Behavioural and population genetic divergence of an invasive ant in a novel environment

Monica Gruber *1, Benjamin Hoffmann 2, Peter Ritchie 1, Phil Lester 1

1 School of Biological Sciences, Victoria University of Wellington, PO Box 600, Wellington, 6140, NZ
2 Tropical Ecosystems Research Centre, CSIRO PMB 44, Winnellie, Northern Territory, Australia 0822

Invasive species may undergo rapid evolutionary changes in their new environment. The introduced unicolonial yellow crazy ant Anoplolepis gracilipes exhibits considerable variation in abundance throughout its current distribution in the tropical monsoonal savanna of Australia’s Northern Territory, where it was first detected in the 1980’s. First, we aimed to determine if A. gracilipes variation in abundance was associated with behavioural and genetic differentiation. Second, we investigated if population divergence of A. gracilipes has occurred since introduction. Anoplolepis gracilipes abundances were assessed at 13 sites throughout the region. We used microsatellite molecular markers to determine population genetic structure at these 13 sites and a further seven sites. Behavioural differentiation was assayed using aggression trials and analysed together with genetic data. Although we found considerable variation in abundance we found no correlation between abundance and population genetic differentiation. Our analyses suggest that A. gracilipes in Arnhem Land are genetically and behaviourally a single supercolony, and resulted from a single introduction. The population is not homogeneous, however, as aggression varied over both genetic and geographic distance, and we found a positive relationship between genetic and geographic distance. The genetic and behavioural differentiation we observed is suggestive of incipient genetic and behavioral divergence, which may be expected when an invasive species enters in a new environment.

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