saltans species group

The saltans species group is exclusively Neotropical in distribution. Magalhaes (1962) and Throckmorton and Magalhaes (1962) proposed five subgroups. The cordata and elliptica subgroups were basal within the saltans group. The subsaltans subgroup was considered the sister group of the clade formed by the more derived sturtevanti and saltans species groups. O’Grady et al. (1998) used four molecular loci to examine the phylogeny of this group. Their results largely agreed with those of Magalhaes (1962). The saltans subgroup, represented by D. saltans, D. lusaltans, D. austrosaltans, and D. prosaltans, was most derived and sister to the subsaltans subgroup (Figure 1.41). The sturtevanti subgroup formed a clade sister to these derived taxa. The elliptica, represented by D. emarginata, and cordata, represented by D. neocordata, subgroups were most basal in the saltans group.

The saltans group phylogeny produced by Rodriguez-Trelles et al. (1999) was quite different. They suggested that the parasaltans subgroup was basal in the saltans group (Figure 1.42). The saltans subgroup was sister taxon to the cordata subgroup and occupied a derived position in the tree. The elliptica and sturtevanti subgroups were successive sister groups to this more derived clade. This topology is not in agreement with the morphological (Magalhaes, 1962), biochemical (Magalhaes and Throckmorton, 1962), or cytological hypotheses (Bicudo, 1973a, 1973b).

Such strong and widespread conflict between two phylogenetic hypotheses is unusual in drosophilid systematics (see, however, DeSalle and Grimaldi, 1991, 1992). Rodriguez-Trelles and Ayala (1999) vehemently argued for their topology over the alternative, based largely on the fact that they had employed a maximum likelihood algorithm and used a large, contiguous sequence fragment, the Xdh gene. It should be noted, however, that O’Grady et al. (1998) also used maximum likelihood, and the sum of their four sequence fragments was nearly the same size (in terms of total character and phylogenetically informative characters) as the Xdh gene. One issue that Rodrigues-Trelles and Ayala (1999) fail to mention is that they examined far fewer species (six versus nine) than the previous study. Furthermore, O’Grady et al. (1998) also examined multiple populations from three widespread species – D. sturtevanti, D. prosaltans, and D. emarginata – such that their ingroup contained fourteen terminal taxa (as opposed to six). Reduced taxon sampling in the latter study (Rodriguez-Trelles and Ayala, 1999) could also be the cause for the difference in tree topology. Reconciling these differences by adding additional characters and taxa will help elucidate relationships within the saltans species group.

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

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