Nocturnal Lizards Research Articles

High-resolution climate data reveal an increasing risk of warming-driven activity restriction for diurnal and nocturnal lizards.

Widespread species experience a variety of climates across their distribution, which can structure their thermal tolerance, and ultimately, responses to climate change. For ectotherms, activity is highly dependent on temperature, its variability and availability of favourable microclimates. Thermal exposure and tolerance may be structured by the availability and heterogeneity of microclimates for species living along temperature and/or precipitation gradients - but patterns and mechanisms underlying such gradients are poorly understood. We measured critical thermal limits (CTmax and CTmin) for five populations of two sympatric lizard species, a nocturnal gecko (Chondrodactylus bibronii) and a diurnal skink (Trachylepis variegata) and recorded hourly thermal variation for a year in three types of microclimate relevant to the activity of lizards (crevice, full sun and partial shade) for six sites across a precipitation gradient. Using a combination of physiological and modelling approaches, we derived warming tolerance for the present and the end of the century. In the present climate, we found an overall wider thermal tolerance for the nocturnal species relative to the diurnal species, and no variation in CTmax but variable CTmin along the precipitation gradient for both species. However, warming tolerances varied significantly over the course of the day, across months and microhabitats. The diurnal skink was most restricted in its daily activity in the three driest sites with up to six daily hours of restricted activity in the open (i.e. outside refugia) during the summer months, while the impacts for the nocturnal gecko were less severe, due to its higher CTmax and night activity. With climate change, lizards will experience more months where activity is restricted and increased exposure to high temperatures even within the more sheltered microhabitats. Together our results highlight the importance of considering the relevant spatiotemporal scale and habitat for understanding the thermal exposure of diurnal and nocturnal species.

First records of Lepidophyma zongolicum García-Vázquez, Canseco-Márquez & Aguilar-López, 2010 (Squamata, Xantusiidae) from Veracruz, Mexico

Lepidophyma Duméril, 1851 is the most diverse genus among the nocturnal lizards, with 23 species distributed from the Atlantic and Pacific slopes of Mexico southeast into Panama. Currently, the available information on the ecology and distribution of these species is limited mainly due to their saxicolous habits. Here we present five new state records of Lepidophyma zongolicum from Atoyac, a locality in the state of Veracruz, Mexico. These new data expand the geographic range of this species by 48 km from its nearest previously known occurrence.

Response to the future climate change effect of two leopard geckos’ distribution (Sauria: Eublepharidae) in Iran

This study investigates the climate change effects on the distribution range of two species of nocturnal lizards in Iran. Using climate change scenarios recently (2021) published by IPCC, two species of leopard geckos that are distributed in the northeast ( Eublepharis turcmenicus ) and southwest ( Eublepharis angramainyu ) of Iran were selected and analyzed because they are only members of the family Eublepharidae in Iran and under high risk of extinction in the wild. We found that the most important bioclimatic variables that could affect the presence of these species are the minimum temperature in the coldest month of the year and the mean temperature in the wettest season; the Mean Temperature of the Driest Quarter and the Mean Temperature of the Coldest Quarter are the most important variables in future (2070) for E. angramainyu and E. turcmenicus , respectively. These variables are important directly at the beginning and end of the hibernation period of ectotherms such as lizards and can disrupt their life cycle by changing this period. Temperature changes over the next 50 years may not be a significant threat to these two species, as their range will be much wider than the current time, indicating that these species will be able to adapt to new conditions.

Nest site selection in a southern and northern population of the velvet gecko (Amalosia lesueurii).

