Flame-forged divergence? Ancient human fires and the evolution of diurnal and nocturnal lineages in moorish geckos

Using a multidisciplinary approach, we investigated whether human-controlled fire has historically influenced temporal niche partitioning between dark-diurnal and pale-nocturnal lineages of the Moorish gecko (Tarentola mauritanica). The pale-nocturnal variant exhibited lower skin melanin levels, smaller and fewer melanosomes, and lower plasma α-Melanocyte Stimulating Hormone levels than its dark-diurnal counterpart. Mitochondrial genome analyses indicated that the common ancestor of these gecko lineages diverged approximately 6,600 years ago, coinciding with the transition of modern humans from nomadic hunter-gatherers to settled agricultural societies. Species distribution models suggested coexistence between humans and geckos during the emergence of these lineages. Additionally, we demonstrated that fire attracts phototactic arthropods, concentrating prey resources. These findings imply that human-controlled fire may have created a novel foraging niche for pale-nocturnal geckos, likely driving the divergence of the two variants.

Seasonal and altitudinal variation in dorsal skin reflectance and thermic rates in a high-altitude montane lizard

Temperature is one of the most important factors in the life histories of ectotherms, as body temperature has an undeniable effect on growth, activity, and reproduction. Lizards have a wide variety of strategies to acquire and maintain body temperature in an optimal range. The "Thermal Melanism Hypothesis" proposes that individuals with lower skin reflectance can heat up faster as a result of absorbing more solar radiation compared to lighter conspecifics. Therefore, having a darker coloration might be advantageous in cold habitats. Dorsal skin reflectance has been found to change rapidly with body temperature in several lizard species, and it can also vary over longer, seasonal time scales. These variations may be important in thermoregulation, especially in lizards that inhabit areas with a large temperature variation during the year. Here, we study how dorsal reflectance fluctuates with body temperature and varies among seasons. We compared dorsal skin reflectance at three body temperature treatments, and measured thermal rates (i.e., heat and cool rate, thermic lapse, and net heat gain) by elevation (2500-4100 m) and seasons (spring, summer, and autumn) in the mesquite lizard, Sceloporus grammicus. Our results show that lizards were darker at high elevations and during the months with the lowest environmental temperatures. The rate of obtaining and retaining heat also varied during the year and was highest during the reproductive season. Our results indicate that the variation of dorsal skin reflectance and thermal rates follows a complex pattern in lizard populations and is affected by both elevation and season.

How seasonality influences the thermal biology of lizards with different thermoregulatory strategies: a meta-analysis

Ectotherms that maintain thermal balance in the face of varying climates should be able to colonise a wide range of habitats. In lizards, thermoregulation usually appears as a variety of behaviours that buffer external influences over physiology. Basking species rely on solar radiation to raise body temperatures and usually show high thermoregulatory precision. By contrast, species that do not bask are often constrained by climatic conditions in their habitats, thus having lower thermoregulatory precision. While much focus has been given to the effects of mean habitat temperatures, relatively less is known about how seasonality affects the thermal biology of lizards on a macroecological scale. Considering the current climate crisis, assessing how lizards cope with temporal variations in environmental temperature is essential to understand better how these organisms will fare under climate change. Activity body temperatures (Tb ) represent the internal temperature of an animal measured in nature during its active period (i.e. realised thermal niche), and preferred body temperatures (Tpref ) are those selected by an animal in a laboratory thermal gradient that lacks thermoregulatory costs (i.e. fundamental thermal niche). Both traits form the bulk of thermal ecology research and are often studied in the context of seasonality. In this study, we used a meta-analysis to test how environmental temperature seasonality influences the seasonal variation in the Tb and Tpref of lizards that differ in thermoregulatory strategy (basking versus non-basking). Based on 333 effect sizes from 137 species, we found that Tb varied over a greater magnitude than Tpref across seasons. Variations in Tb were not influenced by environmental temperature seasonality; however, body size and thermoregulatory strategy mediated Tb responses. Specifically, larger species were subjected to greater seasonal variations in Tb , and basking species endured greater seasonal variations in Tb compared to non-basking species. On the other hand, the seasonal variation in Tpref increased with environmental temperature seasonality regardless of body size. Thermoregulatory strategy also influenced Tpref , suggesting that behaviour has an important role in mediating Tpref responses to seasonal variations in the thermal landscape. After controlling for phylogenetic effects, we showed that Tb and Tpref varied significantly across lizard families. Taken together, our results support the notion that the relationship between thermal biology responses and climatic parameters can be taxon and trait dependent. Our results also showcase the importance of considering ecological and behavioural aspects in macroecological studies. We further highlight current systematic, geographical, and knowledge gaps in thermal ecology research. Our work should benefit those who aim to understand more fully how seasonality shapes thermal biology in lizards, ultimately contributing to the goal of elucidating the evolution of temperature-sensitive traits in ectotherms.

Environmental factors influence cross-talk between a heat shock protein and an oxidative stress protein modification in the lizard Gallotia galloti

Better understanding how organisms respond to their abiotic environment, especially at the biochemical level, is critical in predicting population trajectories under climate change. In this study, we measured constitutive stress biomarkers and protein post-translational modifications associated with oxidative stress in Gallotia galloti, an insular lizard species inhabiting highly heterogeneous environments on Tenerife. Tenerife is a small volcanic island in a relatively isolated archipelago off the West coast of Africa. We found that expression of GRP94, a molecular chaperone protein, and levels of protein carbonylation, a marker of cellular stress, change across different environments, depending on solar radiation-related variables and topology. Here, we report in a wild animal population, cross-talk between the baseline levels of the heat shock protein-like GRP94 and oxidative damage (protein carbonylation), which are influenced by a range of available temperatures, quantified through modelled operative temperature. This suggests a dynamic trade-off between cellular homeostasis and oxidative damage in lizards adapted to this thermally and topologically heterogeneous environment.

Does thermal biology differ between two colour pattern morphs of a widespread Australian lizard?

