Cytotaxonomic differentiation of the Afrotropical Drosophila montium subgroup: D. diplacantha and D. seguyi. The major role of reverse tandem duplications

Abstract

Aiming to establish phylogenetic relationships among species of the montium subgroup, detailed polytene chromosome maps are given showing intraspecific polymorphism and ecdysone induced larval puffing pattern profiles of two Afrotropical members of this subgroup, Drosophila diplacantha and D. seguyi. Both species exhibit two unique characteristics that define the montium subgroup, namely, a large number of reverse tandem duplications and a progressive darkening of anterior spiracles of the late third instar larvae, which is accompanied by a definite temporal and spatial puffing pattern of the salivary gland chromosomes. In contrast with the well-formed Balbiani ring 1 (BR1) observed in Oriental and Indian montium species, BR1 exhibits a different developmental profile in D. diplacantha, while it is obscured in D. seguyi. Although phyletic comparisons of five species from five different complexes within the subgroup show some conservation in banding and puffing pattern homologies, an analysis to assign map sections by sequential rearrangements remains unresolved at this time. The evolution of the subgroup is discussed in relation with the sharing of reverse tandem duplications, especially those including the montium BRs.

The ?-tubulin gene family evolution in the Drosophila montium subgroup of the melanogaster species group

“…The ~-tubulin sequences strongly hybridize on one polytene chromosome band, a simple interpretation of this may be that all three genes are arranged in a cluster; or on two bands, a semiclustered arrangement; or on three bands, a complete dispersion (Table 1, Figs. 1-3; see also Scouras et al 1994). The cluster is found in the sibling species of the NorthOriental auraria complex, D. auraria, D. triauraria, and D. quadraria.…”

“…The chromosome bands on which the most frequent faint signals were observed are at regions 24B (2L) and 56B (2R) of D. auraria, D. triauraria, and D. quadraria, 47 (2R) (8) a The identification of the chromosome regions was based on the polytene chromosome maps published by the following authors: 1Scouras and Kastritsis 1984;Mavragani-Tsipidou et al 1992b;2Mavragani-Tsipidou et al 1990;3Baimai 1970;4Roy and Lakhotia 1977;5Mavragani-Tsipidou et al 1994;6E. Pardali, E. Feggou, and P. Mavragani-Tsipidou (in preparation);7Mavragani-Tsipidou et al 1992a;8parkash and Rajput 1983 the ~-tubulin genes of D. melanogaster--did not hybridize on any of these bands in either D. serrata or D. auraria (Mavragani-Tsipidou et al 1990;Scouras et al 1994). …”

“…The level of differentiation and the pattern of expression and regulation of the ~-tubulin sequences at the cluster situation are not yet known. (See also Scouras et al 1994.) Genomic analysis of ~3-tubulin regions of some selective montium species, which has already started in our laboratory, is expected to give more information on the molecular organization of this important eukaryotic gene family.…”

“…In the genome of D. melanogaster the [3-tubulin genes are dispersed, showing a discrete hybridization pattern: the ~l-tubulin gene is located at region 56D (chromosome arm 2R), the [32 is at region 85D (3R), and the [33 at region 60B (2R) (Sanchez et al 1980;Biolojan et al 1984). However, in D. auraria, an Oriental member of the montium subgroup, the ~-tubulin gene family is arranged in a cluster (Scouras et al 1994). This interesting result, together with the other unique features of the montium species described above, prompted us to investigate the organization of this gene family in the montium subgroup.…”

The Afrotropical Drosophila montium subgroup: Balbiani ring 1, polytene chromosomes, and heat shock response of Drosophila vulcana

“…Parallel to the P-tubulin gene dispersion, a gradual differentiation of the Balbiani rings of the montium species was observed, which also followed a northeast to southwest direction (see MavraganiTsipidou et al 1994 for a review). Based on the above observations, as well as on mtDNA data (Pissios and Scouras 1993), it has been proposed that this direction represents the mode of expansion of the montium subgroup species (Mavragani-Tsipidou et al 1994;Drosopoulou and Scouras 1995; see also Lemeunier et al 1986).…”