Body temperature is fundamental for the ecology of ectotherms due to its direct effect on their fitness. The thermoregulation of small reptiles involves a regulatory process that depends on morphophysiological and behavioural adjustments, along with environmental thermal characteristics, to maintain as close as possible to their optimum temperature. In this study, we evaluated the thermoregulation capacity of Phyllodactylus gerrhopygus, a relatively small and crepuscular-nocturnal gecko. Specifically, the aims of the present work were: 1) to determine if this species behaves as a thermoregulator or thermoconformer species, 2) to examine if the preferred body temperatures (T_pref) vary during the hours of potential thermoregulation and 3) if there are differences in daily patterns of T_pref and thermoregulation between juveniles and adults. In the field, we recorded the T_b of geckos and the substrate (T_s) and air (T_a) temperatures from their refuges. In the laboratory, we evaluated T_pref by recording the temperature geckos selected in a thermal gradient at different times of the day. We found a positive association between T_b and T_s. The positive correlation between T_b and refuge temperature suggests that P. gerrhopygus is a thigmothermic and thermoconformer species. Both juveniles and adults select similar temperatures and neither of them thermoregulates. The T_pref was significantly higher during the evening (32.23 ± 5.91 °C) than the morning period (25.2 ± 9.02 °C). We did not find differences between juveniles and adults. Our results are similar to those found in other phylogenetically close lizards, suggesting a strong phylogenetic inertia in thermal preferences.

desert climate, ectotherms, lizards, micro-habitat, thermoregulation

Body temperature (T_b) plays a crucial role in the ecology of ectotherms because it directly influences their fitness (Huey and Berrigan 2001). The temperature affects various activities, such as foraging, movement and reproduction in these organisms (Peterson et al. 1993; Angilletta 2009). In this regard, thermoregulation is crucial for maintaining body temperature within appropriate ranges and preventing extreme temperatures. For small reptiles like other ectotherms, thermoregulation involves a combination of physiological and behavioural adaptations, enabling animals to achieve a T_b that maximises their physiological functions or overall performance (Cowles and Bogert 1944; Avery 1982; Angilletta et al. 1999; Aguilar and Cruz 2010; Lara-Resendiz et al. 2013; Lapwong et al. 2020; Mouadi et al. 2020). This process of thermoregulation is influenced by several factors related to the organisms’ activity periods, which differ between their active and inactive times (Angilletta et al. 1999).

Small nocturnal reptiles depend on their diurnal microhabitat for shelter and as sites for thermoregulation (Kerney and Predavec 2000; Webb and Shine 2000). For example, during the day, they maintain their T_b within a selected interval of preferred temperature (T_pref) to carry out their physiological temperature-dependent processes, such as digestion, growth and reproduction (Angilletta and Werner 1998; Aguilar and Cruz 2010; Lara-Resendiz et al. 2013). On the other hand, during the night, the thermal quality of the environment decreases and the opportunities to achieve appropriate temperature for foraging, locomotion, socialization, escape or defence from predators are limited (Kearney and Predavec 2000; Aguilar and Cruz 2010). At night, there are decreased opportunities for thermoregulation, but social activities in this period increase the risk of injury and predation and there is higher energy expenditure (Lara-Resendiz et al. 2013). However, the daytime period of ‘inactivity’ could be thermally advantageous since various reptiles can actively control T_b more accurately inside their shelter than when they are out and active, highlighting the importance of microhabitat selection (Cowles and Bogert 1944; Huey et al. 1989; Lara-Resendiz et al. 2013).