Alternative phenotypes allow individuals to pursue different adaptive pathways in response to the same selective challenge. Colour polymorphic species with geographically varying morph frequencies may reflect multiple adaptations to spatial variables such as temperature and climate. We examined whether thermal biology differed between colour morphs of an Australian lizard, the delicate skink, Lampropholis delicata. The delicate skink has two colour pattern morphs, with frequencies varying across latitude and sex: plain (darker, more common at temperate latitudes, more common in males) or striped (lighter, more common at lower latitudes, more common in females). We tested heating and cooling rate, sprint speed, thermal preference, field body temperature and metabolic rate in both morphs and sexes to determine any link between colour and morph frequency distribution. Plain individuals heated more quickly, but other thermal traits showed little variation among morphs. Lampropholis delicata colour influences rates of heat exchange, but the relationship does not appear to be adaptive, suggesting that behavioural thermoregulation homogenises body temperature in the field. While we find no substantial evidence of thermal differences between the two colour morphs, morph-specific behaviour may buffer against differences in heat exchange. Latitudinal variation in species colour may be driven by selection pressures other than temperature.

Incubation temperature alters stripe formation and head colouration in American alligator hatchlings and is unaffected by estradiol-induced sex reversal

Considerations of the impact climate change has on reptiles are typically focused on habitat change or loss, range shifts and skewed sex ratios in species with temperature-dependent sex determination. Here, we show that incubation temperature alters stripe number and head colouration of hatchling American alligators (Alligator mississippiensis). Animals incubated at higher temperatures (33.5°C) had, on average, one more stripe than those at lower temperatures (29.5°C), and also had significantly lighter heads. These patterns were not affected by estradiol-induced sex reversal, suggesting independence from hatchling sex. Therefore, increases in nest temperatures as a result of climate change have the potential to alter pigmentation patterning, which may have implications for offspring fitness.

TRPM8 thermosensation in poikilotherms mediates both skin colour and locomotor performance responses to cold temperature

Thermoregulation is a homeostatic process to maintain an organism's internal temperature within a physiological range compatible with life. In poikilotherms, body temperature fluctuates with that of the environment, with both physiological and behavioral responses employed to modify body temperature. Changing skin colour/reflectance and locomotor activity are both well-recognized temperature regulatory mechanisms, but little is known of the participating thermosensor/s. We find that Xenopus laevis tadpoles put in the cold exhibit a temperature-dependent, systemic, and rapid melanosome aggregation in melanophores, which lightens the skin. Cooling also induces a reduction in the locomotor performance. To identify the cold-sensor, we focus on transient receptor potential (trp) channel genes from a Trpm family. mRNAs for several Trpms are present in Xenopus tails, and Trpm8 protein is present in skin melanophores. Temperature-induced melanosome aggregation is mimicked by the Trpm8 agonist menthol (WS12) and blocked by a Trpm8 antagonist. The degree of skin lightening induced by cooling is correlated with locomotor performance, and both responses are rapidly regulated in a dose-dependent and correlated manner by the WS12 Trpm8 agonist. We propose that TRPM8 serves as a cool thermosensor in poikilotherms that helps coordinate skin lightening and behavioural locomotor performance as adaptive thermoregulatory responses to cold.

Colour scales with climate in North American ratsnakes: a test of the thermal melanism hypothesis using community science images

Animal colour is a complex trait shaped by multiple selection pressures that can vary across geography. The thermal melanism hypothesis predicts that darker coloration is beneficial to animals in colder regions because it allows for more rapid solar absorption. Here, we use community science images of three closely related species of North American ratsnakes (genus Pantherophis) to examine if climate predicts colour variation across range-wide scales. We predicted that darker individuals are found in colder regions and higher elevations, in accordance with the thermal melanism hypothesis. Using an unprecedented dataset of over 8000 images, we found strong support for temperature as a key predictor of darker colour, supporting thermal melanism. We also found that elevation and precipitation are predictive of colour, but the direction and magnitude of these effects were more variable across species. Our study is the first to quantify colour variation in Pantherophis ratsnakes, highlighting the value of community science images for studying range-wide colour variation.

Size-related changes and chemical basis of melanin-based body coloration in the amphisbaenian Trogonophis wiegmanni

Melanin is a fundamental pigment in animal coloration as it is involved in many different adaptive functions such as signaling or thermoregulation. Two forms of melanin are known to produce different colors (eumelanin: black; pheomelanin: yellow or brown). Here, we explored whether there were intersexual differences and/or size-related changes in melanization of the amphisbaenian Trogonophis wiegmanni, a fossorial species with a characteristic black and yellow color pattern of scales. We found a clear effect of body length, but not of sex, on the levels of melanization, which was also dependent on the body region; the proportion of melanin-dependent blackish coloration increased with body length in the dorsum, but decreased with body length in the ventral belly area. We also studied the chemical basis of this coloration using Raman spectroscopy and found that eumelanin was present in both black and yellow scales, but pheomelanin was not found in yellow scales, suggesting that this yellow coloration is caused by the reduction of eumelanin or dispersion of melanosomes and/or perhaps by other pigments.

Genetic and environmental drivers of colour and pattern in the Australian jacky dragon (Amphibolurus muricatus)

The underlying drivers of variation in the colouration (colour and pattern) of animals can be genetic, non‐genetic, or more likely, a combination of both. Understanding the role of heritable genetic elements, as well as non‐genetic factors such as age, habitat or temperature, in shaping colouration can provide insight into the evolution and function of these traits, as well as the speed of response to changing environments. This project examined the genetic and non‐genetic drivers of continuous variation in colouration in a lizard, the jacky dragon (Amphibolurus muricatus). We leveraged a large captive experiment that manipulated parental and offspring thermal environment to simultaneously estimate the genetic and non‐genetic drivers of variation in colouration. We found that the overall brightness, the elongation of the longitudinal stripes on the dorsum and the contrast between light and dark patches of the pattern were all heritable. Colouration varied according to the age of the hatchling; however, the thermal environment of neither the parents nor offspring contributed significantly to colouration. It appears that developmental plasticity and maternal effects associated with temperature are not important drivers of variation in our measures of colouration.

