Independent evolution of mycophagy among Ipini bark beetles

All plant parts from root to shoot are utilized by the nearly 6,000 species of bark beetles (Scolytinae). Individuals of Scolytinae are either ‘true bark beetles’ that feed on and breed in phloem tissue, or ‘ambrosia beetles’ that feed on symbiotic ambrosia fungi within sapwood (mycophagy). Fungal feeding has evolved within the bark beetles seven times in distantly related tribes . Recent phylogenies of scolytines suggest that Premnobini and Ipini spp. are monophyletic, which represents an additional diversification on this fungal resource. However, these phylogenies lacked a diverse representation of Ipini, especially Acanthotomicus, and Premnobini species. This study tests the hypothesis that the Premnobini and Ipini are monophyletic; alternatively Premnobini and Xyleborini are monophyletic. Bayesian analysis using ~800 cytochrome oxidase I nucleotides from 120 Ipini representing all genera (including seven Acanthotomicus spp.), four Premnobini spp. and two Xyleborini species (outgroups) recovered the monophyly of these tribes and of all the genera except Acanthotomicus. The general relationship of the genera followed: Xyleborus (Acanthotomicus (Acanthotomicus, Pseudips), ((Acanthotomicus, Premnobius), ((Orthotomicus, Pityokteines) (Pityogenes, Ips))). The sister relationship of Premnobini to Acanthotomicus suggests that mycophagy evolved from a tropical Angiosperm phloem feeder. Also conifer phloem feeding evolved twice from tropical Angiosperm phloem feeders with Pseudips and with the Holarctic Ipini species (Orthotomicus, Pityokteinse, Pityogenes, Ips) which represented a greater lineage diversification.