Abstract

Orangutans show a pronounced sexual dimorphism, with flanged males (i.e., males with fully grown secondary sexual characteristics) reaching twice the size of adult females. Furthermore, adult orangutans show sex-specific dispersal and activity patterns. This study investigates sex differences in adult foraging behavior and sheds light on how these differences develop in immatures. We analyzed 11 years of feeding data on ten adult female, seven flanged male, and 14 immature Bornean orangutans (Pongo pygmaeus wurmbii) at Tuanan in Central Kalimantan, Indonesia. We found that the diets of the adult females were significantly broader and required more processing steps before ingestion than the diets of flanged males. We also found evidence for a similar difference in overall diet repertoire sizes. For the immatures, we found that whereas females reached 100% of their mothers’ diet spectrum size by the age of weaning, males reached only around 80%. From the age of 4 years on (i.e., years before being weaned) females had significantly broader daily diets than males. We found no difference in daily or overall diet processing intensity of immature males and females but found preliminary evidence that immature males included fewer items of their mother’s diet in their own diets that were processing-intensive. Overall, our results suggest that by eating a broader variety and more complex to process food items, female orangutans go to greater lengths to achieve a balanced diet than males do. These behavioral differences are not just apparent in adult foraging behavior but also reflected in immature development from an early age on.

Significance Statement

In many species, males and females have different nutritional needs and are thus expected to show sex-specific foraging behavior. Sex differences in several aspects of foraging behavior have been found in various species, but it remains largely unclear when and how those develop during ontogeny, which is especially relevant for long-lived altricial species that learn foraging skills over many years. In our study, we analyzed a cross-sectional and longitudinal data set containing more than 750,000 feeding events of adult and immature Bornean orangutans (Pongo pygmaeus wurmbii). We found that adult females had significantly broader and more complex diets than males. We also found that these differences started to develop during infancy, suggesting that immature orangutans prepare for their sex-specific foraging niches long before those become physiologically relevant while they are still in constant association with their mothers and before being frequently exposed to other role models.

中文翻译：

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婆罗洲猩猩饮食广度和复杂性性别差异的发展和维持

摘要

猩猩表现出明显的性别二态性，雄性猩猩（即第二性征完全发育的雄性）体型达到成年雌性的两倍。此外，成年猩猩表现出性别特异性的扩散和活动模式。这项研究调查了成年觅食行为的性别差异，并揭示了这些差异在未成熟动物中是如何发展的。我们分析了印度尼西亚中加里曼丹省图安安10 只成年雌性、7 只雄性雄性和 14 只未成熟婆罗洲猩猩 ( Pongo pygmaeus wurmbii ) 11 年的喂养数据。我们发现，与有凸缘的雄性相比，成年雌性的饮食要广泛得多，并且在摄入前需要更多的加工步骤。我们还发现了整体饮食规模存在类似差异的证据。对于未成熟的动物，我们发现，虽然雌性在断奶时达到了其母亲饮食范围大小的 100%，但雄性仅达到了 80% 左右。从 4 岁起（即断奶前几年），雌性的日常饮食明显多于雄性。我们发现未成熟雄性和雌性的日常或整体饮食加工强度没有差异，但发现初步证据表明，未成熟雄性在自己的饮食中包含较少的母亲饮食中的加工密集型食品。总体而言，我们的研究结果表明，雌性猩猩通过吃种类更丰富、加工更复杂的食物，比雄性猩猩更努力地实现均衡饮食。这些行为差异不仅在成年觅食行为中表现得很明显，而且还反映在幼年时期的不成熟发育中。

意义声明

在许多物种中，雄性和雌性有不同的营养需求，因此预计会表现出性别特异性的觅食行为。不同物种的觅食行为在多个方面都存在性别差异，但目前尚不清楚这些行为在个体发育过程中何时以及如何发育，这对于多年学习觅食技能的长寿晚熟物种尤其重要。在我们的研究中，我们分析了包含超过 750,000 个成年和未成熟婆罗洲猩猩 ( Pongo pygmaeus wurmbii ) 进食事件的横截面和纵向数据集。我们发现，成年女性的饮食比男性更广泛、更复杂。我们还发现这些差异在婴儿期就开始出现，这表明未成熟的猩猩早在这些特定性别的觅食环境变得具有生理相关性之前就已经为它们做好了准备，同时它们仍然与母亲保持着持续的联系，并且在经常接触其他榜样之前。