Thermobiological effects of temperature-induced color variations in Aglais urticae (Lepidoptera, Nymphalidae)

Coloration of animals is important for camouflage, for social behavior, or for physiological fitness. This study investigates the color variation in adults of Aglais urticae obtained on subjecting some pre-imaginal stages to different temperature conditions and their thermobiological consequences. To investigate the evolutionary-ecological interactions of temperature and pigmentation in butterflies, caterpillars, and pupae of the small tortoiseshell, Aglais urticae (Lepidoptera, Nymphalidae), larvae from Central Europe and Scandinavia were reared at temperatures between 7 and 34°C in the laboratory or in the field. After emergence, the intensity of pigmentation of the imagines and their increase in body temperature under defined full-spectrum light irradiation were quantified by image analysis and thermal imaging. At constant conditions, ambient rearing temperature and pigmentation intensity of imagines were negatively and linearly correlated in Central European butterflies, regardless of whether the pupal stage alone or, additionally, the last period of the larval stage was exposed to these conditions: low temperatures induced darker coloration and high temperatures led to lighter individuals. A thermal pulse of a few days alone at the beginning of pupal dormancy led to a similar, albeit weakened, effect. Caterpillars of the Scandinavian subspecies A. urticae polaris, whose pupal dormancy took place under Central European field conditions, developed into strongly pigmented imagines. The thermobiological relevance of more intense pigmentation was shown by significantly higher absorption of light, and thus stronger increased body temperature after 5 min of defined illumination, but this difference ceased after 15 min. Our results show that phenotypic plasticity in wing coloration is adaptive since temperature-induced developmental changes provide thermobiological benefit in adult butterflies. We propose that, in subpolar latitudes, darker coloration likely has a selection advantage favoring individuals with reaction norms gradually shifted to stronger pigmented phenotypes, possibly leading to the establishment of a pigmentation cline.

Fabrication of a tunable photothermal actuator via in situ oxidative polymerization of polydopamine nanoparticles in hydrogel bilayers

Photothermally triggered actuation enables the remote and local control of a material. The complex actuation can be achieved by controlling the photothermal efficiency of the material, which is crucial for the development of soft actuators. In this study, the photothermal efficiency of a hydrogel bilayer actuator consisting of a passive agarose/alginate double-network hydrogel layer and an active poly(N-isopropylacrylamide) (PNIPAm) layer was controlled via in situ oxidative polymerization of polydopamine nanoparticles (PDA NPs). Highly concentrated PDA NPs were successfully incorporated into the hydrogel bilayer without interrupting or weakening the polymer network during polymerization. The photothermal efficiency of the actuator was controlled using the number of polymerization cycles. Upon light irradiation, the heat generated by the photothermal effect of PDA NPs caused the shrinkage of the PNIPAm layer, resulting in the shape-morphing of the bilayer. The broad light absorption properties of PDA NPs allowed the bilayer to actuate under sunlight or visible light. Finally, we demonstrated controlled photothermal actuation using a pinwheel-shaped actuator consisting of four panels with different photothermal efficiencies.

An integrative analysis of the short-term effects of tail autotomy on thermoregulation and dehydration rates in wall lizards

Maintaining body temperature is essential for the optimal performance of physiological functions. Ectotherms depend on external heat sources to thermoregulate. However, thermoregulation may be constrained by body condition and hydration state. Autotomy (i.e., the voluntary shed of a body part) evolved in various animal lineages and allowed surviving certain events (such as predator attacks), but it may affect body condition and volume/surface ratios, increase dehydration and constrain thermoregulation. In the framework of a general analysis of the evolution of autotomy, here we assessed the effects of tail loss on the thermal preferences and evaporative water loss rates (EWL) in the lizard Podarcis bocagei, integrating the thermal and hydric factors. We did not observe shifts in the thermal preferences of experimentally autotomized lizards when compared to the controls, which contradicted the hypothesis that they would raise preferred temperature to increase metabolic rates and accelerate regeneration. Evaporative water loss rates were also similar for tailed and tailless individuals, suggesting negligible increase of water loss through the injury and no specific ecophysiological responses after autotomy. Therefore, the changes observed in autotomized lizards in the field are to be considered primarily behavioural, rather than physiological, and thermoregulation could be secondarily affected by behavioural compensations for an increased predation risk after autotomy. Functional studies are necessary to understand how lizards' interaction with the environment is altered after autotomy, and further studies including different dehydration levels would be useful to fully understand the effect of water shortage on lizards' performance after caudal autotomy.

Intra-specific variation of thermal performance, skin reflectance and body size partially co-vary with climate in a lizard

Thermal adaptation theory posits that variation of thermal traits such as those affecting thermal budgets and the performance of ectotherms should be associated with climate gradients. Under a simple scenario, thermal traits should also co-vary to shape optimal thermal phenotypes under a particular climate. However, geographical variation and covariation of thermal traits can result from other sources of selection and a wide range of other mechanisms. Here, we explore variation and covariation of skin reflectance (melanization), body size and thermal performance traits among three populations of the lizard Cordylus cordylus, a species endemic to South Africa. We also examine relationships between skin reflectance and substrate reflectance, body size and crevice size to test alternative hypotheses. We found partial support for predictions of thermal adaptation to climate regimes for body size, melanization and chill-coma recovery time. Darker lizards also performed optimally at higher temperatures than lighter coloured lizards but there was limited individual covariation between morphological and performance traits. Despite partial support for thermal adaptation, the complex interactions between sex and body size and between substrate reflectance and size underlying skin reflectance emphasized the importance of testing multiple hypotheses when exploring drivers of thermal trait variation within species.

