The Pine Bark Adelgid, Pineus strobi, Contains Two Novel Bacteriocyte-Associated Gammaproteobacterial Symbionts

Abstract

Bacterial endosymbionts of the pine bark adelgid, Pineus strobi (Insecta: Hemiptera: Adelgidae), were investigated using transmission electron microscopy, 16S and 23S rRNA-based phylogeny, and fluorescence in situ hybridization. Two morphologically different symbionts affiliated with the Gammaproteobacteria were present in distinct bacteriocytes. One of them ("Candidatus Annandia pinicola") is most closely related to an endosymbiont of Adelges tsugae, suggesting that they originate from a lineage already present in ancient adelgids before the hosts diversified into the two major clades, Adelges and Pineus. The other P. strobi symbiont ("Candidatus Hartigia pinicola") represents a novel symbiont lineage in members of the Adelgidae. Our findings lend further support for a complex evolutionary history of the association of adelgids with a phylogenetically diverse set of bacterial symbionts.

Buchnera has changed flatmate but the repeated replacement of co‐obligate symbionts is not associated with the ecological expansions of their aphid hosts

“…In some mealybugs, the primary symbiont shelters within its cells another Gammaproteobacterium symbiont that has also been repeatedly replaced (Husnik & McCutcheon 2016). The aphid sister group (Adelgidae) has not established a long-term association with a primary symbiont, but is found associated with a diverse set of obligate bacterial partners throughout its evolutionary history (Toenshoff et al 2012(Toenshoff et al , 2014. Our results suggest that the succession of essential symbionts does not necessarily result from the adaptation of their hosts to changing ecological conditions.…”

“…The aphid sister group (Adelgidae) has not established a long‐term association with a primary symbiont, but is found associated with a diverse set of obligate bacterial partners throughout its evolutionary history (Toenshoff et al . , ). Our results suggest that the succession of essential symbionts does not necessarily result from the adaptation of their hosts to changing ecological conditions.…”

Buchnerahas changed flatmate but the repeated replacement of co-obligate symbionts is not associated with the ecological expansions of their aphid hosts

“…In some mealybugs, the primary symbiont shelter within its cells another Gammaproteobacterium symbiont that has also been repeatedly replaced (Husnik & McCutcheon 2016). The aphid sister group (Adelgidae), has not established a long-term association with a primary symbiont, but is found associated with a diverse set of obligate bacterial partners throughout its evolutionary history (Toenshoff et al 2012; Toenshoff et al 2014). Our results suggest that the succession of essential symbionts does not necessarily result from the adaptation of their hosts to changing ecological conditions.…”

Microbial ecology-based methods to characterize the bacterial communities of non-model insects

“…Bacteriomes are often associated with the external midgut ((tsetse flies (Balmand et al, 2013), louse (Perotti et al, 2007)), appearing as whitish round shaped bodies; their first observation can be traced back to the 17th century (Hooke, 1667). Bacteriocytes can also be located in the fat body, where they can be identified by microscopy because of their cytoplasm, which is densely populated with bacteria (Toenshoff et al, 2014), or intercalated in midgut tissue (Stoll et al, 2010). Separating bacteriomes from gut tissue without breaking the gut epithelium can be difficult in smaller animals, however, the detection of endosymbionts by molecular means, such as diagnostic PCR, allows the analysis of the whole insect, thus avoiding this step (see section 4.5).…”