T_b and T_pref are frequently used to study the thermal ecology of small ectotherms, especially in lizards (Angilletta et al. 1999; Huey and Berrigan 2001; Aguilar and Cruz 2010; Lara-Resendiz et al. 2013). The T_pref can be obtained by placing an animal in a linear temperature gradient selected by organisms in laboratory conditions (Huey and Berrigan 2001; Alfaro et al. 2013; Taucare-Ríos et al. 2020) and it is an environment that is independent of the ecological cost (Hertz et al. 1993). In lizards, such as geckos, T_pref can be influenced by intrinsic (e.g. sex, age and body condition of individuals) and extrinsic factors (environmental conditions) (Angilletta et al. 1999; Aguilar and Cruz 2010; Lapwong et al. 2020; Mouadi et al. 2020). Some authors have suggested that preferred body temperature, being part of the thermal niche, can be considered a phylogenetically conserved trait and/or, in some cases, has high phenotypic flexibility to environmental changes (Labra et al. 2009; Clusella-Trullas et al. 2014; Giacometti et al. 2024).

The thermal quality of the habitat selected by geckos depends on the difference between the available environmental temperatures and their T_pref (Angilletta et al. 1999; Huey and Berrigan 2001; Blouin-Demers and Nadeau 2005; Tan and Schwanz 2015). Night temperatures may influence thermoregulatory strategies if, for example, warm temperatures create numerous microhabitats near the preferred temperature or if cool temperatures limit the availability of microhabitats near the preferred temperature (Tan and Schwanz 2015).

The South American Leaf-toed Gecko Phyllodactylus gerrhopygus (Wiegmann, 1834) is a relatively small gecko (Snout to Vent Length, SVL ≈ 50 mm) that is primarily crepuscular and nocturnal. It is endemic to the desert regions of Chile and Peru (Aguilar et al. 2015; Ruiz de Gamboa 2016) and is currently listed as Least Concern (IUCN 2023). The ecology and behaviour of P. gerrhopygus remain largely unstudied. This gecko inhabits rocky and sandy coastal areas of deserts and even in human environments, they seek refuge during the day under rocks, logs or anthropogenic debris (Mella 2017). The species has a generalist and insectivorous diet and acts as an opportunistic predator, mainly preying on spiders, followed by beetles, insect larvae and solifuges (Pérez and Balta 2011). They remain active throughout the year, including winter (July-September), surviving in conditions with median air temperatures of around 13 °C at sea level and 7 °C at 3400 m above sea level (Kroll and Dixon 1972). However, there is little to no published information regarding its thermal ecology.

This study aimed to investigate the thermal biology of P. gerrhopygus, specifically examining the interplay of intrinsic and extrinsic factors influencing its preferred body temperature and elucidating the thermoregulatory strategies employed by the species in its natural habitat. We addressed the following questions: 1) What is the effect of intrinsic (age class, body size) and extrinsic factors (time of day) on field T_b and preferred laboratory temperatures? 2) What thermoregulatory strategy does P. gerrhopygus employ to maintain its field T_b — thigmothermy or heliothermy?

We collected data from 20 individuals, comprising nine adults and 11 juveniles. The individuals had a body mass of 1.69 ± 0.72 g and measured 47.21 ± 7.5 mm of SVL. The field T_b was 26.1 ± 4.05 °C and the T_s was 25.81 ± 5.13 °C (Table 1). No differences were found between adults and juveniles in field T_b (t-test, t₁₈ = 0.79, p = 0.43). We found a strong positive association between T_b and T_s (r = 0.88, p < 0.05) and a moderate association between T_b and T_a (r = 0.44, p < 0.05). We found that mean db was 5.82 ± 4.3, showing low accuracy in thermoregulation (thermoconformism), with a low difference between juveniles (6.7) and adults (4.2). A linear regression of T_pref versus SVL for all animals collected did not indicate a significant relationship (p = 0.16, F_1,18 = 0.04, R² = 0.002, slope = -0.004). No linear relationship was found between body mass and T_pref either (p = 0.15, F_1,18 = 0.035, R² = 0.001, slope = -0.39). The results show that P. gerrhopygus is a thigmothermic species with a significant relationship between T_b and T_s (p < 0.05, F_1,18 = 64.63, R² = 0.78, slope = 0.69) (Fig. 2) and a significant relationship between T_b and T_a (p < 0.05, F_1,18 = 4.9, R² = 0.21, slope = 0.85). No differences were found between T_b and T_pref (paired t-test, t₁₈ = 1.45, p = 0.15) or T_s and T_pref (paired t-test, t₁₈ = 1.5, p = 0.14). Still, there is a significant difference between T_a and T_pref (paired t-test, t₁₈ = 2.36, p = 0.02).

