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Gloger's rule states that homeotherms are darker at lower latitudes; however, a number of 19th‐century naturalists also suggested that animals are more brightly coloured in the tropics than in temperate regions. Using phylogenetic comparative methods, we investigated and compared both ideas across a global sample of 2726 species of mammals, examining their head, torso, legs and tail regions. Coloration data were obtained from photographs and compared with a colour chart specifically devised for mammals; ecological data were extracted from pre‐existing, open‐source databases. All analyses were conducted using phylogenetic comparative generalised linear mixed models in a Bayesian framework. We found strong support for mammals being darker in the tropics and in areas of high precipitation and evapotranspiration, little support for them being darker in warmer areas, little support for them being redder in more arid regions (a more nuanced interpretation of Gloger's rule), and virtually no support for 19th‐century naturalists' conjecture regarding coloration, contrast, or patterning being more conspicuous in the tropics. These results were replicated at both class and order levels. Our findings provide clear evidence for eumelanic coloration to be more prevalent in more humid climates (one facet of Gloger's rule), operating at a class level, but indicate that 19th‐century observations about bright coloration in the tropics do not pertain to mammals. Our results confirm the importance of Gloger's rule across mammals as a whole and add to a growing tide that darker coloration is linked to humidity at a macroecological scale. Ecogeographical rules for animal coloration include Gloger's rule, which states that homeotherms are darker at lower latitudes; however, 19th‐century naturalists observed that animals are more colourful in the tropics. We investigated these ideas across the head, torso, legs and tail regions of 2726 species of terrestrial mammals using phylogenetic comparative methods. Our findings provide strong evidence for one facet of Gloger's rule operating at a class level but indicate that 19th‐century observations do not pertain to mammals.

Ecological speciation can proceed despite genetic interchange when selection counteracts the homogenizing effects of migration. We tested predictions of this divergence-with-gene-flow model in Coeligena helianthea and C. bonapartei, 2 parapatric Andean hummingbirds with marked plumage divergence. We sequenced putatively neutral markers (mitochondrial DNA [mtDNA] and nuclear ultraconserved elements [UCEs]) to examine genetic structure and gene flow, and a candidate gene (MC1R) to assess its role underlying divergence in coloration. We also tested the prediction of Gloger's rule that darker forms occur in more humid environments, and examined morphological variation to assess adaptive mechanisms potentially promoting divergence. Genetic differentiation between species was low in both ND2 and UCEs. Coalescent estimates of migration were consistent with divergence with gene flow, but we cannot reject incomplete lineage sorting reflecting recent speciation as an explanation for patterns of genetic variation. MC1R variation was unrelated to phenotypic differences. Species did not differ in macroclimatic niches but were distinct in morphology. Although we reject adaptation to variation in macroclimatic conditions as a cause of divergence, speciation may have occurred in the face of gene flow driven by other ecological pressures or by sexual selection. Marked phenotypic divergence with no neutral genetic differentiation is remarkable for Neotropical birds, and makes C. helianthea and C. bonapartei an appropriate system in which to search for the genetic basis of species differences employing genomics.

Phenotypes reflect the adaptations of organisms to their environments, with common rules defining how coloration and body size should vary based on climate and latitude. Hong Kong (HK) cattle present an opportunity to study these adaptations in one of the very few cattle populations not directly controlled by humans. These cattle are free-ranging in a subtropical climate, characterized by high humidity and temperatures during the wet season, and scarce precipitation during the dry season. We studied seasonal coat colour changes in HK feral cattle, and sexual dimorphism in body size and horn length. We provide the first evidence of seasonal changes in coat colour in cattle, with paler coats being more common in the wet season, while darker coats prevailed in the dry season. These seasonal changes were influenced by temperature, wind speed, solar radiation and body condition. We found that males were larger and had longer horns than females. Our results show a male-biased sex dimorphism in the HK feral cattle. Additionally, our findings suggest that thermoregulation costs drive coloration in these cattle. The phenotypic plasticity we demonstrate in these subtropical feral cattle improves our knowledge of the adaptations of ungulates to their habitat.

Gradients in cuticle lightness of ectotherms have been demonstrated across latitudes and elevations. Three key hypotheses have been used to explain these macroecological patterns: the thermal melanism hypothesis (TMH), the melanism‐desiccation hypothesis (MDH) and the photo‐protection hypothesis (PPH). Yet the broad abiotic measures, such as temperature, humidity and UV‐B radiation, typically used to detect these ecogeographical patterns, are a poor indication of the microenvironment experienced by small, cursorial ectotherms like ants. We tested whether these macroecological hypotheses explaining cuticle lightness held at habitat and microclimatic level by using a vertical gradient within a tropical rainforest. We sampled 222 ant species in lowland, tropical rainforest across four vertical strata: subterranean, ground, understory and canopy. We recorded cuticle lightness, abundance and estimated body size for each species and calculated an assemblage‐weighted mean for cuticle lightness and body size for each vertical stratum. Abiotic variables (air temperature, vapour pressure deficit and UV‐B radiation) were recorded for each vertical stratum. We found that cuticle lightness of ant assemblages was vertically stratified: ant assemblages in the canopy and understory were twice as dark as assemblages in ground and subterranean strata. Cuticle lightness was not correlated with body size, and there was no support for the TMH. Rather, we attribute this cline in cuticle lightness to a combination of the MDH and the PPH. Our findings indicate that broad macroecological patterns can be detected at much smaller spatial scales and that microclimatic gradients can shape trait variation, specifically the cuticle lightness of ants. These results suggest that any changes to microclimate that occur due to land‐use change or climate warming could drive selection of ants based on cuticle colour, altering assemblage structure and potentially ecosystem functioning.

