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Heterothermy, a variability in body temperature beyond the limits of homeothermy, has been advanced as a key adaptation of Arabian oryx (Oryx leucoryx) to their arid-zone life. We measured body temperature using implanted data loggers, for a 1-year period, in five oryx free-living in the deserts of Saudi Arabia. As predicted for adaptive heterothermy, during hot months compared to cooler months, not only were maximum daily body temperatures higher (41.1 ± 0.3 vs. 39.7 ± 0.1°C, P = 0.0002) but minimum daily body temperatures also were lower (36.1 ± 0.3 vs. 36.8 ± 0.2°C, P = 0.04), resulting in a larger daily amplitude of the body temperature rhythm (5.0 ± 0.5 vs. 2.9 ± 0.2°C, P = 0.0007), while mean daily body temperature rose by only 0.4°C. The maximum daily amplitude of the body temperature rhythm reached 7.7°C for two of our oryx during the hot-dry period, the largest amplitude ever recorded for a large mammal. Body temperature variability was influenced not only by ambient temperature but also water availability, with oryx displaying larger daily amplitudes of the body temperature rhythm during warm-dry months compared to warm-wet months (3.6 ± 0.6 vs. 2.3 ± 0.3°C, P = 0.005), even though ambient temperatures were the same. Free-living Arabian oryx therefore employ heterothermy greater than that recorded in any other large mammal, but water limitation, rather than high ambient temperature, seems to be the primary driver of this heterothermy.

One of the most apparent examples of cooperation between unrelated individuals is biparental care whereby the male and the female parent share the rearing of the offspring. Theoretical models of care predict that selection should favour biparental care if it substantially improves the survival of the offspring. Although various ecological factors have been proposed to necessitate biparental care, experimental evidence is scant given the challenges of manipulating ecological factors in the natural habitat of animals. We carried out one such experiment in a small shorebird, the Kentish plover, Charadrius alexandrinus, that breeds in an extreme desert environment. Nest cover and thus exposure to solar radiation vary between nests, and we show that parents at exposed nests spent more time incubating than those at nests shaded by a bush (covered nests). Experimental removal and supplementation of nest cover gave results consistent with the observational data; at experimentally exposed nests both males and females increased incubation effort and relieved each other more frequently whereas at experimentally covered nests we observed the opposite. We conclude that exposure to extreme solar radiation influences biparental care and this necessitates parental cooperation in the Kentish plover. Furthermore, since parental care often coevolves with mating strategies, we conjecture that where the environment puts less pressure on the parents and provides the opportunity for reduced care, both mating systems and parental care can diversify over evolutionary time. (C) 2011 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved