Morphological evidence that spermatogenic cells undergo apoptosis within testis of diapausing swallowtail pupa (Atrophaneura alcinous)

Abstract

In many lepidopteran species, degeneration of germ cells occurs in the testis of diapausing pupa. We demonstrated that degenerating cells clearly exhibit apoptotic characteristics by supravital staining, TUNEL assay and ultrastructural observations. These characterizations allowed us to identify several steps of spermatocyte degeneration, segregation of nuclear chromatin, nuclear fragmentation, cytoplasmic condensation and phagocytosis by cyst cells. A cluster of TUNEL-positive cells were observed under the light microscope which coincided with a cyst of degenerating spermatocytes revealed under the electron microscope. Secondary spermatocytes in pupal testis undergo apoptotic cell death during diapause. Therefore, neither cysts of spermatids nor sperm bundles exist in testis of diapausing pupa. Our observations also indicate that spermatogenic cells undergo phagocytosis of cyst cells as the diapause period increased. This phenomenon seems to be associated with the seasonal reproductive strategy. J. Exp. Zool. 283:194–201, 1999. © 1999 Wiley-Liss, Inc.