Relationships between soil pollution by heavy metals and melanin-dependent coloration of a fossorial amphisbaenian reptile

Melanin is the basis of coloration in many animals, and although it is often used in communication, thermoregulation, or camouflage, melanin has many other physiological functions. For example, in polluted habitats, melanin can have a detoxifying function. Melanic coloration would help to sequester in the skin the heavy metal contaminants from inside the body, which will be expelled to the exterior when the skin is sloughed. Moreover, animals should have evolved more melanic colorations in more polluted habitats ("industrial melanism" hypothesis). We examined whether the fossorial amphisbaenian reptile, Trogonophis wiegmanni, is able to eliminate heavy metals, derived from soil pollution by seagull depositions, through sloughing its skin. Our results suggest a covariation between levels of soil pollution by heavy metals and the concentration of heavy metals in the sloughed skins of amphisbaenians. This suggests that amphisbaenians may expel heavy metals from their bodies when they slough the skins. We also tested whether amphisbaenians inhabiting soils with higher levels of heavy metal pollution had darker (melanin-dependent) body colorations. However, contrary to predictions from the "industrial melanization" hypothesis, we found a negative relationship between soil pollution and proportions of melanic coloration. This contradictory result could, however, be explained because heavy metals have endocrine disruption effects that increase physiological stress, and higher stress levels could result in decreased melanogenesis. We suggest that although amphisbaenians might have some detoxifying mechanism linked to melanin in the skin, this process might be negatively affected by stress and result ineffective under conditions of high soil pollution.

Living on the edge: Lower thermal quality but greater survival probability at a high altitude mountain for the mesquite lizard (Sceloporus grammicus)

A 20-month recapture analysis of 1001 individually marked mesquite lizards (Sceloporus grammicus) suggests that variation in thermal quality across three altitudes influences survival probability. Each additional unit of deviation from the temperature selected by these lizards in previous laboratory experiments (i.e. decreased thermal quality) meant an increase of roughly 1.01% in survival probability. Survival probabilities ranged from 0.80 to 0.90 at the lowest elevation site (2600 m), from 0.76 to 0.87 at the middle elevation site (3100 m) and from 0.90 to 0.94 at the highest elevation site (4150 m). These results suggest that in poor thermal quality environments mesquite lizards may employ thermoregulatory strategies (behavioral, physiological and/or morphological) to decrease their metabolic expenditure and their exposure to predators, maximizing survival. These findings highlight the relevance of thermal quality of the habitat in determining survival probability of ectotherms.

To be small and dark is advantageous for gaining heat in mezquite lizards, Sceloporus grammicus (Squamata: Phrynosomatidae)

Body temperature is important in determining individual performance in ectotherms such as lizards. Environmental temperature decreases with increasing altitude, but nevertheless many lizards inhabit high-altitude environments. The ‘thermal melanism hypothesis’ proposes that a dark dorsal coloration enables darker individuals to heat up faster because they absorb more solar radiation and thus being darker may be advantageous in cold habitats. The aim of the present study is to evaluate how heating rate, cooling rate and net heat gain vary with body size and dorsal skin coloration in Sceloporus grammicus lizards along an altitudinal gradient. We measured these traits multiple times in the same individuals with a radiation heat source and spectrophotometry under laboratory conditions. Our results showed that S. grammicus lizards are smaller and darker at high elevations than at low elevations. In addition, the smallest and darkest lizards showed the greatest heating rate and net heat gain. Therefore, in S. grammicus, we suggest that small body size and dark dorsal coloration provide thermoregulatory benefits in high-altitude environments. Hence, this study supports the thermal melanism hypothesis in a lizard species under varied thermal environments.

Thermal melanism explains macroevolutionary variation of dorsal pigmentation in Eurasian vipers

Colouration may endorse thermoregulatory and antipredatory functions in snakes. The thermal melanism hypothesis predicts that dark-coloured individuals are ecologically favoured in cool climates. However, the loss of aposematic and cryptic colourations may imply high predation for melanistic snakes. Here, we used the monophyletic group of Eurasian vipers (subfamily Viperinae) to test whether an increase in the extent of dark area inside the characteristic zigzag dorsal pattern is associated to colder environments. We measured two colouration traits in zigzag-patterned individuals (number of dorsal marks and weighted pigmentation index) and used a phylogenetic comparative approach to explore macroevolutionary patterns of dorsal pigmentation and test whether its extent is associated to ecogeographic characteristics of lineages’ ranges. Phylogenetically-naïve and phylogenetically-informed analyses yielded a significant association between the degree of pigmentation of the zigzag pattern and environmental variables such as solar radiation, elevation and latitude. The degree of pigmentation of the zigzag pattern is highlighted as an adaptive trait that matches range attributes mirroring cold environments irrespective of the phylogeny. These results constitute the first large-scale evidence supporting the thermal melanism hypothesis in snakes, opening new avenues of inquiry for the mechanisms that shape the evolution of colour phenotypes.

Plasticity of haemoglobin concentration and thermoregulation in a mountain lizard

The plastic capability of species to cope with the new conditions created by climate change is poorly understood. This is particularly relevant for organisms restricted to high elevations because they are adapted to cold temperatures and low oxygen availability. Therefore, evaluating trait plasticity of mountain specialists is fundamental to understand their vulnerability to environmental change. We transplanted mountain lizards, Iberolacerta cyreni, 800 m downhill to evaluate the plastic response in body condition, thermoregulation traits, haemoglobin level, and haemoparasite load. Initial measurements of body mass, total haemoglobin concentration ([Hb]), hematic parasite intensities, dorsal luminance, and thermoregulatory behaviour were resampled after two and four weeks of acclimation. We also tested whether an anti-parasitic drug reduced haemoparasite intensity. After only two weeks of acclimation to a lower elevation, lizards decreased 42% in [Hb], had 17% less parasite intensities, increased body condition by 25%, and raised by ~3% their mean preferred temperatures and their voluntary thermal maximum. The anti-parasitic treatment had no significant effect on the intensity of hematic parasites, but our results suggest that negative effects of haemoparasites on [Hb] are relaxed at lower elevation. The rapid plastic changes observed in thermal preferences, body condition, [Hb], and parasite intensity of I. cyreni demonstrate a potential plastic response of a mountain specialist. This may be adaptive under the climatic extremes typical of mountain habitats. However, there is uncertainty in whether the observed plasticity can also help overcome long term environmental changes.

