NOVEL SPERM CRYPTS AND BEHAVIOR OF GAMETES IN THE FALLOPIAN-TUBE OF THE WHITE-TOOTHED SHREW, CROCIDURA-RUSSULA MONACHA

The gametes of an insectivore, the white-toothed shrew Crocidura russu la monacha, present certain idiosyncratic features not seen in most ot her eutherian mammals. The spermatozoa display an acrosome of giant pr oportions, and are produced in relatively small numbers. In trans-illu minated oviducts examined with DIC optics, spermatozoa were first sequ estered in languid clutches within the isthmus in deep narrow crypts, with some eventually ingested by the crypt epithelium. Then, at ovulat ion (ca. 15 hr after hCG), many ascended to occupy ''bubble-like'' cil iated crypts distributed randomly within the ampulla, as active groups of acrosome-intact spermatozoa. However, eggs (3.95; range 2-6) were brst retained for several hours and were fertilized in an upper crypt- free infundibulum before moving down to the ampulla. At fertilization, individual spermatozoa penetrate an unusually compact matrix-free cum ulus oophorus which is stabilized by intercellular junctions, is insen sitive to hyaluronidase, and persists for similar to 13 hr around fert ilized and for similar to 24 hr around unfertilized eggs. In contrast to the free ampullary spermatozoa, active spermatozoa accumulating wit hin the cumulus all had shed the acrosome, an observation consistent w ith evidence from other shrews suggesting that the cumulus may necessa rily induce the acrosome reaction in this ancient line. Hypertrophy of the acrosome, isthmic sperm storage crypts, and stable cumulus oophor us that develops a peri-zona space, all may prove to be typically croc idurine characteristics of use where the classification of a shrew is in doubt. (C) 1997 Wiley-Liss, Inc.