Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany.
Am J Phys Anthropol. 2021 Apr;174(4):776-784. doi: 10.1002/ajpa.24237. Epub 2021 Jan 28.
Weaning is a key life history milestone for mammals that represents both the end of nutritional investment from the perspective of mothers and the start of complete nutritional independence for the infants. The age at weaning may vary depending on ecological, social, and demographic factors experienced by the mother and infant. Bwindi mountain gorillas live in different environmental conditions and have longer interbirth intervals than their counterparts in the Virunga Volcanoes, yet other life history characteristics of this population remain less well known. We use long-term data from Bwindi Impenetrable National Park, Uganda to examine factors related to weaning age.
We analyzed data on infants born in four mountain gorilla groups in Bwindi to quantify their age of weaning (defined as last nipple contact) and to test if the sex of offspring, parity, and dominance rank of mother influences age of weaning. We also compared the age at weaning and time to conception after resumption of mating in Bwindi and Virunga gorillas.
Bwindi gorillas were weaned at an average age of 57.5 months. No difference was found between age of weaning for primiparous and multiparous mothers, nor did maternal dominance rank influence age of weaning, but sons were weaned at a later age than daughters. The majority of Bwindi mothers were still suckling when they resumed mating and mothers generally conceived before they weaned their previous offspring. The age of weaning was significantly later in Bwindi than in Virunga gorillas. After mothers resumed mating, the time to conceiving the next offspring was not significantly longer for Bwindi females than Virungas females (6 vs. 4 months).
Later weaning age for sons than daughters is similar to findings of other studies of great apes. Bwindi mountain gorillas are weaned at approximately the same age as western gorillas and chimpanzees, which is more than a year later than Virunga mountain gorillas. The results of this study suggest that variation in ecological conditions of populations living in close geographic proximity can result in variation in life history patterns, which has implications for understanding the evolution of the unique life history patterns of humans.
断奶是哺乳动物生命历程中的一个关键里程碑，它既代表了母亲对婴儿营养投入的结束，也代表了婴儿完全独立营养的开始。断奶的年龄可能因母亲和婴儿所经历的生态、社会和人口因素而有所不同。布温迪山地大猩猩生活在不同的环境条件下，其产仔间隔比维龙加火山的大猩猩长，但该种群的其他生命史特征仍知之甚少。我们利用乌干达布温迪不可渗透国家公园的长期数据，研究与断奶年龄相关的因素。
我们分析了布温迪四个山地大猩猩群体中出生的幼仔的数据，以量化它们的断奶年龄（定义为最后一次接触乳头），并检验后代的性别、胎次和母亲的支配地位是否影响断奶年龄。我们还比较了布温迪和维龙加大猩猩断奶后恢复交配时的断奶年龄和受孕时间。
布温迪大猩猩的平均断奶年龄为 57.5 个月。初产和多产母亲的断奶年龄没有差异，母亲的支配地位也不影响断奶年龄，但儿子的断奶年龄晚于女儿。大多数布温迪母亲在恢复交配时仍在哺乳，母亲通常在断奶前就已经怀上了前一个孩子。布温迪的断奶年龄明显晚于维龙加大猩猩。母亲恢复交配后，布温迪雌猩猩受孕下一胎的时间并不比维龙加雌猩猩长（6 个月比 4 个月）。
儿子的断奶年龄晚于女儿，这与其他对大型猿类的研究结果相似。布温迪山地大猩猩的断奶年龄与西部大猩猩和黑猩猩大致相同，比维龙加山地大猩猩晚一年多。本研究结果表明，生活在地理上接近的种群的生态条件的变化会导致生命史模式的变化，这对理解人类独特的生命史模式的进化具有重要意义。
