Bergmann's rule: a biophysiological rule examined in birds

Nest complexity correlates with larger brain size but smaller body mass across bird species

Amniotes differ substantially in absolute and relative brain size after controlling for allometry, and numerous hypotheses have been proposed to explain brain size evolution. Brain size is thought to correlate with processing capacity and the brain's ability to support complex manipulation such as nest-building skills. The increased complexity of nest structure is supposed to be a measure of an ability to manipulate nesting material into the required shape. The degree of nest-structure complexity is also supposed to be associated with body mass, partly because small species lose heat faster and delicate and insulated nests are more crucial for temperature control of eggs during incubation by small birds. Here, we conducted comparative analyses to test these hypotheses by investigating whether the complexity of species-typical nest structure can be explained by brain size and body mass (a covariate also to control for allometric effects on brain size) across 1353 bird species from 147 families. Consistent with these hypotheses, our results revealed that avian brain size increases as the complexity of the nest structure increases after controlling for a significant effect of body size, and also that a negative relationship exists between nest complexity and body mass.

Global latitudinal gradients and the evolution of body size in dinosaurs and mammals

Global climate patterns fundamentally shape the distribution of species and ecosystems. For example, Bergmann's rule predicts that homeothermic animals, including birds and mammals, inhabiting cooler climates are generally larger than close relatives from warmer climates. The modern world, however, lacks the comparative data needed to evaluate such macroecological rules rigorously. Here, we test for Bergmann's rule in Mesozoic dinosaurs and mammaliaforms that radiated within relatively temperate global climate regimes. We develop a phylogenetic model that accounts for biases in the fossil record and allows for variable evolutionary dispersal rates. Our analysis also includes new fossil data from the extreme high-latitude Late Cretaceous Arctic Prince Creek Formation. We find no evidence for Bergmann's rule in Mesozoic dinosaurs or mammaliaforms, the ancestors of extant homeothermic birds and mammals. When our model is applied to thousands of extant dinosaur (bird) and mammal species, we find that body size evolution remains independent of latitude. A modest temperature effect is found in extant, but not in Mesozoic, birds, suggesting that body size evolution in modern birds was influenced by Bergmann's rule during Cenozoic climatic change. Our study provides a general approach for studying macroecological rules, highlighting the fossil record's power to address longstanding ecological principles.

Breaking the Law: Is It Correct to Use the Converse Bergmann Rule in Ceroglossus chilensis? An Overview Using Geometric Morphometrics

The converse Bergmann's rule is a pattern of body size variation observed in many ectothermic organisms that contradicts the classic Bergmann's rule and suggests that individuals inhabiting warmer climates tend to exhibit larger body sizes compared to those inhabiting colder environments. Due to the thermoregulatory nature of Bergmann's rule, its application among ectotherms might prove to be more complicated, given that these organisms obtain heat by absorbing it from their habitat. The existence of this inverse pattern therefore challenges the prevailing notion that larger body size is universally advantageous in colder climates. Ceroglossus chilensis is a native Chilean beetle that has the largest latitudinal range of any species in the genus, from 34.3° S to 47.8° S. Within Chile, it continuously inhabits regions extending from Maule to Aysen, thriving on both native and non-native forest species. Beyond their remarkable color variation, populations of C. chilensis show minimal morphological disparity, noticeable only through advanced morphological techniques (geometric morphometrics). Based on both (1) the "temperature-size rule", which suggests that body size decreases with increasing temperature, and (2) the reduced resource availability in high-latitude environments that may lead to smaller body sizes, we predict that C. chilensis populations will follow the converse Bergmann's rule. Our results show a clear converse pattern to the normal Bergmann rule, where smaller centroid sizes were found to be measured in the specimens inhabiting the southern areas of Chile. Understanding the prevalence of the converse Bergmann's rule for ectotherm animals and how often this rule is broken is of utmost importance to understand the underlying mechanisms allowing organisms to adapt to different environments and the selective pressures they face.

Body size and trophic structure explain global asymmetric response of tetrapod diversity to climate effects

Although climate-based hypotheses are widely used to explain large-scale diversity patterns, they fall short of explaining the spatial variation among taxonomic groups. Integrating food web and metabolic theories into macroecology is a promising step forward, as they allow including explicit taxon-specific traits that can potentially mediate the relationship between climate and diversity. Our investigation focuses on the role of body size and trophic structure in mediating the influence of contemporary climate and historical climate change on global tetrapods species richness. We used piecewise structural equation modeling to assess the direct effects of contemporary climate and climate instability of species richness and the indirect effects of climate on tetrapod richness mediated by community-wide species traits. We found that birds and mammals are less sensitive to the direct effect of contemporary climate than amphibians and squamates. Contemporary climate and climate instability favored the species richness of mammals and amphibians. However, for birds and squamates, this link is only associated with contemporary climate. Moreover, we showed that community-wide traits are correlated with species richness gradients. However, we highlight that this relationship is dependent upon the specific traits and taxonomic groups. Specifically, bird communities with smaller bodies and bottom-heavy structures support higher species richness. Squamates also tend to be more diverse in communities with prevalence of smaller bodies, while mammals are correlated with top-heavy structures. Moreover, we showed that higher contemporary climate and climate instability reduce the species richness of birds and mammals through community-wide traits and indirectly increase squamate species richness. We also showed that body size and trophic structure are driving a global asymmetric response of tetrapod diversity to climate effects, which highlights the limitation to use the "typical" climate-based hypotheses. Furthermore, by combining multiple theories, our research contributes to a more realistic and mechanistic understanding of diversity patterns across taxonomic groups.

The magnitude of selection on growth varies among years and increases under warming conditions in a subarctic seabird

Because of ongoing rapid climate change, many ecosystems are becoming both warmer and more variable, and these changes are likely to alter the magnitude and variability of natural selection acting on wild populations. Critically, changes and fluctuations in selection can impact both population demography and evolutionary change. Therefore, predicting the impacts of climate change depends on understanding the magnitude and variation in selection on traits across different life stages and environments. Long-term experiments in wild settings are a great opportunity to determine the impact of environmental conditions on selection. Here we examined variability in the strength of selection on size traits of nestling black-legged kittiwakes (Rissa tridactyla) in a 25-year study including a food supplementation experiment on Middleton Island in the Gulf of Alaska. Using mixed effect models, we examined the annual variability of stage-specific and resource-specific selection gradients across 25 years. We found that (a) larger and heavier hatchlings were the most likely to survive during early ontogeny, (b) non-food supplemented younger nestlings in a brood experienced the strongest selection, and (c) warmer conditions increased the magnitude of selection on nestling mass and affected non-food supplemented and second-hatched nestlings the most. Our results suggested that variable resource dynamics likely caused some of the changes in selection from year to year and that warming conditions increased the strength of selection on subarctic seabird growth. However, our experimental manipulation revealed that local environmental heterogeneity could buffer the selection expected from broader climatic changes. Consequently, understanding the interactive effects of local conditions and general changes in climate seems likely to improve our ability to predict future selection gradients.

