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The Genetic Basis of Family Effects and the Evolutionary Limits to Large Body-Size.

家庭效应的遗传基础和大体型的进化限制。

基本信息

批准号：
NE/P000924/1
负责人：
Jarrod Hadfield
金额：
$ 56.39万
依托单位：
University of Edinburgh
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2017
资助国家：
英国
起止时间：
2017 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FP000924%2F1
关键词：
Genetic Basis Family Effects Evolutionary

项目摘要

In organisms with parental care, a major determinant of an individual's success are the parental decisions that determine how much resource that individual should receive. Blue tit parents vary widely in how much resource they are able to provide to their offspring. Some of this variation will have a genetic basis, but currently we do not know whether genes play a major or minor role. By forcing blue tits to raise offspring that are not their own we can ask if the foster-offspring of two related mothers (e.g. sisters) grow at more similar rates compared to the foster-offspring of unrelated mothers. We can use the degree of similarity to say how much of the variation in growth rate is due to the action of genes expressed in parents. We also don't know whether individuals that have genes that make them provide more resources to their offspring are more successful. Providing more resources to their offspring helps their offspring to survive and transmit their genes into future generations, and so it has often been thought that these individuals have successful genes. However, a parent that provides fewer resources may have a better chance of surviving to the following year and reproducing again, and so maybe it is these individuals that have more successful genes? By looking to see which individuals survive from year to year, and counting how many offspring they have, we will be able to say which of these two strategies is favoured by natural selection, or indeed if the best strategy is a compromise between the two.The amount of resources an individual receives from its parents is not fixed. Individuals can manipulate their parents into providing more food (via behaviours such as begging) but we do not know whether individuals have genes that control how manipulative they are. However, by placing relatives (e.g. brothers) in different nests we can see whether their two sets of foster parents provide food at similar rates. If they did, this would imply that there are genes shared by the two brothers that are manipulating their foster parents. Genes that make the brothers very manipulative would be good for the brothers (it would increase the amount of food they receive) and bad for the parents (they would have to work harder). However, it is unclear whether these genes would have detrimental effects on the brothers' nest mates. If a brother forces the parent to bring more food, is this food shared by all members of the nest, or does the brother commandeer all of the food, leaving less for its nest mates? If the former, manipulative genes would be beneficial for an individuals nest mates, but if the latter, manipulative genes would be detrimental to an individuals nest mates. We can distinguish between these two hypotheses by comparing the nest mates of manipulative brothers, and nest mates of non-manipulative brothers. If the nest mates of manipulative brothers are on average lighter than the nest mates of non-manipulative brothers we know that the genes for manipulation are bad for nest-mates. The answers to these questions may help us to address a long-standing problem: large individuals tend to survive better and have more offspring than small individuals, and because size is heritable we would therefore expect most species to be evolving to be larger over time. This is not what we see. However, if the genes that make an individual large are also bad for parents (because they have had to work harder) or bad for siblings (because they are deprived of food) then perhaps large size will not evolve. This is because identical copies of the genes that make an individual large are also present in that individual's parents and siblings. A gene that makes an individual large directly benefits itself, but a gene that makes an individual small indirectly helps copies of its self in the individual's relatives. In this way genes for large size and small size may do equally well, and then we would not expect large size to evolve.

在有父母照顾的生物体中，个体成功的一个主要决定因素是父母的决定，决定了个体应该得到多少资源。蓝山雀父母在他们能够为后代提供多少资源方面差异很大。其中一些变异将具有遗传基础，但目前我们不知道基因是否发挥主要或次要作用。通过强迫蓝山雀抚养不是自己的后代，我们可以问，与不相关的母亲的寄养后代相比，两个相关母亲（例如姐妹篇）的寄养后代的生长速度是否更相似。我们可以用相似度来说明生长速度的变化有多少是由于亲本中表达的基因的作用。我们也不知道那些拥有能为后代提供更多资源的基因的个体是否更成功。为后代提供更多的资源有助于后代生存并将其基因传递给后代，因此人们通常认为这些个体具有成功的基因。然而，提供较少资源的父母可能有更好的机会存活到第二年并再次繁殖，所以也许是这些个体拥有更成功的基因？通过观察哪些个体每年都能存活下来，并计算出它们有多少后代，我们就能知道自然选择倾向于这两种策略中的哪一种，或者说，最佳策略是否是两者之间的折衷。个体可以操纵他们的父母提供更多的食物（通过乞讨等行为），但我们不知道个体是否有基因控制他们的操纵程度。然而，通过将亲戚（例如兄弟）放在不同的巢穴中，我们可以看到他们的两组养父母是否以相似的速度提供食物。如果他们这样做了，这将意味着有两个兄弟共同的基因正在操纵他们的养父母。使兄弟俩非常善于操纵的基因对兄弟俩有利（这将增加他们获得的食物量），对父母不利（他们将不得不更加努力地工作）。然而，目前还不清楚这些基因是否会对兄弟的巢穴伴侣产生不利影响。如果一个兄弟强迫父母带来更多的食物，这些食物是由所有的成员分享的，还是兄弟征用了所有的食物，留给同伴的食物更少？如果是前者，操纵基因将有利于个体的巢配，但如果是后者，操纵基因将不利于个体的巢配。我们可以通过比较控制型兄弟的巢友和非控制型兄弟的巢友来区分这两种假设。如果有操纵倾向的兄弟的巢友平均比没有操纵倾向的兄弟的巢友轻，我们就知道操纵基因对巢友是有害的。这些问题的答案可能有助于我们解决一个长期存在的问题：大个体往往比小个体生存得更好，有更多的后代，因为大小是可遗传的，因此我们预计大多数物种会随着时间的推移而进化得更大。这不是我们所看到的。然而，如果使个体变大的基因对父母（因为他们不得不更加努力地工作）或兄弟姐妹（因为他们被剥夺了食物）也是有害的，那么也许大尺寸就不会进化。这是因为使个体变大的基因的相同拷贝也存在于该个体的父母和兄弟姐妹中。使个体变大的基因直接使其自身受益，而使个体变小的基因间接地帮助个体的亲属复制其自身。这样，大尺寸基因和小尺寸基因的表现可能是一样好的，那么我们就不会期望大尺寸基因进化。