In many oviparous reptiles, thermal conditions inside nests influence phenotypic traits of hatchlings that are linked to survival. Maternal nest-site selection can therefore have long-term implications for offspring and maternal fitness. We studied nest-site selection in a nocturnal lizard (Amalosia lesueurii) from south eastern Australia. Females of this species lay their eggs communally inside rock crevices, and previous studies have shown that maximum daily nest temperatures are positively correlated with maximum daily air temperatures. The incubation period extends for up to 100d, so during hot summers, embryos may be exposed to stressful thermal conditions. Potentially, mothers could buffer their eggs from thermal extremes via careful selection of nest sites. To evaluate this, we studied nest site selection in a southern population (Morton) and a northern population (Yengo) that experience mild and hot summers respectively. In the field, we measured the physical characteristics, orientation, canopy cover and incident radiation load, and thermal regimes of nest sites and randomly available crevices during one of the hottest Australian summers on record (2018-2019). We found strong inter population differences in the degree of canopy cover and solar radiation loads above nest sites. Nest sites from Morton were more open, and received higher radiation loads, than nest sites from Yengo. Mean nest temperatures were similar in Morton and Yengo, but nests from Yengo experienced higher daily temperatures than those from Morton. During heatwaves, temperatures in some nests exceeded the species critical thermal maximum (39.9°C) for several hours each day. Our results show that females can adjust nest-site choice to match local environments, but future research is necessary to clarify whether exposure to high temperatures influences hatching success or offspring phenotypes in this species.

Thermal heterogeneity of selected retreats in cool-temperate viviparous lizards suggests a potential benefit of future climate warming.

Rocky retreats are limited and geologically constrained resources for rock-dwelling nocturnal lizards. Such lizards should seek retreats that offer thermoregulatory benefits without the risk of overheating during the day, and that protect from predation. For cold-adapted species where air temperature is frequently lower than optimum temperature for performance, factors influencing retreat-site selection and whether future warmer conditions will force superficial rock slabs to be abandoned on hot days remain poorly known. Here, we predicted that retreats selected by a nocturnally foraging, cool-temperate gecko from southern New Zealand would be thermally heterogeneous and that future warmer temperature will force lizards to abandon daytime retreats on hot days. We sampled loose rock slabs (potential retreats) in a tussock-grassland site in all seasons. We measured seasonal rock temperature profiles and field body temperature (Tb) of captured geckos using thermography and quantified the physical characteristics of each potential retreat. We found that both physical characteristics and rock temperatures determine choice of retreats. Field Tb of lizards positively correlated with retreat and air temperatures. Also, retreat temperatures, including those of the substrate below the rock slabs, showed complex heterogeneity enabling lizards to choose microsites within retreats to achieve preferred body temperatures intermittently. Observed seasonal shifts in characteristics of occupied rocks imply that lizards choose retreats to maximise warmth in spring, minimise risk of overheating (remain below voluntary thermal maximum, VTmax) in summer and avoid freezing over winter. Our study demonstrates the importance of microclimatic conditions in influencing retreat-site selection. Climate warming might lead to seasonal changes in use of rock slabs and possibly be beneficial initially, but longer-term implications need to be examined.

The nocturnal leopard gecko (Eublepharis macularius) uses UVb radiation for vitamin D3 synthesis.

Vitamin D is an important regulator of calcium and phosphorus homeostasis in animals. It can be acquired from the diet or synthesised de novo when skin is exposed to UVb. Vitamin D deficiency can lead to a complex of diseases collectively called metabolic bone disease (MBD). Diurnal lizards without access to UVb are prone to develop vitamin D deficiency, even when dietary vitamin D3 is provided. A trial was conducted to determine whether juvenile nocturnal lizards require access to UVb to prevent vitamin D deficiency. All leopard geckos (Eublepharis macularius) were supplemented with dietary vitamin D3. One group was exposed to low level UVb radiation (33-51μW/cm2) from hatching until 6months of age and a second group remained unexposed. Animals were fed ad libitum and their growth and weight gain compared with non-exposed controls. At the end of the trial, blood samples were analysed for vitamin D3 metabolites. The concentration of the vitamin D3 metabolite, 25(OH)D3, was higher in UVb exposed animals (61±20 vs. 38±8nmol/L), confirming cutaneous synthesis with UVb exposure. Growth and weight gain were similar in both groups, and this, together with the absence of clinical symptoms, suggests that dietary vitamin D3 alone can meet the vitamin D requirements for growth of this nocturnal gecko, during the first six months of life. It remains to be investigated whether the higher vitamin D metabolite levels holds other health benefits for this species, such as improved bone density or immune response.

Body temperature and time of day both affect nocturnal lizard performance: An experimental investigation.