Figure 2. 

Linear regression analysis between body temperature (T_b) of Phyllodactylus gerrhopygus and substrate temperature (T_s). The line represents the best fit for the scatter plot data.

The mean T_pref in the thermal gradient was 28.63 ± 9.41 °C (range = 9.2–41 °C; n = 20) with T_pref 25 of 25.55 °C and the T_pref 75 of 35.77 °C. The frequency histogram showed a precise bimodality distribution in the selected temperatures with differences between morning and evening period (Fig. 3). The T_pref was significantly higher during the evening (32.23 ± 5.91 °C) than the morning period (25.2 ± 9.02 °C) (two-way repeated measures ANOVA, F_{1, 17 =} 18.36, p = 0.0005) (Fig. 4). We did not find differences between adults and juveniles (two-way repeated measures ANOVA, F_1,17 = 0.14, p = 0.71).

Figure 3. 

Frequency histogram of preferred temperatures (T_pref) (percentage of all recordings) for Phyllodactylus gerrhopygus. Blue: morning period; Red: evening period.

Figure 4. 

Box plot showing preferred body temperature (T_pref) for Phyllodactylus gerrhopygus. The box represents the middle 50% of observed values. T_pref was significantly higher during the evening than the morning period.

Both field T_b and T_pref obtained in the laboratory showed a preference for warm temperatures. We found that both T_b and T_pref were not influenced by intrinsic factors such as age class or body size, but were affected by changes in the time of day. Geckos had lower body temperatures during the morning and increased them during the evening. This pattern is consistent with nocturnal animals living in arid environments (Angilletta et al. 1991; Alfaro et al. 2013; Lara-Resendiz et al. 2013; Taucare-Ríos et al. 2020).

Warm preferred body temperatures selected by geckos may reflect a phylogenetic inertia in the Phyllodactylidae family. In fact, species such as P. bordai and P. gerrhopygus show similar responses to environmental changes (Lara-Resendiz et al. 2013). Phylogenetic inertia means that these species retain evolutionary adaptations in thermal preferences to variable environments, responding with a similar phenotypic flexibility in both physiological and morphological traits (Labra et al. 2009). Nocturnal geckos tend to select high temperatures in desert environments, showing eurythermic behaviour (Angilletta et al. 1991; Lara-Resendiz et al. 2013; Tan and Schwanz 2015; Cardona-Botero et al. 2019). The study by Lara-Resendiz et al. (2013) in P. bordai shows us that thigmothermy and thermoconformity are common strategies in geckos of the genus Phyllodactylus. The T_pref found in P. bordai was 29.9 °C with an interval by T_pref (25–75%) of 27.8–32.6 °C, while our results show a T_pref of 28.63 °C with an interval by T_pref (25–75%) of 25.55–35.7 °C for P. gerrhopygus.

Our results show that the T_pref is similar to the temperatures found in their microhabitat, indicating that the geckos achieve their preferred temperature by obtaining heat from the environment. This species maintains field T_b within its T_pref range to carry out its temperature-dependent physiological processes, such as digestion and reproduction, which have been found in other nocturnal reptiles (Angilletta and Werner 1998; Angilletta et al. 1999; Aguilar and Cruz 2010; Lara-Resendiz et al. 2013).

On the other hand, we found a significant variation in T_pref during the day, a pattern that can be explained by the changes in the activity of these animals (Hays et al. 2019). The upper surfaces of the rocks would be warmer due to an accumulation of heat during sun exposure (Huey et al. 1989; Angilletta et al. 1999). Previous studies have shown that T_pref in nocturnal geckos, determined in a laboratory thermal gradient, has been found to range between 25 °C and 35 °C and has been linked to the predatory activity of these animals at night (Dawson 1975; Huey et al. 1989; Angilletta and Werner 1998; Angilletta et al. 1999; Lara-Resendiz et al. 2013; Hays et al. 2019). Additionally, activity at night may facilitate predator avoidance, as many lizard predators (e.g. birds) are either inactive at night or have decreased capacity to see prey (Hays et al. 2019).

