Genetic bottlenecks and the geographic distribution of sexual and asexual organisms

有性和无性生物的遗传瓶颈和地理分布

• 批准号: NE/D007658/1
• 负责人: Deborah Charlesworth
• 金额: $ 4.54万
• 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: 2006
• 资助国家: 英国
• 起止时间: 2006 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FD007658%2F1
• 关键词: Genetic; bottlenecks; geographic; distribution; sexual

The lives of many pond animals and plants are precarious, because ponds often dry up, become polluted, or in various ways become uninhabitable. Re-colonisation of ponds often occurs through just a few colonists reaching an empty pond (or a few seeds, in the case of plants). Such colonisation events in ponds (and similar events that must occur in islands, and in patches of environment that are surrounded by unsuitable habitat for a species) are called 'genetic bottlenecks'. Genetic bottlenecks are likely to be particularly frequent or severe in habitats that are marginal or in some way unsuitable for a species, because extinction is more likely to occur if a population is small, as is generally true in marginal habitats. After a bottleneck, the inhabitants of a pond or patch will be the descendants of the colonists, and if there are very few colonists, or just a single female laying eggs, the descendants will be relatives. When they mate, their offspring will be inbred, and a very common consequence is that these animals will have low survival or fertility, compared with normal animals from larger populations. This is called 'inbreeding depression'. In an animal like the water flea, Daphnia, however, mating with other animals is not the only means of reproducing. Many strains in nature, produce offspring asexually (cloning the mother Daphnia). These offspring do not, therefore, suffer from inbreeding depression, as they are just like their mothers. The result is that asexual offspring should survive and reproduce better and therefore be able to outcompete sexual offspring in in marginal habitats, where genetic bottlenecks are common and sexual offspring suffer from inbreeding depression. This could explain why, in general, asexual organisms are more commonly found in unhospitable habitats such as far up in the north or high up in the mountains. It is not clear whether this model is plausible in the real world of Daphnia populations, because we don't know whether inbreeding depression in natural conditions is strong, and whether it affects competition with asexual Daphnia strains. To test the model, we plan experiments in which we make artificial pools (buckets filled with water from natural ponds) and introduce both sexual and asexual Daphnia and allow them to compete. We plan to do this by introducing the female animals at a time of year (early summer) when both kinds reproduce asexually for several generations. This means that we can count the numbers of each type during the course of the summer, using a genetic marker that identifies them. The experiment involves colonising large numbers of buckets, and taking frequent samples of the eggs laid. These will be taken to the lab for the marker to be scored. To test whether the model is plausible, the experiments will use sexual females that have been put through bottlenecks of various sizes, which will lead to different degrees of inbreeding.

许多池塘动物和植物的生活是不稳定的，因为池塘经常干涸，被污染，或以各种方式变得不适合居住。池塘的再殖民通常发生在几个殖民者到达一个空池塘（或几颗种子，在植物的情况下）。这种在池塘中的定殖事件（以及必须发生在岛屿中的类似事件，以及被物种不适合的栖息地包围的环境中的斑块）被称为“遗传检查”。在边缘生境或在某种程度上不适合某一物种的生境中，遗传瓶颈可能特别频繁或严重，因为如果种群很小，灭绝就更有可能发生，边缘生境通常如此。在一个瓶颈之后，池塘或补丁的居民将是殖民者的后代，如果只有很少的殖民者，或者只有一个产卵的雌性，后代将是亲戚。当它们交配时，它们的后代将是近亲繁殖的，一个非常常见的后果是，与来自更大种群的正常动物相比，这些动物的存活率或生育力将很低。这就是所谓的“近亲繁殖衰退”。然而，对于水蚤这样的动物来说，与其他动物交配并不是唯一的繁殖方式。自然界中的许多菌株都是无性繁殖后代（克隆母体水蚤）。因此，这些后代不会患近亲繁殖抑郁症，因为它们就像它们的母亲一样。其结果是，无性后代应该生存和繁殖得更好，因此能够在边缘栖息地中胜过有性后代，在那里遗传瓶颈是常见的，有性后代遭受近亲繁殖抑郁症。这可以解释为什么一般来说，无性生物更常见于荒凉的栖息地，如遥远的北方或高山。目前还不清楚这种模型在真实的水蚤种群世界中是否合理，因为我们不知道自然条件下的近亲繁殖衰退是否很强，以及它是否影响与无性繁殖的水蚤种群的竞争。为了测试这个模型，我们计划进行实验，在实验中我们制造人工水池（装满天然池塘水的水桶），并引入有性和无性的水蚤，让它们竞争。我们计划在一年中的某个时候（初夏）引进雌性动物，这时候两种动物都会无性繁殖几代。这意味着我们可以在夏季期间使用识别它们的遗传标记来计算每种类型的数量。该实验涉及大量的水桶殖民，并经常采取产卵样本。这些将被带到实验室进行标记评分。为了测试这个模型是否合理，实验将使用经过各种大小瓶颈的有性雌性，这将导致不同程度的近亲繁殖。