Abstract
The alfalfa weevil (Hypera postica) is a well‐known example of a worldwide‐distributed pest with high genetic variation. Based on the mitochondrial genes, the alfalfa weevil clusters into two main mitochondrial lineages. However, there is no clear picture of the global diversity and distribution of these lineages; neither the drivers of its diversification are known. However, it appears likely that historic demographic events including founder effects played a role. In addition, Wolbachia, a widespread intracellular parasite/symbiont, likely played an important role in the evolution of the species. Wolbachia infection so far was only detected in the Western lineage of H. postica with no information on the infecting strain, its frequency, and its consequences on the genetic diversity of the host. We here used a combination of mitochondrial and nuclear sequences of the host and sequence information on Wolbachia to document the distribution of strains and the degree of infection. The Eastern lineage has a higher genetic diversity and is found in the Mediterranean, the Middle East, Eastern Europe, and eastern America, whereas the less diverse Western lineage is found in Central Europe and the western America. Both lineages are infected with the same common strain of Wolbachia belonging to Supergroup B. Based on neutrality tests, selection tests, and the current distribution and diversification of Wolbachia in H. postica, we suggested the Wolbachia infection did not shape genetic diversity of the host. The introduced populations in the United States are generally genetically less diverse, which is in line with founder effects.
Highlights
| 9547 neutrality tests, selection tests, and the current distribution and diversification of Wolbachia in H. postica, we suggested the Wolbachia infection did not shape genetic diversity of the host
By analyzing 292 alfalfa weevil specimens from Iran, Bulgaria, Italy, Poland, the Czech Republic, western and eastern parts of North America, Korea, and Japan (Appendix S1 and Figure 1), we improved our current knowledge of the biogeography of introduced and na‐ tive populations of H. postica
A variant of the predominant Wolbachia strain is wHypera2, which is the only other variant of wHypera1 that we found in a large number of samples. wHypera3 is another rare Wolbachia infection, which is observed as a coinfection with wHypera1 in a sample from the Montana population
Summary
The genetic diversity and composition of cosmopolitan pest species can be shaped by several forces (Bazin, Glémin, & Galtier, 2006) in‐ cluding mutations (Wright, 2001), human‐mediated or natural gene flow (Roman & Darling, 2007; Sanaei et al, 2016), and genetic drift (Gonzalez‐Quevedo, Spurgin, Illera, & Richardson, 2015; Grubaugh et al, 2016; Hershberg et al, 2008; Stuckas et al, 2017), includ‐ ing bottlenecks and founder effects (Balick, Do, Cassa, Reich, & Sunyaev, 2015; Hundertmark & Van Daele, 2010). While nuclear genes failed to recover any pat‐ tern of diversification (Böttger, Bundy, Oesterle, & Hanson, 2013; for more information on genes please refer to Appendices S1 and S2), several studies confirmed the strong mitochondrial gene diver‐ gence between Western and Eastern (including American Eastern and Egyptian strains) lineages (Böttger et al, 2013; Iwase, Nakahira, et al, 2015; Kuwata et al, 2005; Sanaei et al, 2016). A study of American populations further suggested that the Western lineage is naturally infected, whereas the Eastern lineage is naturally resistant to Wolbachia (Bundy et al, 2005; Hsaio, 1996).
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