Morphological variability or inter-observer bias? A methodological toolkit to improve data quality of multi-researcher datasets for the analysis of morphological variation

OBJECTIVES

The investigation of morphological variation in animals is widely used in taxonomy, ecology, and evolution. Using large datasets for meta-analyses has dramatically increased, raising concerns about dataset compatibilities and biases introduced by contributions of multiple researchers.

MATERIALS AND METHODS

We compiled morphological data on 13 variables for 3073 individual mouse lemurs (Cheirogaleidae, Microcebus spp.) from 25 taxa and 153 different sampling locations, measured by 48 different researchers. We introduced and applied a filtering pipeline and quantified improvements in data quality (Shapiro-Francia statistic, skewness, and excess kurtosis). The filtered dataset was then used to test for genus-wide sexual size dimorphism and the applicability of Rensch's, Allen's, and Bergmann's rules.

RESULTS

Our pipeline reduced inter-observer bias (i.e., increased normality of data distributions). Inter-observer reliability of measurements was notably variable, highlighting the need to reduce data collection biases. Although subtle, we found a consistent pattern of sexual size dimorphism across Microcebus, with females being the larger (but not heavier) sex. Sexual size dimorphism was isometric, providing no support for Rensch's rule. Variations in tail length but not in ear size were consistent with the predictions of Allen's rule. Body mass and length followed a pattern contrary to predictions of Bergmann's rule.

DISCUSSION

We highlighted the usefulness of large multi-researcher datasets for testing ecological hypotheses after correcting for inter-observer biases. Using genus-wide tests, we outlined generalizable patterns of morphological variability across all mouse lemurs. This new methodological toolkit aims to facilitate future large-scale morphological comparisons for a wide range of taxa and applications.

Phenotypic signatures of urbanization? Resident, but not migratory, songbird eye size varies with urban-associated light pollution levels

Urbanization now exposes large portions of the earth to sources of anthropogenic disturbance, driving rapid environmental change and producing novel environments. Changes in selective pressures as a result of urbanization are often associated with phenotypic divergence; however, the generality of phenotypic change remains unclear. In this study, we examined whether morphological phenotypes in two residential species (Carolina Wren [Thryothorus ludovicianus] and Northern Cardinal [Cardinalis cardinalis]) and two migratory species (Painted Bunting [Passerina ciris], and White-eyed Vireo [Vireo griseus]), differed between urban core and edge habitats in San Antonio, Texas, USA. More specifically, we examined whether urbanization, associated sensory pollution (light and noise) and brightness (open, bright areas cause by anthropogenic land use) influenced measures of avian body (mass and frame size) and lateral eye size. We found no differences in body size between urban core and edge habitats for all species except the Painted Bunting, in which core-urban individuals were smaller. Rather than a direct effect of urbanization, this was due to differences in age structure between habitats, with urban-core areas consisting of higher proportions of younger buntings which are, on average, smaller than older birds. Residential birds inhabiting urban-core areas had smaller eyes compared to their urban-edge counterparts, resulting from a negative association between eye size and light pollution and brightness across study sites; notably, we found no such association in the two migratory species. Our findings demonstrate how urbanization may indirectly influence phenotypes by altering population demographics and highlight the importance of accounting for age when assessing factors driving phenotypic change. We also provide some of the first evidence that birds may adapt to urban environments through changes in their eye morphology, demonstrating the need for future research into relationships among eye size, ambient light microenvironment use, and disassembly of avian communities as a result of urbanization.

Variation in bill surface area is associated with local climatic factors across populations of the plain laughingthrush

Recent studies have found that avian bill and tarsus morphology may have evolved in response to climatic conditions, and these organs play important roles in thermoregulation and water retention in extreme environments. Here, we examined whether bill surface area and tarsus length were associated with climatic conditions in the plain laughingthrush, Garrulax davidi, which mainly occurs in north China and occupies several climatic zones from east to west. We measured bill surface area and tarsus length in 321 adults from 11 populations, almost encompassing all habitat types of the species. We analyzed the relationships among these morphological traits and local climatic factors. Bill surface area was positively correlated with maximum temperature, indicating that bill surface area tended to be larger in hotter environments. Furthermore, we found a negative relationship among bill surface area and winter precipitation, indicating that bill surface area tended to be larger in arid areas. However, we did not find any relationships between tarsus length and climatic factors. These results suggest that local climates may shape the evolution of bill morphology divergence, and summer seems to be the critical season for thermoregulation in this temperate zone passerine.

Complementarity in Allen's and Bergmann's rules among birds

Biologists have long noted that endotherms tend to have larger bodies (Bergmann's rule) and shorter appendages (Allen's rule) in colder environments. Nevertheless, many taxonomic groups appear not to conform to these 'rules', and general explanations for these frequent exceptions are currently lacking. Here we note that by combining complementary changes in body and extremity size, lineages could theoretically respond to thermal gradients with smaller changes in either trait than those predicted by either Bergmann's or Allen's rule alone. To test this idea, we leverage geographic, ecological, phylogenetic, and morphological data on 6,974 non-migratory terrestrial bird species, and show that stronger family-wide changes in bill size over thermal gradients are correlated with more muted changes in body size. Additionally, we show that most bird families exhibit weak but appropriately directed changes in both traits, supporting the notion of complementarity in Bergmann's and Allen's rules. Finally, we show that the few families that exhibit significant gradients in either bill or body size, tend to be more speciose, widely distributed, or ecologically constrained. Our findings validate Bergmann's and Allen's logic and remind us that body and bill size are simply convenient proxies for their true quantity of interest: the surface-to-volume ratio.

Bergmann's Rule under Rocks: Testing the Influence of Latitude and Temperature on a Chiton from Mexican Marine Ecoregions

Bergmann's rule relates the trend of increasing body size with higher latitudes, where colder climates are found. In the Mexican Pacific, three marine ecoregions are distinguishable across a latitudinal gradient. Stenoplax limaciformis is an abundant chiton species that is distributed on rocky shores in these ecoregions. Geometric morphometric analyses were performed to describe the shape and size variation of S. limaciformis between marine ecoregions that vary in sea surface temperature with latitude, thus testing Bergmann's rule. Individuals' body shape ranged from elongated to wide bodies. Although there was variation in chitons' body shape and size, the was no evidence of allometry among localities. The Gulf of California is the northernmost ecoregion evaluated in this work, where larger chitons were observed and lower sea surface temperature values were registered. The results suggest that S. limaciformis follows a trend to Bergmann's rule, such as endotherms. These mollusks do not need heat dissipation, but they do need to retain moisture. In addition, larger chitons were observed in zones with high primary productivity, suggesting that chitons do not delay their maturation due to food shortage.

