Effect of body mass and melanism on heat balance inLiolaemuslizards of thegoetschiclade

Abstract

The body temperature of ectotherms depends on the environmental temperatures and behavioral adjustments, but morphology may also have an effect. For example, in colder environments, animals tend to be larger and to show higher thermal inertia, as proposed by Bergmann's rule and the heat balance hypothesis (HBH). Additionally, dark coloration increases solar radiation absorption and should accelerate heat gain (thermal melanism hypothesis, TMH). We tested Bergmann's rule, the HBH and the TMH within the Liolaemus goetschi lizard clade, which shows variability in body size and melanic coloration. We measured heating and cooling rates of live and euthanized animals, and tested how morphology and color affect these rates. Live organisms show less variable and faster heating rates compared with cooling rates, suggesting behavioral and/or physiological adjustments. Our results support Bergmann's rule and the HBH, as larger species show slower heating and cooling rates. However, we did not find a clear pattern to support the TMH. The influence of dorsal melanism on heating by radiation was masked by the body size effect in live animals, and results from euthanized individuals also showed no clear effects of melanism on heating rates. Comparison among three groups of live individuals with different degrees of melanism did not clarify the influence of melanism on heating rates. However, when euthanized animals from the same three groups were compared, we observed that darker euthanized animals actually heat faster than lighter ones, favoring the TMH. Although unresolved aspects remain, body size and coloration influenced heat exchange, suggesting complex thermoregulatory strategies in these lizards, probably regulated through physiology and behavior, which may allow these small lizards to inhabit harsh weather environments.

Are the number and size of scales in Liolaemus lizards driven by climate?

“…In fact, the ventral surface is less exposed to climate conditions, such as ultraviolet radiation or wind, and, therefore, it is under less pressure to change in response to alterations in the climate. This result may be related to the findings of Moreno Azócar et al (2016), who observed that although the ventral melanism of Liolaemus species is present in several species of Patagonian Liolaemus, it is not informative in relation to the thermal melanism hypothesis (Clusella Trullas et al 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 ) and we are aware that our exploratory analysis must be taken with caution because it should be run with females rather than with males, but it is also possible that the scale area in males and females could be the result of correlative evolution With regard to the dorsal area, this feature is more exposed to the environment, being the main surface that protects against abrasion and solar radiation. Dorsal scales are related to climate without a phylogenetic signal in the PGLS residual...…”

Functions of fungal melanin beyond virulence

“…These ideas form the basis of the theory of thermal melanism of ectotherms, which can predict their geographical distribution and ecology (Clusella Trullas et al, 2007; Gates, 1980; Jong et al, 1996; Kingsolver, 1987; Watt, 1969). Examples of thermal melanism have been reported in a number of reptiles and insects (Clusella Trullas et al, 2007; Clusella-Trullas et al, 2008; Clusella-Trullas et al, 2009; Jong et al, 1996; Moreno Azocar et al, 2016; Muri et al, 2015; Tanaka, 2005). A recent study showed that turtles ( Trachemys scripta elegans ) reared in colder temperatures developed darker integument relative to those reared in warmer conditions (Rowe et al, 2016).…”

Substrate thermal properties influence ventral brightness evolution in ectotherms

“…The sun's energy-rich radiation spans from the UV-visible (300-700 nm) to the near infrared (NIR: 700-2500 nm). Brightness is the relative amount of light reflected from a surface, and it can have a strong effect on temperature because, all things being equal, a bright material absorbs less solar radiation than a dark material 11 .…”

“…Fewer studies have investigated the ecological significance of ventral coloration e.g., refs. [32][33][34][35] , and only a handful have examined the link between it and thermoregulation 8,11,36 . Older studies investigated the effect of substrate use on thermoregulation 37 and mentioned the thermoecological significance of ventral color reflectivity 2,38,39 .…”

“…Moreover, as latitude in part determines how much of the sun's radiation is received by the organism, while also directly affecting transmission of energy to the substrate 40 , we expected higher latitude species to express a greater melanic ventral integument than lower latitude counterparts. Furthermore, body size can have a strong effect on the overall thermal inertia of an organism 41 , therefore we advanced that larger species will benefit from a brighter venter given the slower cooling rates relative to smaller species 11 . Finally, we predicted that high altitude species will display a darker ventral integument than low altitude organisms, as high altitudes are generally colder than lower altitudes, and a more melanic venter may confer a thermal advantage.…”