Interaction of hydric and thermal conditions drive geographic variation in thermoregulation in a widespread lizard

The Shape of Water: Physiological Adaptations to Habitat Aridity in the Ornate Tree Lizard (Urosaurus ornatus)

Deserts have always amazed researchers due to their high diversity of habitats, where plant and animal species have been able to adapt and diversify, even when these areas impose several constraints on an organism's activity patterns. In particular, deserts support several lizard species adapted to the thermal and water restrictions found in such biomes. Although several studies have attempted to understand how lizard species might respond to water deficits or droughts in deserts, few have addressed how these responses might vary along a latitudinal gradient. This raises the question of whether physiological buffering of the organism or the climatic environment affects water loss in lizards. Here, we used six populations of Urosaurus ornatus to test whether water loss is influenced more by the intrinsic physiology of the lizard or by the climatic niche. We found that water loss is primarily influenced by the climatic niche of the lizard. However, future studies should focus on how microclimatic variables can influence water loss in organisms found across large latitudinal gradients.

Flexibility in thermal requirements: a comparative analysis of the wide-spread lizard genus Sceloporus

Adaptation or acclimation of thermal requirements to environmental conditions can reduce thermoregulation costs and increase fitness, especially in ectotherms, which rely heavily on environmental temperatures for thermoregulation. Insight into how thermal niches have shaped thermal requirements across evolutionary history may help predict the survival of species during climate change. The lizard genus Sceloporus has a widespread distribution and inhabits an ample variety of habitats. We evaluated the effects of geographical gradients (i.e. elevation and latitude) and local environmental temperatures on thermal requirements (i.e. preferred body temperature, active body temperature in the field, and critical thermal limits) of Sceloporus species using published and field-collected data and performing phylogenetic comparative analyses. To contrast macro- and micro-evolutional patterns, we also performed intra-specific analyses when sufficient reports existed for a species. We found that preferred body temperature increased with elevation, whereas body temperature in the field decreased with elevation and increased with local environmental temperatures. Critical thermal limits were not related to the geographic gradient or environmental temperatures. The apparent lack of relation of thermal requirements to geographic gradient may increase vulnerability to extinction due to climate change. However, local and temporal variations in thermal landscape determine thermoregulation opportunities and may not be well represented by geographic gradient and mean environmental temperatures. Results showed that Sceloporus lizards are excellent thermoregulators, have wide thermal tolerance ranges, and the preferred temperature was labile. Our results suggest that Sceloporus lizards can adjust to different thermal landscapes, highlighting opportunities for continuous survival in changing thermal environments.

Ecological responses of squamate reptiles to nocturnal warming

Nocturnal temperatures are increasing at a pace exceeding diurnal temperatures in most parts of the world. The role of warmer nocturnal temperatures in animal ecology has received scant attention and most studies focus on diurnal or daily descriptors of thermal environments' temporal trends. Yet, available evidence from plant and insect studies suggests that organisms can exhibit contrasting physiological responses to diurnal and nocturnal warming. Limiting studies to diurnal trends can thus result in incomplete and misleading interpretations of the ability of species to cope with global warming. Although they are expected to be impacted by warmer nocturnal temperatures, insufficient data are available regarding the night-time ecology of vertebrate ectotherms. Here, we illustrate the complex effects of nocturnal warming on squamate reptiles, a keystone group of vertebrate ectotherms. Our review includes discussion of diurnal and nocturnal ectotherms, but we mainly focus on diurnal species for which nocturnal warming affects a period dedicated to physiological recovery, and thus may perturb activity patterns and energy balance. We first summarise the physical consequences of nocturnal warming on habitats used by squamate reptiles. Second, we describe how such changes can alter the energy balance of diurnal species. We illustrate this with empirical data from the asp viper (Vipera aspis) and common wall lizard (Podarcis muralis), two diurnal species found throughout western Europe. Third, we make use of a mechanistic approach based on an energy-balance model to draw general conclusions about the effects of nocturnal temperatures. Fourth, we examine how warmer nights may affect squamates over their lifetime, with potential consequences on individual fitness and population dynamics. We review quantitative evidence for such lifetime effects using recent data derived from a range of studies on the European common lizard (Zootoca vivipara). Finally, we consider the broader eco-evolutionary ramifications of nocturnal warming and highlight several research questions that require future attention. Our work emphasises the importance of considering the joint influence of diurnal and nocturnal warming on the responses of vertebrate ectotherms to climate warming.

