Biogeography and Phylogeography

• Economo, E. P., N. Narula, N. R. Friedman, M. D. Weiser, and B. Guénard. 2018. Macroecology and macroevolution of the latitudinal diversity gradient in ants. Nature Communications. 9:1778. doi:10.1038/s41467-018-04218-4

The latitudinal diversity gradient—the tendency for more species to occur toward the equator—is the dominant pattern of life on Earth, yet the mechanisms responsible for it remain largely unexplained. Recently, the analysis of global data has led to advances in understanding, but these advances have been mostly limited to vertebrates and trees and have not provided consensus answers. Here we synthesize large-scale geographic, phylo-genetic, and fossil data for an exemplar invertebrate group—ants—and investigate whether the latitudinal diversity gradient arose due to higher rates of net diversification in the tropics, or due to a longer time period to accumulate diversity due to Earth’s climatic history. We find that latitudinal affinity is highly conserved, temperate clades are young and clustered within tropical clades, and diversification rate shows no systematic variation with latitude. These results indicate that diversification time—and not rate—is the main driver of the diversity gradient in ants.

• Villalta, I., Amora, F., Galarza, J.A., Dupont, S., Ortega, P., Hefetze, A., Dahbif, A., Cerdáa, X. and R. Boulay. 2018. Origin and distribution of desert ants across the Gibraltar Straits. Molecular Phylogenetics and Evolution. 118:122-134. doi:10.1016/j.ympev.2017.09.026

The creation of geographic barriers has long been suspected to contribute to the formation of new species. We investigated the phylogeography of desert ants in the western Mediterranean basin in order to elucidate their mode of diversification. These insects which have a low dispersal capacity are recently becoming important model systems in evolutionary studies. We conducted an extensive sampling of species belonging to the Cataglyphis albicans group in the Iberian Peninsula (IP) and the northern Morocco (North Africa; NA). We then combined genetic, chemical and morphological analyses. The results suggest the existence of at least three and five clades in the IP and NA, respectively, whose delineation partially encompass current taxonomic classification. The three Iberian clades are monophyletic, but their origin in NA is uncertain (79% and 22% for Bayesian and Maximum Likelihood support, respectively). The estimation of divergence time suggests that a speciation process was initiated after the last reopening of the Gibraltar Straits ≈5.33 Ma. In the IP, the clades are parapatric and their formation may have been triggered by the fragmentation of a large population during the Pleistocene due to extended periods of glaciation. This scenario is supported by demographic analyses pointing at a recent expansion of Iberian populations that contrasts with the progressive contraction of the NA clades. Niche modeling reveals that this area, governed by favorable climatic conditions for desert ants, has recently increased in the IP and decreased in NA. Altogether, our data points at geoclimatic events as major determinants of species formation in desert ants, reinforcing the role of allopatric speciation.