Environment and activity affect skin temperature in breeding adult male elephant seals (Mirounga angustirostris)

Abstract

SUMMARYThe large body size and high rates of metabolic heat production associated with male mating success in polygynous systems creates potential thermoregulatory challenges for species breeding in warm climates. This is especially true for marine predators carrying large blubber reserves intended for thermoregulation in cold water and fuel provision during extended fasts. Thermographic images were used to measure changes in skin temperature (T S ) in adult male northern elephant seals (Mirounga angustirostris) over the breeding season. Environmental variables, primarily ambient temperature and solar radiation, were the principal determinants of mean and maximum T S . When controlled for environmental variables, dominance rank significantly impacted mean T S , being highest in alpha males. Behavioral activity significantly influenced T S but in a counter-intuitive way, with inactive males exhibiting the highest T S . This was likely due to strong impacts of environmental variables on the kinds of behavior exhibited, with males being less active on warm, humid days at peak solar radiation. We classified thermal windows as areas in which T S was one standard deviation greater than mean T S for the individual seal within a thermograph. Thermal features suggest active physiological thermoregulation during and after combat and significant circulatory adaptations for heat dumping, as evidenced by recurring locations of thermal windows representing widely varying T S values. Frequent observations of localized T S above 37°C, particularly after combat, suggest the production of thermoregulatory stress during breeding behavior. Our findings demonstrate the importance of environmental drivers in shaping activity patterns during breeding and provide evidence for thermoregulatory costs of successful breeding in large polygynous males.

Effects of Solar Radiation on Animal Thermoregulation

“…Elephant seals are no exception, with males weighing over 2 tons. Male northern elephant seals must compete for reproductive access to females and physical combat among competing males can last upwards to 45 minutes (Norris et al, 2010). Blubber acts as insulation both in and out of water but is much heavier on land.…”

“…Weaker males may retreat to the ocean for multiple cooling avenues that aid in thermoregulation but alpha males, if they wish to maintain their access to females and increase mating success, cannot leave their harem and thus are subjected to environmental variables such as T A , solar radiation, wind, and humidity. The only heat loss mechanisms readily available to alpha males on land are conduction and radiation to a cooler substrate and convection from prevailing winds (Norris et al, 2010). Solar radiation has a significant effect on the circulatory physiology of male northern elephant seals.…”

“…By increasing skin temperature in specific areas, males are able to increase the temperature gradient more so than if blood was perfused along the entire body surface. On warm days, conduction and radiation work against the males, thus on days with high solar radiation and low wind the males are inactive, allowing skin temperature to rise 42°C (Figure 7) (Norris et al, 2010). In this manner they can lower their metabolic rate and conserve energy.…”

“…Even pups of the California sea lion have been observed to sleep and stay still during periods of intense solar radiation for the same reason. On days when wind speed is high and/or clouds block direct solar radiation, male elephant seals are more likely to be active or engage in combat behavior, enabling them to rely on convection or even evaporation via precipitation to increase the rate of heat transfer (Norris et al, 2010). Males of some pinniped species claim a territory rather than a harem and must rely on the habitat within their territory to entice or gain access to reproductive females.…”

“…Thermal cameras allow for a non-invasive scrutiny of an organism's skin surface temperature, giving the ability to see temperature variability across the body rather than just one to a few individual areas recorded by a thermocouple or other device (Figure 9) (McCafferty, 2007;Norris et al, 2010). Clear links between heat loss and areas of the body such as the head and appendages have been established due to thermal imaging (McCafferty, 2007;McCafferty et al, 2011).…”