Resource and seasonality drive interspecific variability in simulations from a dynamic energy budget model

Animals show a vast array of phenotypic traits in time and space. Such variation patterns have traditionally been described as ecogeographical rules; for example, the tendency of size and clutch size to increase with latitude (Bergmann's and Lack's rules, respectively). Despite considerable research into these variation patterns and their consequences for biodiversity and conservation, the processes behind trait variation remain controversial. Here, we show how food variability, largely set by climate and weather, can drive interspecific trait variation by determining individual energy input and allocation trade-offs. Using a dynamic energy budget (DEB) model, we simulated different food environments, as well as interspecific variability in the parameters for energy assimilation, mobilization and allocation to soma. We found that interspecific variability is greater when the resource is non-limiting in both constant and seasonal environments. Our findings further show that individuals can reach larger biomass and greater reproductive output in a seasonal environment than in a constant environment of equal average resource due to the peaks of food surplus. Our results agree with the classical patterns of interspecific trait variation and provide a mechanistic understanding that supports recent hypotheses which explain them: the resource and the eNPP (net primary production during the growing season) rules. Due to the current alterations to ecosystems and communities, disentangling the mechanisms of trait variation is increasingly important to understand and predict biodiversity dynamics under climate change, as well as to improve conservation strategies.

Long-term consistency in susceptibility of prey species to predation by an avian predator

Selection by predators affects prey through competition for limiting resources. This not only has consequences for direct mortality but also indirectly affects disturbance. Changes in the intensity of selection on prey by predators may affect the size of prey populations, with consequences for their short- or long-term interactions. We assessed whether predation by northern goshawks Accipiter gentilis modified the composition of prey communities consistently along a temporal gradient, showing long-term consistency in susceptibility of prey species to predation. We followed six populations of the goshawk in two biomes in Denmark and Finland during 1949-2019. Susceptibility to goshawk predation in 2005-2017 in Denmark was only weakly related to susceptibility to goshawk predation in 1977-2004. In Finland, susceptibility of shared prey species to goshawk predation was positively related between periods. The average difference in susceptibility to goshawk predation between periods was considerably higher in Denmark than in Finland. Susceptibility of prey species to predation in goshawks increased with latitude and body mass of prey species, and decreased with period of time and population density of prey species. The changes in susceptibility to predation suggest changes in the characteristics of the local prey pools.

Generation of raptor diversity in Europe: linking speciation with climate changes and the ability to migrate

Europe holds a rich community of diurnal birds of prey, and the highest proportion of transcontinental migratory raptorial species of any landmass. This study will test the hypotheses that the high diversification of the raptor assemblage in Europe is a recent event, that closely related species sharing the same trophic niches can only coexist in sympatry during the breeding period, when food availability is higher, and finally that migration is a function of size, with the smaller species in every trophic group moving further. A consensus molecular phylogeny for the 38 regular breeding species of raptors in Europe was obtained from BirdTree (www.birdtree.org). For the same species, a trophic niche cluster dendrogram was constructed. Size and migratory strategy were introduced in the resulting phylogeny, where trophic groups were also identified. Multispecific trophic groups tended to be composed of reciprocal sister species of different sizes, while monospecific groups (n = 3) were composed of highly specialized species. Many speciation events took place recently, during the glacial cycles of the Quaternary, and size divergence among competing species may be due to character displacement. Nowadays, the smaller species in every trophic group migrate to sub-Saharan Africa. This investigation illustrates how the rich assemblage of diurnal birds of prey in Europe, more diverse and more migratory than, for instance, the North American assemblage at equivalent latitudes, has emerged recently due to the multiplication of look-alike species with similar trophic ecologies, possibly in climate refugia during cold periods.

Test of Ecogeographical Rules on Sparrows (Passer spp.) along the Elevation Gradient of the Himalaya in Central Nepal

Animals inhabiting colder climates have a larger body size (Bergmann’s rule) and smaller body extremities (Allen’s rule), which help homeothermic animals to retain heat. Such ecogeographical phenomena have frequently been observed in animals along the latitudinal gradient and have occasionally been tested along the elevational gradient. This study tested whether these ecogeographic rules hold true for the morphology of sparrows (Passer spp.) along the elevational gradient offered by the Himalaya in central Nepal. Seventy house sparrows and twenty-eight tree sparrows were captured from 22 different localities of central Nepal between 100 and 3400 m asl, and morphological traits such as body size (body mass, tarsus length, wing length and tail length) and body extremities (bill length and bill width) were measured. Linear regression analysis was used to test the association of morphological measurements with elevation and climatic variables. House sparrows (Passer domesticus) had a wider elevational distribution range and exhibited significantly larger body sizes than the Eurasian tree sparrows (P. montanus). House sparrows had larger body sizes and smaller bills at higher elevations in adherence to Bergmann’s rule and Allen’s rule. Bill length in house sparrows showed a positive association with the temperature following the proposition of Allen’s rule. However, the morphological measurements in Eurasian tree sparrows did not show a distinct pattern with elevation and climatic variables. Therefore, this study concludes that ecogeographical phenomena such as Bergmann’s rule and Allen’s rule could be species-specific based on their biological and ecological characteristics.

Evolutionary allometry and ecological correlates of fang length evolution in vipers

Traits for prey acquisition form the phenotypic interface of predator-prey interactions. In venomous predators, morphological variation in venom delivery apparatus like fangs and stingers may be optimized for dispatching prey. Here, we determine how a single dimension of venom injection systems evolves in response to variation in the size, climatic conditions and dietary ecology of viperid snakes. We measured fang length in more than 1900 museum specimens representing 199 viper species (55% of recognized species). We find both phylogenetic signal and within-clade variation in relative fang length across vipers suggesting both general taxonomic trends and potential adaptive divergence in fang length. We recover positive evolutionary allometry and little static allometry in fang length. Proportionally longer fangs have evolved in larger species, which may facilitate venom injection in more voluminous prey. Finally, we leverage climatic and diet data to assess the global correlates of fang length. We find that models of fang length evolution are improved through the inclusion of both temperature and diet, particularly the extent to which diets are mammal-heavy diets. These findings demonstrate how adaptive variation can emerge among components of complex prey capture systems.

Changes in bee functional traits at community and intraspecific levels along an elevational gradient in a Mexical-type scrubland

Understanding the causes of morphological variation of organisms along climatic gradients has been a central challenge in ecological research. We studied the variation of community weighted mean (CWM) and two functional diversity metrics (Rao-Q and functional richness) computed for five morphological traits of wild bees (Hymenoptera: Apoidea) related to thermal performance (namely body size, relative appendage length and hairiness), at community and interspecific levels, along an elevation gradient in a Mexical-type scrubland. At the community level we found a decreasing CWM of body size pattern with increasing elevation which is consistent with the species-energy theory (and contrary to Bergmann's rule). We also found an increase in the CWM of relative tibia length, which is contrary to Allen's rule. Additionally, we found an increase in the CWM of relative hair length towards high levels of elevation, which would be consistent with the hypothesis that hairiness plays an important role as thermal insulation. We found that functional diversity was larger at low elevations with respect to high elevation for body size and hair length, which could imply that highland communities were more sensitive towards environmental changes than lowland communities. Overall, at intraspecific level, most of species showed no pattern for any of the traits along the elevation gradient. Future research should provide further evidence on the possible behavioral or physiological mechanisms behind it.

