ARS | Publication request: A multi-gene phylogeny provides additional insight into the relationships between several Ascosphaera species

Submitted to: Journal of Invertebrate Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 30, 2012
Publication Date: January 1, 2013
Citation: Klinger, E.G., James, R.R., Youssef, N.N., Welker, D.L. 2013. A multi-gene phylogeny provides additional insight into the relationships between several Ascosphaera species. Journal of Invertebrate Pathology. 112:41-8.

Interpretive Summary: Chalkbrood is a disease that affects bees and kills wild and commercial pollinator populations. This disease is caused by fungi in the genus Ascosphaera. The Ascosphaera species that cause chalkbrood in bees can be difficult to distinguish from each other because not all of them can be grown readily in the laboratory, and identifications are usually based on how the fungi look as they grow. We developed molecular techniques to assist with identifications. Also, we identified evolutionary relationships between the Ascosphaera species. We better defined the true relationship using six different genetic regions of the fungal DNA, unlike previous studies that only used one. We found one species previously identified as Ascosphaera torchioi may not even belong to this group. Also, the two most commercially important of these pathogens, the ones that infect honey bees and alfalfa leafcutting bees, are not as closely related as previously thought, and their relationship to each other might help us understand how some fungi become pathogens.

Technical Abstract: Ascosphaera fungi are highly associated with social and solitary bees. This genus includes an important group of bee pathogens, the chalkbrood fungi, and thus proper identification of species and an understanding of their relationships are important. However, Ascosphaera spp. are often unculturable, making morphological identifications difficult, and previous phylogenies have only used one genetic region. We evaluated multiple phylogenies of Ascosphaera using up to six loci: the Internal Transcribed Spacer (ITS) region, 18S rRNA, 28S rRNA, Elongation Factor ¬¬¬-1a (EF-1a) and the RNA polymerase II largest subunit (RPB1) and second largest subunit (RPB2). The ITS sequence alone produced an inadequate phylogeny, the addition of the EF-1a locus, or of both the 18S and 28S rRNA loci to the ITS sequence produced phylogenies more similar to but not identical with a phylogeny based on all six genetic regions. For these three multi-gene phylogenies, A. torchioi was not within the main Ascosphaera clade and may render Ascosphaera paraphyletic. Also, we suggest that A. apis, which is weakly pathogenic to honey bees, arose within a group of saprophytes, and the Megachile (leafcutting bees) pathogens, which are strongly pathogenic, arose separately.