Global biogeography of ant social parasites: Exploring patterns and mechanisms of an inverse latitudinal diversity gradient

Aim: One of the most consistent global biogeographic patterns is the latitudinal diversity gradient where species richness peaks within the equatorial tropics and decreases towards the poles. Here, we explore the global biogeography of socially parasitic ants, which comprises the most diverse group of social parasites in the Hymenoptera. We test the biogeographic hypothesis that ant social parasites are distributed along an inverse latitudinal diversity gradient by peaking in diversity outside of the equatorial tropics. Location: Global Taxon: Ants (Hymenoptera: Formicidae) Methods: We assembled a comprehensive biogeographic dataset for all 371 taxonomically described socially parasitic ant species. We used phylogenetic and taxonomic studies to compare species richness with the number of species representing independent evolutionary origins of social parasitism across a latitudinal gradient. In addition, we compared ant social parasite diversity across biogeographic regions using rarefaction to account for different sampling efforts. Finally, we tested for a correlation between latitude and the proportion of ant social parasite species within regional ant faunae. Results: The geographic distribution records and the inferred 91 origins of socially parasitic life histories show that both species richness and the number of species representing independent evolutionary origins of social parasitism peak in the northern hemisphere outside of the equatorial tropics. Based on rarefaction curves, northern latitude regions harbour the most ant social parasite species, but the diversity of independent evolutionary origins is not significantly different between northern and southern hemispheres. The proportion of ant social parasite species within regional faunae is correlated with latitude only in the northern hemisphere. Main conclusions: The inverse latitudinal diversity gradient of ant social parasites contrasts with the biogeographic pattern observed in free-living, non-parasitic ant species and appears to be driven by large species radiations as well as by the presence of specialized life histories exclusive to the northern hemisphere.研究目的：全球最稳定的生物地理格局之一为纬度多样性格局（latitudinal diversity gradient），即物种丰富度在赤道热带达到峰值，并向极地逐渐递减。本研究聚焦膜翅目（Hymenoptera）中社会性寄生蚂蚁（socially parasitic ants）这一类群——该类群是膜翅目内物种多样性最高的社会性寄生类群，旨在探讨其全球生物地理分布特征。我们验证如下生物地理假说：蚂蚁社会性寄生类群呈现反向纬度多样性格局，其物种多样性峰值并非出现在赤道热带，而是分布于其他区域。 研究范围：全球 研究类群：蚂蚁（膜翅目：蚁科（Formicidae）） 研究方法：我们整合了已完成分类学描述的全部371种社会性寄生蚂蚁的完整生物地理数据集。通过系统发育与分类学研究，对比沿纬度梯度分布的物种丰富度，以及代表社会性寄生独立演化起源的物种数量。此外，我们采用稀疏化分析（rarefaction）比较不同生物地理区域的社会性寄生蚂蚁多样性，以消除采样强度差异带来的影响。最后，我们检验了纬度与区域蚁类区系中社会性寄生蚂蚁物种占比之间的相关性。 研究结果：地理分布记录与已推断的91次社会性寄生生活史演化起源表明，社会性寄生蚂蚁的物种丰富度及代表独立演化起源的物种数量，均在赤道热带以外的北半球达到峰值。基于稀疏化曲线，北半球高纬度区域拥有最多的社会性寄生蚂蚁物种，但南北半球间独立演化起源的多样性并无显著差异。仅在北半球范围内，区域蚁类区系中社会性寄生蚂蚁的物种占比与纬度存在相关性。 主要结论：蚂蚁社会性寄生类群的反向纬度多样性格局，与自由生活的非寄生性蚂蚁所呈现的生物地理格局相悖，该格局似乎由大规模物种辐射演化，以及仅存在于北半球的特化生活史所共同驱动。