How and when melanic coloration is an advantage for lizards: the case of three closely-related species of Liolaemus

Body temperature affects various aspects of ectotherm biology. Reptiles, as ectotherms, gain and control their temperature mainly through behavioural adjustments, although some body traits may also be advantageous. According to the thermal melanism hypothesis (TMH) dark colour may be thermally advantageous in cold environments. Additionally, differences in thermoregulatory capacity may also affect performance. We analysed the role of melanism in the thermoregulation and sprint speed performance of three species of Liolaemus lizards from Argentinean Patagonia. Liolaemus shitan, L. elongatus and L. gununakuna are phylogenetically close, with similar body sizes and life history traits, but differ in their melanic colouration, L. shitan being the darkest and L. gununakuna the lightest species. We estimated sprint speed performance curves and heating rates, and recorded final body temperature and sprint speed achieved after a fixed heating time, from two different initial body temperatures, and with and without movement restriction. Performance curves were similar for all the species, but for L. gununakuna the curve was more flattened. Darker species showed faster heating rates, ran faster after fixed heating trials at the lowest temperature, and reached higher body temperatures than L. gununakuna, but this was compensated for by behavioural adjustments of the lighter lizards. Similarity of sprint speed performance may be due to the conservative nature of this character in these species, while variation in heating ability, particularly when starting from low temperatures, may reflect plasticity in this trait. The latter provides support for the TMH in these lizards, as melanism helps them increase their body temperature. This may be especially advantageous at the beginning of the day or on cloudy days, when temperatures are lower.

Lizard colour plasticity tracks background seasonal changes

Environmental heterogeneity on a spatial and temporal scale fosters an organism's capacity to plastically alter coloration. Predation risk might favour the evolution of phenotypic plasticity in colour patterns, as individuals who change colour throughout the year may be able to improve their fitness. Here we explored the change in dorsal pigmentation of the Italian wall lizard (Podarcis siculus campestris) at three time points (March, July, October) during a period of activity in a Mediterranean natural area in southern Italy. Following a preliminary investigation conducted in 2018, during 2019 we captured 135 lizards and took a picture of their ventral scales to check for possible recapture over the sessions. Lizard dorsal pictures were collected in the field with the support of a reference chart to quantitatively estimate chromatic variables (hue, saturation and value). At the same time, pictures of the environmental background were collected. Our findings suggest that lizards are capable of altering dorsal coloration during seasonal change. They vary from green at the onset of spring, to brownish in the middle of summer and to a greyish colour in October. This modification closely followed environmental background colour variation and enhanced lizard crypsis during each season.

Ecological variability is associated with functional trait diversity in the western fence lizard (Sceloporus occidentalis)

A major goal of evolutionary ecology is to understand the ways in which ecological variability has structured morphological diversity. The aim of this study was to examine intraspecific phenotypic variation in the western fence lizard (Sceloporus occidentalis) for functional traits previously shown to be linked to variation across latitude and climate at a genus-wide level. We found that body size in S. occidentalis was negatively related to minimum temperatures during the coldest month, potentially implicating overwintering survival as a mechanism leading to this relationship. We also demonstrated that scale size in S. occidentalis was negatively associated with aridity, which is consistent with several other studies in squamate reptiles and the known functional role of scale size in moderating evaporative water loss. However, contrary to predictions of the thermal melanism hypothesis, we found no association between lizard colour and temperature during the active season. Overall, our results are largely at odds with interspecific patterns examining the relationship between these traits and environmental conditions. It is unclear to what degree intraspecific trait variation generally agrees with inferences made at the interspecific level. In any case, more studies at the intraspecific level are needed to resolve this question.

Age-dependent effects of moderate differences in environmental predictability forecasted by climate change, experimental evidence from a short-lived lizard (Zootoca vivipara)

Whether and how differences in environmental predictability affect life-history traits is controversial and may depend on mean environmental conditions. Solid evidence for effects of environmental predictability are lacking and thus, the consequences of the currently observed and forecasted climate-change induced reduction of precipitation predictability are largely unknown. Here we experimentally tested whether and how changes in the predictability of precipitation affect growth, reproduction, and survival of common lizard Zootoca vivipara. Precipitation predictability affected all three age classes. While adults were able to compensate the treatment effects, yearlings and juvenile females were not able to compensate negative effects of less predictable precipitation on growth and body condition, respectively. Differences among the age-classes' response reflect differences (among age-classes) in the sensitivity to environmental predictability. Moreover, effects of environmental predictability depended on mean environmental conditions. This indicates that integrating differences in environmental sensitivity, and changes in averages and the predictability of climatic variables will be key to understand whether species are able to cope with the current climatic change.

High-mountain altitudinal gradient influences thermal ecology of the Mesquite Lizard (Sceloporus grammicus)

The thermal requirements of ectotherms may vary among species due to adaptation to different thermal environments. Nevertheless, some of these requirements are evolutionarily conserved, leading organisms to compensate behaviorally for harsh environmental conditions. High-mountain systems provide temperature gradients that allow for studies of evolutionary and plastic variation in thermal ecology under natural conditions. We evaluated the thermoregulation strategies of Sceloporus grammicus Wiegmann, 1828 at three points (2600, 3100, and 4150 m above sea level) along an altitudinal gradient. We found that the thermal quality of the site and the body temperatures of lizards are influenced by altitude and decrease with increasing elevation. However, lizards from the three different elevations have similar thermal requirements. High-altitude lizards have lower thermal accuracy and efficiency indices compared with those from the lower sites, owing to the low thermal quality of their environment. Nevertheless, they are efficient in thermoregulation, increasing their body temperature above the ambient temperature. We found that pregnant females from all three elevations had similar preferred body temperatures. Compared with nonpregnant females and males, they exhibited lower preferred temperatures and more accurate thermoregulation. The wide altitudinal distribution of S. grammicus is thus not caused by variable thermal requirements. Instead, the wide repertoire of physiological and behavioral strategies of these lizards allows this species to successfully inhabit contrasting environments.

