Department of Biology, Utah State University, Logan, Utah.
Ecology Center, Utah State University, Logan, Utah.
J Anim Ecol. 2019 Mar;88(3):461-472. doi: 10.1111/1365-2656.12936. Epub 2019 Jan 24.
Oxidative stress is a potential cost of reproduction, but conclusive evidence for this relationship is lacking. The goal of this study was to serially assess across a seasonal gradient the relationship between reproduction, circulating plasma energy metabolites and oxidative state. Here, we examine a study animal ideally suited to test for the oxidative costs of reproduction: the Allen Cays Rock Iguana. Female rock iguanas reproduce at varying frequencies, often skipping years, allowing for a comparison between reproductive and non-reproductive females during the same narrow, annual breeding season. This feature of iguana life history enabled us to address not just sex and seasonal differences in physiology, but also potential oxidative costs of reproduction in females. Male and female iguanas were sampled during the early (vitellogenic), late (gravid) and post-reproductive seasons. Ultrasound examinations were performed on females to quantify reproductive investment, and blood samples were collected for physiology assays, which included reactive oxygen metabolites (d-ROMs), antioxidants, triglycerides, free glycerol and glucose. The early reproductive season was characterized by significant increases in reproductive female's triglycerides, free glycerol and oxidative stress compared to late and post-reproductive periods and non-reproductive females and males during all sampling periods. Antioxidants were significantly elevated during the early reproductive season for reproductive females, non-reproductive females and males when compared to late and post-season. Follicle number in early reproductive females was positively related to d-ROMs, triglycerides and free glycerol, negatively related to antioxidants and showed no relationship with glucose. Measures of oxidative stress, d-ROMs and oxidative index were positively correlated with circulating levels of the lipid metabolite free glycerol during the early reproductive period, but this relationship weakened in the late season and disappeared in the post-season. Broadly, this study supports the hypothesis that the relationship between reproduction and oxidative stress is driven by energy investment, being greatest during early reproduction when vitellogenesis is occurring.
氧化应激是繁殖的潜在代价，但缺乏确凿的证据证明这种关系。本研究的目的是在季节性梯度上连续评估繁殖、循环血浆能量代谢物和氧化状态之间的关系。在这里，我们研究了一种非常适合测试繁殖氧化成本的研究动物：艾伦环礁岩鬣蜥。雌性岩鬣蜥以不同的频率繁殖，经常跳过几年，这使得在同一狭窄的年度繁殖季节内，可以比较繁殖和非繁殖雌性。这种鬣蜥生活史的特征使我们不仅能够解决生理性别和季节性差异的问题，还能够解决雌性繁殖的潜在氧化成本问题。在早期（卵黄生成期）、晚期（妊娠）和产后季节对雄性和雌性鬣蜥进行了采样。对雌性进行超声检查以量化繁殖投资，并采集血液样本进行生理分析，包括活性氧代谢物（d-ROMs）、抗氧化剂、甘油三酯、游离甘油和葡萄糖。早期繁殖季节的特征是，与晚期和产后时期以及所有采样时期的非繁殖雌性和雄性相比，繁殖雌性的甘油三酯、游离甘油和氧化应激显著增加。与晚期和产后时期相比，早期繁殖季节繁殖雌性、非繁殖雌性和雄性的抗氧化剂显著升高。早期繁殖雌性的卵泡数与 d-ROMs、甘油三酯和游离甘油呈正相关，与抗氧化剂呈负相关，与葡萄糖无关。在早期繁殖期间，氧化应激、d-ROMs 和氧化指数等指标与循环脂质代谢物游离甘油水平呈正相关，但这种关系在晚期季节减弱，在产后季节消失。总的来说，本研究支持繁殖与氧化应激之间的关系是由能量投资驱动的假设，即在卵黄生成期间发生时最大。
