size, since metabolic rate is reduced further and longer during colder, longer winters, leading to decreased energy depletion during hibernation, improved survival and increased longevity (and hence growth). Supporting this, a higher post-hibernation body condition in animals from areas of greater seasonality was found.ConclusionsDespite largely recognized effects of temperature on metabolic rate in ectotherms, its importance in determining body size in a gradient of seasonality has been largely overlooked so far. Based on our results, we present and discuss an alternative mechanism, the “hibernation hypothesis”, underlying geographical body size variation, which can be helpful to improve our understanding of biogeographical patterns in ectotherms.

Body size evolution under character release in the ground beetleCarabus japonicus

AbstractAimWe tested the hypothesis of character release in body size among allopatric populations of the carabid beetleCarabus japonicusby analysing geographical variation in body size in relation to habitat temperature and sympatry/allopatry with the larger congeneric speciesCarabus dehaanii.LocationThe main and satellite islands of Kyushu in the south‐western part of the Japanese archipelago.MethodsWe studied geographical variation in the body length and genital size ofC. japonicuspopulations at different sites to examine the effects of both habitat temperature and sympatry/allopatry withC. dehaanii. To determine whether the conditions for character release were fulfilled, we then estimated the heritable differences in body size by common garden rearing, and estimated the phylogenetic relationships among populations by molecular phylogenetic analysis.ResultsWhile body size was positively correlated with annual mean temperature, it was consistently small in sympatry but larger in some allopatric populations in warmer regions. The body size differences among populations were heritable. AllopatricC. japonicuspopulations on satellite islands were derived from the sympatric mainland populations. In a few sympatric areas, mitochondrial haplotypes were shared between the species because of introgressive hybridization, suggesting the occurrence of reproductive interference between the species. We also found that genital size was not affected by sympatry/allopatry, but was positively correlated with body size.Main conclusionsWe demonstrated that the increased body size of allopatricC. japonicushas evolved through a character release process. However, not all allopatric populations had enlarged body size, thus suggesting that some additional environmental factors are also involved. Geographical differentiation in body size and associated genital dimensions may result in prezygotic reproductive isolation among populations and promote allopatric differentiation leading to speciation.

Relationships between environmental gradients and geographic variation in the intraspecific body size of three species of frogs (Anura)

The relationship between environmental gradients and patterns of geographic variation in body size has been a controversial topic for ectothermic organisms globally. To examine whether the patterns that generally hold in more temperate species also hold for tropical ones, we examined the intraspecific body size variation in three species of Neotropical frogs, Dendropsophus minutus, Hypsiboas faber and Physalaemus cuvieri, along different environmental gradients (e.g. temperature, precipitation and topography). We analysed four competing hypotheses: (i) the water availability hypothesis that predicts a negative relationship between body size and precipitation; (ii) the heat balance hypothesis that predicts a negative relationship between body size and temperature; (iii) the topography hypothesis that predicts a negative relationship between body size and altitude; and (iv) the mixed-effect hypothesis that predicts that individuals occurring in wet and cold sites would be larger than individuals occurring in dry and warm sites. The spatial pattern of geographic variation in body size among populations of H. faber was associated with the mixed-effect hypothesis. In localities with low precipitation seasonality and cold conditions, H. faber individuals were larger than in localities with high precipitation seasonality and warm conditions. Variation in the body size of D. minutus was the opposite of that predicted by the heat balance hypothesis. Individuals in localities with high temperatures were larger than in localities with low temperatures. On the other hand, variation in the body size of P. cuvieri was not associated with the variables used in this study. Our results suggest that intraspecific variation in anuran body size is more dependent on species-specific response than on the region (i.e. temperate or tropical) where they occur.

Lean‐season primary productivity and heat dissipation as key drivers of geographic body‐size variation in a widespread marsupial

Geographic body‐size variation characterises many mammal species. Hypotheses centring around heat conservation, heat dissipation, primary productivity and seasonality have been advanced to explain geographic body‐size patterns. However, identification of the primary body‐size drivers has often been hampered by a paucity of data for broadly distributed species and the application of regression models that have not explicitly accounted for the spatial clustering inherent in such datasets. We used Australia's most widespread marsupial, the common brushtail possum Trichosurus vulpecula, as a model species with which to test five proposed drivers of geographic body‐size variation. Using geo‐referenced skull measurements from 588 specimens and a suite of putative environmental covariates, we employed spatial simultaneous autoregressive models, together with information criteria, to evaluate these different hypotheses. Our analysis identified a strong, positive relationship between possum body size and primary productivity during the least productive season, whereas the relationship with mean annual productivity received less support. Consistent with the heat‐dissipation hypothesis, T. vulpecula body size also decreased with increasing mean summer maximum temperature. Spatial autoregression coefficients estimated from the simultaneous autoregressive models were always high, suggesting that additional abiotic or biotic factors might contribute to the spatial patterns observed. We argue that the analysis of geographic body‐size variation should consider multi‐causal possibilities rather than treating the numerous hypotheses as competing, mutually exclusive alternatives.

