Hydric and Thermal Traits of Northern Australian Geckos: Water Loss Is Not Explained by Aridity

Abstract

Behavioural and physiological adaptations are important for maintaining stable hydric states and viable body temperatures under challenging conditions experienced in variable terrestrial environments. For example, reptiles from arid locations tend to have lower rates of evaporative water loss (EWL). Here we test the prediction that geckos adapt their physiology to match the local environment to reduce hydric and thermal stress. Specifically, we compared EWL and preferred temperature among closely related species living under a range of climatic conditions. EWL rates were measured using a flow-through system in 18 species in the genus Gehyra collected from 11 locations across a strong gradient in aridity in tropical northern Australia during the dry season (Austral winter), and preferred temperatures were measured for nine of these species. Rates of EWL did not differ significantly among most species except between those with the highest and lowest rates. There was no association between EWL and the aridity of the locations where geckos were captured, and microhabitat conditions (temperature and humidity in rock crevices, used as retreats) did not explain this lack of association. Thermal preferences differed among species, with G. koira selecting significantly cooler temperatures than all other species. Gehyra moritzi, from the most arid and hottest location (Kurundi Station), had the highest preferred body temperature, overlapping only with two sympatric species (G. minuta and G. purpurascens). Unlike some reptiles, there was no evidence Gehyra geckos specialise in their EWL to match the local climate despite the strong gradient in aridity across our sampling sites. Nocturnal activity or seasonal plasticity in EWL may explain the lack of association between physiological traits of these species and the broad climatic conditions in the places they live.

Keywords: Gehyra; aridity; climate; evaporative water loss; phylogeny; thermal preference.

FIGURE 1

(a) Phylogenetic tree (Lau et al. 2025) and corresponding sampling locations for Gehyra geckos sampled during the dry season between 2019 and 2021 for evaporative water loss (EWL) and thermal preference (T_Pref) analyses. Sampling locations correspond with (b); bold locations in (a) indicate sites for T_Pref analyses in addition to EWL analyses. (b) Map of sampling locations and habitat types in the Northern Territory and Western Australia. For context, the map color overlap represents mean annual 3 PM relative humidity (%RH) between 1976 and 2005. Figure modified from map provided by the Australian Bureau of Meteorology, http://www.bom.gov.au/. See Appendix 1; Figure A3 for an alternative map using a color overlap based on vapor pressure (Pa).

FIGURE 2

Mean monthly temperature and humidity measured by data loggers placed across sites between 2019 and 2021. Red lines are grand mean values; black lines are mean maximum and mean minimum values. Solid lines represent data collected from inside crevice microhabitats, dashed lines represent data collected from the external environment in the shade. Significant differences in measures between crevice and external conditions were found in Gogo Station (maximum temperature, minimum temperature, maximum humidity, minimum humidity) and Litchfield (mean temperature, minimum temperature).

FIGURE 3

Mean surface area‐adjusted evaporative water loss (EWL) rates of Gehyra species sampled in the dry season from the Northern Territory and Western Australia. Data were acquired during May and June, except for species marked with ‘*’ which were sampled in September. Species marked ‘a’ are significantly different from species marked ‘b’ in post hoc emmeans. Error bars display ±1 standard error.

FIGURE 4

Means of preferred temperatures of Gehyra species sampled from locations in the Northern Territory. Measurements were taken during the dry season. Horizontal bars indicate species similarities from post hoc tests. Error bars display ±1 standard error.

FIGURE A1

Species of the three Gehyra clades represented in this study, including: (a) the G. australis clade, characterized by large bodies and preferring trees and rock boulder habitats (photo: G. lapistola); (b) the small‐bodied G. nana clade, which inhabits various rocky environments (photo: G. nana ); and (c) the arid radiation of Gehyra (photo: G. minuta ). Photos: Stephen Zozaya.

FIGURE A2

Habitat terrain types of rock‐dwelling north Australian Gehyra, including (a) granite boulders, cliffs (Mt. Nyulasy), (b) small, fractured basalt ground rocks (Kidman Springs), and (c) limestone outcrops (Gogo Station).

FIGURE A3

Sites in the Northern Territory (NT) and Western Australia (WA) where Gehyra geckos were sampled. The background map is colour‐coded by vapor pressure, calculated with data from New et al. (2002), which provides average values for 1960–1990.

FIGURE A4

Thermal image of a Gehyra showing the temperature sampling site in the lower abdominal region (M1) and the corresponding temperature scale as displayed in the Testo IRSoft thermal imaging software (v4.8) interface. Image taken using a Testo 868 thermal imaging camera (0.08°C thermal sensitivity).

FIGURE A5

Mean rates of adjusted evaporative water loss (EWL) in relation to the mean aridity score for each of the 18 sampled Gehyra species. EWL rates are adjusted to a surface area (SA) of 33.1 cm² (the average SA across the 18 species). Whiskers represent one standard deviation. There was no significant relationship between adjusted EWL and aridity among species.