virilis species group

The virilis group has served as a model system for comparative studies and, as such, the phylogenetic relationships within this group have been extensively examined. Spicer has used a variety of techniques, including two-D gel electrophoresis (Spicer, 1988), nucleotide sequences (Spicer, 1992; Spicer and Bell, 2002), and quantitative characters (Spicer, 1995) to infer phylogeny in this group. The virilis species group consists of about thirteen described species that are typically found in a boreal distribution (Baechli, 2005). Currently, the status of two, D. americana and D. texana, is somewhat questionable. The latter was initially described as a subspecies (Patterson et al., 1940), but has since been considered a full species (Throckmorton, 1982) on the basis of chromosome and molecular (Spicer and Bell, 2002) differences. McAllister (2002) points out that this chromosomal difference is a widespread polymorphism and subdivision of D. americana is not warranted. Spicer and Bell (2002) also report that the eastern and western forms of another species, D. borealis, do not form a monophyletic assemblage, and may represent two separate species.

Nurminski et al. (1996) also examined the evolution of the Adh locus in the virilis group, and proposed that either this gene had duplicated prior to the diversification of the virilis group and duplicate copies had been lost independently several times, or the duplication even had taken place independently in both the virilis and montana subgroups

(excerpted from Markow and O’Grady, 2006, Chapter 1)

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