The eggshell of hawaiian Drosophila: structural and biochemical studies in D. grimshawi and comparison to D. melanogaster.

The eggshell of the Hawaiian species Drosophila grimshawi was analyzed in terms of its structure and biochemical composition. It is generally similar to D. 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 in D. 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 entire D. grimshawi eggshell (various layers and specialized regions) is the product of at least eight follicle cell subpopulations. In addition, in vitro culturing withH-proline indicates that the eggshell is made according to a strict developmental program (analogous to D. melanogaster) and consists of several proteins ranging in molecular weight from 14,000 to 37,000 daltons. [ABSTRACT FROM AUTHOR]