How do ectotherms perform in cold environments? Physiological and life-history traits in an Andean viviparous lizard

Both the mean and the variation in environmental temperature are increasing globally. Indeed, the predicted increases in temperature range from 2 to 4°C in the next 50 years. Ectotherms control body temperature by means of behavior selecting microsites with different temperatures, which makes them more susceptible to changes in climate. Nevertheless, lizards living in high mountain environments have developed several mechanisms to inhabit and colonize variable environments with extreme temperatures. These mechanisms include a high metabolism to be active at lower temperatures and viviparity to improve embryonic development. Despite behavioral thermoregulation acting as a buffer to changes in environmental temperature, other traits such as life-history traits may be less flexible. Consequently, in an attempt to understand how lizards cope with harsh habitats, we evaluated some physiological traits and responses of females of Liolaemus bellii from two contrasting slope sites with differences in environmental temperature and humidity, but at the same altitude in the southern Andes range. We collected pregnant females from opposite slopes and maintained them until parturition in a common-garden experiment. Females from the south-facing slope (S-slope) had higher preferred body temperature (Tpref) values before and after parturition and exhibited higher daily energy expenditure before parturition. Nevertheless, no difference in Tpref was shown by their offspring, suggesting a developmental plastic response or adaptation to lower environmental temperature. For instance, the higher metabolism during pregnancy could be associated with a shorter activity period on the snowy S-slope. Additionally, females from the S-slope had larger kidneys and gave birth later than N-slope females, likely due to developmental plasticity or genetic differentiation. How fixed these traits are, in individuals from the contrasting slopes, will determine the response capacity of the L. bellii population to climate change.

Climate aridity and habitat drive geographical variation in morphology and thermo-hydroregulation strategies of a widespread lizard species

Thermo-hydroregulation strategies involve concurrent changes in functional traits related to energy, water balance and thermoregulation and play a key role in determining life-history traits and population demography of terrestrial ectotherms. Local thermal and hydric conditions should be important drivers of the geographical variation of thermo-hydroregulation strategies, but we lack studies that examine these changes across climatic gradients in different habitat types. Here, we investigated intraspecific variation of morphology and thermo-hydroregulation traits in the widespread European common lizard (Zootoca vivipara louislantzi) across a multidimensional environmental gradient involving independent variation in air temperature and rainfall and differences in habitat features (access to free-standing water and forest cover). We sampled adult males for morphology, resting metabolic rate, total and cutaneous evaporative water loss and thermal preferences in 15 populations from the rear to the leading edge of the distribution across an elevational gradient ranging from sea level to 1750 m. Besides a decrease in adult body size with increasing environmental temperatures, we found little effect of thermal conditions on thermo-hydroregulation strategies. In particular, relict lowland populations from the warm rear edge showed no specific ecophysiological adaptations. Instead, body mass, body condition and resting metabolic rate were positively associated with a rainfall gradient, while forest cover and water access in the habitat throughout the season also influenced cutaneous evaporative water loss. Our study emphasizes the importance of rainfall and habitat features rather than thermal conditions for geographical variation in lizard morphology and physiology.

Lizards from warm and declining populations are born with extremely short telomeres

Aging is the price to pay for acquiring and processing energy through cellular activity and life history productivity. Climate warming can exacerbate the inherent pace of aging, as illustrated by a faster erosion of protective telomere DNA sequences. This biomarker integrates individual pace of life and parental effects through the germline, but whether intra- and intergenerational telomere dynamics underlies population trends remains an open question. Here, we investigated the covariation between life history, telomere length (TL), and extinction risk among three age classes in a cold-adapted ectotherm (Zootoca vivipara) facing warming-induced extirpations in its distribution limits. TL followed the same threshold relationships with population extinction risk at birth, maturity, and adulthood, suggesting intergenerational accumulation of accelerated aging rate in declining populations. In dwindling populations, most neonates inherited already short telomeres, suggesting they were born physiologically old and unlikely to reach recruitment. At adulthood, TL further explained females' reproductive performance, switching from an index of individual quality in stable populations to a biomarker of reproductive costs in those close to extirpation. We compiled these results to propose the aging loop hypothesis and conceptualize how climate-driven telomere shortening in ectotherms may accumulate across generations and generate tipping points before local extirpation.

Environmental conditions and male quality traits simultaneously explain variation of multiple colour signals in male lizards

Male lizards often display multiple pigment‐based and structural colour signals which may reflect various quality traits (e.g. performance, parasitism), with testosterone (T) often mediating these relationships. Furthermore, environmental conditions can explain colour signal variation by affecting processes such as signal efficacy, thermoregulation and camouflage. The relationships between colour signals, male quality traits and environmental factors have often been analysed in isolation, but simultaneous analyses are rare. Thus, the response of multiple colour signals to variation in all these factors in an integrative analysis remains to be investigated.

Here, we investigated how multiple colour signals relate to their information content, examined the role of T as a potential mediator of these relationships and how environmental factors explain colour signal variation.

We performed an integrative study to examine the covariation between three colour signals (melanin‐based black, carotenoid‐based yellow–orange and structural UV), physiological performance, parasitism, T levels and environmental factors (microclimate, forest cover) in male common lizards Zootoca vivipara from 13 populations.

