TWO NEW SPECIES OF THE DROSOPHILA SERIDO SIBLING SET ( DIPTERA , DROSOPHILIDAE )

Drosophila antonietae sp. nov. and D. gouveai sp. nov. are members of the D. buzzatii cluster of the D. repleta species group of the genus Drosophila. They can be distinguished from their cryptic species, D. borborema Vilela & Sene, 1977, D. koepferae Fontdevila & Wasserman, 1988, D. serido Vilela & Sene, 1977, and D. seriema Tidon-Sklorz & Sene, 1995 by morphological, genetic and ecological criteria.


INTRODUCTION
The serido sibling set is part of the buzzatii cluster (buzzatii complex) of the genus Drosophila.The buzzatii complex consists of several cactus breeding species inhabiting South and Central America and sharing chromosomal similarities (RUIZ et al., 1982;RUIZ & WASSERMAN, 1993).Drosophila serido was described in 1977 by VILELA & SENE, and in the following years populations of this species from several regions were studied by means of several genetic markers.These studies suggest that D. serido is a polytypic species based on the male genitalia morphology (SILVA & Sene, 1991), presence of paracentric inversions in the polytene chromosomes (TOSI & SENE, 1989), metaphase chromosome morphology (BAIMAI et al., 1983), esterase isozyme pattern (LAPENTA et al., 1995(LAPENTA et al., , 1998) ) and degree of reproductive isolation (MADI-RAVAZZI et al., 1997).However, until recently the distribution pattern of these genetic markers was not fully understood (SENE et al., 1982(SENE et al., , 1988)).
A comprehensive sampling program carried out in several locations in South America, has enabled a more detailed characterization of each member of these closely related species.In 1988, SENE et al. argued that the distribution of D. serido in South America is particularly interesting because some populations differ from others in several characters.This is the case for the Argentinean and Bolivian populations, raised to species level as Drosophila koepferae by FONTDEVILA et al. (1988), and for those living in the "Cadeia do Espinhaço" in Brazil.The latter were described by TIDON-SKLORZ & SENE (1995a)  External characters of imagines.Arista with 4 dorsal and 3 ventral branches; antennae yellowish with bases dark brown; front light brown, pollinose.Anterior, middle orbital, and posterior vertical arising from a yellowish area.Hairs of anterior orbits, posterior orbital, anterior vertical, and postvertical with basal dark spots.Middle orbital about half the length of other two.Second oral about half the length of first.Carina broad below, sulcated.Palpi pale yellow, with several bristles.Face yellowish brown.Cheeks yellowish gray, their greatest width about 1/4 greatest diameter of eye.Eyes vermilion slightly lighter than those of D. gouveai, with short black pile.Acrostichal hairs in 8 rows; no prescutellars; anterior scutellars convergent.Sterno-index about 0.8.Mesonotum gray, pollinose, bristles arising from dark spots with tendency to fuse.Scutellum gray with fused brown spots, pleurae brown.Halteres pale yellow.Legs uniformly light brown.Apical bristles on first and second tibiae, preapicals on all three.Abdomen pale yellow, each segment with strongly contrasting, interrupted, wide, dark brown band, this bending to anterior margin at angle of tergite, leaving a small irregular pale area.Wings clear, veins brown, apex of first costal section black.Costal index about 2.6; 4th vein index about 1.8; 5X index about 1.2; 4C index about 0.9.Two welldeveloped bristles at apex of first costal section; third costal section with heavy bristles on its basal 1/3.Length of body 2.2-3.1 mm (in living specimens); wings about 2.5mm.
Etymology.Named in honor of the late drosophilist Maria Antonieta Milani de Moraes.
Diagnosis.Drosophila antonietae can be distinguished from the other species of the D. serido sibling set by the shape of the aedeagus (figs.1-6), although the external morphology of these species is very similar.The metaphase plate, described above, is considered also an autapomorphic character state of this species.
Classification.Drosophila antonietae belongs to the D. buzzatii cluster of the D. buzzatii complex (D. mulleri subgroup) of the D. repleta species group.Biology.Data on the breeding and feeding niches indicate that this species lives primarily on columnar cacti.We found this species in decayed portions of cacti Cereus hildmaniannus Schumman, 1890 and Opuntia monacantha Haworth, 1819.Drosophila (Drosophila) gouveai sp.nov.(Figs. 3,7) The first part of the following description only lists the differences between D. antonietae and D. gouveai.
External characters of imagines.Antennae yellowish with brown spots.Eyes vermilion, slightly darker than those of D. antonietae with short black pile.Scutellum dark brown, pleurae dark brown.Legs uniformly dark brown.Costal index about 2.7.Length of body 2.4-3.0 mm (in living specimens); wings about 2.4mm.
Etymology.Named in honor of the drosophilist Antonio Fernando Gouvêa da Silva.
Diagnosis.Drosophila gouveai can be distinguished from the other species of the D. serido sibling set by the shape of aedeagus (figs.1-6), although the external morphologies of these species are very similar.
Classification.Drosophila gouveai belongs to the D. buzzatii cluster of the D. buzzatii complex (D. mulleri subgroup) of the D. repleta species group.
Biology.Drosophila gouveai is found in vegetation of rock outcrops: granite inselbergs and sandstone table mountains.Data on the breeding and feeding niches indicate that this species lives, primarily, on columnar cacti.We have found specimens in decayed portions of cacti Pilosocereus machrisii Dawson, 1960in Altinópolis, São Paulo, and Opuntia ficus-indica Miller, 1788in Bela Vista, Mato Grosso do Sul (PEREIRA et al., 1983).
Reproductive isolation.Although individuals identified as Drosophila gouveai produce offspring when crossed (without mate choice) with closely related species (MADI-RAVAZZI et al., 1997), the resulting hybrids generally have low fertility or are sterile.