Chromatic variability and sexual dimorphism in the rocky lizard Phymaturus verdugo

The genus Phymaturus comprises lizards that inhabit cold environments at high altitudes or latitudes. Phymaturus verdugo Cei and Videla, 2003 is characterized by cephalic melanism, which is interpreted as a character present only in males and associated with sexual dimorphism. Using spectrophotometry and photography, we demonstrate that this species has high chromatic variability and that melanism is also present in females. By comparing colour variables on 15 patches of the body, we find significant differences between sexes in all patches, indicating strong sexual dichromatism for the entire body, not only the cephalic region. Body temperature had no effect on skin reflectance or melanism, which indicates that thermoregulation early in the day is not mediated by colour changes. Contrary to our predictions, we found no evidence of better body condition in darker individuals. Our study breaks some paradigms about the genus Phymaturus and suggests that human perception of colour, as well as working with small samples, can lead to misidentification or erroneous descriptions of species. We believe that future studies should explore heating rates and other functions of melanism such as crypsis, sexual selection, immune response, and UV protection to understand chromatic variability within this genus.

An integrative and citizen science based approach to the rediscovery and redescription of the only known high-altitude endemic Pill Millipede, Glomeris aurita Koch (Diplopoda, Glomerida)

The pill millipede species Glomeris auritaKoch, 1847 remained of relative unknown origin and appearance until its recent rediscovery in samples from the Bergamasque Alps, northern Italy. In order to provide an integrative redescription and accurate identification of the high-altitude microendemic G. aurita, COI barcode sequences from three individuals coming from two different localities were obtained. These sequences are compared with those of the syntopic endemic G. oblongoguttataVerhoeff, 1894, the widespread black morph of G. romanaVerhoeff, 1900, as well as several widespread species including G. marginataVillers, 1789, G. connexaKoch, 1847, and G. klugiiBrandt, 1833, which have rare colour morphs that exhibit some similarity to G. aurita. To rule-out any identity confusion of G. aurita with other high-altitude or little-known Italian Glomeris, specimens of G. transalpinaKoch, 1836, G. oropensisVerhoeff, 1934, and G. primordialisVerhoeff, 1932 were also added to the dataset. Altogether, 24 sequences were compared. Morphologically, the specimens of G. aurita were studied utilizing scanning electron microscopy as well as non-invasive micro-CT technology. The distribution of both Bergamasque endemics, G. aurita and G. oblongoguttata, could be mapped and compared utilizing samples from the Museo civico di Scienze Naturali di Bergamo, as well as photographic evidence from an Italian naturalist forum. G. aurita has a very short active period and is the first known pill millipede species restricted to mountain tops and cold places, possibly representing a Nunatak survivor.

Avian predation intensity as a driver of clinal variation in colour morph frequency

Phenotypic variation provides the framework for natural selection to work upon, enabling adaptive evolution. One of the most discernible manifestations of phenotypic variability is colour variation. When this variation is discrete, genetically based colour pattern morphs occur simultaneously within a population. Why and how colour polymorphisms are maintained is an evolutionary puzzle. Several evolutionary drivers have been hypothesized as influencing clinal patterns of morph frequency, with spatial variation in climate and predation being considered especially important. Despite this, no study has examined both of their roles simultaneously. The aims of this study were to: (a) examine the covariation of physiology, environmental variables and colouration at a local scale; and (b) determine if these factors and their interplay explain broad clinal variation in morph frequency. We used the lizard Liopholis whitii as a model system, as this species displays a discrete, heritable polymorphism for colour pattern (plain-backed, patterned morphs) whose morph frequency varies latitudinally. We measured reflectance, field activity temperatures and microhabitat structure to test for differences in crypsis, thermal biology and microhabitat selection of patterned and plain-backed morphs within a single population where colour morphs occur sympatrically. We then used data from the literature to perform a broad-scale analysis to identify whether these factors also explained the latitudinal variation of morph frequency in this species. At the local scale, plain-backed morphs were found to be less cryptic than patterned morphs while no other differences were detected in terms of thermal biology, dorsal reflectance and microhabitat use. At a broader scale, predation was the most influential factor mediating morph frequency across latitudes. However, the observed pattern of morph frequency is opposite to what the modelling results suggest in that the incidence of the least cryptic morph is highest where predation pressure is most severe. Clinal variation in the level of background matching between morphs or the potential reproductive advantage by the plain-backed morph may, instead, be driving the observed morph frequency. Together, these results provide key insights into the evolution of local adaptation as well as the ecological forces involved in driving the dynamics of colour polymorphism.

Impact of Yeast Pigmentation on Heat Capture and Latitudinal Distribution

Pigmentation is a fundamental characteristic of living organisms that is used to absorb radiation energy and to regulate temperature. Since darker pigments absorb more radiation than lighter ones, they stream more heat, which can provide an adaptive advantage at higher latitudes and a disadvantage near the Tropics, because of the risk of overheating. This intuitive process of color-mediated thermoregulation, also known as the theory of thermal melanism (TTM), has been only tested in ectothermic animal models [1-8]. Here, we report an association between yeast pigmentation and their latitude of isolation, with dark-pigmented isolates being more frequent away from the Tropics. To measure the impact of microbial pigmentation in energy capture from radiation, we generated 20 pigmented variants of Cryptococcus neoformans and Candida spp. Infrared thermography revealed that dark-pigmented yeasts heated up faster and reached higher temperatures (up to 2-fold) than lighter ones following irradiation. Melanin-pigmented C. neoformans exhibited a growth advantage relative to non-melanized yeasts when incubated under the light at 4°C but increased thermal susceptibility at 25°C ambient temperatures. Our results extend the TTM to microbiology and suggest pigmentation as an ancient adaptation mechanism for gaining thermal energy from radiation. The contribution of microbial pigmentation in heat absorption is relevant to microbial ecology and for estimating global temperatures. The color variations available in yeasts provide new opportunities in chromatology to quantify radiative heat transfer and validate biophysical models of heat flow [9] that are not possible with plants or animals.

