Seppa, P. | bioRxiv Science

bioRxiv2025

Dispersal behavior rather than dispersal morphology creates social polymorphism in Formica ants

O_LIDispersal evolution and social evolution are interlinked. Dispersal is necessary for avoiding kin competition and inbreeding, but limited dispersal also allows beneficial social interactions with kin. In ants, a correlation between poor dispersal and complex societies, where a big proportion of queens are philopatric, is well documented, but the underlying causal mechanisms are not clear. C_LIO_LIIn this study we investigate the dispersal ability of six Formica species that vary in their colony queen number and nest founding mode, from three different subgenera. Investigating resource allocation in the bodies of young queens and males allows us to analyze the evolutionary causalities between dispersal ability and social organization. We measured the body ratios including wing-muscle ratio; glycogen, triglyceride and protein resources with colorimetric assays; and microscopic wing muscle structures with transmission electron microscopy, with an overall sample size of 1515 individual males and queens. C_LIO_LIOur results suggest that the physical condition of individuals does not strongly correlate with the dispersal patterns of the species, contrary to assumptions based on earlier studies in both ants and other insects. There was still a minor effect of social organization on male wing-muscle ratio, which is an interesting case of sexual coevolution of dispersal traits: it is likely that the queen philopatric behavior is reflected in male behavior and consequently in male morphology - even when our overall results support the hypothesis that ant dispersal is male biased regardless of social organization. Further, our intraspecific analyses in two of the six species reveal different patterns in their flight abilities in connection to their social organization, further pointing towards a mismatch between dispersal behavior and ability. C_LIO_LIIn Formica queens, philopatry seems to be a behavioral trait of the individuals rather than a consequence of colony-level resource allocation into dispersal ability, pointing towards a "behavior first" evolutionary route. The queens may selfishly choose not to disperse even when their society provides them with the resources for it. This raises new questions about conflicts over dispersal in these highly social systems. C_LI

evolutionary biology↗

bioRxiv2021

Landscape genetics across the Andes Mountains: Environmental variation drives genetic divergence in the leaf-cutting ant Atta cephalotes

Disentangling the mechanisms underlying spatial distribution of genetic variation into those due to environment or physical barriers from mere geographic distance is challenging in complex landscapes. The Andean uplift represents one of the most heterogeneous habitats where these questions remain unexplored as multiple mechanisms might interact, confounding their relative roles. We explore this broad question in the leaf-cutting ant Atta cephalotes, a species distributed across the Andes Mountains using nuclear microsatellite markers and mtCOI gene sequences. We investigate spatial genetic divergence across the Western range of Northern Andes in Colombia by testing the relative role of alternative scenarios of population divergence, including geographic distance (IBD), climatic conditions (IBE), and physical barriers due to the Andes Mountains (IBB). Our results reveal substantial genetic differentiation among A. cephalotes populations for both types of markers, but only nuclear divergence followed a hierarchical pattern with multiple models of genetic divergence imposed by the Western range. Model selection showed that IBD, IBE (temperature and precipitation), and IBB (Andes mountains) models, often proposed as individual drivers of genetic divergence, interact, and explain up to 33% of genetic divergence in A. cephalotes. IBE models remained significant after accounting for IBD, suggesting that environmental factors play a more prominent role when compared to IBB. These factors in combination with idiosyncratic dispersal patterns of ants appear to determine hierarchical patterns of gene flow. This study enriches our understanding of the forces shaping population divergence in complex habitat landscapes.

genetics↗