School of Biological Sciences, The University of Queensland, St. Lucia, Queensland 4072, Australia.
Department of African Zoology, Royal Museum for Central Africa, Leuvensesteenweg, 3080 Tervuren, Belgium.
Proc Biol Sci. 2019 Nov 6;286(1914):20191712. doi: 10.1098/rspb.2019.1712. Epub 2019 Oct 30.
The hippocampus is well known for its roles in spatial navigation and memory, but it is organized into regions that have different connections and functional specializations. Notably, the region CA2 has a role in social and not spatial cognition, as is the case for the regions CA1 and CA3 that surround it. Here, we investigated the evolution of the hippocampus in terms of its size and organization in relation to the evolution of social and ecological variables in primates, namely home range, diet and different measures of group size. We found that the volumes within the whole cornu ammonis coevolve with group size, while only the volume of CA1 and subiculum can also be predicted by home range. On the other hand, diet, expressed as a shift from folivory towards frugivory, was shown to not be related to hippocampal volume. Interestingly, CA2 was shown to exhibit phylogenetic signal only against certain measures of group size, but not with ecological factors. We also found that sex differences in the hippocampus are related to body size sex dimorphism. This is in line with reports of sex differences in hippocampal volume in non-primates that are related to social structure and sex differences in behaviour. Our findings support the notion that in primates, the hippocampus is a mosaic structure evolving in line with social pressures, where certain subsections evolve in line with spatial ability too.
海马体以其在空间导航和记忆方面的作用而闻名，但它组织成具有不同连接和功能专业化的区域。值得注意的是，CA2 区域在社会认知而非空间认知方面发挥作用，就像它周围的 CA1 和 CA3 区域一样。在这里，我们研究了海马体在大小和组织方面的进化，以及在灵长类动物中与社会和生态变量（即活动范围、饮食和不同的群体大小度量）相关的进化。我们发现，整个角回的体积与群体大小共同进化，而只有 CA1 和 subiculum 的体积也可以由活动范围来预测。另一方面，饮食，表现为从食叶性向果食性的转变，与海马体体积无关。有趣的是，CA2 仅针对某些群体大小度量表现出系统发育信号，但与生态因素无关。我们还发现，海马体的性别差异与身体大小的性别二态性有关。这与非灵长类动物中海马体体积的性别差异与社会结构和行为性别差异有关的报告一致。我们的发现支持这样一种观点，即在灵长类动物中，海马体是一种与社会压力相一致的镶嵌结构，其中某些部分也与空间能力一起进化。
