No consistent effect of daytime versus night-time measurement of thermal tolerance in nocturnal and diurnal lizards

Abstract

While essential in understanding impacts of climate change for organisms, diel variation remains an understudied component of temporal variation in thermal tolerance limits [i.e. the critical thermal minimum (CTmin) and maximum (CTmax)]. For example, a higher Ctmax might be expected for an individual if the measurement is taken during the day (when heat stress is most likely to occur) instead of at night. We measured thermal tolerance (Ctmin and Ctmax) during both the daytime and night-time in 101 nocturnal and diurnal geckos and skinks in Hong Kong and in South Africa, representing six species and covering a range of habitats. We found that period of measurement (day vs. night) only affected Ctmin in South Africa (but not in Hong Kong) and that Ctmax was unaffected. Body size and species were important factors for determining Ctmax in Hong Kong and Ctmin in South Africa, respectively. Overall, however, we did not find consistent diel variation of thermal tolerance and suggest that measurements of critical thermal limits may be influenced by timing of measurement—but that such effects, when present, are likely to be context-dependent.

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

“…Animals were subjected to trials of critical thermal minimum (CT min ) and maximum (CT max ) before being released in their natural habitats. Experiments were conducted between 10 am and 4 pm to minimize the potential effect of diel variation (Dufour et al., 2022 ). Each animal was placed in a small thin metal container, covered by a transparent plastic sheet pierced by small holes to let fresh air in but without risking escape.…”

“…For example, Herrando-Pérez et al (2019) found that not accounting for intraspecific differences in CT max resulted in both under-and over-estimating impacts of climate change in altering species fitness. Furthermore, for some species, thermal tolerance can vary from day to night (Dufour et al, 2022). Habitat type can also be associated with thermal tolerance variation within species as Landry Yuan et al (2018) showed that warming benefited ecotone populations but not forest populations of the lizard Trachylepis affinis.…”

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

“…Animals were subjected to trials of critical thermal minimum (CT min ) and maximum (CT max ) before being released in their natural habitats. Experiments were conducted between 10 am and 4 pm to minimize the potential effect of diel variation (Dufour et al., 2022 ). Each animal was placed in a small thin metal container, covered by a transparent plastic sheet pierced by small holes to let fresh air in but without risking escape.…”

“…For example, Herrando-Pérez et al (2019) found that not accounting for intraspecific differences in CT max resulted in both under-and over-estimating impacts of climate change in altering species fitness. Furthermore, for some species, thermal tolerance can vary from day to night (Dufour et al, 2022). Habitat type can also be associated with thermal tolerance variation within species as Landry Yuan et al (2018) showed that warming benefited ecotone populations but not forest populations of the lizard Trachylepis affinis.…”

Sexual Dimorphism and Female Reproductive Characteristics in the Hainan Water Skink (<italic>Tropidophorus hainanus</italic>) from Hainan, South China

“…[e.g., the Brook's Water Skink T. brookei (Sah et al, 2016) and the Bavay's Water Skink T. baviensis (Bobrov, 1997)], nocturnal (e.g., the Broad-scaled Water Skink T. latiscutatus and the Murphy's Water Skink T. murphyi, Hikida et al, 2002), or cathemeral [e.g., the Partello's Water Skink Tropidophorus partelloi and T. sinicus (Dufour et al, 2022) that are active during the day and/or night]. Third, Tropidophorus skinks show a strong preference for moist to semiaquatic forest habitats (Smith, 1923;Greer and Biswas, 2004;Ikhwan et al, 2022).…”

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

“…Animals were subjected to trials of critical thermal minimum (CT min ) and maximum (CT max ) before being released in their natural habitats. Experiments were conducted between 10 am and 4 pm to minimize the potential effect of diel variation (Dufour et al., 2022 ). Each animal was placed in a small thin metal container, covered by a transparent plastic sheet pierced by small holes to let fresh air in but without risking escape.…”

“…For example, Herrando-Pérez et al (2019) found that not accounting for intraspecific differences in CT max resulted in both under-and over-estimating impacts of climate change in altering species fitness. Furthermore, for some species, thermal tolerance can vary from day to night (Dufour et al, 2022). Habitat type can also be associated with thermal tolerance variation within species as Landry Yuan et al (2018) showed that warming benefited ecotone populations but not forest populations of the lizard Trachylepis affinis.…”

Sexual Dimorphism and Female Reproductive Characteristics in the Hainan Water Skink (<italic>Tropidophorus hainanus</italic>) from Hainan, South China

“…[e.g., the Brook's Water Skink T. brookei (Sah et al, 2016) and the Bavay's Water Skink T. baviensis (Bobrov, 1997)], nocturnal (e.g., the Broad-scaled Water Skink T. latiscutatus and the Murphy's Water Skink T. murphyi, Hikida et al, 2002), or cathemeral [e.g., the Partello's Water Skink Tropidophorus partelloi and T. sinicus (Dufour et al, 2022) that are active during the day and/or night]. Third, Tropidophorus skinks show a strong preference for moist to semiaquatic forest habitats (Smith, 1923;Greer and Biswas, 2004;Ikhwan et al, 2022).…”

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

“…Animals were subjected to trials of critical thermal minimum (CT min ) and maximum (CT max ) before being released in their natural habitats. Experiments were conducted between 10 am and 4 pm to minimize the potential effect of diel variation (Dufour et al., 2022 ). Each animal was placed in a small thin metal container, covered by a transparent plastic sheet pierced by small holes to let fresh air in but without risking escape.…”

“…For example, Herrando-Pérez et al (2019) found that not accounting for intraspecific differences in CT max resulted in both under-and over-estimating impacts of climate change in altering species fitness. Furthermore, for some species, thermal tolerance can vary from day to night (Dufour et al, 2022). Habitat type can also be associated with thermal tolerance variation within species as Landry Yuan et al (2018) showed that warming benefited ecotone populations but not forest populations of the lizard Trachylepis affinis.…”

Sexual Dimorphism and Female Reproductive Characteristics in the Hainan Water Skink (<italic>Tropidophorus hainanus</italic>) from Hainan, South China

“…[e.g., the Brook's Water Skink T. brookei (Sah et al, 2016) and the Bavay's Water Skink T. baviensis (Bobrov, 1997)], nocturnal (e.g., the Broad-scaled Water Skink T. latiscutatus and the Murphy's Water Skink T. murphyi, Hikida et al, 2002), or cathemeral [e.g., the Partello's Water Skink Tropidophorus partelloi and T. sinicus (Dufour et al, 2022) that are active during the day and/or night]. Third, Tropidophorus skinks show a strong preference for moist to semiaquatic forest habitats (Smith, 1923;Greer and Biswas, 2004;Ikhwan et al, 2022).…”