Thermal adaptation best explains Bergmann's and Allen's Rules across ecologically diverse shorebirds

Bergmann's and Allen's rules state that endotherms should be larger and have shorter appendages in cooler climates. However, the drivers of these rules are not clear. Both rules could be explained by adaptation for improved thermoregulation, including plastic responses to temperature in early life. Non-thermal explanations are also plausible as climate impacts other factors that influence size and shape, including starvation risk, predation risk, and foraging ecology. We assess the potential drivers of Bergmann's and Allen's rules in 30 shorebird species using extensive field data (>200,000 observations). We show birds in hot, tropical northern Australia have longer bills and smaller bodies than conspecifics in temperate, southern Australia, conforming with both ecogeographical rules. This pattern is consistent across ecologically diverse species, including migratory birds that spend early life in the Arctic. Our findings best support the hypothesis that thermoregulatory adaptation to warm climates drives latitudinal patterns in shorebird size and shape.

The impact of paleoclimatic changes on body size evolution in marine fishes

General rules are useful tools for understanding how organisms evolve. Cope’s rule (tendency to increase in size over evolutionary time) and Bergmann’s rule (tendency to grow to larger sizes in cooler climates) both relate to body size, an important factor that affects the biology, ecology, and physiology of organisms. These rules are well studied in endotherms but remain poorly understood among ectotherms. Here, we show that paleoclimatic changes strongly shaped the trajectory of body size evolution in tetraodontiform fishes. Their body size evolution is explained by both Cope’s and Bergmann’s rules, highlighting the impact of paleoclimatic changes on aquatic organisms, which rely on their environment for temperature regulation and are likely more susceptible than terrestrial vertebrates to climatic changes.

Body size is an important species trait, correlating with life span, fecundity, and other ecological factors. Over Earth’s geological history, climate shifts have occurred, potentially shaping body size evolution in many clades. General rules attempting to summarize body size evolution include Bergmann’s rule, which states that species reach larger sizes in cooler environments and smaller sizes in warmer environments, and Cope’s rule, which poses that lineages tend to increase in size over evolutionary time. Tetraodontiform fishes (including pufferfishes, boxfishes, and ocean sunfishes) provide an extraordinary clade to test these rules in ectotherms owing to their exemplary fossil record and the great disparity in body size observed among extant and fossil species. We examined Bergmann’s and Cope’s rules in this group by combining phylogenomic data (1,103 exon loci from 185 extant species) with 210 anatomical characters coded from both fossil and extant species. We aggregated data layers on paleoclimate and body size from the species examined, and inferred a set of time-calibrated phylogenies using tip-dating approaches for downstream comparative analyses of body size evolution by implementing models that incorporate paleoclimatic information. We found strong support for a temperature-driven model in which increasing body size over time is correlated with decreasing oceanic temperatures. On average, extant tetraodontiforms are two to three times larger than their fossil counterparts, which otherwise evolved during periods of warmer ocean temperatures. These results provide strong support for both Bergmann’s and Cope’s rules, trends that are less studied in marine fishes compared to terrestrial vertebrates and marine invertebrates.

Bergmann’s Rule Holds in Birds Inhabiting Southern Guinea Forests but Not in the Northern Savanna of Nigeria

The Bergmann’s rule predicts that in endotherms, body sizes will differ with respect to thermal gradients. Larger bodied individuals will inhabit colder environments while in warmer environments, individuals will be smaller-bodied. This hypothesis has been proved and disproved many times due to inconsistencies in body size differences along latitudinal gradients. We tested this hypothesis in 30 Afrotropical resident bird species inhabiting two vegetation types at different latitudes (southern guinea forests and northern savanna) and at different altitudes in Nigeria, West Africa. Using principal component analyses of body mass and wing length, the first principal component, the component of size, indicated that individuals in montane areas were larger than lowland populations in southern guinea forests. However, in the northern guinea savanna, there was no significant difference in body sizes between lowland and montane populations. General linear models show that body size increases as temperature decreases. In species found in both southern guinea forests and northern savanna (i.e., African Thrush Turdus pelios and Snowy-crowned Robin Chat Cossypha niveicapilla), variations in body sizes were significantly dependent on sites. Our study indicates that other macro-scale factors such as vegetation and rainfall patterns might modulate conformity to Bergmann’s rule in Afrotropical environments.

Oh, the places you will grow: Intraspecific latitudinal clines in butterfly size suggest a phylogenetic signal

Within an animal species, the body sizes of individuals at higher latitudes are often different from individuals at lower latitudes. For homeothermic species that maintain a relatively constant body temperature, such as mammals and birds, individuals at higher latitudes tend to be larger. For ectothermic species, such as insects, that do not retain their own body heat and which often do not maintain a relatively constant body temperature, patterns of body size with latitude are highly variable. This has led some authors to contend that patterns in even closely related species cannot be expected to be similar. Indeed, to our knowledge, no studies of invertebrates have found that more closely related species have more similar relationships between body size and latitude. Further, no studies have investigated the potential influence of diet quality on interspecific differences in these clines. We measured wing lengths of specimens (N = 1753) in eight lycaenid butterfly species and one species of the sister family, Riodinidae to determine if more closely related species have similar latitudinal trends. We also estimated the mean nitrogen content of caterpillars’ hosts to investigate whether this often‐limiting nutrient influences the strength and direction of latitudinal clines in body size. We found that four species are significantly smaller at higher latitudes, an additional species is marginally smaller at higher latitudes (p < .06), and four species had no significant relationship with latitude. We also found a strong phylogenetic signal for latitudinal clines in body size among our species, which indicates that some closely related species may have similar clines. However, the strength and direction of these clines did not depend on the estimated nitrogen content of caterpillars’ hosts. Our results indicate that mean nitrogen content of hosts may not be an important driver in latitudinal clines but that phylogenetic relationships among species should be accounted for when exploring other potential drivers of body‐size clines in invertebrate species.

Bigger or long-winged male common crossbills exhibit redder carotenoid-based plumage coloration

Carotenoid-based ornaments are often considered reliable (honest) individual condition signals because their expression implies physiological costs unaffordable for low-quality animals (handicap signals). Recently, it has been suggested that efficient cell respiration is mandatory for producing red ketocarotenoids from dietary yellow carotenoids. This implies that red colorations should be entirely unfalsifiable and independent of expression costs (index signals). In a precedent study, male common crossbills Loxia curvirostra showing a red plumage reported higher apparent survival than those showing yellowish-orange colors. The plumage redness in this species is due to ketocarotenoid accumulation in feathers. Here, we correlated the male plumage redness (a four-level visual score: yellow, patchy, orange and red) and the body morphology in more than 1000 adult crossbills captured in three Iberian localities to infer the mechanisms responsible for color evolution. A principal component analysis summarized morphometry of ten variables (beak, wing, tarsus length, etc.). The overall body size (PC1) and the length of flight feathers regarding body size (PC3) showed significant positive relationships with plumage redness. Plumage redness was barely correlated to bill shape measures suggesting no constraint in acquiring carotenoids from pine cones. However, large body sizes or proportionally long flying feathers could help carotenoid acquisition via social competition or increased foraging ranges. Proportionally longer flight feathers might also be associated with a specific cell respiration profile that would simultaneously favor flying capacities and enzymatic transformations needed for ketocarotenoid synthesis. Such a phenotypic profile would agree with the hypothesis of ketocarotenoid-based colors acting as individual quality index signals.

