Department of Human Origins, Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany.
Centre for the Exploration of the Deep Human Journey, University of the Witwatersrand, Johannesburg, South Africa.
Am J Biol Anthropol. 2024 Nov;185(3):e25007. doi: 10.1002/ajpa.25007. Epub 2024 Jul 26.
Many early fossil hominins are associated with savanna-mosaic paleohabitats, and high sexual dimorphism that may reflect differences in positional behavior between sexes. However, reconstructions of hominin behavior and the selective pressures they faced in an open habitat are limited by a lack of studies of extant apes living in contemporary, analogous habitats. Here, we describe adult chimpanzee positional behavior in the savanna-mosaic habitat of the Issa Valley, Tanzania, to test whether Issa chimpanzees show larger sex-differences in positional behavior than their forest-dwelling counterparts.
We quantified and compared adult locomotor and postural behavior across sexes (6 females, 7 males) in the riparian forest (closed) and miombo woodland (open) vegetation types at Issa Valley (13,743 focal observations). We then compared our results to published data of chimpanzee communities living in more forested habitats.
Issa females and males both spent less time arboreally in open vegetation and showed similar locomotor and postural behavior on the same substrates, notably using a high level of suspensory locomotion when arboreal. Females were, however, more arboreal than males during locomotor behavior, as well as compared with females from other communities. Issa males behaved similarly to males from other communities.
Results suggest that open habitats do not elicit less arboreal behaviors in either sex, and may even select for suspensory locomotion to effectively navigate an open canopy. An open habitat may, however, increase sex differences in positional behavior by driving female arboreality. We suggest this is because of higher energetic demands and predator pressures associated with open vegetation, which are likely exaggerated for reproducing females. These results have implications for the interpretation of how sexual dimorphism may influence reconstructions of hominin positional behavior.
许多早期的人科化石与稀树草原镶嵌的古生境有关，并且存在高度的性别二态性，这可能反映了两性之间姿势行为的差异。然而，由于缺乏对生活在当代类似生境中的现生猿类行为的研究，对人科动物在开阔生境中行为和所面临的选择压力的重建受到了限制。在这里，我们描述了坦桑尼亚伊萨山谷稀树草原镶嵌生境中成年黑猩猩的姿势行为，以检验伊萨黑猩猩的姿势行为是否存在比其森林栖息地更大的性别差异。
我们对河岸森林（封闭）和米邦古木林地（开放）植被类型中的成年雄性（6 只）和雌性（7 只）的运动和姿势行为进行了量化和比较（伊萨山谷 13743 个焦点观察）。然后，我们将我们的结果与生活在森林覆盖度更高的栖息地的黑猩猩社区的已发表数据进行了比较。
伊萨雌性和雄性在开阔植被中的树栖时间都较少，在相同的基质上表现出相似的运动和姿势行为，特别是在树栖时使用高度的悬停运动。然而，与其他社区的雌性相比，雌性在运动行为中比雄性更具树栖性。伊萨雄性的行为与其他社区的雄性相似。
结果表明，开阔生境不会引起任何性别的树栖行为减少，甚至可能选择悬停运动来有效地穿越开阔的树冠。然而，开阔的生境可能会通过驱动雌性的树栖性来增加姿势行为的性别差异。我们认为这是因为与开阔植被相关的更高的能量需求和捕食者压力，而这些压力对于繁殖的雌性来说可能会被夸大。这些结果对解释性别二态性如何影响人科动物姿势行为的重建具有启示意义。
