Eggshells of Drosophila melanogaster and D. simulans: Ultrastructure, Measurement and Analyses

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.