Life-history theory suggests that individuals should reproduce until death, yet females of a small number of mammals live for a significant period after ceasing reproduction, a phenomenon known as post-reproductive lifespan. It is thought that the evolution of this trait is facilitated by increasing local relatedness throughout a female’s lifetime. This allows older females to gain inclusive fitness through helping their offspring (known as a mother effect) and/or grandoffspring (known as a grandmother effect), rather than gaining direct fitness through reproducing. However, older females may only benefit from stopping reproducing when their direct offspring compete with those of their daughters. Here, we investigate whether a lack of post-reproductive lifespan in long-finned pilot whales (Globicephala melas) results from minimal benefits incurred from the presence of older females, or from a lack of costs resulting from mother–daughter co-reproduction. Using microsatellite data, we conducted parentage analysis on individuals from 25 pods and find that younger females were more likely to have offspring if their mother was present in their pod, indicating that mothers may assist inexperienced daughters to reproduce. However, we found no evidence of reproductive conflict between co-reproducing mothers and daughters, indicating that females may be able to reproduce into old age while simultaneously aiding their daughters in reproduction. This highlights the importance of reproductive conflict in the evolution of a post-reproductive lifespan and demonstrates that mother and grandmother effects alone do not result in the evolution of a post-reproductive lifespan.

中文翻译：

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缺乏代际生殖冲突，而不是缺乏包容性的健康益处，解释了长鳍领航鲸缺乏繁殖后寿命

生命史理论表明，个体应该繁殖直至死亡，但少数哺乳动物的雌性在停止繁殖后仍能存活很长一段时间，这种现象称为繁殖后寿命。人们认为，这种特征的进化是通过在女性一生中增加局部相关性来促进的。这使得年长的雌性可以通过帮助后代（称为母亲效应）和/或孙辈（称为祖母效应）来获得包容性的健康，而不是通过繁殖来直接获得健康。然而，年长的雌性可能只有在其直系后代与女儿竞争时才能从停止繁殖中受益。在这里，我们调查了长鳍领航鲸（Globicephala melas）繁殖后寿命不足的原因是年长雌性鲸鱼的存在所带来的收益极小，还是由于母女共同繁殖造成的成本不足。利用微卫星数据，我们对 25 个群体中的个体进行了亲子关系分析，发现如果母亲在群体中，年轻雌性更有可能生育后代，这表明母亲可能会帮助没有经验的女儿繁殖。然而，我们没有发现共同生育的母亲和女儿之间存在生殖冲突的证据，这表明雌性可能能够在老年时帮助女儿生育。这凸显了生殖冲突在生殖后寿命进化中的重要性，并表明母亲和祖母效应本身并不会导致生殖后寿命的进化。