Evolutionary novelties in islands:Drosophila santomea, a newmelanogastersister species from São Tomé

Abstract

The finding of new melanogaster sister species may help us in understanding more about how the emergence of genetic novelties, particularly in insular habitats, can result in speciation. Here we report on the discovery of Drosophila santomea, which is the first melanogaster sibling found off West-equatorial Africa, on São Tomé, one of the Gulf of Guinea islands. Although the eight other melanogaster sister species are remarkably conservative in their morphology except for their terminalia, the new find has a morphological trait distinguishing it from all of these: a pure yellow body coloration of both sexes without the normal black abdominal banding. Evidence from the terminalia, polytene and mitotic chromosomes, period gene and allozymes are provided indicating that it is nonetheless the nearest relative of Drosophila yakuba with which it coexists on the island. The new find is a clear-cut taxon as shown by the production of sterile male hybrids, eventually with developmental defects, in both directions of cross with yakuba and by the existence of an altitudinal divide accompanied by a hybrid zone at mid-elevation on the island. Molecular and karyotypic data further support this conclusion. In contrast to the significant divergence of their nuclear DNAs, an intriguing similarity in their cytochrome b sequences was observed indicating a recent coalescence common to santomea, yakuba and also teissieri cytoplasms. These were shown to harbour the same Wolbachia endosymbiotic bacteria which could possibly be responsible for mitochondrial DNA hitchhiking across the species barrier.

Genetic mechanisms and constraints governing the evolution of correlated traits in drosophilid flies

“…In D. santomea (Figs 2 and 3a), a close relative to D. melanogaster, both sexes are devoid of dark pigments. This is a recent loss of the melanic pattern, because its sister species D. yakuba is dimorphic 10 . One might expect Bab2 to be expressed uniformly throughout the abdomen in D. santomea to repress pigmentation, but that is not so.…”

“…It has been shown 11 that the transcription factor Svb acts to switch cells between naked cuticle and the production of trichomes. In D. melanogaster embryos, svb is genetically required for trichome formation; when svb is expressed in a cell, that cell autonomously differentiates trichomes, whose morphology is determined by other patterning genes 4,10 . Therefore svb integrates numerous sources of information (including the wg, hh, DER (for Drosophila epidermal growth factor receptor), homeotic and dorsal-ventral patterning systems) to specify the final pattern of trichomes.…”

“…For example, the wingless (wg) and hedgehog (hh) pathways and the lines gene are involved in patterning the trichomes on the dorsal epidermis 4,10 . It might therefore be interesting to test whether evolution of patterning genes involved in segmentation can account for the evolution of trichome patterns.…”

Natural Wolbachia Infections in the Drosophila yakuba Species Complex Do Not Induce Cytoplasmic Incompatibility but Fully Rescue the wRi Modification

“…D. orena and D. In this article, we focus on species from the Drosophila melanogaster subgroup. This clade includes nine species erecta are not thought to be infected (Bourtzis et al 1994 but more systematic surveys could change (Lachaise et al 2000(Lachaise et al , 2003 contrast, Wolbachia was detected by PCR in the three species of the yakuba complex (Lachaise et al 2000). yakuba (forming the yakuba complex).…”

“…To date, most Wolbachia studies have focused on Furthermore, the infection in D. santomea was reported to be identical to the wAu infection from D. simulans the melanogaster subgroup (Hoffmann et al 1986(Hoffmann et al , 1994(Hoffmann et al , 1996Hoffmann 1988;O'Neill and Karr 1990;Rous-judged by partial wsp gene sequences (Lachaise et al 2000). set et al 1992Boyle et al 1993;Holden et al 1993;Bourtzis et al 1994Bourtzis et al , 1996Bourtzis et al , 1998 In this study, we initially aimed to characterize infections in the yakuba complex through CI assays and DNA 1994; Giordano et al 1995;Merç ot et al 1995;Rousset and Solignac 1995;Poinsot et al 1998).…”