The ability to express different phenotypes can help define species distributions by allowing access to, and exploitation of, new environments. Social insects employ two markedly different reproductive strategies with contrasting cost/benefit characteristics: independent colony foundation (ICF), which is associated with high dispersal range and high risk, and dependent colony foundation (DCF), characterized by low risk but low dispersal. The ant Myrmecina nipponica employs both of these strategies, with the frequency of each apparently varying between populations. We combine molecular data with data on reproductive strategy from different populations of this species throughout Japan to explore how this polymorphism is linked to environmental factors and if this relationship can help explain the current and historical biogeography of this species. Reproductive strategy exhibited a strong geographic pattern, with ICF predominant in southern populations and DCF more common in northern and southern highland populations. Molecular analyses clearly divided populations into broad geographic regions, with the southern-lowland populations basal to (southern-highland (+ northern)) populations. Intra-population polymorphism in colony founding strategy was widespread, and polymorphism was reconstructed as the likely ancestral state. The frequency of different strategies was linked with climate, with DCF more common in colder areas. A recent inferred origin to the northern lineage suggests that colonization of northern Japan was a rapid event coincident with warming at the end of the last glacial maxima, likely facilitated by the cold-adaptive advantages of DCF. We discuss how such polymorphisms could help explain the biogeography of this and other social insects.

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These data include:

1. Supporting methods and results = additional details for methods described in the main text and additional data analyses
2. The following genetic datasets for Myrmecina nipponica in Japan.
   • MIG_seq_SNPs-3716.fa = fasta file containing SNP data from MIG-Seq analysis for 39 indivdiuals from 13 Japanese populations and one outgroup.
   • SNP_dataset_-_1564.fa = fasta file containing SNP data from MIG-Seq analysis for 37 individuals from 11 Japanese populations and one outgroup following filtering for missing data.
   • Demographic_data.dat = Tab-delimited file containing demographic data from seven populations of M. nipponica in Japan over multiple years.
   • Binary_SNP_matrix_for_PCA.dat = Tab-delimited file of binary (presence/abosence) data of 3716 SNPs.
   • COI_dataset.nexus = A nexus alignment for the 1281 bp region of the Cytochrome Oxidase subunit 1 for 51 individuals from 13 populations plus outgroups. These data are available from GenBank under accession numbers KX016598 - KX016638, KX021820 and MG592252 - MG592256.