The locomotor performance of reptiles is profoundly influenced by temperature, but little is known about how the time of day when the animal is usually active may influence performance. Time of day may be particularly relevant for studies on nocturnal reptiles that thermoregulate by day, but are active at night when ambient temperatures are cooler. If selection favours individuals that match their performance to activity times, then nocturnal species should perform better during the night, when they are normally active, than during the day. To test this hypothesis, we investigated how the time of day and body temperature affected the locomotor performance of adult females of the velvet gecko (Amalosia lesueurii). We measured the sprint speeds, running speeds and number of stops of 43 adult females at four different body temperatures (20, 25, 30 and 35 °C) during the day and at night. At night, sprint speeds were higher at 20 and 35 °C but sprint speeds were similar at 25 and 30 °C. By day, sprint speed increased with body temperature, peaking at 30 °C, before declining at 35 °C. However, gecko speeds over 1 m was higher at night at all four test temperatures than by day. Number of stops showed broadly similar patterns and females stopped almost twice as often on the racetrack during the day than they did at night. Furthermore, the thermal breadth of performance differed depending on when geckos were tested. Our results demonstrate that both body temperature and the time of day affects the behaviour and locomotor performance of female velvet geckos, with geckos running faster at night, the time of day when they are usually active. This study adds to evidence that both body temperature and the time of day are crucial for estimating the performance of ectotherms and evaluations and predictions of their vulnerability to climate warming should consider the context of laboratory experimental design.

Warmer isn't always better: Performance eurythermy in a cold‐climate gecko

Most aspects of the lives of ectotherms are temperature dependent. Achieving the warmer body temperatures (Tb s) typically required for optimal performance can be particularly challenging for nocturnal ectotherms. Homonota darwinii-the world's southernmost gecko-is broadly distributed in southern Argentina (35-52 °S latitude) where cold climates over parts of its range likely pose an additional performance challenge for this nocturnal lizard. We hypothesized that the southernmost populations of this species would be the most thermally challenged, as evidenced by a decline in temperature-dependent sprint performance with increasing latitude. A temperature-dependent depression in locomotory performance may indicate suboptimal performance in other thermally dependent traits linked to fitness (e.g., foraging efficiency, metabolism). We measured sprint performance at five ecologically relevant Tb s for four populations spanning most of the latitudinal range of H. darwinii. We also recorded annual operative temperatures (Te s) at each site on the surface and in refuges used by the geckos. Sprint data indicated differences in maximum performance over the range of H. darwinii, but not the latitudinal decline predicted. Instead, sprint performance was likely influenced by climatic variability associated with each site's elevation. Geckos from most populations had a broad range of Tb s over which sprint performance was optimal, albeit twofold to threefold lower than other geckos. This is indicative of eurythermy, the ability to perform well over a wide range of temperatures. We discuss this finding in the context of alternative hypotheses concerning performance tradeoffs in nocturnal ectotherms.

The lizard that never sleeps: activity of the pampa marked gecko Homonota uruguayensis

ABSTRACT It is generally assumed that lizards are active whenever climatic conditions are favorable. Homonota uruguayensis (Vaz-Ferreira & Sierra de Soriano, 1961) is the only native gecko - and nocturnal lizard - living in the northern Pampa biome, and its ecology is poorly known. This study aimed at describing this species’ pattern of daily and annual activity and its relation with environmental temperatures. The study was conducted in the extreme south of Brazil (Rosário do Sul, State of Rio Grande do Sul), between May 2010 and January 2011 at a rocky outcrop located in the Pampa biome. The study was carried out in a total of four seasonal field trips, totalizing 1185 hours of field work. The data were collected, both during the day and the night in 6-hour shifts (duration of the sampling period). The area was randomly covered at each shift to record activity and microhabitat use by the lizards. In total 1541 specimens were recorded throughout the study. Homonota uruguayensis showed diurnal and nocturnal activity in the four seasons, with periods of daily activity varying significantly between all seasons in a cyclic and multimodal pattern, with no significant relation with environmental temperatures. There was no difference in activity related to sex and age classes. Most active lizards were found when air temperatures ranged from 14 °C to 32.9 °C (82% of active lizards) and substrate temperatures ranged from 10 °C to 32.9 °C (87% of active lizards).