We found that the three colour signals conveyed information on different aspects of male condition, supporting a multiple message hypothesis. T influenced only parasitism, suggesting that T does not directly mediate the relationships between colour signals and their information content. Moreover, colour signals became more saturated in forested habitats, suggesting an adaptation to degraded light conditions, and became generally brighter in mesic conditions, in contradiction with the thermal melanism hypothesis.

We show that distinct individual quality traits and environmental factors simultaneously explain variations of multiple colour signals with different production modes. Our study therefore highlights the complexity of colour signal evolution, involving various sets of selective pressures acting at the same time, but in different ways depending on colour production mechanism.

Designing a Seasonal Acclimation Study Presents Challenges and Opportunities

Organisms living in seasonal environments often adjust physiological capacities and sensitivities in response to (or in anticipation of) environment shifts. Such physiological and morphological adjustments (“acclimation” and related terms) inspire opportunities to explore the mechanistic bases underlying these adjustments, to detect cues inducing adjustments, and to elucidate their ecological and evolutionary consequences. Seasonal adjustments (“seasonal acclimation”) can be detected either by measuring physiological capacities and sensitivities of organisms retrieved directly from nature (or outdoor enclosures) in different seasons or less directly by rearing and measuring organisms maintained in the laboratory under conditions that attempt to mimic or track natural ones. But mimicking natural conditions in the laboratory is challenging—doing so requires prior natural-history knowledge of ecologically relevant body temperature cycles, photoperiods, food rations, social environments, among other variables. We argue that traditional laboratory-based conditions usually fail to approximate natural seasonal conditions (temperature, photoperiod, food, “lockdown”). Consequently, whether the resulting acclimation shifts correctly approximate those in nature is uncertain, and sometimes is dubious. We argue that background natural history information provides opportunities to design acclimation protocols that are not only more ecologically relevant, but also serve as templates for testing the validity of traditional protocols. Finally, we suggest several best practices to help enhance ecological realism.

Intraspecific diversity alters the relationship between climate change and parasitism in a polymorphic ectotherm

Climate-modulated parasitism is driven by a range of factors, yet the spatial and temporal variability of this relationship has received scant attention in wild vertebrate hosts. Moreover, most prior studies overlooked the intraspecific differences across host morphotypes, which impedes a full understanding of the climate-parasitism relationship. In the common lizard (Zootoca vivipara), females exhibit three colour morphs: yellow (Y-females), orange (O-females) and mixed (mixture of yellow and orange, M-females). Zootoca vivipara is also infested with an ectoparasite (Ophionyssus mites). We therefore used this model system to examine the intraspecific response of hosts to parasitism under climate change. We found infestation probability to differ across colour morphs at both spatial (10 sites) and temporal (20 years) scales: M-females had lower parasite infestations than Y- and O-females at lower temperatures, but became more susceptible to parasites as temperature increased. The advantage of M-females at low temperatures was counterbalanced by their higher mortality rates thereafter, which suggests a morph-dependent trade-off between resistance to parasites and host survival. Furthermore, significant interactions between colour morphs and temperature indicate that the relationship between parasite infestations and climate warming was contingent on host morphotypes. Parasite infestations increased with temperature for most morphs, but displayed morph-specific rates. Finally, infested M-females had higher reductions in survival rates than infested Y- or O-females, which implies a potential loss of intraspecific diversity within populations as parasitism and temperatures rise. Overall, we found parasitism increases with warming temperatures, but this relationship is modulated by host morphotypes and an interaction with temperature. We suggest that epidemiological models incorporate intraspecific diversity within species for better understanding the dynamics of wildlife diseases under climate warming.

Effect of climate change on the potential distribution of Helodermaalvarezi (Squamata, Helodermatidae)

Climate change represents a real threat to biodiversity conservation worldwide. Although the effects on several species of conservation priority are known, comprehensive information about the impact of climate change on reptile populations is lacking. In the present study, we analyze outcomes on the potential distribution of the black beaded lizard (Helodermaalvarezi Bogert & Martin del Campo, 1956) under global warming scenarios. Its potential distribution, at present and in projections for the years 2050 and 2070, under both optimistic and pessimistic climate change forecasts, were computed using current data records and seven bioclimatic variables. General results predict a shift in the future potential distribution of H.alvarezi due to temperature increase. The optimistic scenario (4.5 W/m²) for 2070 suggests an enlargement in the species' distribution as a response to the availability of new areas of suitable habitat. On the contrary, the worst-case scenario (7 W/m²) shows a distribution decrease by 65%. Moreover, the range distribution of H.alvarezi is directly related to the human footprint, which consequently could magnify negative outcomes for this species. Our research elucidates the importance of conservation strategies to prevent the extinction of the black beaded lizard, especially considering that this species is highly threatened by aversive hunting.