Introduction
Population structure analyses using genetic data provide extensive information about populations, including genetic distribution, genetic diversity, gene flow, and selection. Furthermore, these analyses can be used to evaluate relationships between secondary traits such as phenotype, reproductive strategy, and symbiotic bacterial communities. Among secondary traits, wing morph is the principal phenotype associated with direct dispersal, distribution, and reproductive strategies in insects (Roff, 1986). In ants, wings play a salient role in nuptial flight, which determines dispersal and breeding success. However, the wing is not a sine qua non in several species. Winglessness and wing reduction in reproductive ants are widespread across all subfamilies (Buschinger & Heinze, 1992; Heinze & Tsuji, 1995; Peeters, 1991; Peeters, 2012; Peeters & Ito, 2001; Tinaut & Heinze, 1992; Villet, 1991).
Vollenhovia emeryi Wheeler (Hymenoptera: Myrmicinae) is a common ant species endemic to East Asia; this species has invaded North America (Kjar & Suman, 2007; Wetterer, Guenard, & Booher, 2015; Wright & Kubik, 2011). It is polymorphic for normal long and aberrant short wing length in queens. The two morphs are not thought to coexist in nature, and colonies of the long-winged (L) morph are typically monogynous, while short-winged (S) morph colonies are polygynous (Kinomura & Yamauchi, 1994). Unlike other ant species and Hymenopteran insects in general, queens and males are produced clonally, while sterile workers arise sexually (Kobayashi, Hasegawa, & Ohkawara, 2008, 2011; Ohkawara, Nakayama, Satoh, Trindl, & Heinze, 2006). This unusual clonal reproduction system is very similar to the system first found in some populations of the little fire ant Wasmannia auropunctata(Foucaud, Estoup, Loiseau, Rey, & Orivel, 2010; Foucaud et al., 2007; Foucaud et al., 2006; Fournier et al., 2005) and in the highly invasive longhorn crazy ant Paratrechina longicornis (Pearcy, Goodisman, & Keller, 2011). Selfish clonal reproduction in both sexes might evolve without allowing genetic contamination by the opposite sex, thereby giving rise to genetically homogeneous clonal lineages. Such an unusual reproductive system might be due to infection by a selfish reproductive manipulator (Jeong & Stouthamer 2004).
The Wolbachia bacterium is a maternally-inherited endosymbiont that infects a wide variety of invertebrates such as insects (including ants) and other arthropods (Bourtzis, & Miller, 2008; Correa & Ballard, 2016; Hilgenboecker, Hammerstein, Schlattmann, Telschow, & Werren, 2008; Kautz, Rubin, Russell, & Moreau, 2013; Werren, 1997; Zientz , Feldhaar, Stoll, & Gross, 2005; Zug, & Hammerstein, 2014). Infection induces various types of reproductive alterations in the host, including cytoplasmic incompatibility, feminization, male-killing, and parthenogenesis (Fujii, Kubo, Ishikawa, & Sasaki, 2004; Jeong & Suh, 2008; Stouthamer, Breeuwer, & Hurst, 1999).
Despite the ecological and evolutionary importance of V. emeryiand Wolbachia , little is known about their distribution and population biology. The specific aims of this study were to examine 1) the population genetic structure of the mitochondrial genes of V. emeryi ; 2) the phylogeographic relationships among the two winged morphs from Korea and Japan; 3) the approximate divergence time of the two winged morphs; 4) the ubiquity of Wolbachia infection in ant species; and 5) potential relationships between host phenotype andWolbachia infection.