Thermal consequences of colour and near-infrared reflectance

The importance of colour for temperature regulation in animals remains controversial. Colour can affect an animal's temperature because all else being equal, dark surfaces absorb more solar energy than do light surfaces, and that energy is converted into heat. However, in reality, the relationship between colour and thermoregulation is complex and varied because it depends on environmental conditions and the physical properties, behaviour and physiology of the animal. Furthermore, the thermal effects of colour depend as much on absorptance of near-infrared ((NIR), 700-2500 nm) as visible (300-700 nm) wavelengths of direct sunlight; yet the NIR is very rarely considered or measured. The few available data on NIR reflectance in animals indicate that the visible reflectance is often a poor predictor of NIR reflectance. Adaptive variation in animal coloration (visible reflectance) reflects a compromise between multiple competing functions such as camouflage, signalling and thermoregulation. By contrast, adaptive variation in NIR reflectance should primarily reflect thermoregulatory requirements because animal visual systems are generally insensitive to NIR wavelengths. Here, we assess evidence and identify key research questions regarding the thermoregulatory function of animal coloration, and specifically consider evidence for adaptive variation in NIR reflectance.This article is part of the themed issue 'Animal coloration: production, perception, function and application'.

Immunocompetence and parasite infestation in a melanistic and normally-coloured population of the lacertid lizard, Podarcis siculus

Melanism is the occurrence of individuals that are darker in skin pigmentation than their conspecifics, which is a common colour polymorphism among vertebrates. Due to the pleotropic effects of the POMC gene that is responsible for melanin-based colouration, dark pigmentation often co-varies with a range of other phenotypic traits. Still, not much is known on the link between melanin-based colouration and immunity in lizards. In this study, we examined and compared the immunocompetence and degree of ectoparasite infestation of Podarcis siculus lizards from a fully melanistic population on an islet in the Tyrrhenian Sea, with conspecifics from a ‘normally’-coloured population on the mainland. Our findings show that both males and females from the melanistic population were less parasitized by ectoparasites and had a greater cellular immune response to a phytohemagglutinin injection than normally-coloured conspecifics. This outcome is in line with the “genetic link hypothesis”, which predicts that melanistic individuals will be more resistant to parasites than non-melanistic individuals due to the pleiotropic POMC gene. In addition, we found correlative evidence for a link between ectoparasite load and PHA immune response, but this was only true for males from the normally-coloured population. Immunological data on additional melanistic and non-melanistic populations of Podarcis siculus in the Mediterranean basin would provide us better insight into patterns of co-variation between immunity and melanism in lizards.

Functions of fungal melanin beyond virulence

Melanins are ancient biological pigments found in all kingdoms of life. In fungi, their role in microbial pathogenesis is well established; however, these complex biomolecules also confer upon fungal microorganisms the faculty to tolerate extreme environments such as the Earth's poles, the International Space Station and places contaminated by toxic metals and ionizing radiation. A remarkable property of melanin is its capacity to interact with a wide range of electromagnetic radiation frequencies, functioning as a protecting and energy harvesting pigment. Other roles of fungal melanin include scavenging of free radical, thermo-tolerance, metal ion sequestration, cell development, and mechanical-chemical cellular strength. In this review, we explore the various functions ascribed to this biological pigment in fungi and its remarkable physicochemical properties.

Repeatability and correlation of physiological traits: Do ectotherms have a "thermal type"?

Across a range of taxa, individuals within a species differ in suites of correlated traits. These trait complexes, known as syndromes, can have dramatic evolutionary consequences as they do not evolve independently but rather as a unit. Current research focuses primarily on syndromes relating to aspects of behavior and life history. What is less clear is whether physiological traits also form a syndrome. We measured 10 thermal traits in the delicate skink, Lampropholis delicata, to test this idea. Repeatability was calculated and their across‐context correlations evaluated. Our results were in alignment with our predictions in that individual thermal traits varied consistently and were structured into a physiological syndrome, which we are referring to as the thermal behavior syndrome (TBS). Within this syndrome, lizards exhibited a “thermal type” with each being ranked along a cold–hot continuum. Hot types had faster sprint speeds and higher preferred body temperatures, whereas the opposite was true for cold types. We conclude that physiological traits may evolve as a single unit driven by the need to maintain optimal temperatures that enable fitness‐related behaviors to be maximized.

Cool habitats support darker and bigger butterflies in Australian tropical forests

Morphology mediates the relationship between an organism's body temperature and its environment. Dark organisms, for example, tend to absorb heat more quickly than lighter individuals, which could influence their responses to temperature. Therefore, temperature‐related traits such as morphology may affect patterns of species abundance, richness, and community assembly across a broad range of spatial scales. In this study, we examined variation in color lightness and body size within butterfly communities across hot and cool habitats in the tropical woodland–rainforest ecosystems of northeast Queensland, Australia. Using thermal imaging, we documented the absorption of solar radiation relative to color lightness and wingspan and then built a phylogenetic tree based on available sequences to analyze the effects of habitat on these traits within a phylogenetic framework. In general, darker and larger individuals were more prevalent in cool, closed‐canopy rainforests than in immediately adjacent and hotter open woodlands. In addition, darker and larger butterflies preferred to be active in the shade and during crepuscular hours, while lighter and smaller butterflies were more active in the sun and midday hours—a pattern that held after correcting for phylogeny. Our ex situ experiment supported field observations that dark and large butterflies heated up faster than light and small butterflies under standardized environmental conditions. Our results show a thermal consequence of butterfly morphology across habitats and how environmental factors at a microhabitat scale may affect the distribution of species based on these traits. Furthermore, this study highlights how butterfly species might differentially respond to warming based on ecophysiological traits and how thermal refuges might emerge at microclimatic and habitat scales.

