The bean common mosaic virus lineage of potyviruses: where did it arise and when?

There are more than 30 species in the bean common mosaic virus lineage of the genus Potyvirus. We have used their partial coat protein gene sequences to infer their phylogenies and have compared these with host and provenance information. Members of six species of the lineage have been isolated from crops distributed around the world, but three of these show clear links with South and East Asia. Members of the remaining species have been found in wild plants, minor crop species or ornamentals, and the majority of these have only been found in south-east and East Asia, Oceania or Australia. This phylogeographic pattern suggests that the bean common mosaic virus lineage arose in that region. Maximum-likelihood trees of the sequences were dated using the report that the initial major radiation of all potyviruses was 6,600 years ago. In this way, the bean common mosaic virus lineage was found to have first diverged 3,580 years ago, and one sub-lineage of seven species, found only in Australia, probably diverged there 2005 years ago. We discuss the ways in which the viruses could have moved from south-east Asia to Australia and note that their movement coincided with the spread of the Austronesian sea-faring/farming culture from China/Taiwan throughout the islands of the southern and eastern Pacific Ocean. Our study shows that virus isolates from wild or minimally domesticated plants, and from islands, are probably more useful indicators of the origins of viruses than those from widely grown well-travelled crop species.

Evolution of larval host plant associations and adaptive radiation in pierid butterflies.

Butterflies in the family Pieridae (Lepidoptera: Papilionoidea) feed as larvae on plants belonging primarily to three distantly related angiosperm orders: Fabales (legumes and allied plants), Brassicales (crucifers and related plants containing mustard oil glucosides), and Santalales ('mistletoes'). However, some utilize plants from 13 other families in a further eight orders. We investigated the evolutionary history of host plant use of the Pieridae in the context of a recent phylogenetic hypothesis of the family, using simple character optimization. Although there is a close association between host plant and butterfly higher classification, we find no evidence for cospeciation but a pattern of repeated colonization and specialization. The ancestral host of the family appears to be Fabaceae or Fabales, with multiple independent shifts to other orders, including three to Santalales. The shift to Brassicales, which contain secondary compounds (glucosinolates), promoted diversification and adaptive radiation within the subfamily Pierinae. Subsequent shifts from crucifers to mistletoes (aerial-stem hemiparasites) facilitated further diversification, and more recent shifts from mistletoes to mistletoe host trees led to exploitation of novel host plants outside the conventional three orders. Possible mechanisms underlying these host shifts are briefly discussed. In the Pierinae, a striking association between host plant, larval and adult behaviour, adult phenotype, and mimicry calls for further research into possible relationships between host specialization, plant chemistry and butterfly palatability.

Bemisia argentifolii is a race of B. tabaci (Hemiptera: Aleyrodidae): the molecular genetic differentiation of B. tabaci populations around the world.

The phylogenetic relationships between genotypes of Bemisia tabaci were compared using ITS1 and CO1 nucleotide sequences. Phylogenetic and minimum spanning network analyses identified six major races, Asia, Bali, Australia, sub-Saharan Africa, Mediterranean/Asia Minor/Africa and New World as well as a large collection of genotypes from the Asia region with no strong association with any of the races. The term race is based on its usage in Mallet (2001). Mating incompatibility occurs between some races. There is insufficient data to raise races to species status, but the data supports the recognition of the six races and an unresolved core of ungrouped genotypes under the single Bemisia tabaci (Gennadius) species name. To clarify the identity of the race to which the B. tabaci under investigation is known, the following nomenclature is suggested, B. tabaci (Asia), B. tabaci (Bali), B. tabaci (Australia) B. tabaci (sub-Saharan Africa), B. tabaci (Mediterranean/Asia Minor/Africa) and B. tabaci (New World). Further, there is insufficient molecular or biological data to support the separation of B. tabaci and B. argentifolii Bellows & Perring and its use should be discontinued.

The structure of the USP/RXR of Xenos pecki indicates that Strepsiptera are not closely related to Diptera.

The receptor for the insect molting hormone, ecdysone, is a heterodimer consisting of the Ecdysone Receptor and Ultraspiracle (USP) proteins. The ligand binding domain sequences of arthropod USPs divide into two distinct groups. One group consists of sequences from members of the holometabolous Lepidoptera and Diptera, while the other arthropod sequences group with vertebrate retinoid-X-receptors (RXRs). We therefore wondered whether USP/RXR structure could be used to clarify the contentious phylogenetic position of the order Strepsiptera, which has proposed affinities with either Diptera or Coleoptera. We have cloned and sequenced the USP/RXR from the strepsipteran Xenos pecki. Phylogenetic analyses are not consistent with a close affinity between Strepsiptera and Diptera.