Experimental hybridization within the genus Triturus (Urodela: Salamandridae)

The spermatogenesis of 9 F₁ hybrids of Triturus cristatus carnifex × T. vulgaris meridionalis was studied in squash preparations of testicular fragments, treated by the C-staining method. The chromosome number of these hybrids was examined in spermatogonial metaphases and found to be diploid. The two parental sets were always recognized, which means that a regular, although heterospecific, amphimixis occurred (2n=n+n). Meiotic prophase I is greatly altered owing to a failure of typical chromosome pairing and chiasma formation. At metaphase I and/or meta-anaphase I, the effects of the hybrid combination of the 2 specific parental sets are clearly visible. Most primary spermatocytes contain only univalents. A few show chromosome associations (bivalents, trivalents and, more rarely, quadrivalent chains) besides univalents. Such associations are of 2 types: (a) intragenomal associations = associations of 2 chromosomes by a terminal (a¹) or subterminal chiasma (a²); (b) intergenomal associations = associations of 2 chromosomes by a terminal (b¹) or subterminal chiasma (b²). Univalents segregate at random while the associations often lag on the equatorial plane or migrate entire to a spindle pole. Primary spermatocytes with chromosome multivalents can encounter greater difficulties in accomplishing the first cytokinesis. Secondary spermatocytes are numerically and qualitatively unbalanced; however, some of them undergo spermiogenesis and can give rise to a small number of sperms, generally abnormal and never united in bundles. — Problems related to the occurrence of anomalous chiasmata and of intra- and inter-genomal homologies are discussed.