Data from: Tournament ABC analysis of the western palaearctic population history of an oak gallwasp, Synergus umbraculus

Approximate Bayesian computation (ABC) is a powerful and widely used
approach in inference of population history. However, the computational
effort required to discriminate among alternative historical scenarios
often limits the set that is compared to those considered more likely a
priori. While often justifiable, this approach will fail to consider
unexpected but well-supported population histories. We used a hierarchical
tournament approach, in which subsets of scenarios are compared in a first
round of ABC analyses and the winners are compared in a second analysis,
to reconstruct the population history of an oak gallwasp, Synergus
umbraculus (Hymenoptera, Cynipidae) across the Western Palaearctic. We
used 4233 bp of sequence data across 7 loci to explore the relationships
between four putative Pleistocene refuge populations in Iberia, Italy, the
Balkans, and Western Asia. We compared support for 148 alternative
scenarios in eight pools, each pool comprising all possible rearrangements
of four populations over a given topology of relationships, with or
without founding of one population by admixture and with or without an
unsampled ‘ghost’ population. We found very little support for the
directional ‘out of the east’ scenario previously inferred for other
gallwasp community members. Instead, the best-supported models identified
Iberia as the first regional population to diverge from the others in the
late Pleistocene, followed by divergence between the Balkans and Western
Asia, and founding of the Italian population through late Pleistocene
admixture from Iberia and the Balkans. We compare these results with what
is known for other members of the oak gall community, and consider the
strengths and weaknesses of using a tournament approach to explore
phylogeographic model space.