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From egg-laying to live-bearing: Unravelling the genetics of a major evolutionary transition

从产卵到生育：揭示重大进化转变的遗传学

基本信息

批准号：
NE/N003942/1
负责人：
Kathryn Elmer
金额：
$ 57.58万
依托单位：
University of Glasgow
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2016
资助国家：
英国
起止时间：
2016 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FN003942%2F1
关键词：
egg laying live bearing Unravelling

项目摘要

The process of reproduction is incredibly complex. From attracting the right mate, being genetically compatibility, and incubating a baby, there are many steps that must all work in concert. Each step is under stark natural selection because if unsuccessful then an individual's genes are not passed to the next generation. Tinkering with this process sees like tempting a Darwinian dead-end. So how can major, transformative changes in reproductive process happen during evolution? The evolution of live-bearing (viviparity) from egg-laying (oviparity) in animals is an example of such a transformation, which has profound and wide-ranging consequences for a species. Yet live-bearing has evolved many times independently, in fishes, amphibians, early in the origin of therian mammals, and more than 100 times in reptiles. Usually there is no opportunity to watch how changes from egg-laying to live-bearing happen because they occurred deep in the evolutionary past. Lizards are are an exception as some species have evolved live-bearing quite recently. Most species are completely either egg-laying or live-bearing: eggs are incubated for a relatively short time and then laid with a thick, calcified shell (oviparity) or babies are nurtured in the uterus until fully developed and then born covered with only a thin membrane (viviparity). The genetic basis of live-bearing is not known in any vertebrate. The recent revolution in genomic sequencing technologies is allowing evolutionary biologists to address questions never before possible. One of these is the extent to which similar, complex adaptations have evolved from the same genetic bases across lineages. This issue is pivotal to understand how, and at what rate, natural selection shapes genomes so animals can adapt to their environment. Despite the 300 million years of evolutionary distance between reptiles and mammals, the basic structures, physiology, and molecular mechanisms of pregnancy are comparable between lizards and mammals, so the answer is relevant beyond just reptiles. The first step is to identify the genetic basis of live-bearing in a single species.Europe's common lizard (Zootoca vivipara) has the remarkable attribute of both reproductive modes within one species. The reproductive modes are genetically fixed and egg-layer and live-bearers are found in different geographic areas, except in one part of the Alps where oviparous and viviparous individuals come into contact and interbreed. This hybrid zone offers a unique and amazing 'natural experiment' where the genetics of reproductive traits can be studied. This project will be the first to identify the genetic mechanisms of reproductive mode To do so we will focus on the common lizard. Our objectives are to: (1) Characterise the genetic basis of reproductive mode and its traits shown by mothers, such as eggshell structure and the developmental stage at which embryos are laid as eggs or born as fully developed neonates. This is done by an experiment in the hybrid zone; (2) Quantify how oviparous individuals' and viviparous individuals' genomes mix through hybridization, and locate the genetic variations that are under strong natural selection in either reproductive mode; (3) Resolve the phylogenetic tree of the entire species complex and determine the timing and order of changes in reproductive style. Surprisingly, there is some evidence that reversals back to oviparity might occur in common lizards, but the evidence has not been well supported. Our genomic experiments will identify if multiple independent origins of viviparity, or a reversal to oviparity, have occurred in the species' history. We will identify whether those transitions involve the same genetic mechanism each time.This research will examine for the first time the genetic architecture of reproductive mode, with direct relevance to biodiversity adaptation and reproductive biology.

繁殖的过程极其复杂。从吸引合适的伴侣，基因兼容性，到孵化一个孩子，有许多步骤必须协调一致。每一步都是严格的自然选择，因为如果不成功，个体的基因就不会传给下一代。修补这一过程看起来像是在诱惑达尔文的死胡同。那么，在进化过程中，生殖过程中的重大变革是如何发生的呢？动物从卵生（oviparity）到活胎（viviparity）的进化就是这种转变的一个例子，它对一个物种有着深远而广泛的影响。然而，在鱼类、两栖动物和早期的兽类哺乳动物中，活胎已经独立进化了许多次，在爬行动物中则进化了100多次。通常没有机会观察到从产卵到生育的变化是如何发生的，因为它们发生在进化的历史深处。蜥蜴是一个例外，因为一些物种最近才进化出活胎。大多数物种要么完全是卵生的，要么完全是活的：卵在相对较短的时间内孵化，然后产下厚厚的、钙化的壳（卵生），或者婴儿在子宫里培育，直到完全发育，然后出生时只覆盖一层薄薄的膜（胎生）。在任何脊椎动物中都不知道生儿育女的遗传基础。最近基因组测序技术的革命使进化生物学家能够解决以前不可能解决的问题。其中之一是相似的，复杂的适应在多大程度上是从相同的遗传基础进化而来的。这个问题对于理解自然选择如何以及以何种速度塑造基因组以使动物适应环境至关重要。尽管爬行动物和哺乳动物之间有3亿年的进化距离，但蜥蜴和哺乳动物怀孕的基本结构、生理学和分子机制是相似的，所以这个答案不仅仅适用于爬行动物。第一步是确定单个物种的活胎遗传基础。欧洲的普通蜥蜴（Zootoca vivipara）在一个物种中具有两种繁殖模式的显著特征。它们的繁殖方式在遗传上是固定的，除了阿尔卑斯山脉的一个地区卵生和胎生个体接触并杂交的地方外，在不同的地理区域都发现了卵生和胎生个体。这个杂交区提供了一个独特而惊人的“自然实验”，在这里可以研究生殖性状的遗传学。这个项目将是第一个确定繁殖模式的遗传机制的项目。为此，我们将把重点放在普通蜥蜴上。我们的目标是：(1)描述生殖模式的遗传基础及其母亲所表现出的特征，例如蛋壳结构和胚胎作为卵或作为完全发育的新生儿出生的发育阶段。这是通过混合区的实验完成的；(2)量化卵生个体和胎生个体的基因组如何通过杂交混合，定位两种繁殖模式下强自然选择的遗传变异；(3)解析整个物种复合体的系统发育树，确定繁殖方式变化的时间和顺序。令人惊讶的是，有一些证据表明，在普通蜥蜴中可能会发生卵巢逆转，但这些证据并没有得到很好的支持。我们的基因组实验将确定在该物种的历史中是否发生了多个独立的胎生起源，或者卵生逆转。我们将确定这些转变是否每次都涉及相同的遗传机制。本研究将首次研究生殖模式的遗传结构，与生物多样性适应和生殖生物学直接相关。