Bergmann meets Scholander: geographical variation in body size and insulation in the koala is related to climate

AbstractAimBody size often varies clinally, with dominant explanations centred on how body size influences heat exchange (e.g. Bergmann's rule). However, for endotherms, pelage properties can also dramatically alter heat exchange – a point emphasized by Scholander in the 1950s but which has received little attention in biogeographical analyses. Here, we investigate how geographical variation in both body size and fur properties of the koala (Phascolarctos cinereus) is related to climate.LocationEastern Australia.MethodsWe measured head length and fur depths of koala museum specimens from across its geographical range, and quantified the relationship between fur depth and insulation. We used linear regression and regression tree analyses to test for associations between morphological traits and climate variables relating to four hypotheses: heat conservation (Bergmann's rule), heat dissipation, fasting endurance/survival of extremes, and productivity.ResultsBoth body size and fur depth of koalas decrease substantially towards the tropics. Consistent with Scholander's view, fur properties showed stronger associations with climate than body size. Males, the larger sex, had shorter fur than females in hot environments but not in more temperate regions, suggesting that shorter fur compensates for sexual size dimorphism. While fur depth and male body size were more strongly associated with variables relating to heat dissipation, female body size was most strongly associated with minimum temperatures.Main conclusionsBody size interacts strongly with other traits, such as fur properties, to influence how animals experience climate. Our results emphasize how the consideration of geographical variation in suites of functionally related traits can provide important insight into how species persist across broad environmental gradients.

Geographical variation in body size and sexual size dimorphism in an Australian lizard, Boulenger's Skink (Morethia boulengeri).

Ecogeographical rules help explain spatial and temporal patterns in intraspecific body size. However, many of these rules, when applied to ectothermic organisms such as reptiles, are controversial and require further investigation. To explore factors that influence body size in reptiles, we performed a heuristic study to examine body size variation in an Australian lizard, Boulenger's Skink Morethia boulengeri from agricultural landscapes in southern New South Wales, south-eastern Australia. We collected tissue and morphological data on 337 adult lizards across a broad elevation and climate gradient. We used a model-selection procedure to determine if environmental or ecological variables best explained body size variation. We explored the relationship between morphology and phylogenetic structure before modeling candidate variables from four broad domains: (1) geography (latitude, longitude and elevation), (2) climate (temperature and rainfall), (3) habitat (vegetation type, number of logs and ground cover attributes), and (4) management (land use and grazing history). Broad phylogenetic structure was evident, but on a scale larger than our study area. Lizards were sexually dimorphic, whereby females had longer snout-vent length than males, providing support for the fecundity selection hypothesis. Body size variation in M. boulengeri was correlated with temperature and rainfall, a pattern consistent with larger individuals occupying cooler and more productive parts of the landscape. Climate change forecasts, which predict warmer temperature and increased aridity, may result in reduced lizard biomass and decoupling of trophic interactions with potential implications for community organization and ecosystem function.

Empirical tests of harvest-induced body-size evolution along a geographic gradient in Australian macropods.

Life-history theory predicts the progressive dwarfing of animal populations that are subjected to chronic mortality stress, but the evolutionary impact of harvesting terrestrial herbivores has seldom been tested. In Australia, marsupials of the genus Macropus (kangaroos and wallabies) are subjected to size-selective commercial harvesting. Mathematical modelling suggests that harvest quotas (c. 10-20% of population estimates annually) could be driving body-size evolution in these species. We tested this hypothesis for three harvested macropod species with continental-scale distributions. To do so, we measured more than 2000 macropod skulls sourced from wildlife collections spanning the last 130years. We analysed these data using spatial Bayesian models that controlled for the age and sex of specimens as well as environmental drivers and island effects. We found no evidence for the hypothesized decline in body size for any species; rather, models that fit trend terms supported minor body size increases over time. This apparently counterintuitive result is consistent with reduced mortality due to a depauperate predator guild and increased primary productivity of grassland vegetation following European settlement in Australia. Spatial patterns in macropod body size supported the heat dissipation limit and productivity hypotheses proposed to explain geographic body-size variation (i.e. skull size increased with decreasing summer maximum temperature and increasing rainfall, respectively). There is no empirical evidence that size-selective harvesting has driven the evolution of smaller body size in Australian macropods. Bayesian models are appropriate for investigating the long-term impact of human harvesting because they can impute missing data, fit nonlinear growth models and account for non-random spatial sampling inherent in wildlife collections.

