Département de Biologie, Université de Sherbrooke, 2500 boul. de l'Université, Sherbrooke, QC J1K 2R1, Canada; Department of Biology, Institute of Ecology and Evolution, University of Bern, Ethologische Station Hasli, Wohlenstrasse 50a, CH-3032 Hinterkappelen, Switzerland.
Department of Biology, Bishop's University, 2600 College St., Sherbrooke, QC J1M 1Z7, Canada.
Curr Biol. 2019 Feb 18;29(4):651-656.e3. doi: 10.1016/j.cub.2019.01.027. Epub 2019 Feb 7.
Life-history theory predicts that selection could favor the decoupling of somatic and reproductive senescence if post-reproductive lifespan (PRLS) provides additional indirect fitness benefits [1, 2]. The grandmother hypothesis proposes that prolonged PRLS evolved because post-reproductive grandmothers gain inclusive fitness benefits by helping their daughters and grandchildren [3, 4]. Because most historical human data do not report direct evidence of help, we hypothesized that geographic distance between individuals may be inversely related to their capacity to help. Using an exceptionally detailed dataset of pre-industrial French settlers in the St. Lawrence Valley during the 17 and 18 centuries, we assessed the potential for grandmothers to improve their inclusive fitness by helping their descendants, and we evaluated how this effect varied with geographic distance, ranging between 0 and 325 km, while accounting for potential familial genetic and environmental effects [5-9]. Grandmothers (F0) who were alive allowed their daughters (F1) to increase their number of offspring (F2) born by 2.1 and to increase their number of offspring surviving to 15 years of age by 1.1 compared to when grandmothers were dead. However, the age at first reproduction was not influenced by the life status (alive or dead) of grandmothers. As geographic distance increased, the number of offspring born and lifetime reproductive success decreased, while the age at first reproduction increased, despite the grandmother being alive in these analyses. Our study suggests that geographic proximity has the potential to modulate inclusive fitness, supporting the grandmother hypothesis, and to contribute to our understanding of the evolution of PRLS.
生活史理论预测，如果生殖后寿命（PRLS）提供额外的间接适合度益处，选择可能有利于体躯和生殖衰老的解耦[1,2]。祖母假说提出，延长 PRLS 是因为生殖后祖母通过帮助女儿和孙子孙女获得包容性适合度益处而进化的[3,4]。由于大多数历史人类数据没有报告直接帮助的证据，我们假设个体之间的地理距离可能与其帮助能力呈反比。我们使用 17 至 18 世纪圣劳伦斯河谷的工业化前法国移民的异常详细数据集，评估了祖母通过帮助后代提高包容性适合度的潜力，并且评估了这种效果如何随地理距离（0 至 325 公里）而变化，同时考虑了潜在的家族遗传和环境效应[5-9]。活着的祖母（F0）使她们的女儿（F1）增加了 2.1 个后代（F2）的出生数量，并增加了 1.1 个活到 15 岁的后代数量，而祖母去世时则没有这种效果。然而，祖母的生活状况（活着还是去世）并不影响首次繁殖的年龄。随着地理距离的增加，出生的后代数量和终生繁殖成功率下降，而首次繁殖的年龄增加，尽管在这些分析中祖母仍然活着。我们的研究表明，地理接近度有可能调节包容性适合度，支持祖母假说，并有助于我们理解生殖后寿命的进化。