Thermal and substrate color-induced melanization in laboratory reared red-eared sliders (Trachemys scripta elegans)

Color and pigmentation patterns of the integument can facilitate crypsis, thermoregulation, and social signaling. According to the "thermal melanism hypothesis", cold environmental temperature should increase the quantity of melanin that is deposited in the integument thereby facilitating radiative warming. We studied the influences of water temperature (26°C or 31°C) and substrate color (black or white) on the degree of melanization in the red-eared slider, Trachemys scripta elegans, under laboratory conditions. Turtles reared on a black substrate, or in 26°C water, for 120 days were darker than those reared on a white substrate or in 31°C water. A potential tradeoff between the fitness benefits of crypsis and the benefits of radiative warming through melanism was detected because turtles reared in 26°C water and on a white substrate were darker than those reared on a white substrate and in 31°C water. Low temperatures limited metabolic processes because turtles reared in 26°C water grew more slowly than those reared in 31°C water. However, histological analyses revealed that melanization was a dynamic process in all treatments confirming that the degree of melanization in the cool water treatment was not influenced by the initial and relatively dark hatchling coloration in individuals that grew relatively slowly.

The effect of skin reflectance on thermal traits in a small heliothermic ectotherm

Variation in colour patterning is prevalent among and within species. A number of theories have been proposed in explaining its evolution. Because solar radiation interacts with the pigmentation of the integument causing light to either be reflected or absorbed into the body, thermoregulation has been considered to be a primary selective agent, particularly among ectotherms. Accordingly, the colour-mediated thermoregulatory hypothesis states that darker individuals will heat faster and reach higher thermal equilibria while paler individuals will have the opposite traits. It was further predicted that dark colouration would promote slower cooling rates and higher thermal performance temperatures. To test these hypotheses we quantified the reflectance, selected body temperatures, performance optima, as well as heating and cooling rates of an ectothermic vertebrate, Lampropholis delicata. Our results indicated that colour had no influence on thermal physiology, as all thermal traits were uncorrelated with reflectance. We suggest that crypsis may instead be the stronger selective agent as it may have a more direct impact on fitness. Our study has improved our knowledge of the functional differences among individuals with different colour patterns, and the evolutionary significance of morphological variation within species.

Effect of body mass and melanism on heat balance in Liolaemus lizards of the goetschi clade

Body temperature of ectotherms depends on the environmental temperatures and behavioral adjustments, but morphology may also affect it. For example, in colder environments animals tend to be larger and show higher thermal inertia, as proposed by Bergmann's rule and the heat balance hypothesis (HBH). Additionally, dark coloration increases solar radiation absorption and should accelerate heat gain (Thermal melanism hypothesis, TMH).

We tested Bergmann's rule, HBH and TMH within the Liolaemus goetschi lizards clade that show variability in body size and melanic coloration. We measured heating and cooling rates of live and euthanized animals, and tested how morphology and color affect these rates. Live organisms show less variable and faster heating rates, compared to cooling rates, suggesting behavioral and/ or physiological adjustments.

Our results support Bergmann's rule and the HBH, as larger species show slower heating and cooling rates. However, we did not find a clear pattern to support TMH. The influence of dorsal melanism on heating by radiation was masked by body size effect in live animals, while results from euthanized individuals show no clear effects of melanism on heating rates either. However, when compared three groups of live individuals with different degree of melanism we found that that darker euthanized animals actually heat faster than lighter ones, favoring TMH. Although unresolved aspects remain, body size and coloration influenced heat exchange suggesting complex thermoregulatory strategies in these lizards, probably regulated through physiology and behavior, what may allow these small lizards to inhabit harsh weather environments.

Thermoregulation and microhabitat choice in the polymorphic asp viper (Vipera aspis)

In ectotherms, thermoregulation strongly depends on environmental conditions, as well as on intrinsic factors, such as skin colour. Indeed, due to its physical properties, melanin pigments allow melanistic morphs to benefit of a more efficient thermoregulation compared to non-melanistic ones. Despite thermal benefits of melanism have often been highlighted under experimental conditions, such field data remain scarce. In this study, we investigated the influence of colouration on body temperature and microhabitat choice in a montane population of colour polymorphic asp viper (Vipera aspis) characterized by a strong presence of melanism (64%). Results highlighted a difference in internal body temperature, but only within gravid females, with melanistic individuals having higher body temperatures compared to non-melanistic ones. No differences were found when considering both sexes. We also showed that melanistic and non-melanistic vipers were found in different microhabitat types, i.e. melanistic snakes used areas marked by a scarcer sun exposure and by higher vegetation cover compared to non-melanistic ones. This result has important implications. Indeed, besides providing a possible explanation for the lack of difference in body temperature (except for gravid females), it confirms that melanistic individuals can potentially use their efficient thermoregulation in order to inhabit less exposed and thermally unfavourable microhabitats.

Orientation to the sun by animals and its interaction with crypsis

Orientation with respect to the sun has been observed in a wide range of species and has generally been interpreted in terms of thermoregulation and/or ultraviolet (UV) protection. For countershaded animals, orientation with respect to the sun may also result from the pressure to exploit the gradient of coloration optimally to enhance crypsis.

Here, we use computational modelling to predict the optimal countershading pattern for an oriented body. We assess how camouflage performance declines as orientation varies using a computational model that incorporates realistic lighting environments.

Once an optimal countershading pattern for crypsis has been chosen, we determine separately how UV protection/irradiation and solar thermal inflow fluctuate with orientation.

We show that body orientations that could optimally use countershading to enhance crypsis are very similar to those that allow optimal solar heat inflow and UV protection.

Our findings suggest that crypsis has been overlooked as a selective pressure on orientation and that new experiments should be designed to tease apart the respective roles of these different selective pressures. We propose potential experiments that could achieve this.

An Opposite Pattern to the Conventional Thermal Hypothesis: Temperature-Dependent Variation in Coloration of Adults of Saccharosydne procerus (Homoptera: Delphacidae)

Melanism is a common polymorphism in many insect species that also influences immune function. According to the thermal melanin hypothesis, ectothermic individuals from cooler environments have darker cuticles and higher polyphenol oxidase (PO) levels, which represent a better immunocompetence. In this study, the links among environmental temperature, melanism, and PO activity of Saccharosydne procerus (Matsumura) were examined. Most S. procerus have a black spot on their forewings at high temperatures in the field and in the laboratory. In PO activity assay, a positive association between PO level and temperature was found. Our results showed that a diversification of melanism occurred under different temperatures and that melanism in S. procerus presented an opposite pattern to the one proposed by the thermal hypothesis.