Behavioral thermoregulation and habitat selection in desert-dwelling lizard species

Behavioral thermoregulation refers to the active selection of microhabitats that allow ectotherms to maintain body temperatures within a preferred range despite fluctuating ambient conditions. This research compared thermoregulatory behaviour and habitat use among three sympatric lizard species (Liolaemus darwinii, L. multimaculatus, and Ctenophorus kingii) inhabiting the Monte Desert scrubland near Rosario, Argentina. Focal observations were conducted on 180 individuals across 36 transects between October 2022 and February 2023. Body temperature was recorded using cloacal thermometry at each capture event. L. darwinii maintained a mean field body temperature of 36.8 ± 1.2 °C and shuttled between sun and shade at a rate of 4.7 transitions per hour. L. multimaculatus was more thermally lax, tolerating a wider range (34.3 ± 1.8 °C) and showing fewer shuttling bouts (2.3/h). C. kingii preferred the highest temperatures (38.1 ± 0.9 °C) and occupied open rocky substrates almost exclusively during midday. Habitat selection modelling indicated that substrate type and shrub canopy cover were the strongest predictors of species occurrence. These patterns suggest that interspecific differences in thermal preference mediate habitat partitioning in this arid assemblage.

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Comparative Thermoregulatory StrategiesClose ×

AI-generated conceptual illustration (Desert-dwelling lizards (specifically Ctenosaura kingii, Liolaemus darwinii, and Liolaemus multimaculatus)). It explains the idea and does not show study data.

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de index (°C): L. Darwinii vs L. Multimac. vs C. KingiiClose ×

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Shuttling rate (/h): L. Darwinii vs L. Multimac. vs C. KingiiClose ×

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Introduction

Thermoregulation is an old problem in reptile ecology that hasn't lost its relevance. Desert lizards face a daily balancing act: they need warmth for digestion, locomotion, and immune function, but overheating can be lethal within minutes [1] . Unlike endotherms, lizards manage this trade-off by shuttling between sun-exposed and shaded microhabitats, adjusting their body posture, and selecting substrates that match their thermal preferences [2] . The Monte Desert of central Argentina supports a diverse lizard fauna, with several Liolaemus species co-occurring in scrubland dominated by Larrea and Prosopis [3] . How these ecologically similar species partition thermal resources is not well understood, partly because most thermoregulatory work in the region has focused on single-species laboratory setups rather than multi-species field comparisons [4] . When two or more ectotherms share a habitat, differences in preferred body temperature can translate into differences in activity timing, substrate use, and microhabitat selection effectively reducing niche overlap and promoting coexistence [5] . This research tested that idea by measuring field body temperatures, shuttling behaviour, and microhabitat use in three sympatric species L. darwinii, L. multimaculatus, and Ctenophorus kingii along transects in the Monte Desert near Rosario during the warm season of 2022-2023. The objectives were to (1) quantify interspecific variation in field body temperature and thermal precision, (2) describe diel patterns of shade use and substrate selection, and (3) model the environmental predictors of species occurrence to assess the degree of thermal niche partitioning [6] .

Material and Methods

Material and Methods

Study area description

Study area description

Instrumentation

Temperature loggers (iButton DS1921G, Maxim Integrated) recorded operative temperatures at 15-minute intervals inside copper lizard models painted to match average lizard reflectance. Models were deployed in sun, partial shade, and full shade at each transect for the duration of the research.

Results

The three species differed significantly in mean field body temperature (Kruskal-Wallis H = 47.3, Table 1). C. kingii maintained the highest and narrowest temperature range, while L. multimaculatus was the most thermally variable. L. darwinii showed intermediate temperatures but the highest shuttling rate, consistent with active thermoregulatory behaviour.

