Temperature sensitive male fertility; uncovering the mechanisms that make fertility in some species more vulnerable to high temperature

气候正在变暖，预计这将导致极端温度的增加。如果我们要防止物种灭绝和有害生物的入侵，了解这将如何影响生物的生存和分布是至关重要的。气候变化的影响通常是通过检查导致动物死亡的温度来估计的。然而，我们可能低估了非致命高温对生物体的影响。在大多数动物中，从甲虫到鸟类再到獾，雄性通常会在远低于杀死它们所需温度的温度下失去生育能力。这也影响到牲畜，因此在温带国家表现良好的品种在热带地区可能无法繁殖。即使是人类，尽管能够通过衣服、房子和空调来控制温度，但有证据表明，在热浪期间，生育率也会下降。如果温度升高导致一个动物种群中的所有雄性不育，那么这个种群将无法生存，即使温度远没有高到足以杀死任何动物的程度。最近，我们系统地测试了温度对43种果蝇繁殖力的影响。在超过一半的情况下，雄性在低于其致命极限的温度下失去了生育能力。然后，我们研究了在世界各地发现苍蝇的地方。我们发现，在物种和栖息地之间，一个物种在自然界中经历的最高温度，通过绝育温度限制比致命温度限制更好地预测。这有力地表明，温度导致的不育在自然界中确实很重要，许多物种的分布受到它们在高温下保持繁殖能力的限制。如果是这样，那么我们很可能低估了气候变化对物种的影响，因为我们现在才意识到生育能力的丧失可能是一个主要问题。然而，对生理和遗传过程知之甚少，这意味着物种对温度不育的敏感性不同。例如，虽然人们早就知道热休克蛋白对保护细胞免受高温的影响至关重要，但我们还不知道同样的蛋白质是否能保护精子。我们之前的工作表明，热休克可能不会影响现有的成熟精子，但当这些精子被使用时，物种变得不育，似乎无法恢复。这表明是制造精子（精子发生）的过程被热破坏了。我们将对7种果蝇进行研究，这7种果蝇既涵盖了耐温性的绝对差异，也涵盖了繁殖力和生存极限的差异。我们将评估精子发生何时中断，使用显微镜图像来描述热量是否破坏了精子形态或包装在里面的DNA。为了了解哪些基因是重要的，我们将测量热休克前后睾丸中的基因表达，以评估某些物种是否会更快地做出反应。至关重要的是，我们不仅要将这些发现联系起来，还要使用遗传和化学操作来直接测试特定基因的功能。一旦我们知道是什么导致了这些苍蝇物种之间的差异，就可以在其他动物身上进行测试。最终，这些信息可用于快速评估哪些物种易受高温影响，并确定牲畜育种中的特定基因，以产生更耐热的品种。

The climate is warming, and this is predicted to result in an increase in extremes of temperature. Understanding how this will affect the survival and distribution of organisms is vital if we are to prevent extinctions, and invasions by harmful pests. The impacts of climate change are often estimated by examining the temperatures that kill animals. However, we may be underestimating the impact that non-lethal high temperatures have on organisms. In most animals, from beetles to birds to badgers, males typically lose their fertility at a far lower temperature than that required to kill them. This also affects livestock, so that breeds which do well in temperate countries can be infertile in the tropics. Even humans, despite being able to control temperatures using clothes, houses, and air conditioning, show evidence of reductions in fertility during heatwaves. If increasing temperatures cause all the males in an animal population to become sterile, then that population will not survive, even if the temperatures are nowhere near high enough to actually kill any animals. Recently we systematically tested the impact of temperature on the fertility of 43 species of fruit fly. In more than half, males lost fertility at a much cooler temperatures than their lethal limits. We then looked at where the flies were found worldwide. We found that across species and habitats, the highest temperature a species experiences in nature was far better predicted by sterilising temperature limits than by lethal temperature limits. This strongly suggests that temperature-induced sterility really does matter in nature, and that distributions of many species are limited by their ability to remain fertile at high temperatures. If so, then we are likely underestimating the impact of climate change on species, because we are only now realising that losses of fertility may be a major problem.However, very little is known about the physiological and genetic processes which mean species are differently sensitive to temperature-based infertility. For example, whilst it has long been known that Heat Shock Proteins are critical to protecting cells from high temperatures in terms of survival, we don't yet know if the same proteins protect sperm. Our previous work shows that heat-shock might not affect existing mature sperm, but when these are used, species become infertile and don't seem to be able to recover. This suggests that it is the process of making sperm (spermatogenesis) that is damaged by heat.We will study 7 species of fruit fly, which cover the range both in absolute differences in temperature tolerance, and the difference between the limits of fertility and survival. We will assess when spermatogenesis breaks down, using microscope images to describe if heat damages the sperm morphology or the DNA packaged inside. To understand which genes are important, we will measure gene expression in testes both before and after heat shock, to assess if some species are primed to respond more quickly. Crucially, we will not just correlate these findings, but use genetic and chemical manipulations to directly test the function of specific genes. Once we know what causes variation between these fly species, this can then be tested across other animals. Ultimately, this information could be used to quickly assess which species will be vulnerable to high temperature and identify particular genes to target in livestock breeding, to generate more thermally robust breeds.