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The Evolution of Prolonged Post-Reproductive Lifespan in a Non-Human Mammal

非人类哺乳动物延长生殖后寿命的进化

基本信息

批准号：
NE/K01286X/1
负责人：
Darren Croft
金额：
$ 41.06万
依托单位：
UNIVERSITY OF EXETER
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2014
资助国家：
英国
起止时间：
2014 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FK01286X%2F1
关键词：
Evolution Prolonged Post Reproductive Lifespan

项目摘要

Understanding why females stop reproduction prior to the end of their lives is a key objective in the biological, medical and social sciences. In traditional human societies for example, women typically have their last child at 38 but may live for a further 20 years or so. This phenomenon is by no means restricted to humans and across many species of mammals, birds and fish, females may have a lifespan that extends far beyond their last birth. Why is this? Three possible reasons have been suggested: i) It could simply be a byproduct of females living for a long time; ii) it may benefit post-reproductive females by increasing the survival of their offspring and/or grand offspring or iii) old females may lose out to young females when competing for the food needed to support pregnancy and producing milk. In humans it seems that a combination of ii and iii have driven the evolution of menopause. Currently however, almost nothing is known about the forces that have shaped the post-reproductive lifespan in non-human animals that live in close-knit family groups. In this project we will test for the first time the current evolutionary theory for the post-reproductive lifespan in a non-human animal.Our study will focus on two populations of killer whales Orcinus orca that live off the coast of North America. Killer whales have the longest post-reproductive lifespan of all non-human animals; females stop reproducing in their 30s-40s but can survive into their 90s. We will use data collected over the last three decades during which time more than 600 whales have been recorded. We will use information about births and deaths to examine how social factors shape fertility and survival. In particular we will ask the following questions: (1) How do post-reproductive females benefit from a post-reproductive lifespan? (2) In what ways do older females provide support to their offspring / grand offspring? (3) Do older females lose out when competing with younger females for the food needed to reproduce? (4) Can the observed benefits (question 1) and the consequences of reproductive competition (question 3) explain the evolution of the long post-reproductive lifespan in killer whales? We will address questions 1 and 3 by using the long term data documenting births and deaths in both populations. We will use analysis techniques similar to those used by insurance companies to calculate life expectancy when deciding what premiums to charge people on their life insurance. In our analysis we will examine how survival is affected by the presence and behavior of post-reproductive females. We will address question 2 by using video and photographic records to examine social interactions between mothers and their offspring / grand offspring. We will test how important this relationship is for survival. Finally we will address question 4 by building a simulation model of the populations. We will use our observations from the whales to set the parameters in the model [e.g. the amount by which post-reproductive females increase the survival of their offspring]. The model will then simulate evolution, allowing us to examine if the effects we are seeing in the populations are sufficient to have driven the evolution of the long post-reproductive lifespan in killer whales. This programme of research promises to advance our understanding of how natural selection has shaped life history evolution in species that live in close-knit family groups. Our work will provide the first test of the current evolutionary theory for the evolution of menopause in non-human animals and the outputs of this work will provide an informative comparison for the evolution of human life history. More generally, our work will advance our understanding of the ageing process in social species and the interplay between an individual's social relationships and its life expectancy.

了解女性在生命结束前停止生育的原因是生物学、医学和社会科学的一个关键目标。例如，在传统的人类社会中，女性通常在38岁生最后一个孩子，但可能还能再活20年左右。这种现象绝不仅限于人类，许多哺乳动物、鸟类和鱼类都存在这种现象，雌性的寿命可能远远超过它们最后一次出生的时间。为什么会这样？人们提出了三种可能的原因：1)这可能只是女性长时间生活的副产品；Ii)通过提高后代和/或后代的存活率，这可能有利于生育后的雌性；iii)在争夺维持怀孕和产奶所需的食物时，年老的雌性可能会输给年轻的雌性。在人类中，似乎是ii和iii的结合推动了更年期的进化。然而，目前，对于那些生活在紧密家庭群体中的非人类动物的生殖后寿命形成的力量，我们几乎一无所知。在这个项目中，我们将首次在非人类动物身上测试目前关于生殖后寿命的进化理论。我们的研究将集中在两个种群的虎鲸虎鲸生活在北美海岸。虎鲸是所有非人类动物中生殖后寿命最长的；雌性在30 -40岁时停止繁殖，但可以存活到90多岁。我们将使用过去三十年收集的数据，在此期间，有600多只鲸鱼被记录下来。我们将利用有关出生和死亡的信息来研究社会因素如何影响生育率和存活率。我们将特别提出以下问题：(1)生殖期后的女性如何从生殖期后的寿命中获益？(2)老年女性以什么方式赡养后代/孙辈？(3)在与年轻的雌性竞争繁殖所需的食物时，年长的雌性会输掉吗？(4)观察到的好处（问题1）和繁殖竞争的后果（问题3）能否解释虎鲸繁殖后较长寿命的进化？我们将利用记录这两个群体出生和死亡的长期数据来解决问题1和3。我们将使用类似于保险公司用来计算预期寿命的分析技术，以决定向人们收取人寿保险的保费。在我们的分析中，我们将研究生殖后雌性的存在和行为是如何影响生存的。我们将通过使用视频和摄影记录来解决问题2，以检查母亲与其后代/后代之间的社会互动。我们将测试这种关系对生存有多重要。最后，我们将通过建立人口的模拟模型来解决问题4。我们将使用我们对鲸鱼的观察来设置模型中的参数（例如，生殖后雌性增加其后代存活率的数量）。然后，该模型将模拟进化，使我们能够检查我们在种群中看到的影响是否足以推动虎鲸繁殖后较长寿命的进化。这一研究项目有望促进我们对自然选择如何影响生活在紧密家庭群体中的物种的生活史进化的理解。我们的工作将为非人类动物更年期进化的当前进化理论提供第一次测试，这项工作的结果将为人类生活史的进化提供信息比较。更广泛地说，我们的工作将促进我们对社会物种衰老过程的理解，以及个体社会关系与其预期寿命之间的相互作用。