Heat and water loss versus shelter: a dilemma in thermoregulatory decision making for a retreat-dwelling nocturnal gecko.

Understanding the interaction between upper voluntary thermal limit (VTmax) and water loss may aid in predicting responses of ectotherms to increasing temperatures within microhabitats. However, the temperature at which climate heating will force cool-climate nocturnal lizards to abandon daytime retreats remains poorly understood. Here, we developed a new laboratory protocol for determining VTmax in the retreat-dwelling, viviparous Woodworthia 'Otago/Southland' gecko, based on escape behaviour (abandonment of heated retreat). We compared the body temperature (Tb) at VTmax, and duration of heating, between two source groups with different thermal histories, and among three reproductive groups. We also examined continuous changes in Tb (via an attached biologger) and total evaporative water loss (EWL) during heating. In the field, we measured Tb and microhabitat thermal profiles to establish whether geckos reach VTmax in nature. We found that VTmax and duration of heating varied between source groups (and thus potentially with prior thermal experience), but not among reproductive groups. Moreover, geckos reached a peak temperature slightly higher than VTmax before abandoning the retreat. Total EWL increased with increasing VTmax and with the duration of heating. In the field, pregnant geckos with attached biologgers reached VTmax temperature, and temperatures of some separately monitored microhabitats exceeded VTmax in hot weather implying that some retreats must be abandoned to avoid overheating. Our results suggest that cool-climate nocturnal lizards that inhabit daytime retreats may abandon retreats more frequently if climate warming persists, implying a trade-off between retention of originally occupied shelter and ongoing water loss due to overheating.

What geckos are – an ecological-biogeographic perspective

Geckos are a hyper-diverse, ancient, and globally distributed group. They have diverged early from other squamates and thus can be expected to differ from them along multiple ecological, life history, and biogeographic axes. I review a wide range of gecko traits, comparing them to those of other lizard taxa, to identify the unique, and unifying, attributes of geckos among lizards, based on comprehensive databases of lizard distributions and biological attributes. Few traits completely separate geckos from other lizard taxa, yet they differ to a large degree along many axes: they are more restricted to low latitudes and altitudes, are especially diverse on islands, but relatively scarce in America. They are small lizards, that lay small, fixed clutch sizes, for which they compensate only partially by laying frequently. Because they mature at relatively similar ages and have similar lifespans to other lizards, geckos produce fewer offspring over a year, and over their lifetimes, perhaps implying that they enjoy higher survival rates. While being the only large lizard clade of predominantly nocturnal lizards a large proportion of species is active by day. Gecko body temperatures and preferred temperatures are lower than those of other lizards –even when they are compared to lizards with similar activity times. Worryingly, most geckos have small ranges that often reside completely outside of protected areas – much more frequently than in other reptile and vertebrate taxa.

Heat seekers: A tropical nocturnal lizard uses behavioral thermoregulation to exploit rare microclimates at night.

Environmental temperatures play a vital role in the physiological and behavioral activity of ectotherms. Behavioral thermoregulation allows animals to modify their body temperature to optimize functions critical to fitness, including digestion, growth, reproduction, and locomotor performance. Diurnal reptiles are a classic model system to answer questions related to thermal ecology, whereas behavioral thermoregulation in nocturnal species is thought to be strongly constrained by low environmental thermal heterogeneity at night. The few studies describing the thermal ecology of nocturnal reptiles indicate a majority of thermoregulatory behavior (if any) occurs during the day within diurnal retreats, but few examined this behavior throughout the night. In tropical systems, thermal heterogeneity may remain high, even at night, allowing nocturnal ectotherms to thermoregulate through conduction on surfaces that retain heat after sunset. We investigated the thermoregulatory behavior of a tropical nocturnal gecko (Australian house gecko, Gehyra dubia) by measuring its preferred temperature in a thermal gradient, and selected body temperatures using radio telemetry, in relation to available operative environmental temperatures obtained using thermal models. Preferred body temperatures of geckos ranged from 31.4 ± 0.59-34.5 ± 0.55 °C in a laboratory thermal gradient. In the field, during winter, geckos were more effective thermoregulators than in the summer. In low thermal quality habitats, geckos sought rare, warm microclimates at night to maintain body temperatures warmer than most available environmental temperatures, and were highly effective thermoregulators. For ectotherms, appropriate environmental temperatures are a vital resource for survival, similar to food or shelter. The ability to exploit rare microclimates is especially important for nocturnal species, as heterogeneity of environmental temperatures is reduced at night compared to the day. In a warming world, it is vital to understand the thermal ecology of nocturnal ectotherms, as other species may shift to become more nocturnal to avoid lethal diurnal temperatures.