Bergmann's rule is a "just-so" story of human body size

Carl Bergmann was an astute naturalist and physiologist. His ideas about animal size and shape were important advances in the pre-Darwinian nineteenth century. Bergmann's rule claims that that in cold climates, large body mass increases the ratio of volume-to-surface area and provides for maximum metabolic heat retention in mammals and birds. Conversely, in warmer temperatures, smaller body mass increases surface area relative to volume and allows for greater heat loss. For humans, we now know that body size and shape are regulated more by social-economic-political-emotional (SEPE) factors as well as nutrition-infection interactions. Temperature has virtually no effect. Bergmann's rule is a "just-so" story and should be relegated to teaching and scholarship about the history of science. That "rule" is no longer acceptable science and has nothing to tell us about physiological anthropology.

Unraveling a century of global change impacts on winter bird distributions in the eastern United States

One of the most pressing questions in ecology and conservation centers on disentangling the relative impacts of concurrent global change drivers, climate and land-use/land-cover (LULC), on biodiversity. Yet studies that evaluate the effects of both drivers on species' winter distributions remain scarce, hampering our ability to develop full-annual-cycle conservation strategies. Additionally, understanding how groups of species differentially respond to climate versus LULC change is vital for efforts to enhance bird community resilience to future environmental change. We analyzed long-term changes in winter occurrence of 89 species across nine bird groups over a 90-year period within the eastern United States using Audubon Christmas Bird Count (CBC) data. We estimated variation in occurrence probability of each group as a function of spatial and temporal variation in winter climate (minimum temperature, cumulative precipitation) and LULC (proportion of group-specific and anthropogenic habitats within CBC circle). We reveal that spatial variation in bird occurrence probability was consistently explained by climate across all nine species groups. Conversely, LULC change explained more than twice the temporal variation (i.e., decadal changes) in bird occurrence probability than climate change on average across groups. This pattern was largely driven by habitat-constrained species (e.g., grassland birds, waterbirds), whereas decadal changes in occurrence probabilities of habitat-unconstrained species (e.g., forest passerines, mixed habitat birds) were equally explained by both climate and LULC changes over the last century. We conclude that climate has generally governed the winter occurrence of avifauna in space and time, while LULC change has played a pivotal role in driving distributional dynamics of species with limited and declining habitat availability. Effective land management will be critical for improving species' resilience to climate change, especially during a season of relative resource scarcity and critical energetic trade-offs.

Polymorphism in a Neotropical toad species: ontogenetic, populational and geographic approaches to chromatic variation in Proceratophrys cristiceps (Müller, 1883) (Amphibia, Anura, Odontophrynidae)

Quantifying variability is important for understanding how evolution operates in polymorphic species such as those of the genus Proceratophrys Miranda-Ribeiro, 1920, which is widely distributed in South America. P. cristiceps distribution is limited to the Caatinga biome in Brazil. We examined its chromatic variation from a populational perspective, looking at different phenetic polymorphism levels and probable chromotypic association by applying statistical and GIS tools that could facilitate future taxonomic research regarding this and other species. We characterized P. cristiceps colour patterns and re-evaluated its geographic variation, highlighting potential consequences for the taxonomy of the genus. Our results revealed six principle chromotypes whose frequencies varied among sex and ontogenetic classes. Phenotypic expression appeared to respect defined proportions and evidenced selective value for the species. We conclude that individual variation, together with typological traditionalism may overestimate the polymorphic magnitude at the population level and cause taxonomic inflation. Our data support the usefulness of P. cristiceps as a model for microevolutionary studies.

Physiological responses of Holstein calves to heat stress and dietary supplementation with a postbiotic from Aspergillus oryzae

Increased ambient temperature causes heat stress in mammals, which affects physiological and molecular functions. We have recently reported that the dietary administration of a postbiotic from Aspergillus oryzae (AO) improves tolerance to heat stress in fruit flies and cattle. Furthermore, heat-induced gut dysfunction and systemic inflammation have been ameliorated in part by nutritional interventions. The objective of this study was to characterize the phenotypic response of growing calves to heat stress compared to thermoneutral ad libitum fed and thermoneutral feed-restricted counterparts and examining the physiologic alterations associated with the administration of the AO postbiotic to heat-stressed calves with emphasis on intestinal permeability. In this report, we expand previous work by first demonstrating that heat stress reduced partial energetic efficiency of growth in control (45%) but not in AO-fed calves (62%) compared to thermoneutral animals (66%). While heat stress increased 20% the permeability of the intestine, AO postbiotic and thermoneutral treatments did not affect this variable. In addition, AO postbiotic reduced fecal water content relative to thermoneutral and heat stress treatments. Heat stress increased plasma concentrations of serum amyloid A, haptoglobin and lipocalin-2, and administration of AO postbiotic did not ameliorate this effect. In summary, our findings indicated that heat stress led to reduced nutrient-use efficiency and increased systemic inflammation. Results suggest that the AO postbiotic improved energy-use efficiency, water absorption, and the intestinal permeability in heat stress-mediated increase in gut permeability but did not reduce heat stress-mediated rise in markers of systemic inflammation.

Functional biogeography of parasite traits: hypotheses and evidence

Functional biogeography, or the study of trait-based distributional patterns, not only complements our understanding of spatial patterns in biodiversity, but also sheds light on the underlying processes generating them. In parallel with the well-studied latitudinal diversity gradient, decades-old ecogeographical rules also postulate latitudinal variation in species traits. Notably, species in the tropics are predicted to have smaller body sizes (Bergmann's rule), narrower niches (MacArthur's rule) and smaller geographical ranges (Rapoport's rule) than their counterparts at higher latitudes. Although originally proposed for free-living organisms, these rules have been extended to parasitic organisms as well. In this review, I discuss the mechanistic hypotheses most likely to explain latitudinal gradients in parasite traits, and assess the empirical evidence obtained from comparative studies testing the above three rules as well as latitudinal gradients in other parasite traits. Overall, there is only weak empirical support for latitudinal gradients in any parasite trait, with little consistency among comparative analyses. The most parsimonious explanation for the existence of geographical patterns in parasite traits is that they are primarily host-driven, i.e. ecological traits of parasites track those of their hosts, with a direct influence of bioclimatic factors playing a secondary role. Thus, geographical patterns in parasite traits probably emerge as epiphenomena of parallel patterns in their hosts.

This article is part of the theme issue ‘Infectious disease macroecology: parasite diversity and dynamics across the globe’.

