ULTRASTRUCTURE OF SPERMATOZOA IN INDUCED TETRAPLOID MUSSEL MYTILUS-GALLOPROVINCIALIS (LMK)

Ultrastructure of spermatozoa in artificially induced tetraploid musse ls, Mytilus galloprovincialis, was examined by light and electron micr oscopy and compared to that in normal diploid mussels. Sixteen tetrapl oid mussels were examined. Eight were found to be males, seven had spe nt or undeveloped gonads for which sex could not be determined, and on e was an hermaphrodite. Ultrastructure of spermatozoa from tetraploids was similar to diploids, but there were some differences. Differences included the number of mitochondria (5 to 7 in tetraploids compared t o only 5 in diploids) and the presence of abnormal acrosomes (2.4% in tetraploids, 0% in diploids). The mean size of spermatozoa in tetraplo ids was larger than that from diploids: acrosome length (4.2 mu m vs. 3.0 mu m), nuclear width (2.1 mu m vs. 1.8 mu m), nuclear length(2.1 m u m vs. 1.9 mu m), and flagellar length (73 mu m vs. 63 mu m). The DNA content of spermatozoa in tetraploids was about 2 times that of sperm atozoa from diploids. Oocytes were observed in the hermaphroditic tetr aploid, but only in very low numbers. These findings indicate spermato zoa will be capable of fertilization, and therefore, useful in the pro duction of triploids by crossing to normal haploid oocytes.