The Eurasian hot nightlife: Environmental forces associated with nocturnality in lizards

AbstractAimLizards are ancestrally diurnal, and most of them remain so. Nocturnality is common among lizards, but the environmental factors associated with lizard nocturnal activity are still unknown. Here, we contrasted the ambient temperature and productivity hypotheses, where we predicted that cold temperatures will pose a stonger limit to nocturnal species richness than diurnal lizards. Moreover, we contrasted the relative importance of annual, day and night mean temperatures to pinpoint the drivers of nocturnal lizard richness.LocationMainland Eurasia.MethodsWe collected distribution range and activity time data for all 1,113 lizard species found throughout mainland Eurasia. This represents the largest geographical scope to date, for studies of lizard species richness. We examined the spatial patterns of nocturnal species richness in relationship to diurnal species richness across environmental gradients of ambient temperature and productivity.ResultsNocturnal lizards are richest in the tropics and in deserts, and their richness decreases with latitude. However, nocturnal lizards are absent from the highest latitudes and coldest regions inhabited by lizards. Diurnal and nocturnal lizards respond in a similar manner to climatic factors. Ambient temperature has a strong influence on both, whereas productivity is more tightly related to the proportion of nocturnal species.Main conclusionsNocturnality is widespread among Eurasian lizards. However, nocturnal lizards are absent from invariably cold regions, and low temperatures seem to be a limiting factor for lizard activity period. We suggest that the year‐round warm nights of the tropics reduce the cost of being active at night and open the nocturnal niche for many lizards. In hot deserts, the combination of hot days and aridity increases the cost of diurnal activity, whereas nocturnal activity provides a shelter from these extreme conditions.

Taxonomic analysis of Paraguayan samples of Homonota fasciata Duméril & Bibron (1836) with the revalidation of Homonota horrida Burmeister (1861) (Reptilia: Squamata: Phyllodactylidae) and the description of a new species.

Homonota is a Neotropical genus of nocturnal lizards characterized by the following combination of characters: absence of femoral pores, infradigital lamellae not dilated, claws without sheath, inferior lamellae laterally not denticulate, and presence of a ceratobranchial groove. Currently the genus is composed of 10 species assembled in three groups: two groups with four species, and the fasciata group with only two species. Here, we analyzed genetic and morphologic data of samples of Homonota fasciata from Paraguay; according to Maximum Likelihood and Bayesian inference analyses, the Paraguay population represents an undescribed species. Additionally, morphological analysis of the holotype of H. fasciata (MNHN 6756) shows that it is morphologically different from the banded, large-scaled Homonota commonly referred to as “H. fasciata”. Given the inconsistency between morphological characters of the name-bearing type of H. fasciata and the species commonly referred to as H. fasciata, we consider them as different taxa. Thus, H. fasciata is a species inquirenda which needs further studies, and we resurrect the name H. horrida for the banded, large-scaled Homonota. The undescribed species from Paraguay is similar to H. horrida, but can be differentiated by the high position of the auditory meatus relative to the mouth commissure (vs. low position in H. horrida); and less developed tubercles on the sides of the head, including a narrow area between the orbit and the auditory meatus covered with small granular scales with or without few tubercles (vs. several big tubercles on the sides of the head even in the area between the orbit and the auditory meatus). The new species is distributed in the Dry Chaco in South America. With the formal description of this species, the actual diversity of the genus Homonota is increased to 12 species. Furthermore, we infer phylogenetic relationships for 11 of the 12 described species of the genus, based on 11 molecular markers (two mitochondrial and nine nuclear genes), with concatenated and species tree approaches.

