Aim: A crucial step to protecting biodiversity is assessing species diversity and endemism. We delineate spatial patterns of diversity in Malagasy ants on a phylogenetic and taxonomic level to identify centers of diversity and endemism, and evaluate the ‘museum vs cradle’ hypothesis with regard to ant endemism.

Location: Madagascar

Taxon: Ants, genus Crematogaster.

Methods: We estimated distribution models for 33 Crematogaster species and generated a phylogeny based on ultraconserved elements. We calculated species richness (SR), phylogenetic diversity (PD), weighted (WE), phylogenetic endemism(PE), randomized phylogenetic diversity (PD-sig), and relative phylogenetic diversity (RPD) and endemism (RPE). Categorical analyses of neo- and paleo-endemism (CANAPE) and the phylo-jaccard index were used to delineate centers of neo- and paleo-endemism. We correlated these measures with elevation metrics to investigate the role of mountains in generating ant endemism.

Results: We found extensive phylogenetic clustering (significantly low PD-sig) and short branches (low RPD) at higher elevations in central and south-central to southern Madagascar. In contrast, phylogenetic overdispersion (significantly high PD-sig) and long branches (high RPD) predominate at lower elevations in eastern humid and northern western dry forests. CANAPE and phylo-jaccard estimated five centers of endemism, whereby neo- and mixed endemism were significantly correlated with higher elevations, and paleo-endemism with lower elevations. 

Main Conclusions: Centers of ant endemism are located in western dry and humid forests of northern Madagascar, eastern humid forests, and in the southern Central Highland region. Mountainous areas appear to be cradles of recent diversification for acrobat ants, whereas lower elevations may be regarded as centers of paleo-endemism and thus museums for relict lineages. Species diversification among acrobat ants may have coincided with the arrival of a new biome in the central highlands of Madagascar.