Oxidative Shielding of Sperm and Inter-generational Costs of Reproduction in a Wild African Mammal

在繁殖上的高投入会降低存活率和未来的繁殖成功率。这种所谓的“繁殖成本”被认为是由氧化应激介导的，在氧化应激中，代谢活动的副产品活性氧（ROS）的产生压倒了身体的抗氧化防御，并对DNA、蛋白质和脂质造成严重损害。我们最近提出了一个关于繁殖成本的新观点：父母的氧化状态对其生理依赖的后代的潜在影响。在母亲中，氧化应激可能通过破坏卵子中的DNA、损害胎盘功能和牛奶质量而产生代际影响。因此，选择母亲时应尽量减少这种损害传播（“氧化屏蔽”假说）。作为nerc资助的一个大型项目的一部分，我们目前正在研究这种母子影响，研究对象是生活在乌干达伊丽莎白女王国家公园的野生带状猫鼬（www.bandedmongoose.org）。氧化屏蔽对父亲可能同样重要。氧化应激可能导致精子DNA损伤，从而降低生育能力，但也可能影响后代的发育和生存。拟议中的博士研究生将首次评估父亲的氧化状态如何对代际影响。成功的候选人将结合在非洲的实地考察、行为观察、前沿的生理分析和纵向数据分析，以推进对生命史进化的基本理解。精子极易受到氧化损伤，富含多不饱和脂肪酸，但缺乏损伤检测和修复机制。这种氧化损伤会损害受精能力，并导致DNA损伤，包括染色体畸变、表观遗传修饰、突变、碱基氧化和精子DNA断裂，所有这些都可能降低生殖成功率并对后代产生代际影响。男性可以通过在繁殖活跃时期对精子进行更多的抗氧化防御来调节这种风险。事实上，我们最近报道了雄性条纹猫鼬在繁殖期间血液中维生素E水平急剧上升，尽管对精子DNA损伤、生育能力、后代生长和存活的影响有待研究。这个博士研究生的首要目标是在我们乌干达的田野现场测试雄性带状猫鼬的氧化屏蔽假说。过去25年来一直在对这一种群进行研究，对个体从出生到死亡进行常规监测，包括对生殖投资、后代发育和生存的详细观察。在整个生命过程中定期收集血液样本，以便确定幼崽的亲子关系，并能够测量氧化应激。也有可能通过实验操纵营养状况，以检查对氧化状态和“屏蔽”精子的影响。该奖学金将解决以下问题：男性氧化状态的变化是否影响精子DNA损伤和生育能力？精子DNA损伤是否会对幼崽的生长、发育、存活和未来的繁殖成功产生负面影响？完整的生活史记录是通过详细的行为观察收集的。精子将通过电射精收集。氧化状态的标记物（氧化损伤和一系列抗氧化剂）使用诸如高效液相色谱等现有技术进行测量。DNA损伤将用EIA测量8-羟基-2'-脱氧鸟苷（8-OHdG）。

High investment in reproduction can decrease survival, and future reproductive success. This so-called 'cost of reproduction' is thought to be mediated by oxidative stress, where reactive oxygen species (ROS) arising as a by-product of metabolic activity overwhelm the body's antioxidant defences, and cause serious damage to DNA, proteins and lipids. We recently proposed a new perspective on the cost of reproduction: the potential for parents' oxidative state to impact on their physiologically-dependent offspring. In mothers, oxidative stress may have such inter-generational impacts by damaging DNA in the ova, and by impairing placental function and milk quality. Mothers should therefore be selected to minimise such damage transmission (the 'oxidative shielding' hypothesis). We are currently studying such mother-offspring impacts as part of a large NERC-funded project using wild banded mongooses living at Queen Elizabeth National Park in Uganda (www.bandedmongoose.org).Oxidative shielding is likely to be similarly important for fathers. Oxidative stress may cause DNA damage in sperm, which reduces fertility, but may also impair offspring development and survival1. The proposed PhD studentship will assess for the first time how oxidative state in fathers can have inter-generational impacts. The successful candidate will combine fieldwork in Africa, behavioural observations, cutting-edge physiological assays and longitudinal data analysis to advance fundamental understanding of life history evolution.Sperm are extremely susceptible to oxidative damage, being richly endowed with polyunsaturated fatty acids, while having deficient damage detection and repair mechanisms. Such oxidative damage can impair fertilization capacity, and contribute to DNA damage including chromosomal aberrations, epigenetic modifications, mutations, base oxidation and sperm DNA fragmentation, all of which may reduce reproductive success and impose inter-generational impacts on offspring. Males may be able to modulate this risk by investing more into antioxidant defence of sperm during reproductively active periods1. Indeed, we recently reported that blood levels of vitamin E increase sharply during breeding in male banded mongooses, although the consequences for sperm DNA damage, fertility, and offspring growth and survival await study. The over-arching aim of this PhD studentship is to test the oxidative shielding hypothesis in male banded mongooses at our Uganda field site. The population has been studied for the last 25 years, and individuals are routinely monitored from birth to death including detailed observations of reproductive investment, offspring development and survival. Blood samples are collected at regular intervals over the life course, in order to assign parentage to pups, and to enable measurements of oxidative stress. It is also possible to experimentally manipulate nutritional condition, in order to examine effects on oxidative state and 'shielding' of sperm. The studentship will address the following questions:1. Does variation in males' oxidative state influence DNA damage in sperm, and fertility?2. Does sperm DNA damage negatively impact on pup growth, development and survival, and future reproductive success? Full life history records are collected by detailed behavioural observations. Sperm will be collected by electro-ejaculation. Markers of oxidative state (oxidative damage, and a range of antioxidants) are measured using established techniques such as HPLC. DNA damage will be measured in terms of 8-hydroxy-2'-deoxyguanosine (8-OHdG) using EIA.