A significant component of ageing (DNA damage) is reflected in fading breeding colors: an experimental test using innate antioxidant mimetics in painted dragon lizards

A decade ahead of their time, von Schantz and coworkers united sexual selection and free radical biology by identifying causal links between deep-rooted physiological processes that dictate resistance to toxic waste from oxidative metabolism (reactive oxygen species), and phenotypic traits, such as ornaments. Ten years later, these ideas have still only been tested with indirect estimates of free radical levels (oxidative stress) subsequent to the action of innate and dietary antioxidants. Here we measure net superoxide (a selection pressure for antioxidant production) and experimentally manipulate superoxide antioxidation using a synthetic mimetic of superoxide dismutase, Eukarion 134 (EUK). We then measure the toxic effect of superoxide in terms of DNA erosion and concomitant loss of male breeding coloration in the lizard, Ctenophorus pictus. Control males suffered more DNA damage than EUK-males. Spectroradiometry showed that male coloration is lost in relation to superoxide and covaries with DNA erosion; in control males these variables explained 72 % of color loss, whereas in EUK males, the fading of coloration was unaffected by superoxide and unrelated to DNA damage. Thus, EUK’s powerful antioxidation removes the erosion effect of superoxide on coloration and experimentally verifies the prediction that colors reflect innate capacity for antioxidation.

该研究较学界现有认知超前十年，von Schantz及其团队通过明确调控氧化代谢（oxidative metabolism）产生的毒性副产物（即活性氧（reactive oxygen species））抗性的深层生理过程，与装饰性体征等表型性状之间的因果关联，将性选择与自由基生物学两大研究领域相融合。时隔十年，相关理论仍仅通过检测先天与膳食抗氧化剂发挥作用后的自由基水平（即氧化应激（oxidative stress））的间接估计值进行验证。本研究首先测定了净超氧阴离子水平——该物质是驱动抗氧化系统生成的选择压力，并利用合成超氧化物歧化酶（superoxide dismutase）模拟物Eukarion 134（EUK）对超氧化物的抗氧化作用进行实验操控；随后以饰纹龙蜥（Ctenophorus pictus）的DNA侵蚀程度及伴随出现的雄性繁殖体色丧失情况为指标，测定了超氧化物的毒性效应。结果显示，对照组雄性个体的DNA损伤程度显著高于EUK处理组雄性。光谱辐射测定结果表明，雄性体色褪色程度与超氧化物水平相关，且与DNA侵蚀程度呈共变关系；在对照组雄性中，这两个变量可解释72%的体色褪色现象，而在EUK处理组雄性中，体色褪色不受超氧化物水平影响，且与DNA损伤无关联。综上，EUK强大的抗氧化作用消除了超氧化物对体色的侵蚀效应，实验验证了"体色可反映个体先天抗氧化能力"的理论预测。