On the evolution of orbiviruses.

The genomes of orbiviruses consist of 10 segments of double-stranded RNA. In cells simultaneously infected with two or more related viruses, recombinants are derived by independent reassortment of parental genes. The process is analogous to sexual reproduction in higher organisms and provides a mechanism for generating extensive diversity within this group of viruses. This genetic diversity can be explained by reference to modern concepts of the structure of natural populations of organisms. A species in the phylogenetic sense is the largest aggregate of individual organisms that evolves as a unit. The biological species concept stresses the community gene pool and reproductive isolation. The orbiviruses are now classified into 13 distinct serological groups, but confusion exists in defining species. Classification by reference to concepts of evolutionary species would define genetically interacting groups, estimate the extent of diversity within these groups, and establish phylogenetic relationships between species.