Primates, the most colorful mammalian radiation, have previously served as an interesting model to test the functions and evolutionary drivers of variation in eye color. We assess the contribution of photo-regulatory and communicative functions to the external eye appearance of nine macaque species representing all the branches of their radiation. Macaques’ well described social structure and wide geographical distribution make them interesting to explore. We find that (1) the posterior option of the anterior eyeball is more pigmented closer to the equator, suggesting photoprotective functions. We also find that (2) the temporal side of the eyeball is more heavily pigmented than the nasal side. This suggests that eyeball pigmentation in macaques is distributed to reduce damage to the corneal limbus. The inclusion of a translocated population of M. fuscata in our analyses also suggests that external eye appearance may change quickly, perhaps owing to phenotypic plasticity. We find no evidence that communicative functions drive variation in external eye appearance in macaques. These results suggest that the amount of light in a species’ environment drives variation in eye coloration across macaque species. Furthermore, the geographical distribution of macaques hints at important factors that have yet to be accounted for, such as the reflectivity of the terrain a given species inhabits.

Integrating color polymorphism with intra‐species morphological traits offers substantial opportunities to study the eco‐evolutionary mechanisms underlying local population responses to heterogeneous and dynamic environments. In this study, we examined the head phenotypic diversity and intraspecific morphological traits of Camponotus japonicus (Mayr, 1866) workers across 22 sites in mainland China, ranging from 24°47′ N to 47°51′ N in latitude and 88°07′ E to 126°43′ E in longitude, covering an altitudinal range up to 1243 m. We classified the head phenotypes of these workers into four types and investigated environmental variables explaining the levels of polymorphism, quantified by the Shannon diversity index and head phenotype ratios. Phylogenetic analysis based on the mitochondrial COI gene classified all samples into four clades. By controlling the genetic distance in our analysis, we revealed the correlations between temperature, precipitation, and the prevalence and distribution of this color polymorphism across the sampled populations. Contrary to the thermal melanism hypothesis, our findings reveal that the prevalence of maroon‐headed workers (lighter coloration) increases with latitude, with the highest proportion of these individuals found in high‐latitude populations (colder, drier regions). Moreover, temperature and precipitation also show significant correlations with the morphological traits of workers, implying that specific traits may be environmentally influenced, potentially contributing to colony‐level survival in fluctuating environments. By emphasizing the often‐overlooked intraspecific variations, our research contributes to understanding how head color polymorphism and intraspecific morphological traits in ants are associated with local population responses to environmental changes. This study explores head color polymorphism and morphological traits in Camponotus japonicus ants across 22 sites in China, revealing that maroon‐headed workers (lighter color) are more common in colder, high‐latitude regions, contrary to the thermal melanism hypothesis. Temperature and precipitation significantly correlate with both color patterns and morphological traits, suggesting environmental influences on colony survival.

Aim: Animal coloration often shows high degrees of evolutionary lability, producing variation among species that is easily apparent. This variation may produce consistent geographical patterns as species converge on adaptive phenotypes in similar environments. Some such geographical patterns in colour variation have been recently predicted as a response to the light environment in different habitats. Others like Gloger's rule — the negative relationship between brightness and humidity -have long been observed but still demand explanation. Finally, the conventional wisdom that tropical birds are more colourful remains largely untested. Location: Australia, New Guinea. Methods: Here, we compared plumage coloration across two families of Australian birds(Meliphagidae, n = 97 species; Acanthizidae, n = 40 species) in a combined spatial and phylogenetic framework. We assessed the extent to which environmental variables extracted from species ranges explain variation in colour traits, while correcting for the autocorrelation inherent in spatially structured data using extensive simulations. Results: We found several strong effects of environment on plumage coloration. Inland species with ranges marked by high aridity and temperature seasonality showed greater colour span among acanthizids, and greater saturation among meliphagids. Gloger's rule was supported in both clades, but more strongly for dorsal plumage. The most consistent correlate in this relationship was vegetation: birds in regions with more vegetation had markedly darker plumage. Ornament hue showed no significant associations with vegetation or climate. Main conclusions: Birds living close to the equator were not more colourful, but species inhabiting arid regions were. Species may respond to the shorter and less predictable breeding seasons of arid environments by evolving increased ornamentation. The consistent relationship we observed between vegetation and dorsal brightness supports a primary role for countershading and background matching in Gloger's rule.

