The 'hybrid' character of the gametes and reproductive tracts of the African shrew, Myosorex varius, supports its classification in the Crocidosoricinae.
The Soricidae are generally considered to comprise two subfamilies--Crocidurinae and Soricinae--each of which has distinctive reproductive characteristics. Although Myosorex varius is classified as a crocidurine, the features of its reproductive system call that classification into question. Compared with three other shrew genera, Myosorex exhibited a number of specific features including a relatively prolonged time (about 22 h) for ovulation to be induced by hCG injection and the smallest diameter (75 microns) recorded for any mammal egg. Moreover, the relative testis mass and the number of epididymal spermatozoa were somewhat greater than in some other shrews studied recently. However, many reproductive features in Myosorex have a 'hybrid' character. The glans penis has spines similar to those evident in crocidurines but absent in soricines, yet the accessory sperm storage site, midway along the vas deferens, is similar to that in soricine shrews. The ultrastructure of Myosorex spermatozoa was primarily soricine, despite an unduly large acrosome, which reaches its apogee in the Crocidurinae. Whereas the Fallopian tube displays a crocidurine-type isthmus characterized by deep crypts throughout, the ampulla is richly endowed with ciliated crypts, which in soricines contain spermatozoa. The first polar body persists in the Myosorex ovum, as it does in the soricines Cryptotis and Blarina, but not in the crocidurine Suncus and Crocidura. However, the cumulus oophorus of Myosorex appears largely crocidurine by virtue of its persistent intercellular junctions, long term stability, and the absence of a matrix, lacking only the unique perizonal space that finally characterizes the cumulus of the crocidurines, Suncus and Crocidura. The 'hybrid' character of the reproductive system of Myosorex is more consistent with the proposal that the genus is a survivor of a primitive subfamily--the Crocidosoricinae--from which present day Soricinae and Crocidurinae have arisen.
Bedford
J M
JM
Department of Obstetrics and Gynecology, Cornell University Medical College, New York, NY 10021, USA.
Bernard
R T
RT
Baxter
R M
RM
D000818:Animals; D005075:Biological Evolution; D004822:Epididymis / Q000033:anatomy & histology; D005187:Fallopian Tubes / Q000033:anatomy & histology; D005260:Female; D005835:Genitalia / Q000033:anatomy & histology*; D008297:Male; D008854:Microscopy, Electron; D009865:Oocytes / Q000166:cytology; D010060:Ovulation / Q000502:physiology; D010413:Penis / Q000033:anatomy & histology; D012098:Reproduction / Q000502:physiology*; D012788:Shrews / Q000033:anatomy & histology / Q000145:classification*; D013094:Spermatozoa / Q000648:ultrastructure