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

在生殖方面的高投资可能会降低存活率和未来的生殖成功。这种所谓的繁殖成本被认为是由氧化应激引起的，氧化应激是代谢活动的副产品，产生的活性氧物种(ROS)压倒了人体的抗氧化防御系统，并对DNA、蛋白质和脂质造成严重损害。我们最近提出了一种关于生殖成本的新观点：父母的氧化状态对他们依赖生理的后代产生影响的可能性。对于母亲来说，氧化应激可能会通过破坏卵子中的DNA，以及通过损害胎盘功能和牛奶质量来产生这种代际影响。因此，母亲应该被选为将这种损害传递降至最低的母亲(“氧化屏蔽”假说)。我们目前正在研究这种母子影响，这是NERC资助的一个大型项目的一部分，该项目使用生活在乌干达伊丽莎白女王国家公园(www.bandedmongoose.org)的野生斑点猫鼬。氧化防护对父亲可能也同样重要。氧化应激可能导致精子中的DNA损伤，从而降低生育能力，但也可能损害后代的发育和存活1。拟议的博士学位将首次评估父亲的氧化状态如何产生代际影响。成功的候选人将结合非洲的实地考察、行为观察、尖端生理分析和纵向数据分析，以促进对生活史进化的基本理解。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，包括染色体异常、表观遗传修饰、突变、碱基氧化和精子DNA片段化，所有这些都可能降低生殖成功率，并对后代产生代际影响。男性也许能够通过在生殖活跃时期投入更多的资金在精子的抗氧化防御上来调节这种风险。事实上，我们最近报告了雄性斑点猫鼬在繁殖过程中血液中维生素E水平的急剧上升，尽管对精子DNA损伤、生育能力以及后代生长和存活的影响仍有待研究。这个博士生项目的主要目的是在我们乌干达实地考察的雄性斑点猫鼬身上测试氧化屏蔽假说。在过去的25年里，对种群进行了研究，并对个体从出生到死亡进行例行监测，包括对生殖投资、后代发育和生存的详细观察。血液样本在整个生命过程中定期采集，以便为幼崽分配亲子关系，并能够测量氧化应激。为了检测对精子氧化状态和“屏蔽”的影响，还可以通过实验来控制营养状况。这项研究将解决以下问题：1.雄性氧化状态的变化是否会影响精子中的DNA损伤和生育能力？2.精子DNA损伤是否会对幼崽的生长、发育和存活以及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。精子将通过电射精来收集。氧化状态的标记物(氧化损伤和一系列抗氧化剂)是使用诸如高效液相色谱等成熟的技术来测量的。DNA损伤将以8-羟基-2‘-脱氧鸟苷(8-OHdG)的形式使用EIA进行测量。

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.