Autoradiographic Studies on Reproduction in Philophthalmus megalurus (Cort, 1914) (Trematoda)

Incorporation of 3H-thymidine in gonial cells but not thereafter permitted timing of certain aspects of gametogenesis and studies on selfand cross-insemination. From oogonia until the primary oocyte is enclosed in the egg required from 7 days in 6-day-old worms to 13 days when 68 days of age. From labeled vitelline cells until their nuclei were detected in eggs required 96 hr. From tertiary spermatogonia to primary spermatocytes required 48 hr; to secondary spermatocytes, 60 hr; to spermatids, 96 hr; to sperm bundles, 120 hr; and to sperms in the seminal vesicle, 132 hr. Timing of the above events was not affected by the age of the worms after sexual maturity was attained. When 37 labeled worms, 6 to 90 days of age, were returned singly to the host for 6 to 16 days, 28 inseminated themselves as demonstrated by radioactive sperms in the female system. When each of 33 such worms was in the company of one to three nonlabeled worms of the same age, only one inseminated itself whereas the 33 inseminated 47 of 61 nonlabeled worms available. The extent of cross-insemination was less when only old worms were present but not when young and old worms were together, even though there was about a threefold size difference. Disappearance of labeled sperms from the uterine seminal receptacle within 14 to 16 days of copulation demonstrated a rate of turnover requiring repeated insemination during the life of the worms for continued production of viable eggs. Numerous papers have dealt with aspects of reproduction in digenetic trematodes but none has applied autoradiography to such studies. In investigating the incorporation of tritiated compounds by adults of Philophthalmus megalurus, it was found that various cells concerned with reproduction could easily be labeled in vitro with such compounds and followed by returning the worms to the host for various periods of time before they were prepared for autoradiography (Nollen, 1968). That study demonstrated that tyrosine is incorporated in vitelline cells to appear later in the eggshell, and that 10 days after labeling, eggs with labeled shells reach the metraterm and contain fully developed miracidia. Using the same materials and methods, other aspects of reproduction in P. megalurus were investigated as reported in the present paper. Nollen (1968) should be consulted for details of technique.