Coping with extremes: High-altitude sparrows enhance metabolic and thermogenic capacities in the pectoralis muscle and suppress in the liver relative to their lowland counterparts

Animals living at high altitudes are challenged by the extreme environmental conditions of cold temperature and hypobaric hypoxia. It is not well understood how high-altitude birds enhance the capacity of metabolic thermogenesis and allocate metabolic capacity in different organs to maximize survival in extreme conditions of a cold winter. The Qinghai-Tibet Plateau (QTP) is the largest and highest plateau globally, offering a natural laboratory for investigating coping mechanisms of organisms inhabiting extreme environments. To understand the adaptive strategies in the morphology and physiology of small songbirds on the QTP, we compared plasma triiodothyronine (T₃), pectoralis muscle mitochondrial cytochrome c oxidase (COX) and state IV capacities, the expression of peroxisome proliferator-activated receptor γ coactivator α (PGC-1α), adenine nucleotide translocase (ANT), uncoupling protein (UCP), and adenosine monophosphate-dependent kinase (AMPK) α1 mRNA in the pectoralis and liver of Eurasian tree sparrows (Passer montanus) from high-altitude (3,230 m), medium-altitude (1400 m), and low-altitude (80 m) regions. Our results showed that high-altitude sparrows had greater body masses, longer wings and tarsometatarsi, but comparable bill lengths relative to medium- and low-altitude individuals. High-altitude sparrows had higher plasma T₃ levels and pectoralis muscle mitochondrial COX capacities than their lowland counterparts. They also upregulated the pectoralis muscle mRNA expression of UCP, PGC-1α, and ANT proteins relative to low-altitude sparrows. Unlike pectoralis, high-altitude sparrows significantly down-regulated hepatic AMPKα1 and ANT protein expression as compared with their lowland counterparts. Our results contribute to understanding the morphological, biochemical, and molecular adaptations in free-living birds to cope with the cold seasons in the extreme environment of the QTP.

Morphological variations in a widely distributed Eastern Asian passerine cannot be consistently explained by ecogeographic rules

Ecogeographic rules that describe quantitative relationships between morphologies and climate might help us predict how morphometrics of animals was shaped by local temperature or humidity. Although the ecogeographic rules had been widely tested in animals of Europe and North America, they had not been fully validated for species in regions that are less studied. Here, we investigate the morphometric variation of a widely distributed East Asian passerine, the vinous-throated parrotbill (Sinosuthora webbiana), to test whether its morphological variation conforms to the prediction of Bergmann's rule, Allen's rules, and Gloger's rule. We at first described the climatic niche of S. webbiana from occurrence records (n = 7838) and specimen records (n = 290). The results of analysis of covariance (ANCOVA) suggested that the plumage coloration of these parrotbills was darker in wetter/warmer environments following Gloger's rule. However, their appendage size (culmen length, beak volume, tarsi length) was larger in colder environments, the opposite of the predictions of Allen's rule. Similarly, their body size (wing length) was larger in warmer environments, the opposite of the predictions of Bergmann's rule. Such disconformity to both Bergmann's rule and Allen's rule suggests that the evolution of morphological variations is likely governed by multiple selection forces rather than dominated by thermoregulation. Our results suggest that these ecogeographic rules should be validated prior to forecasting biological responses to climate change especially for species in less-studied regions.

Taxonomic scale dependency of Bergmann’s patterns: a cross-scale comparison of hawkmoths and birds along a tropical elevational gradient

Bergmann’s rule predicts a larger body size for endothermic organisms in colder environments. The contrasting results from previous studies may be due to the differences in taxonomic (intraspecific, interspecific and community) and spatial (latitudinal vs elevational) scales. We compared Bergmann’s patterns for endotherms (Aves) and ectotherms (Lepidoptera: Sphingidae) along the same 2.6 km elevational transect in the eastern Himalayas. Using a large data spanning 3,302 hawkmoths (76 morpho-species) and 15,746 birds (245 species), we compared the patterns at the intraspecific (hawkmoths only), interspecific and community scales. Hawkmoths exhibited a positive Bergmann’s pattern at the intraspecific and abundance-weighted community scale. Contrary to this, birds exhibited a strong converse Bergmann’s pattern at interspecific and community scales, both with and without abundance. Overall, our results indicate that incorporation of information on intraspecific variation and/or species relative abundances influences the results to a large extent. The multiplicity of patterns at a single location provides the opportunity to disentangle the relative contribution of individual- and species-level processes by integrating data across multiple nested taxonomic scales for the same taxa. We suggest that future studies of Bergmann’s patterns should explicitly address taxonomic and spatial scale dependency, with species relative abundance and intraspecific trait variation as essential ingredients especially at short elevational scales.

Patterns of morphological differentiation within Manacus manacus (Aves: Pipridae) in Colombia: revisiting hypotheses of isolation and secondary contact

Determining the factors responsible for phenotypic variation within species is a fundamental task in evolutionary ecology. Isolation by distance, isolation by environment and clines along secondary contact zones between formerly isolated populations are common patterns of morphological variation. In this study, we evaluated whether patterns of morphological variation exhibit association with isolation by distance, isolation by environment or secondary contact in populations of Manacus manacus with contrasting plumage colour. We used field and museum measurements of five morphological characters from 311 individuals from 88 localities distributed across a highly heterogeneous environmental range within Colombia. Climatic variables explained a higher proportion of the variation than geographic distance among localities. We found differences in wing and culmen length between white and yellow phenotypes of M. manacus in Colombia. Overall morphology did not change in a clinal fashion in relation to the contact zone and the few traits that exhibit clinal variation suggest a distant locality for the contact zone, not in line with our expectations by secondary contact between differentiated populations, suggesting alternative mechanisms for differentiation between subspecies. Our results suggest that this species exhibits marked morphological variation associated with changes in temperature and precipitation. These associations are consistent throughout the geographic range analysed, leading us to postulate that dispersal and local adaptation jointly shape the distribution of phenotypic variation.

The Effects of Weather on Avian Growth and Implications for Adaptation to Climate Change

Climate change is forecasted to generate a range of evolutionary changes and plastic responses. One important aspect of avian responses to climate change is how weather conditions may change nestling growth and development. Early life growth is sensitive to environmental effects and can potentially have long-lasting effects on adult phenotypes and fitness. A detailed understanding of both how and when weather conditions affect the entire growth trajectory of a nestling may help predict population changes in phenotypes and demography under climate change. This review covers three main topics on the impacts of weather variation (air temperature, rainfall, wind speed, solar radiation) on nestling growth. Firstly, we highlight why understanding the effects of weather on nestling growth might be important in understanding adaptation to, and population persistence in, environments altered by climate change. Secondly, we review the documented effects of weather variation on nestling growth curves. We investigate both altricial and precocial species, but we find a limited number of studies on precocial species in the wild. Increasing temperatures and rainfall have mixed effects on nestling growth, while increasing windspeeds tend to have negative impacts on the growth rate of open cup nesting species. Thirdly, we discuss how weather variation might affect the evolution of nestling growth traits and suggest that more estimates of the inheritance of and selection acting on growth traits in natural settings are needed to make evolutionary predictions. We suggest that predictions will be improved by considering concurrently changing selection pressures like urbanization. The importance of adaptive plastic or evolutionary changes in growth may depend on where a species or population is located geographically and the species’ life-history. Detailed characterization of the effects of weather on growth patterns will help answer whether variation in avian growth frequently plays a role in adaption to climate change.