Body Size Variation of European Storm PetrelsHydrobates pelagicusin Relation to Environmental Variables

Body size differentiation may have developed in response to environmental gradients. A pattern of large individuals prevailing in colder areas is often observed and is explained by the heat conservation hypothesis (Bergmann's rule). To understand patterns driving body size variation in a pelagic seabird, the European Storm Petrel Hydrobates pelagicus, we examined the relationship between wing length, body mass and environmental variables in breeding areas (sea surface temperature, air temperature and wind speed). As this species has been divided into two subspecies: Mediterranean H. p. melitensis and Atlantic H. p. pelagicus, we performed the analyses at different scales (species, Atlantic subspecies and regional North Atlantic). At the species and subspecies scales, there was a longitudinal increase in wing length from west to east. At the subspecies and regional scale, we found a latitudinal increase in this variable from south to north. This result and the significant increase of wing length with decreasing sea surface and air temperatures are concordant with Bergmann's rule. In addition, body mass at the species and subspecies scales decreased with increasing wind speed, what may have a functional implication (small body mass may increase manoeuvrability over waves in conditions of stronger wind). Both genetic (two subspecies differing in body size) and environmental factors seem to be important forces driving intercolony variation in body size. Our study on sexual size dimorphism (SSD) revealed that in 156 molecularly sexed adults from the Faeroes, wing and tail length, and body mass exhibited female-biased SSD, while head-bill length showed male-biased SSD. The best discriminant function for sexing based on body measurements correctly classified 75% of individuals. Considering low correctness of proposed functions and geographical variation of body size, use of alternative methods (e.g. molecular tools) is recommended for sex discrimination in the European Storm Petrel.

Length of activity season drives geographic variation in body size of a widely distributed lizard

AbstractUnderstanding the factors that drive geographic variation in life history is an important challenge in evolutionary ecology. Here, we analyze what predicts geographic variation in life‐history traits of the common lizard,Zootoca vivipara, which has the globally largest distribution range of all terrestrial reptile species. Variation in body size was predicted by differences in the length of activity season, while we found no effects of environmental temperature per se. Females experiencing relatively short activity season mature at a larger size and remain larger on average than females in populations with relatively long activity seasons. Interpopulation variation in fecundity was largely explained by mean body size of females and reproductive mode, with viviparous populations having larger clutch size than oviparous populations. Finally, body size‐fecundity relationship differs between viviparous and oviparous populations, with relatively lower reproductive investment for a given body size in oviparous populations. While the phylogenetic signal was weak overall, the patterns of variation showed spatial effects, perhaps reflecting genetic divergence or geographic variation in additional biotic and abiotic factors. Our findings emphasize that time constraints imposed by the environment rather than ambient temperature play a major role in shaping life histories in the common lizard. This might be attributed to the fact that lizards can attain their preferred body temperature via behavioral thermoregulation across different thermal environments. Length of activity season, defining the maximum time available for lizards to maintain optimal performance, is thus the main environmental factor constraining growth rate and annual rates of mortality. Our results suggest that this factor may partly explain variation in the extent to which different taxa follow ecogeographic rules.

An Intercontinental Analysis of Climate-Driven Body Size Clines in Reptiles: No Support for Patterns, No Signals of Processes

Climatic gradients impose clinal selection on animal ecological and physiological performance, often promoting geographic body size clines. Bergmann’s rule predicts that body size increases with decreasing environmental temperatures given the need to retain body-heat through adjustments of body-mass-to-surface-area ratio. This prediction generally holds for endotherms, but remains controversial for ectotherms. An alternative interpretation, the ‘resource rule’, suggests that food abundance, primary productivity and precipitation (which, unlike temperature, do not necessarily correlate with geography), drive body size clines. We investigate geographic variation in body size within 65 species of lizards and snakes (squamates) based on an intercontinental dataset (6,500+ specimens belonging to 56 Israeli species, and multiple populations of nine Liolaemus species from Argentina and Chile). Bergmann’s rule is only rarely supported by our data (in four species, 6 %), whereas six species (9 %) follow its converse (hence, it is unsupported in 94 % of cases). Similarly, size increases with resource abundance in only 12 species (18 %). Therefore, although neither of the rules is supported, factors suggested by the resource rule are better predictors of body size than temperature. Surprisingly, we show that some measures of the extent of a species’ climatic envelope do not affect the likelihood of it showing a size-climate relationship. We conclude that negative size-temperature associations are an exception rather than a generality among squamates.

Latitudinal pattern in body size in a cockroach, Eupolyphaga sinensis

AbstractBody size of insects with flexible life cycles is expected to conform to the saw‐tooth model, a model in which the relationship between size and developmental time depends on length of the growing season. In species with high variability in terms of voltinism, however, more complex patterns can be expected. Few empirical studies have demonstrated the existence of such relationships, or whether climatic factors contribute to these relationships. In this study, we investigated the geographic variation in body size of the Chinese cockroach, Eupolyphaga sinensis Walker (Blattaria: Polyphagidae), which has a variable life cycle length. The sizes of adults – collected from 14 localities ranging from temperate to subtropical zones in China – were measured, using body length, body width, and pronotum width as parameters. The relationship between size, latitude, and climate factors (encompassing 10 variables) was then investigated. We found that the body size of E. sinensis varied considerably with latitude: cockroaches were larger at low and high latitudes, but smaller at intermediate latitudes. Thus, the relationship between climate and body size conformed to a saw‐tooth pattern. Results indicate that two factors were significantly associated with body size clines: season length and variability in life cycle length. Our results also demonstrated that climatic factors contribute to latitudinal clines in body size, which has important ecological and evolutionary implications. It can be expected that global climate change may alter latitudinal clines in body size of E. sinensis.