Evidence for Horizontal Transmission of Secondary Endosymbionts in the Bemisia tabaci Cryptic Species Complex

Abstract

Bemisia tabaci (Hemiptera: Aleyrodidae) is a globally distributed pest composed of at least 34 morphologically indistinguishable cryptic species. At least seven species of endosymbiont have been found infecting some or all members of the complex. The origin(s) of the associations between specific endosymbionts and their whitefly hosts is unknown. Infection is normally vertical, but horizontal transmission does occur and is one way for new infections to be introduced into individuals. The relationships between the different members of the cryptic species complex and the endosymbionts have not been well explored. In this study, the phylogenies of different cryptic species of the host with those of their endosymbionts were compared. Of particular interest was whether there was evidence for both coevolution and horizontal transmission. Congruence was observed for the primary endosymbiont, Portiera aleyrodidarum, and partial incongruence in the case of two secondary endosymbionts, Arsenophonus and Cardinium and incongruence for a third, Wolbachia. The patterns observed for the primary endosymbiont supported cospeciation with the host while the patterns for the secondary endosymbionts, and especially Wolbachia showed evidence of host shifts and extinctions through horizontal transmission rather than cospeciation. Of particular note is the observation of several very recent host shift events in China between exotic invader and indigenous members of the complex. These shifts were from indigenous members of the complex to the invader as well as from the invader to indigenous relatives.

Species in Wolbachia? Proposal for the designation of ‘Candidatus Wolbachia bourtzisii’, ‘Candidatus Wolbachia onchocercicola’, ‘Candidatus Wolbachia blaxteri’, ‘Candidatus Wolbachia brugii’, ‘Candidatus Wolbachia taylori’, ‘Candidatus Wolbachia collembolicola’ and ‘Candidatus Wolbachia multihospitum’ for the different species within Wolbachia supergroups

“…Some insects and their endosymbionts have a parallel evolutionary history, and cospeciation events have been described for both host and bacteria, especially primary endosymbionts [1,10,21,79,87]. For endosymbionts that have cospeciated with their hosts, endosymbionts in different hosts would be distinct species.…”

“…For endosymbionts that have cospeciated with their hosts, endosymbionts in different hosts would be distinct species. It seems that cospeciation is rare in Wolbachia and insects as their phylogenies are usually not congruent [1,49,86,88]. Thus, adaptations to different hosts would not necessarily mean bacterial speciation.…”

Identification of mungbean lines with tolerance or resistance to yellow mosaic in fields in India where different begomovirus species and different Bemisia tabaci cryptic species predominate

“…In all cases MEAM1 were collected from tomato plants suggesting this species may have a preference for solanaceous hosts compared to legumes, though MEAM1 usually is reported to have a very broad host range. Host preference of different whitefly species and a better performance depending on the host were described earlier (Lisha et al 2003;Xu et al 2011;Ahmed et al 2013;Ahmed et al 2014). MEAM1 was not found in this study, and nor in the study by Prasanna et al (2015).…”

Novel Endosymbioses as a Catalyst of Fast Speciation

“…However, since in many cases, there is no concordance between the phylogeny of bacteria and their hosts, and there is indication of horizontal transmission (Vavre et al 1999;Thao et al 2000;Russell et al 2003;Ahmed et al 2013). It is conceivable that in an environment inhabited by organisms infected and non-infected with bacteria, given enough time, high densities and reiterated contacts, the probability of horizontal transmission of symbionts is not negligible (Gehrer and Vorburger 2012;Le Clec'h et al 2013).…”