Opposing pressures of climate and land-use change on a native bee

Anthropogenic activities are rapidly changing the environment, and species that do not respond face a higher risk of extinction. Species may respond to environmental changes by modifying their behaviors, shifting their distributions, or changing their morphology. Recent morphological responses are often measured by changes in body size. Changes in body size are often attributed to climate change, but may instead be due to differences in available resources associated with changes in local land-use. The effects of temperature and land-use can be uncoupled in populations of the small carpenter bee Ceratina calcarata, which have experienced changes in agricultural and urban cover independent of climate change. We studied how the morphology of this bee has changed over the past 118 years (1902-2019) in relation to climate change and the past 45 years (1974-2019) in relation to agricultural and urban cover. Over this time, summer temperatures increased. We found that male and female size decreased with increasing temperature. Male size also decreased with agricultural expansion. Female size, however, increased with agricultural expansion. These results suggest that rising temperatures correlate with a decrease in female body size, while, opposite to predicted, agricultural land-use may select for increased female body size. These opposing pressures act concurrently and may result in bee extirpation from agricultural habitats if selection for large sizes is unsustainable as temperatures continue to increase. Furthermore, this study emphasizes the need to consider multiple environmental stressors when examining the effects of climate change due to their interactions.

Age and annual growth rate cause spatial variation in body size in Phrynocephalus przewalskii (Agamid)

Whether or not biogeographic rules dealing with spatial patterns of animal body sizes are valid for ectotherms is controversial. As the ectotherms grow all their lives, we explored the role of age and annual growth rate in body size variation in Phrynocephalus przewalskii in northern China. Morphological data were collected from 11 populations across a broad geographic gradient. Correlations between age, sex, climatic factors, and body size were analyzed using generalized linear model (GLM) and generalized linear mixed model (GLMM). GLM analysis indicated that the general body size of both sexes and the appendage size of females increased significantly with increasing temperature; however, the coefficient of determination was very small. GLMM analysis indicated that body size only correlated with age, whereas appendage size was affected by age, temperature, rainfall, and sunshine. Annual growth rates were positively correlated with temperature. We concluded that body size variation was mainly caused by age structure and plasticity of the growth rate in P. przewalskii and did not follow Bergmann's rule; however, females followed Allen's rule. Future studies to investigate the effect of energy restriction are needed to further understand the relationship between growth rate and body size. We also suggest that further studies on thermal advantage and sexual selection may be helpful to understand appendage size variation in P. przewalskii.

Adaptations to thermal stress in social insects: recent advances and future directions

Thermal stress is a major driver of population declines and extinctions. Shifts in thermal regimes create new environmental conditions, leading to trait adaptation, population migration, and/or species extinction. Extensive research has examined thermal adaptations in terrestrial arthropods. However, little is known about social insects, despite their major role in ecosystems. It is only within the last few years that the adaptations of social insects to thermal stress have received attention. Herein, we discuss what is currently known about thermal tolerance and thermal adaptation in social insects - namely ants, termites, social bees, and social wasps. We describe the behavioural, morphological, physiological, and molecular adaptations that social insects have evolved to cope with thermal stress. We examine individual and collective responses to both temporary and persistent changes in thermal conditions and explore the extent to which individuals can exploit genetic variability to acclimatise. Finally, we consider the costs and benefits of sociality in the face of thermal stress, and we propose some future research directions that should advance our knowledge of individual and collective thermal adaptations in social insects.

Temperature drives caste-specific morphological clines in ants

The morphology of organisms relates to most aspects of their life history and autecology. As such, elucidating the drivers of morphological variation along environmental gradients might give insight into processes limiting species distributions. In eusocial organisms, the concept of morphology is more complex than in solitary organisms. Eusocial insects such as ants exhibit drastic morphological differences between reproductive and worker castes. How environmental selection operates on the morphology of each caste, and whether caste-specific selection has fitness consequences is largely unknown, but is potentially crucial to understand what limits ant species' distributions. Here we aimed to examine whether ant shape and body size covaries with climate at the scale of an entire continent, and whether such relationship might be caste specific. We used 26,472 georeferenced morphometric measurements from 2,206 individual ants belonging to 32 closely related North American species in the genus Formica to assess how ant morphology relates to geographic variation in the abiotic environment. Although precipitation and seasonality explained some of the geographic variation in morphology, temperature was the best predictor. Specifically, geographic variation in body size was positively related to temperature, meaning that ants are smaller in cold than in warm environments. Moreover, the strength of the relationship between size and temperature was stronger for the reproductive castes (i.e. queens and males) than for the worker caste. The shape of workers and males also varied along these large-scale abiotic gradients. Specifically, the relative length of workers' legs, thoraxes and antennae positively related to temperature, meaning that they had shorter appendages in cold environments. In contrast, males had smaller heads, but larger thoraxes in more seasonal environments. Overall, our results suggest that geographic variation in ambient temperature influences the morphology of ants, but that the strength of this effect is caste specific. In conclusion, whereas ant ecology has traditionally focused on workers, our study shows that considering the ecology of the reproductive castes is imperative to move forward in this field.

Geographic variation in body size of five Australian marsupials supports Bergmann’s thermoregulation hypothesis

Despite a large body of research, little agreement has been reached on the ultimate driver(s) of geographic variation in body size (mass and/or length). Here we use skull length measurements (as a surrogate for body mass) from five Australian marsupial species to test the primary hypotheses of geographic variation in body size (relating to ambient temperature, productivity, and seasonality). We used a revised articulation of Bergmann’s rule, wherein evidence for thermoregulation (heat dissipation or heat conservation) is considered supportive of Bergmann’s rule. We modeled the skull lengths of four Petaurid glider species and the common brushtail possum (Trichosurus vulpecula) as a function of indices of ambient temperature, productivity, and seasonality. The skull length of Petaurus ariel, P. notatus, and the squirrel glider (P. norfolcensis), increased with increasing winter minimum temperature, while that of T. vulpecula decreased with increasing summer maximum temperature. The skull length of P. ariel decreased with indices of productivity, falsifying the productivity hypothesis. Only P. ariel met the hypothesis of seasonality, as skull length increased with increasing seasonality. Thermoregulation was the most consistently supported driver of geographic variation in body size, as we found evidence of either heat conservation or heat dissipation in four of the five species examined. We found the geographic range of the individual species and the climate space in which the species occurred was integral to understanding the species’ responses to climate variables. Future studies should use specimens that are representative of a species’ entire geographic range, encompass a variety of climatic regions, and use consistent methodologies and terminology when testing drivers of geographic variation in body size.

Investigating the role of environment in pika (Ochotona) body size patterns across taxonomic levels, space, and time

Body size is an important trait in animals because it influences a multitude of additional life history traits. The causal mechanisms underlying body size patterns across spatial, temporal, and taxonomic hierarchies are debated, and of renewed interest in this era of climate change. Here, we tested multiple hypotheses regarding body mass patterns at the intraspecific and interspecific levels. We investigated body size patterns within a climate-sensitive small mammal species, Ochotona princeps (n = 2,873 individuals), across their range with local environmental variables. We also examined body mass of populations over time to determine if body size has evolved in situ in response to environmental change. At the interspecific level we compared the mean mass of 26 pika species (genus Ochotona) to determine if environmental temperatures, food availability, habitat variability, or range area influence body size. We found correlations between temperature, vegetation, and particularly precipitation variables, with body mass within O. princeps, but no linear relationship between body size and any climate or habitat variable for Ochotona species. Body size trends in relation to climate were stronger at the intraspecific than the interspecific level. Our results suggest that body size within O. princeps likely is related to food availability, and that body size evolution is not always a viable response to temperature change. Different mechanisms may be driving body size at the interspecific and intraspecific levels and factors other than environment, such as biotic interactions, may also be influential in determining body size over space and time.

