Abstract
Calligrapha is a New World leaf beetle genus that includes several unisexual species in northeastern North America. Each unisexual species had an independent hybrid origin involving different combinations of bisexual species. However, surprisingly, they all cluster in a single mtDNA clade and with some individuals of their parental species, which are in turn deeply polyphyletic for mtDNA. This pattern is suggestive of a selective sweep which, together with mtDNA taxonomic incongruence and occurrence of unisexuality in Calligrapha, led to hypothesize that Wolbachia might be responsible. I tested this hypothesis studying the correlation between diversity of Wolbachia and well‐established mtDNA lineages in >500 specimens of two bisexual species of Calligrapha and their derived unisexual species. Wolbachia appears highly prevalent (83.4%), and fifteen new supergroup‐A strains of the bacteria are characterized, belonging to three main classes: wCallA, occupying the whole species ranges, and wCallB and wCallC, narrowly parapatric, infecting beetles with highly divergent mtDNAs where they coexist. Most beetles (71.6%) carried double infections of wCallA with another sequence class. Bayesian inference of ancestral character states and association tests between bacterial diversity and the mtDNA genealogy show that each mtDNA lineage of Calligrapha has specific types of infection. Moreover, shifts can be explained by horizontal or vertical transfer from local populations to an expanding lineage and cytoplasmic incompatibility between wCallB and wCallC types, suggesting that the symbionts hitchhike with the host and are not responsible for selective mtDNA sweeps. Lack of evidence for sweeps and the fact that individuals in the unisexual clade are uninfected or infected by the widespread wCallA type indicate that Wolbachia does not induce unisexuality in Calligrapha, although they may manipulate host reproduction through cytoplasmic incompatibility.
Highlights
Alphaproteobacteria of the genus Wolbachia (Rickettsiales: Anaplasmataceae) have been shown to live as endosymbionts of a large proportion of arthropods and nematodes (Hilgenboecker, Hammerstein, Schlattmann, Telschow, & Werren, 2008; Weinert, Araujo, Ahmed, & Welch, 2015; Zug, Koehncke, & Hammerstein, 2012)
Each unisexual species had an independent hybrid origin involving different combinations of bisexual species. They all cluster in a single mitochondrial DNA (mtDNA) clade and with some individuals of their parental species, which are in turn deeply polyphyletic for mtDNA
This pattern is suggestive of a selective sweep which, together with mtDNA taxonomic incongruence and oc‐ currence of unisexuality in Calligrapha, led to hypothesize that Wolbachia might be responsible
Summary
Alphaproteobacteria of the genus Wolbachia (Rickettsiales: Anaplasmataceae) have been shown to live as endosymbionts of a large proportion of arthropods and nematodes (Hilgenboecker, Hammerstein, Schlattmann, Telschow, & Werren, 2008; Weinert, Araujo, Ahmed, & Welch, 2015; Zug, Koehncke, & Hammerstein, 2012). Bisexual species of Calligrapha are deeply polyphyletic for mtDNA, with individuals in at least two highly divergent clades, one with populations with nor‐ mal sex ratios and named B‐clade and one exclusively comprised of females, including representatives of the unisexual species evo‐ lutionarily derived from them, or U‐clade (Gómez‐Zurita & Cardoso, 2019; Montelongo & Gómez‐Zurita, 2015) This pattern is inter‐ preted as each of the unisexual species of Calligrapha having had a history with a minimum of two waves of interspecific hybridization, with available evidence suggesting that sex was not lost immediately (Montelongo & Gómez‐Zurita, 2015). Based on this informa‐ tion, the main objective of the study will be testing for links between Wolbachia and unisexuality in Calligrapha, and more generally inves‐ tigating if and how Wolbachia may have affected mtDNA diversity in this host
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
