In Drosophila melanogaster, the intersex (ix) is a terminally positioned gene in somatic sex determination hierarchy and function with the female specific product of double sex (DSX(F)) to implement female sexual differentiation. The null phenotype of ix is to transform diplo-X individuals into intersexes while leaving haplo-X animals unaffected. This study on the effect of different intersex mutations on genital disc development provides the following major results: (i) similar range of a characteristic array of morphological structures (from almost double sex terminalia to extreme reduction of terminal appendages) was displayed by the terminalia of XX ix(1)/ix(1) , XX ix(2)/ix(2) and XX ix(5)/ix(5) individuals; (ii) an increased number of apoptotic cells were found to occur in a localized manner in mature third instar larval genital discs of ix individuals; (iii) ix mutations can induce high frequency of neoplastic tumours in genitals in the presence of decapentaplegic (dpp(disk)) mutations; and (iv) heteroallelic combinations of dpp(disk) mutations can also induce tumours in intersex genitals with variable expressivity. On the basis of these findings, we suggest that: (i) loss of function of ix causes massive cell death in both male and female genital primordia of genital discs, resulting phenotype mimicking in male and female characteristics in genitals; and (ii) at the discs, the apoptotic cells persist as 'undead' cells that can induce oncogenic transformation in the neighbouring disc cells when dpp signalling is blocked or reduced by dpp(disk) mutations.
Phenotypic divergence of eggshells between D. melanogaster and D. simulans strains, was compared, using SEM, for analyzing fitness related eco-physiological traits of the eggshells in the two sibling species. The variations of eggshell traits between strains within species, between species and asymmetry in hybrids of two species have been calculated for understanding the demographic success of the two species. The present results revealed that variation of traits between strains within species was not always same which suggest that many traits are not strongly constrained within species. The main findings show that following eco-physiological traits of eggshells are mostly diverged between two species: (i) dorsal appendages (DA) length, (ii) insertion position of DA in main body of eggshell, (iii) the number and size of respiratory pores in dorsal and ventral side of DA, (iv) average length and volume of eggshells and (v) the thickness of chorionic hexagonal ridges. Examination of interspecific hybrids showed that the traits have undergone considerable genetic changes during evolutionary divergence of the two species. The authors propose that divergent ovipositional preference of the females of two species, may be the driving force in establishing species specific life history parameters for avoiding competition at pre-adult stages and demographic success.
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