Aim We explore geographic variation in body size within the wingless grasshopper, Phaulacridium vittatum, along a latitudinal gradient, and ask whether melanism can help explain the existence of clinal variation. We test the hypotheses that both male and female grasshoppers will be larger and lighter in colour at lower latitudes, and that reflectance and size will be positively correlated, as predicted by biophysical theory. We then test the hypothesis that variability in size and reflectance is thermally driven, by assessing correlations with temperature and other climatic variables. Location Sixty‐one populations were sampled along the east coast of Australia between latitudes 27.63° S and 43.10° S, at elevations ranging from 10 to 2000 m a.s.l. Methods Average reflectance was used as a measure of melanism and femur length as an index of body size for 198 adult grasshoppers. Climate variables were generated by BIOCLIM for each collection locality. Hierarchical partitioning was used to identify those variables with the most independent influence on grasshopper size and reflectance. Results Overall, there was no simple relationship between size and latitude in P. vittatum. Female body size decreased significantly with latitude, while male body size was largest at intermediate latitudes. Rainfall was the most important climatic variable associated with body size of both males and females. Female body size was also associated with radiation seasonality and male body size with reflectance. The reflectance of females was not correlated with latitude or body size, while male reflectance was significantly higher at intermediate latitudes and positively correlated with body size. Analyses of climate variables showed no significant association with male reflectance, while female reflectance was significantly related to the mean temperature of the driest quarter. Main conclusions Geographic variation in the body size of the wingless grasshopper is best explained in terms of rainfall and radiation seasonality, rather than temperature. However, melanism is also a significant influence on body size in male grasshoppers, suggesting that thermal fitness does play a role in determining adaptive responses to local conditions in this sex.

Aim Animal coloration is expected to differ between populations in different habitats according to Gloger's rule, with darker animals found in more humid, vegetated or warmer environments. Yet despite considerable support across the globe, the mechanisms behind this biogeographical rule are currently still unclear. Exploiting a ring species with plumage coloration from crimson to pale yellow, we test Gloger's rule and the mechanisms behind phenotypic divergence. Location South‐eastern Australia. Major taxa studied Crimson rosellas (Platycercus elegans). Methods We combined three modelling approaches (spatial regression; random decision forest species distribution and conditional inference tree) to test the association between 10 environmental variables (based on long‐term climate data and remotely sensed reflectance of the land) and plumage coloration across the distribution of P. elegans. We also took in‐situ measurements of background coloration of dominant vegetation to examine the relationship between (a) background coloration measured locally and remotely, (b) P. elegans coloration and (c) known differences in visual sensitivity of the subspecies using species‐specific visual models. Results On both a continental and a local scale, the distribution of yellow‐red plumage coloration was strongly predicted by average rainfall, summer temperature and the Earth's reflectance between 620–670 nm. Remotely sensed radiance measures correlated strongly and positively with reflectance of the leaves of the dominant tree species at sites across the P. elegans distribution. Visual modelling indicated that differences in background colour could affect signalling efficacy in dim‐light conditions. Main conclusions Our study shows that the highly variable plumage coloration conforms to Gloger's rule, and indicates that background coloration of the vegetation and thermoregulation are likely to be important mechanisms. Our results also show that Gloger's rule can explain variation in pigmentary systems other than melanin, and highlight that selection from environmental variation could be an important force behind the geographic diversity found in ring species.

Background Pigmentation has a long history of investigation in evolutionary biology. In Drosophila melanogaster , latitudinal and altitudinal clines have been found but their underlying causes remain unclear. Moreover, most studies were conducted on cosmopolitan populations which have a relatively low level of genetic structure and diversity compared to sub-Saharan African populations. We investigated: 1) the correlation between pigmentation traits within and between the thorax and the fourth abdominal segment, and 2) their associations with different geographical and ecological variables, using 710 lines belonging to 30 sub-Saharan and cosmopolitan populations. Results Pigmentation clines substantially differed between sub-Saharan and cosmopolitan populations. While positive correlations with latitude have previously been described in Europe, India and Australia, in agreement with Bogert's rule or the thermal melanism hypothesis, we found a significant negative correlation in Africa. This correlation persisted even after correction for altitude, which in its turn showed a positive correlation with pigmentation independently from latitude. More importantly, we found that thoracic pigmentation reaches its maximal values in this species in high-altitude populations of Ethiopia (1,600-3,100 m). Ethiopian flies have a diffuse wide thoracic trident making the mesonotum and the head almost black, a phenotype that is absent from all other sub-Saharan or cosmopolitan populations including high-altitude flies from Peru (~3,400 m). Ecological analyses indicated that the variable most predictive of pigmentation in Africa, especially for the thorax, was ultra-violet (UV) intensity, consistent with the so-called Gloger's rule invoking a role of melanin in UV protection. Conclusion Our data suggest that different environmental factors may shape clinal variation in tropical and temperate regions, and may lead to the evolution of different degrees of melanism in different high altitude populations in the tropics.