ECR feature: Kyle William Gray

Kyle is a PhD candidate at the Arizona State University, U.S.A. He is a evolutionary biologist with special focus on natural history, biogeography and evolution of ants. Here, Kyle shares his recent work on global biogeography of ant social parasites.

Kyle enjoys collecting ants in beautiful places such as Bishop, California, U.S.A.

Personal links. Website

Institute. Arizona State University, U.S.A. & University of Hohenheim, Germany.

Academic life stage. PhD candidate

Major research themes. Biodiversity, biogeography, and evolution of ants.

Current study system. My doctoral dissertation focuses on the biodiversity, biogeography and evolution of socially parasitic ants and ants in the South Pacific. Ant social parasites are a diverse set of species that exploit the parental caring behaviour of other ant species and do so in a variety of ways. Ants in the South Pacific are equally interesting to me because there have been numerous radiations of endemic species across different archipelagos that exhibit a fascinating diversity of morphologies, and there are still under-sampled archipelagos that offer much room for novel discoveries.

Recent JBI paper. Gray, K. W., & Rabeling, C. (2022). Global biogeography of ant social parasites: Exploring patterns and mechanisms of an inverse latitudinal diversity gradient. Journal of Biogeography, 50(2), 316-329.

Motivation behind this paper. The motivation for this paper was to use distribution data and our current understanding of the ant tree of life to test the historical biogeographic hypothesis that ant social parasites are most species-rich in the northern hemisphere where the fewest free-living ant species exist, i.e., that ant social parasites are distributed along an inverse latitudinal diversity gradient. Although previous works have discussed this pattern, these were either qualitative or focused on a few species. Given the significant increase in our understanding of ant biodiversity around the globe, especially in tropical regions, the time was ripe to look closely at the current global biogeography of ant social parasites. Furthermore, we hoped our research would serve as a basis for future works that aim to answer how abiotic and biotic factors possibly shape the geographic distribution of socially parasitic Hymenoptera.

Key methodologies. We assembled a comprehensive biogeographic and life history dataset of all 371 described socially parasitic ant species using published data sources. We then used phylogenetic and taxonomic studies to estimate independent evolutionary origins of ant social parasitism to compare species richness with the number of species representing independent evolutionary origins of social parasitism across a latitudinal gradient. This corrects for phylogenetic non-independence caused by species radiations in some clades of ant social parasites. In addition, we compared ant social parasite diversity across biogeographic regions using rarefaction to account for different sampling efforts and data availability – which is important given the historic sampling bias for ant social parasites in the northern hemisphere. Finally, we tested for a correlation between latitude and the proportion of ant social parasite species within regional ant faunae.

Workers of the dulotic ant social parasite species Polyergus mexicanus taking a stolen pupa back to its nest. Bishop, California, U.S.A.

Unexpected challenges. I think the primary challenge was the breadth of the study both in terms of the history of ant social parasite research (at least since the days of Darwin) and that these species span numerous genera and subfamilies. I ended up reading over seven hundred papers to extract all the data used in this study, which included a significant portion of papers written in 19th or early 20th century German, French, and Italian. Reading through these historic papers was a struggle sometimes, but I began to enjoy the historical aspect of this. I was not only learning about the biology of these fascinating ants, but also learning about ant biology history. In addition, given that the study was on a global scale, I learned about different places across the globe. Overall, this project ended up being a scientific, historical, linguistic, and geographical endeavour.

Major results. Ant social parasites peak in both species richness and in the number of evolutionary origins of parasitism in the northern hemisphere where the least free-living ant diversity exists. Thus, ant social parasites exhibit an inverse latitudinal diversity gradient by peaking in diversity outside the equatorial tropics. The dulotic social parasites, which refers to species that perform interspecific brood raids to capture workers for colony maintenance tasks, contribute significantly to the pattern because they are still only found in the northern hemisphere mostly within temperate regions. It also appears that this inverse latitudinal diversity gradient is driven by large species radiations in the northern hemisphere. Additionally, the proportion of ant parasite species increases significantly with latitude only in the northern hemisphere, which resembles a pattern reported in parasitic bees. Overall, the biogeography of ant social parasites provides another interesting example of how specialized life histories shape global biodiversity patterns.

Exploring a vast landscape in southern Arizona, U.S.A. for the ant social parasite species Pogonomyrmex anergismus.

Next steps for this research. We hope this work reinforces the need for continued sampling and in-depth natural history studies for ant social parasites, especially in under-sampled tropical regions of Africa and Asia where exciting discoveries undoubtedly wait to be revealed. For example, one of the most puzzling observations in ant social parasite research is that dulotic species are still only found in the northern hemisphere. Is this due to some special aspect of the northern hemispheric ant fauna facilitating the evolution of dulosis? Possibly. Or do dulotics occur in the southern hemisphere but we just have not found them yet? One can only speculate. The answer will come with more field work!

If you could study any organism on Earth, what would it be? I am happy to say that I would keep studying ants! There are enough interesting phenomena in the ants to keep me busy for multiple lifetimes. Plus, I just love the way ants look. I can watch ant colonies do their thing for hours or look at images and illustrations of ants all day. They are beautiful, savage little beasts.

Anything else to add? This study would not have been possible without the efforts of other ant biologists as well as AntMaps (, AntWeb ( and AntWiki ( The fact that we have these wonderful resources is truly a blessing and I cannot express my gratitude enough for the people that made these resources happen.

Two males of the ant social parasite species Pogonomyrmex anergismus at the nest of its host species Pogonomyrmex rugosus in southern Arizona, U.S.A.

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