The eggshell of hawaiianDrosophila: structural and biochemical studies inD. grimshawi and comparison toD. melanogaster.

The eggshell of the Hawaiian speciesDrosophila grimshawi was analyzed in terms of its structure and biochemical composition. It is generally similar toD. melanogaster in radial structure except that the inner endochorion is relatively compact and the outer endochorion is thick (1.9 μm) and traversed by numerous 50-nm-wide aeropyles (not present inD. melanogaster). Regionally the eggshell consists of the various specialized regions, which are: the holey posterior pole; the dorsal ridge; the operculum with very tall imprint borders; the collar with discontinuous outer endochorion; the micropyle with an external eccentric hole and an internal eccentric paracrystalline region; and the four very long respiratory appendages which exhibit tightly covered surface features for underwater plastron respiration. On the basis of the above structural data we suggest that the entireD. grimshawi eggshell (various layers and specialized regions) is the product of at least eight follicle cell subpopulations. In addition, in vitro culturing with3H-proline indicates that the eggshell is made according to a strict developmental program (analogous toD. melanogaster) and consists of several proteins ranging in molecular weight from 14,000 to 37,000 daltons.