Research Article: Thermal physiology of Amazonian lizards (Reptilia: Squamata)

Date Published: March 7, 2018

Publisher: Public Library of Science

Author(s): Luisa M. Diele-Viegas, Laurie J. Vitt, Barry Sinervo, Guarino R. Colli, Fernanda P. Werneck, Donald B. Miles, William E. Magnusson, Juan C. Santos, Carla M. Sette, Gabriel H. O. Caetano, Emerson Pontes, Teresa C. S. Ávila-Pires, Michael Sears.

http://doi.org/10.1371/journal.pone.0192834

Abstract

We summarize thermal-biology data of 69 species of Amazonian lizards, including mode of thermoregulation and field-active body temperatures (Tb). We also provide new data on preferred temperatures (Tpref), voluntary and thermal-tolerance ranges, and thermal-performance curves (TPC’s) for 27 species from nine sites in the Brazilian Amazonia. We tested for phylogenetic signal and pairwise correlations among thermal traits. We found that species generally categorized as thermoregulators have the highest mean values for all thermal traits, and broader ranges for Tb, critical thermal maximum (CTmax) and optimal (Topt) temperatures. Species generally categorized as thermoconformers have large ranges for Tpref, critical thermal minimum (CTmin), and minimum voluntary (VTmin) temperatures for performance. Despite these differences, our results show that all thermal characteristics overlap between both groups and suggest that Amazonian lizards do not fit into discrete thermoregulatory categories. The traits are all correlated, with the exceptions of (1) Topt, which does not correlate with CTmax, and (2) CTmin, and correlates only with Topt. Weak phylogenetic signals for Tb, Tpref and VTmin indicate that these characters may be shaped by local environmental conditions and influenced by phylogeny. We found that open-habitat species perform well under present environmental conditions, without experiencing detectable thermal stress from high environmental temperatures induced in lab experiments. For forest-dwelling lizards, we expect warming trends in Amazonia to induce thermal stress, as temperatures surpass the thermal tolerances for these species.

Partial Text

Body temperature (Tb) in ectotherms influences all physiological and behavioral processes [1]. Consequently, maintenance of Tb within suitable limits is essential for ectotherms survival [2]. Thermoregulators actively maintain Tb within a restricted range of temperatures by heliothermy, i.e., by basking in the sun, or by thigmothermy, i.e., by contact with warm surfaces [3]. Thermoconformers do not actively thermoregulate, so their Tb parallels fluctuations in the environmental temperature [1, 4]. However, no lizard species has been shown to be a complete thermoconformer; all will move to avoid unfavorable extreme temperatures. This category is often used for species that select areas with relatively uniform temperatures, such as shaded forest, where active thermoregulation is not needed to maintain relatively stable body temperatures. Using a strictly thermoconforming strategy requires that species have broad thermal tolerances [1], and experience high variation in Tb throughout the day, season and geographic range.

We obtained thermal data for 69 lizard species from eleven families (Table 1), including new data on field-active Tb, Tpref, thermal performance and tolerance from 27 species (Table 2). Among all species with physiological data, 64 are diurnal, one is cathemeral, and four nocturnal. Based on the literature, 38 species are classified as thermoconformers, while 31 are thermoregulators.

We observed a non-significant phylogenetic correlation between Topt and CTmax, and considering that Topt is correlated with all other thermal traits, this is in agreement with the argument that tolerance limits have less relevance to thermoregulation than Topt [43–44]. On the other hand, this is incongruent with the results of Huey and Kingsolver [12] and Huey et al. [45], who found that Topt and CTmax are correlated and tend to coevolve. Possibly this is because these studies included many shade-loving species in which the highest obtainable temperatures are well below those likely to cause physiological stress. Conversely, the correlation between CTmin and Topt suggests that directional selection on CTmin will have a direct effect on locomotor performance, raising or lowering Topt and the mid-level performance temperature range. This is also in accordance with the hypothesis that species that restrict their activities to deeply-shaded areas may be more limited by low rather than high temperatures [46–47].

This study represents the first effort to compile and provide novel thermal-biology data obtained across wide geographic ranges and taxonomic diversity of Amazonian lizards. We integrated field and literature data with phylogenetic inferences to better understand how updated ecophysiological traits can serve as a baseline to inform predictions of global warming effects on the future of rainforest lizards.

 

Source:

http://doi.org/10.1371/journal.pone.0192834

 

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