Parameter	L. Darwinii	L. Multimac.	C. Kingii	P-value
Mean Tb (°C)	36.8 ± 1.2	34.3 ± 1.8	38.1 ± 0.9	< 0.001
Preferred range (°C)	35.2–38.4	31.8–37.1	36.9–39.6
de index (°C)	1.4 ± 0.6	2.7 ± 1.1	0.9 ± 0.4	< 0.001
Shuttling rate (/h)	4.7 ± 1.3	2.3 ± 0.8	1.6 ± 0.5	< 0.001

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Table 1Close ×

Thermoregulatory parameters for three desert lizard species in the Monte Desert, Argentina

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Comprehensive interpretation

Rocky substrates and low canopy cover were the strongest habitat predictors (Table 2). C. kingii was almost exclusively associated with rock outcrops, while L. darwinii used mixed substrates. The diel activity pattern (Figure 2) showed peak sun exposure at 09:00-11:00 and a pronounced midday retreat to shade when operative temperatures exceeded 42 °C, followed by a secondary activity window in the late afternoon.

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Figure 2Close ×

Diel pattern of shade use and sun exposure across all three species pooled, Monte Desert, October 2022–February 2023

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Predictor	Estimate	Se	Z-value	P-value
Substrate: rock	1.83	0.41	4.46	< 0.001
Canopy cover (%)	−0.94	0.28	−3.36	< 0.001
Operative temp (°C)	0.67	0.19	3.53	< 0.001
Distance to rock (m)	−0.38	0.14	−2.71	0.007

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Table 2Close ×

Habitat selection model results (best AIC model) for species occurrence

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Discussion

The 3.8 °C gap in mean body temperature between C. kingii and L. multimaculatus is consistent with thermal niche partitioning models that predict coexistence through divergence in preferred temperature [5] . C. kingii's narrow thermal range and low shuttling rate suggest it relies on basking-site fidelity rather than active shuttling, a strategy that works well on exposed rock surfaces where solar radiation is predictable [2] . L. darwinii, by contrast, shuttled nearly five times per hour, indicating a more energyintensive thermoregulatory style suited to the heterogeneous shrubland it occupies. The midday retreat to shade across all species mirrors the bimodal activity pattern documented in numerous desert lizard assemblages [1] . Operative temperatures in full sun exceeded 48 °C at midday during peak summer, well above the critical thermal maximum for all three species, making shade-seeking essential for survival. The importance of substrate type in the habitat model supports earlier work showing that surface thermal properties albedo, heat capacity shape microhabitat quality for ectotherms more than vegetation structure alone [4] . A limitation worth noting is that this research covered only the warm season. Cool-season thermoregulatory data might reveal different patterns, particularly for L. multimaculatus, whose broad thermal tolerance could allow year-round activity in mild winters when the other species are inactive [3] .

Conclusion

This field comparison of three sympatric desert lizards revealed clear interspecific differences in body temperature, thermal precision, and shuttling behaviour that align with distinct microhabitat preferences. C. kingii occupied hot, rocky substrates with minimal canopy cover; L. darwinii used mixed shrubland and shuttled actively; and L. multimaculatus tolerated a wide thermal range across varied microhabitats. These differences support the hypothesis that divergence in thermoregulatory strategy facilitates coexistence in thermally challenging environments. From a conservation perspective, the strong dependence of C. kingii on exposed rock outcrops makes it vulnerable to habitat modification. Any land-use change that reduces rock availability or increases shrub encroachment could shift competitive dynamics in favour of the more thermally flexible species. Future work should incorporate seasonal data and test whether climate warming narrows the thermal safety margins that currently allow all three species to persist in the Monte Desert.

Acknowledgement

Acknowledgements Funding sourcesThis research was supported by internal departmental funds from the Centro de Ciencias Biológicas del Litoral, Rosario. No external grant funding was received. Institutional supportThe authors acknowledge the Centro de Ciencias Biológicas del Litoral, Rosario for providing laboratory access and logistical support.

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Box plot and violin plot of field body temperatures for three sympatric lizard species in the Monte Desert

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