Thigmothermic animals exhibit this pattern, as they maintain relatively high temperatures within their shelters during the day to increase metabolic efficiency and, at night, they operate at low or suboptimal body temperatures (Bustard 1967; Avery 1982; Rock and Cree 2008; Lara-Resendiz et al. 2013). Therefore, the bimodality in T_pref found in this study would account for a physiological adaptation of nocturnal animals to high daily thermal oscillations (Angilletta et al. 1999; Alfaro et al. 2013; Taucare-Ríos et al. 2020). This same T_pref variation has been found in other nocturnal ectotherms (e.g. reptiles and arthropods) from desert climates (Angilletta et al. 1999; Aguilar and Cruz 2010; Lara-Resendiz et al. 2013; Mouadi et al. 2020; Taucare-Ríos et al. 2020).

Refuge temperature and microhabitat selection are fundamental aspects of small ectotherms (Webb and Shine 2000; Goldsbrough et al. 2004). In this case, P. gerrhopygus selects warm shelters (T_s = 25.81 ± 5.13 °C; T_b = 26.1 ± 4.05 °C) during the day. This selection of microhabitat could increase locomotion, sprint speed, growth, possibly auditory sensitivity, predation and predatory avoidance (Avery 1982; Huey et al. 1989; Rock and Cree 2008; Aguilar and Cruz 2010; Hays et al. 2019). This species is highly dependent on the T_s, employing a thigmothermic strategy similar to that of other Neotropical geckos (Marquet et al. 1990; Aun and Martori 1994; Colli et al. 2003; Aguilar and Cruz 2010; Lara-Resendiz et al. 2013). Some studies suggest that diurnal refuge temperature may stem from the necessity of reaching high enough T_b to complete digestive and physiological processes related to the previous night’s activity (Kearney and Predavec 2000; Aguilar and Cruz 2010). Similarly, P. gerrhopygus is a thermoconformer species that depends directly on the thermal fluctuations of its environment. These fluctuations would force them to remain hidden in thermally adequate shelters during the day, limiting their thermoregulation capacity. This thermoconformity may enable these animals to conserve time and energy for hunting and feeding, rather than devoting it to thermoregulatory activities (Huey and Slatkin 1976; Labra and Vidal 2003).

Finally, we found that adults and juveniles have similar T_pref in laboratory conditions. Previous studies suggest that P. gerrhopygus does not exhibit ontogenetic differences in microhabitat use and does not compete for access to suitable rocks (Mella and Reyes 2022). We assume that both juveniles and adults require the exact thermal requirements for their growth and foraging activities. Similar results were found by Angilletta and Werner (1998) and Angilletta et al. (1999) for nocturnal geckos. On the contrary, other studies have found opposite results, where juveniles had a lower T_pref than adults (Hitchcock and McBrayer 2006). Future studies should provide more in-depth information on these results, as we are uncertain about the underlying causes of this phenomenon.

In conclusion, P. gerrhopygus is an eurythermic species that can select a wide range of temperatures during the day. The T_pref increases during the evening as part of its strategy to maximise locomotor activity, prey capture and digestion. This reptile selects thermally favourable shelters that allow it to reach its T_pref. Our results suggest that this gecko is a thigmothermic and thermoconformer species. Both juveniles and adults choose the same temperatures and may share the same microhabitats. This paper represents the first work on the thermal ecology of this species. Future studies should focus on the effect that climate change could have on this gecko and its distribution.

The authors thank SAG (Servicio Agrícola y Ganadero) for the authorisation to capture specimens (Resolución Exenta N°: 6695/2023). The first author thanks Núcleo de Investigación Aplicada e Innovación en Ciencias Biológicas, Universidad Arturo Prat, Iquique, Chile. CR-O thanks the ANID Postdoctoral FONDECYT grant N°3230799. Finally, we appreciate the valuable comments provided by two anonymous reviewers.