Drosophila, A Laboratory Handbook, Drosophila, A Laboratory Handbook

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33 |
THE MELANOGASTER 
SPECIES SUBGROUP
33/1 IDENTIFICATION
33/2 RELATIONSHIPS
33/3 THE SPECIES
33/3.1 D. melanogaster
33/3.2 D. simulans
33/3.3 D. mauritiana
33/3.4 D. sechellia
33/3.5 D. erecta
33/3.6 D. orena
33/3.7 D. teissieri
33/3.8 D. yakuba
33/3.9 D. santomea
33/4 HYBRIDIZATION
33/4.1 D. melanogaster Hybrids
33/4.2 Hybridization within the D. simulans Complex
33/4.3 Hybridization between D. melanogaster and D. simulans, D. mauritiana,
and
D. sechellia
33/4.4 Hybridization with the D. yakuba Species Complex
33/5 PREMATING ISOLATION
33/1 IDENTIFICATION
The nine species of the melanogaster species subgroup are morphologically very similar to one another. For a general review of this species subgroup, see Lachaise et al. 2004. The only reliable characteristics for the identification of eight of these species are the male genitalia. In each of D. melanogaster, D. simulans, D. mauritiana, and D. sechellia, the process of the genital arch (epandrium) has a characteristic shape, which readily allows these species to be distinguished (Fig. 33.1). The genitalia of the other species are also distinctive, and these are illustrated in Figure 33.2. A key for the identification of the nine species is given in Table 33.1.
Sturtevant (1919; see also Gallo 1973) found that D. melanogaster and D. simulans can be distinguished, in either sex, by the width of the cheek, which is narrower in D. simulans than in D. melanogaster (Fig. 33.3). McNamee and Dytham (1993), apparently in ignorance of this work, express it more quantitatively: In D. melanogaster, the cheek width is greater than one-eighth, and in D. simulans it is less than one-eighth, of the maximum long axis of the eye. The extent to which this characteristic is diagnostic across all populations of these species has not been tested, nor has the pigmentation of the abdominal tergites (Gallo 1973; Thompson et al. 1979). In D. melanogaster, the area of pigmentation on the sixth tergite is larger than that in D. simulans. In the latter species, the pigmented area on the sixth tergite only rarely reaches the
01_Dros_CH33_GS
FIGURE 33.1 Male genital arches of D. melanogaster (a), D. simulans (b), D. mauritiana (c), and D. sechellia (d). (ac Reprinted, with permission, from Coyne 1983; d original from F. Lemeunier.)
ventral margin of the tergite. The maxillary palps of D. melanogaster normally have three stout bristles on their outer surface, and those of D. simulans have two (Fig. 33.4), but this character­istic is also variable within the species. Males of D. mauritiana have significantly more sex comb teeth (mean 13.56) than either D. melanogaster (mean 10.17) or D. simulans (mean 10.14) (Coyne 1985b). This result was confirmed by True et al. (1997), who also found significant ­differences among D. melanogaster and the simulans complex species in other male secondary
02ab_Dros_CH33_LW
FIGURE 33.2 Diagrams of the male genitalia of species of the melanogaster species subgroup. (A) D. sechellia. (Reprinted, with permission, from Tsacas and Bächli 1981.) (B) D. mauritiana. (Reprinted, with permission, from Tsacas and David 1974.) (C) D. teissieri. (Reprinted, with permission, from Tsacas 1971.) (D) D. erecta. (Reprinted from Tsacas and Lachaise 1974.) (E) D. orena. (Reprinted, with permission, from Tsacas and David 1978.) (a,b) Caudal and lateral views of epandrium; (c,d) ventral and lateral views of hypandrium and associated structures. Bars: (A,C,E) 0.1 mm.
02ab_Dros_CH33_LW
FIGURE 33.2 (Continued)
characters, including the numbers of bristles on the anal plate, clasper, and fifth sternite. The area of the posterior second femur that is naked of trichomes is larger in D. simulans than in D. melanogaster; this is due, at least in part, to regulatory differences in the Ubx genes of these species (Stern 1998). There are also differences in the color of the testis sheath: In D. simulans, it is a bright buttery yellow, and in D. mauritiana, it is a very pale yellow (David et al. 1976; Coyne 1985b).
01_Dros_CH33_GS
The eggs of D. melanogaster have shorter chorionic filaments than do those of D. simulans or D. mauritiana (Tsacas and David 1978). The ovipositors of some of the species can also be used to distinguish between them (Tsacas and David 1978). In D. teissieri, the ovipositor has a long posterior lobe with six marginal teeth, and there is a triangular sclerite between its valves. In D. erecta, the ovipositor is truncated and the first two teeth are set wider apart than the ­others, whereas in D. orena, it has a rod-shaped sclerite attached to each valve (Fig. 33.5). Male
04_Dros_CH33_LW
04_Dros_CH33_LW
D. santomea have a distinctive abdominal coloration, lacking the black pigmentation characteristic of other members of this subgroup.
The full sequence genomes of four species of this species subgroup (D. simulans, D. sechellia, D. yakuba, and D. erecta), in addition to that of D. melanogaster, will soon be ­available (see AAA : 12 Drosophila Genomes and FlyBase).
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FIGURE 33.5 Ovipositors (left) and maxillary palps (right) of species of the melanogaster species subgroup. (a) D. sechellia. (Reprinted, with permission, from Tsacas and Bächli 1981.) (b) D. mauritiana. (Reprinted, with permission, from Tsacas and David 1974.) (c) D. teissieri. (Reprinted, with permission, from Tsacas 1971.) (d) D. erecta. (Reprinted, with permission, from Tsacas and Lachaise 1974.) (e) D. orena. (Reprinted, with ­permission, from Tsacas and David 1978.)
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