Functional adaptation rather than ecogeographical rules determine body-size metrics along a thermal cline with elevation in the Chinese pygmy dormouse (Typhlomys cinereus)

Phenotypic plasticity is crucial for how organisms respond to variation in their environment, affecting their diversity and distribution, especially in the light of rapid environmental change. Ecogeographical rules predict an association between specific adaptive morphological and physiological traits with cooler conditions due to higher latitude, elevation, or climate change. Such ecogeographical effects are often most evident in ancient species due to continuous selective adaptation occurring over long periods of time. Here, we use the suitably ancient Chinese pygmy dormouse (Typhlomys cinereus) to test whether body-size, appendage length and heart size vary in accordance with Bergmann's, Allen's and Hesse's rule, respectively. Based on a sample of 67 adult individuals (female, n = 29; male n = 38) trapped at 37 sites transcending an elevational range from 414 to 1757 m, we tested for trait concordance with Bergmann's rule (body mass, length and SMI), Allen's rule (length of tail, foot, ear, snout), and Hesse's rule (wet and dry heart mass). Effects of elevation (and thus temperature lapse rate; calculated as 0.61 °C per 100 m) on body size, appendage length and heart size, were tested by fitting Standardized Major Axis (SMA) models. We observed substantial heterogeneity in morphometric traits allowing for the detection of ecogeographical clines. However, none conformed with Bergmann's, Allen's (except ear size), or Hesse's rule. However, our results indicate some support for Geist's rule of net primary productivity. We conclude that pervasive functional life-history adaptations in this blind, arboreal, echolocating ancient species exceeded selection for morphological energy efficiency constraints, with the notable exception of reduced ear pinnae size at colder, elevated sites. This is an important consideration for predicting how species, and populations in general, may adapt to human induced rapid environmental change, contrary to expectations of warming driving selection for smaller body-size.

The fiddler crab, Minuca pugnax, follows Bergmann's rule

Bergmann's rule predicts that organisms at higher latitudes are larger than ones at lower latitudes. Here, we examine the body size pattern of the Atlantic marsh fiddler crab, Minuca pugnax (formerly Uca pugnax), from salt marshes on the east coast of the United States across 12 degrees of latitude. We found that M. pugnax followed Bergmann's rule and that, on average, crab carapace width increased by 0.5 mm per degree of latitude. Minuca pugnax body size also followed the temperature-size rule with body size inversely related to mean water temperature. Because an organism's size influences its impact on an ecosystem, and M. pugnax is an ecosystem engineer that affects marsh functioning, the larger crabs at higher latitudes may have greater per-capita impacts on salt marshes than the smaller crabs at lower latitudes.

Rabbits and Bergmann’s rule: how cold was Portugal during the last glaciation?

Osteometric data from > 450 modern wild rabbits, mostly from Portugal, Spain and France, show an inverse correlation between their size and the temperature of the environment, in accordance with Bergmann’s rule. Similar measurements made on some 1660 rabbit bones from 14 Portuguese late Pleistocene and Holocene archaeological sites indicate that rabbits became considerably smaller at the Pleistocene–Holocene boundary. Thus, rabbit size varies or varied with temperature both today and in the past. A direct temperature–size relationship was assumed, and the regression of modern rabbit bone size on temperature was then used to calibrate the temperature equivalent for the change of size of rabbit bones in the past. The result indicates a Last Glacial Maximum to present-day difference, Δt°, of 7 or 8 °C. An alternative interpretation that does not assume a direct temperature–size relationship would indicate that the environment in Portugal 15 000–30 000 years ago was similar to that in northern France today.

Influence of phylogenetic structure and climate gradients on geographical variation in the morphology of Mexican flycatcher forests assemblages (Aves: Tyrannidae)

Morphological variation is strongly related to variation in the ecological characteristics and evolutionary history of each taxon. To explore how geographical variation in morphology is related to different climatic gradients and phylogenetic structure, we analyzed the variation of morphological traits (body size, bill, and wing) of 64 species of tyrant flycatchers (Tyrannidae) distributed in Mexico. We measured these morphological traits in specimens from biological collections and related them to the climatic and topographic data of each collection locality. We performed the analyses separately at two levels: (1) the regional level and (2) the assemblage level, which was split into (assemblage I) lowland forests and (assemblage II) highland forests and other vegetation types. We also calculated the phylogenetic structure of flycatchers of each locality in order to explore the influence of climatic variables and the phylogenetic structure on the morphological variation of tyrant flycatchers, by means of linear mixed-effects models. We mapped the spatial variation of the relationship between morphological traits and environmental gradients, taking into account the phylogenetic structure. Important climatic variables explaining the morphological variation were those of temperature ranges (seasonality) and the results suggest that the phylogenetic clustering increases towards the highlands of Sierra Madre Oriental and Sierra Madre del Sur, and the lowlands of Balsas Depression. For the regional level, the spatial distribution of body size showed a pattern coincident with Bergmann's rule, with increasing in size from south to north. In the tropical lowland forests assemblage, body size tend to increase in seasonally dry forests (western Mexico) and decrease in the humid ones (eastern Mexico). In the assemblage of highland forests and other types of vegetation, morphological trait values increased northeast to southwest. Phylogenetic structure helped to explain the variation of morphology at the assemblage level but not at the regional level. The patterns of trait variation in the lowland and highland assemblages suggest that parts of morphological variation are explained both by the climatic gradients and by the lineage relatedness of communities. Overall, our results suggest that morphological variation is best explained by a varied set of variables, and that regression models representing this variation, as well as integrating phylogenetic patterns at different community levels, provide a new understanding of the mechanisms underlying the links among biodiversity, its geographical setting, and environmental change.

Morphological differences between coastal bottlenose dolphin (Tursiops aduncus) populations identified using non-invasive stereo-laser photogrammetry

Obtaining morphometric data on free-ranging marine megafauna is difficult, as traditional methods rely on post-mortem or live-capture techniques. We linked stereo-laser photogrammetry with long-term demographic data to compare length-at-age (LaA) growth curves of two well-studied populations of Indo-Pacific bottlenose dolphins (Tursiops aduncus) in south-western (SW) and Shark Bay (SB), mid-western Australia. First, we determined the relationship between total length (TL) and blowhole-to-dorsal fin (BH-DF) length from post-mortem subjects (R² = 0.99, n = 12). We then predicted TL from laser-derived BH-DF measurements of 129 and 74 known-age individuals in SW and SB, respectively. Richards growth models best described our LaA data. While birth length (103-110 cm) was similar between study regions, TL estimates at 1, 3, 12, and 25 years differed significantly (p < 0.001). Asymptotic length of adult males (SW = 246 cm, SB = 201 cm) and females (SW = 244 cm, SB = 200 cm) also differed significantly. Morphotypic variations likely reflect regional adaptations to local water temperatures, with the temperate SW having cooler waters than sub-tropical SB. We demonstrate the effectiveness of a non-invasive technique to understand ecological, demographic and life-history characteristics of long-lived marine megafauna, which are critical parameters for informing conservation and management actions.