DISCUSSION
Several studies of populations of the buzzatii cluster using different markers have shown very clearly that D. serido corresponds to a polytypic species.A phylogenetic analysis of characters obtained with these markers, however, demonstrated that the taxon D. serido corresponds to a non-monophyletic entity (TIDON-SKLORZ & SENE, 1995c).The description of D. koepferae and D. seriema on the one hand, and D. antonietae and D. gouveai on the other, removed from this sibling set of species differentiated monophyletic groups of populations that deserve specific status.
It is interesting to emphasize that species of this set are morphologically very similar to each other: females are undistinguishable and males can only be identified by their terminalia.However, these species show genetic differences (such as fixed and polymorphic chromosomal inversions), ecological preferences (host plants) and therefore belong to distinct phylogenetic lineages.Drosophila antonietae shares the 2x 7 inversion with D. serido (stricto sensu), the latter occurring in the northeastern and eastern coast of South America and having a different metaphase plate and terminalia from the former.Drosophila gouveai shares the 2e 8 fixed inversion with D. seriema and D. borborema.These three species, nevertheless, differ with respect to morphology of male terminalia, polymorphic chromosomal inversions and, in addition, are reproductively isolated.The morphological resemblance among the species of this sibling set is probably due to a recent common phylogenetic origin, coupled with an apparent absence of selective pressure that led to morphological differentiation (since these species are cactophilic and live in similar environments).This suggests the occurrence of stabile coadapted genic complexes, responsible for the external phenotype.

Fig. 7 .
Fig. 7. South America distribution of the known Drosophila serido sibling set.

Drosophila (Drosophila) antonietae sp. nov.
as Drosophila seriema.At present, four species are included in the Drosophila serido sibling set: D. koepferae (Argentina and Bolivia), D. borborema VILELA & SENE, 1977 and D. seriema (both from northeastern Brazil), and the group of populations currently known as D. serido (in various areas of open vegetation in South America: VILELA et al.