Competition during thermoregulation altered the body temperatures and hormone levels of lizards

Abstract

Summary Every organism must thermoregulate to maximize its performance, but competing organisms limit access to preferred microclimates. Such competition often creates hierarchies in which dominant individuals have more access to limited resources than subordinate individuals. To assess the costs of competition during thermoregulation, we measured thermoregulation, movement, and hormones of male lizards (Sceloporus jarrovi) when alone and when paired with a smaller or larger conspecific. Large males were 31% closer to the heat source when paired than when alone, resulting in a higher mean body temperature (35·7 vs. 33·9 °C). Conversely, small males were 40% farther from the heat source when paired, resulting in lower mean body temperature (32·1 vs. 33·6 °C). When paired, large and small males circulate 26 and 44% more corticosterone, respectively. Conversely, large males circulated 26% more testosterone when paired, whereas small males circulated 26% less testosterone. Both dominant and subordinate males incurred costs when paired, including poorer thermoregulation, more movement and greater physiological stress. Thus, competition for thermal resources should feature more prominently in ecological and evolutionary models of thermoregulation. A http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.12869/suppinfo is available for this article.

Dehydration constrains thermoregulation and space use in lizards

“…Usually, lizards being tested in thermal gradients are not provided with water, because some definitions of thermal gradients stated that they should provide an environment free from ecological costs and constraints [62, 63]. Few authors justified the choice to not provide water if the studied species is insensitive to water loss in the short term [64]. We believe that such awareness is still rare and, given the results obtained here, we advise for caution.…”

Regulate or tolerate: Thermal strategy of a coral reef flat resident, the epaulette shark, Hemiscyllium ocellatum

“…However, moving to another area may expose individuals to greater risk of predation, as many large, mobile predators are unable to inhabit the shallow coral reef flats, especially during low tide (Harborne, 2013;Rizzari et al, 2014;Vivien, 1973). Additionally, moving to a different habitat such as the reef slope could potentially limit access to prey (e.g., Villén-Pérez et al, 2013) or shelter (e.g., Nielsen & McGaw, 2016), and/or lead to increased competition for resources (e.g., Rusch et al, 2017).…”

The thermal ecology and physiology of reptiles and amphibians: A user's guide

“…iButtons are typically used to study animals that are large enough such that the data‐logger mass (3.5 g after dipping in sealant) along with the radio‐transmitter mass if present are together <5% of the animal. However, several groups have recently developed methods to miniaturize iButtons (Lovegrove, 2009; Robert & Thompson, 2003; Virens & Cree, 2018) to as low as 0.3 g such that they can reasonably be attached to animals as small as 6.6 g. When properly coated, these miniaturized iButtons can also be surgically implanted to collect internal T b from small animals, such as lizards (Rusch & Angilletta, 2017; Sears et al, 2016). For very large animals, like crocodilians and some turtles, lizards, and snakes, it is possible to attach or implant larger data loggers like Onset HOBO Tidbit data loggers (e.g., Fitzgerald & Nelson, 2011; Harlow, Purwandana, Jessop, & Phillips, 2010; Merchant, Williams, Trosclair, Elsey, & Millsa, 2007; Wolf, Walters, Rochford, Snow, & Mazzotti, 2016).…”

“…For example, the thermal biology of organisms will be dependent on interactions with other extrinsic and intrinsic factors to affect performance, including oxygen availability and capacity (Gangloff & Telemeco, 2018), hydric conditions (Garcia‐Porta et al, 2019; Riddell, Roback, Wells, Zamudio, & Sears, 2019; Rozen‐Rechels et al, 2019; Sannolo & Carretero, 2019), and metabolic state (Virens & Cree, 2019). Another frequently ignored context that could greatly affect thermal performance and behavior is the presence (or absence) of competitors on the landscape (Rusch & Angilletta, 2017). Ecological theory tells us that partitioning the fundamental niche into realized niches will largely determine whether or not a species can persist in a given habitat (Case & Gilpin, 1974; Jacob et al, 2018; Tracy & Christian, 1986).…”