Genomic Evidence for Dual Introductions, Limited Gene Flow and Niche Preferences in the Invasive Wasp Vespula germanica in South Africa.

Biological invasions are major drivers of recent biodiversity changes, yet the genetic structure and ecological mechanisms underlying invasion dynamics remain poorly resolved in invasive social insects. In South Africa, the European wasp Vespula germanica (Hymenoptera: Vespidae), introduced in the 1970s, has spread remarkably more slowly than in other regions and its geographical distribution in the country remains limited. Although two mitochondrial haplotypes have been reported in South Africa, the species' range expansion and fine-scale population structure remain poorly understood. Using 2b-RAD sequencing of 47 colonies across its entire range in South Africa, we identified two main genetic clusters that correspond to previously identified mitochondrial haplotypes, strongly supporting the double introduction scenario. This well-defined genetic structure is sustained by limited gene flow and possibly by niche preferences. Spatial patterns reveal a dispersal system of short-range natural movements and human-mediated jumps, with Stellenbosch acting as a secondary introduction point. Ecological niche preferences appear to maintain a genetic structure through isolation by environment: one group occupies warmer, drier sites, while the other is confined to cooler, wetter microclimates near Cape Town. This pattern reflects ecological adaptation that is likely tied to distinct population origins. As the first genome-wide study of V. germanica, this work illuminates how introduction history and ecological constraints shape invasion dynamics, laying a foundation for understanding the genetic structure and invasion dynamics of the species and for developing predictive management frameworks.