Plasticity of thermoregulatory behavior in leopard geckos (Eublepharis macularius, Blyth 1954).

Studies on thermoregulation in nocturnal lizards have shown that their thermal regimes are similar to those of diurnal lizards, even though they hide during the daytime and are active mostly at night, when heat sources are very scarce. As a result, nocturnal lizards display an active thermoregulatory behavior consisting of seeking warm shelters to hide during the daytime, using accumulated heat for the nocturnal activity. Based on this information, we hypothesize that when leopard geckos (Eublepharis macularius, Blyth 1954) are presented with the choice of safety in cool shelters or vulnerability in heated open areas, suitable temperature will prevail in importance, i.e. they will trade the advantages provided by the shelter for an exposed, but physiologically necessary heat source. Data on the time juvenile E. macularius spent in shelters, and in open areas along a thermal gradient and under a 12/12 hr photoperiod, from eight individuals confirmed our hypothesis. We found that, not only did they select heat sources over shelters, but, along with the light/dark cycle, temperature may also represent a cue for activity. Additionally we found that substrate moisture plays an important role in shelter preference.

Nest-site selection and the factors influencing hatching success and offspring phenotype in a nocturnal skink

Nest-site selection in ectothermic animals influences hatching success and offspring phenotype, and it is predicted that females should choose nesting sites that maximise their reproductive fitness, ultimately through the reproductive success of their offspring. We completed nest-site choice experiments on a nocturnal lizard, the egg-laying skink (Oligosoma suteri), to determine whether eggs (and subsequent hatchlings) from cooler nests do better at cooler incubation temperatures, and conversely if those laid in warmer nests perform better at warmer incubation temperatures. We provided a simple nest-choice experiment, with oviposition-retreat sites available in either a hot or a cool sector of the enclosure; in the wild females nest under objects. Female O. suteri laid eggs both during the day and night, and nested more in the hot than cool sector. Eggs from each clutch were split across three egg incubation temperatures (18°C, 22°C, 26°C) to decouple the impact of initial nest-site choice from the subsequent incubation temperature regime. Whether eggs were initially laid in the hot or cool sector was not related to hatching success, offspring phenotype or offspring locomotor performance. We conclude that offspring phenotype and performance is primarily influenced by the temperature during incubation, rather than the initial thermal environment of the nest location. Thus, female O. suteri may select warmer nesting sites to ensure higher incubation temperature and enhanced offspring fitness.

The beauty and the beast: Endemic mutualistic interactions promote community-based conservation on Socotra Island (Yemen)

The understanding that biodiversity is supported by an entangled network of interactions is fundamental if we are to guarantee the persistence of endemic and restricted-range taxa. When it comes to remote, isolated and rural areas, local human communities play a pivotal role in preserving their native flora and fauna. Locals typically show contrasting aesthetic appreciation for different species, unaware that the fate of highly valued species might be closely linked to the activity of non-charismatic and disregarded species. Therefore, conveying the importance of biotic interactions in sustaining biodiversity is important to incentivise environmental awareness in those areas. The remote Socotra Archipelago (Yemen), a Natural World Heritage, hosts one of the oldest forest ecosystems on Earth and 31 endemic reptile species. The relic dragon’s blood tree Dracaena cinnabari is classified as Vulnerable and it is highly valued among locals. On the contrary, reptiles are typically persecuted and feared by them, in spite of the fact that they might provide services to D. cinnabari. In order to document the role of nocturnal lizards as pollinators of D. cinnabari, we conducted a trip to Socotra Island and we examined 11 tree populations at night for the presence of reptiles and whether they carry pollen in their snouts. Our results confirmed that three species of geckos carried pollen grains of D. cinnabari and at least seven other unidentified species. This result indicates that these geckos visit D. cinnabari flowers, likely to feed upon pollen or nectar, suggesting that they may pollinate this relic tree. We point out that by focusing on the need of preserving mutualistic biotic interactions, instead of individual species, environmental awareness would increase and Socotri people would steadily shift their attitude towards an holistic preservation of D. cinnabari.

