Characterization of defects in adult germline development and oogenesis ofsterile and rescued female hybrids in crosses between Drosophila simulans and Drosophila melanogaster

Crosses between Drosophila melanogaster and D. simulans normally result in progeny that are either inviable or sterile. Recent discovery of strains th at rescue these inviability and sterility phenotypes has made it possible t o study the developmental basis of reproductive isolation between these two species in greater detail. By producing both rescued and unrescued hybrids and examining the protein product staining patterns of genes known to be i nvolved in early germline development and gametogenesis, we have found that in crosses between D. simulans and D. melanogaster, hybrid female sterilit y results from the improper control of primordial germline proliferation, g ermline stem cell maintenance, and cystoblast formation and differentiation during early oogenesis. Rescued hybrid females are fertile, yet they gener ally have lower amounts of adult germline from the outset and show a premat ure degeneration of adult germline cells with age. In addition, older rescu ed hybrid females also exhibit mutant egg phenotypes associated with defect s in dorso-ventral patterning which may result from the improper partitioni ng of cytoplasmic factors during early oogenesis that could stem from the e arly defect. Although a variety of germline and oogenic defects are describ ed for the hybrid females, all of them can potentially result from the same underlying primary defect. Hybrid males from these same crosses, on the ot her hand, have no detectable germline in adult reproductive tissues, even w hen hybrid sterility rescue strains are used, indicating that male sterilit y and female sterility stem from distinctly different developmental defects . J. Exp. Zool. (Mol. Dev. Evol.) 288:205-218, 2000. (C) 2000 Wiley-Liss, I nc.