Ancient coevolution of baculoviruses and their insect hosts

Abstract

If the relationships between baculoviruses and their insect hosts are subject to coevolution, this should lead to long-term evolutionary effects such as the specialization of these pathogens for their hosts. To test this hypothesis, a phylogeny of the Baculoviridae, including 39 viruses from hosts of the orders Lepidoptera, Diptera, and Hymenoptera, was reconstructed based on sequences from the genes lef-8 and ac22. The tree showed a clear division of the baculoviruses according to the order of their hosts. This division highlighted the need to reconsider the classification of the baculoviruses to include one or possibly two new genera. Furthermore, the specialization of distinct virus lineages to particular insect orders suggests ancient coevolutionary interactions between baculoviruses and their hosts.

FIG. 1.

ML trees obtained from the Lef-8 & Ac22 data set. T1, unconstrained tree; T2, GV monophyletic constraint tree. The trees were found by a heuristic search starting with neighbor joining and nearest-neighbor interchange branch swapping. Virus abbreviations are shown in Table 1.

FIG. 2.

Robustness of the Lef-8 & Ac22 ML tree (T2). Numbers in roman type (ML/MP ratio of >50) indicate bootstrap scores obtained by the ML method with 100 replicates. The second number, when present, indicates the score obtained by the MP method with 1,000 replicates. Numbers in bold italic type indicate the Bayesian posterior probabilities of the nodes.

FIG. 3.

Evolution of the Baculoviridae. (A) Phylogeny of the baculoviruses, highlighting four main groups of the unrooted tree (T2); numbers indicate branch lengths in substitutions per site. (B) Relationships of the three arthropod orders infected by the baculoviruses shown in panel A (57).