Phylogenetic comparisons of pedestrian locomotion costs: confirmations and new insights.

The energetic costs for animals to locomote on land influence many aspects of their ecology. Size accounts for much of the among‐species variation in terrestrial transport costs, but species of similar body size can still exhibit severalfold differences in energy expenditure. We compiled measurements of the (mass‐specific) minimum cost of pedestrian transport (COTmin, mL/kg/m) for 201 species – by far the largest sample to date – and used phylogenetically informed comparative analyses to investigate possible eco‐evolutionary differences in COTmin between various groupings of those species. We investigated number of legs, ectothermy and endothermy, waddling, and nocturnality specifically in lizards. Thus, our study primarily revisited previous theories about variations in COTmin between species, testing them with much more robust analyses. Having accounted for mass, while residual COTmin did not differ between bipedal and other species, specifically waddling bipeds were found to have relatively high COTmin. Furthermore, nocturnal lizards have relatively low COTmin although temperature does not appear to affect COTmin in ectotherms. Previous studies examining across‐species variation in COTmin from a biomechanical perspective show that the differences between waddling birds and nonwaddling species, and between nocturnal lizards and other ecotherms, are likely to be attributable to differences in ground reaction forces, posture, and effective limb length.

Absence of temporal pattern in courtship signals suggests loss of species recognition in gecko lizards

According to the concept of ritualization, acquisition of signal function (i.e., species recognition) leads to formalization of specific signal structure (i.e., species-specific pattern). By contrast, loss of species recognition may result in specific pattern collapse of the signal, from a temporally regular pattern to an irregular form. Several studies have reported the loss of species recognition driven by release from selective pressure against hybridization under isolation from close relatives, but no study has reported collapse of a regular signal pattern that serves in species recognition. In nocturnal lizards of the genus Gekko, several species pairs hybridize when brought together, whereas other species pairs never hybridize, despite being sympatric. I investigated the relationship between the existence of natural hybridization, courtship call similarity and species recognition ability in eight species of Gekko. I found that males of all eight species court using calls, and four of these species have species-specific regular patterns in the courtship calls, whereas the other four have no temporal patterns. In playback experiments, females of the species-specific pattern call species discriminated species by the call. On the other hand, in the patternless call species, females did not discriminate species by the call, suggesting that natural hybridization has resulted from the loss of species recognition ability in the patternless call species. In insular Gekko isolated from congeners, acoustic species recognition might have been lost, followed by pattern collapse of the courtship calls. This unique example of the signal pattern collapse would provide a key to answer basic questions concerning the causes and consequences of signal evolution.

Adherence to Bergmann’s rule by lizards may depend on thermoregulatory mode: support from a nocturnal gecko

Bergmann's rule predicts an increase in body size with decreasing environmental temperature; however, the converse pattern has been found in the majority of lizards studied to date. For these ectotherms, small body size may provide thermal benefits (rapid heat uptake when basking), which would be highly advantageous in cold environments. Yet such an advantage may not exist in nocturnal lizards (which do not avidly bask), in which Bergmann's rule has not been closely studied. We have examined whether the body size of a primarily nocturnal gecko, Woodworthia "Otago/Southland" changed with elevation and operative temperature (determined using physical copper models). In a laboratory study, we investigated whether thermoregulatory mode (heliothermy or thigmothermy) alters the effect of body size on heating and cooling rates. This gecko followed Bergmann's rule, thereby showing the opposite of the dominant pattern in diurnal lizards. Size at maturity, maximum size of adults and size at birth were larger at higher elevations and at lower operative temperatures. Using physical models, we found that large body size can confer thermal benefits for nocturnal lizards that remain within diurnal retreats. Bergmann's rule should not be dismissed for all lizards. Our results clearly support Bergmann's rule for at least one thigmothermic species, for which large body size may provide thermal benefits. Future studies on Bergmann's rule in lizards should consider thermoregulatory mode. We advocate that this ecogeographic rule be examined in relation to operative temperature measured at field sites. Finally, we predict that climate warming may weaken the relationship between body size and elevation in this gecko.