Baird Troy A, Lovern Matthew B, Shine Richard
Department of Biology, University of Central Oklahoma, USA.
Department of Zoology, Oklahoma State University, Stillwater, OK, USA 74078.
Horm Behav. 2014 Jul;66(2):393-400. doi: 10.1016/j.yhbeh.2014.05.008. Epub 2014 Jun 4.
Water dragons (Intellegama [Physignathus] lesueurii) are large (to >1m) agamid lizards from eastern Australia. Males are fiercely combative; holding a territory requires incessant displays and aggression against other males. If a dominant male is absent, injured or fatigued, another male soon takes over his territory. Our sampling of blood from free-ranging adult males showed that baseline levels of both testosterone and corticosterone were not related to a male's social tactic (territorial versus non-territorial), or his frequency of advertisement display, aggression, or courtship behavior. Even when we elicited intense aggression by non-territorial males (by temporarily removing territory owners), testosterone did not increase with the higher levels of aggression that ensued. Indeed, testosterone levels decreased in males that won contests. In contrast, male corticosterone levels increased with the heightened aggression during unsettled conditions, and were higher in males that won contests. High chronic male-male competition in this dense population may favor high testosterone levels in all adult males to facilitate advertisement and patrol activities required for territory maintenance (by dominant animals), and to maintain readiness for territory take-overs (in non-territorial animals). Corticosterone levels increased in response to intense aggression during socially unstable conditions, and were higher in contest winners than losers. A positive correlation between the two hormones during socially unstable conditions suggests that the high stress of contests decreased androgen production. The persistent intense competition in this population appears to exact a high physiological cost, which together with our observation that males sometimes lose their territories to challengers may indicate cycling between these two tactics to manage long-term energetic costs.
水龙（Intellegama [Physignathus] lesueurii）是来自澳大利亚东部的大型（体长超过1米）鬣蜥科蜥蜴。雄性极具攻击性；保卫领地需要不断地展示并攻击其他雄性。如果占主导地位的雄性缺席、受伤或疲惫，另一只雄性很快就会接管其领地。我们对自由放养的成年雄性水龙进行采血检测，结果显示睾酮和皮质酮的基线水平与雄性的社交策略（领地型与非领地型）、广告展示频率、攻击性或求偶行为均无关。即使我们通过暂时赶走领地所有者引发非领地型雄性的强烈攻击，睾酮水平也不会随着随之而来的更高攻击水平而增加。事实上，赢得争斗的雄性睾酮水平会下降。相反，在不稳定情况下，雄性皮质酮水平会随着攻击性增强而升高，且在赢得争斗的雄性中更高。在这个高密度种群中，长期激烈的雄性间竞争可能有利于所有成年雄性保持高睾酮水平，以促进领地维护（占主导地位的动物）所需的广告展示和巡逻活动，并保持对领地接管的准备状态（非领地型动物）。在社会不稳定情况下，皮质酮水平会因强烈攻击而升高，且争斗获胜者高于失败者。在社会不稳定情况下，这两种激素之间的正相关表明争斗带来的高压力会降低雄激素的产生。这个种群中持续激烈的竞争似乎需要高昂的生理成本，再加上我们观察到雄性有时会将领地输给挑战者，这可能表明这两种策略之间存在循环，以管理长期的能量成本。
