<b><i>Wolbachia</i></b> Induced Cytogenetical Effects as Evidenced in <b><i>Chorthippus parallelus</i></b> (Orthoptera)

Abstract

The cytoplasmic incompatibility induced by the bacterial endosymbiont Wolbachia is attributed to chromatin modification in the sperm of infected individuals and is only ‘rescued’ by infected females after fertilization. Chorthippus parallelus is a grasshopper with 2 subspecies that form a hybrid zone in the Pyrenees in which this Wolbachia-generated cytoplasmic incompatibility has recently been described. The analysis of certain cytogenetic traits (sex chromosome-linked heterochromatic bands, nucleolar organizing region expression, spermatid size and morphology, and number of chiasmata formed) in pure and hybrid Chorthippus parallelus that are infected and not infected by this bacterium indicates that the infection affects some of these traits and, in the case of the spermatids, reveals a synergism between the infection and the hybrid condition. These results are interpreted as being secondary effects of the chromatin modification induced by Wolbachia which thereby support this model of modification/rescue. The possible effects of these cytogenetic variations on affected individuals are also considered.

Wolbachiaeffects in natural populations ofChorthippus parallelusfrom the Pyrenean hybrid zone

“…Here, the high variability that we have found in F strains (Zabal‐Aguirre et al ., ) suggests an ancient origin of infection and thus, a long time to evolve towards such mutualism in this grasshopper. An increment in host recombination rate has recently been proposed as another Wolbachia ‐induced effect in C. parallelus (Sarasa et al ., ). However, our evidence for any increment in fecundity is equivocal, due to the low number of crosses obtained in this study; more effort would be required to discern any Wolbachia effects on the females.…”

“…Recently, the presence of Wolbachia has been described in C. parallelus populations (Dillon et al ., ; Martínez et al ., ; Bella et al ., ; Zabal‐Aguirre et al ., ; Martínez‐Rodríguez, ; Sarasa et al ., ). The genus Wolbachia (Hertig & Wolbach, ) includes a diverse group of alpha proteobacteria belonging to the order Rickettsiales.…”

“…Asynchrony of male and female pronuclei at the initial stages of mitosis has been observed in the first embryonic divisions of several host species (Reed & Werren, ; Lassy & Karr, ; Tram & Sullivan, ). Indirect support for this model has been obtained in the C. parallelus system (Sarasa et al ., ).…”

First detection of Wolbachia in the New Zealand biota

“…Wolbachia was detected in HTS DNA sequence datasets from six orthopteran individuals that are endemic to New Zealand, representing two families and five genera ( Macropathus sp., Hemiandrus brucei , Talitropsis sedilloti , Miotopus diversus , and two Neonetus specimens). Orthoptera elsewhere in the world are known to be hosts of Wolbachia [ 57 , 58 ], but we present the first documented cases of Wolbachia infection of any endemic New Zealand invertebrate. The samples from cave weta Macropathus sp .…”

Chromosomal localization of Wolbachia inserts in the genomes of two subspecies of Chorthippus parallelus forming a Pyrenean hybrid zone

“…CI-inducing Wolbachia present in both subspecies of Cp may contribute to the evolutionary dynamics of the hybrid zone by preventing hybridization of grasshoppers with incompatible Wolbachia strains (Zabal-Aguirre et al 2010, Zabal-Aguirre et al 2014). Furthermore, a previous study found that Wolbachia negatively affects chiasmata formation and induces spermatid malformation in hybrid males of this species; these cytogenetical effects may result in modifications of paternal chromatin that contribute to the pathology of CI (Sarasa et al 2013). …”