Allopolyploidy in the Melaniid Snails

Abstract

IN a recent communication1, I recorded the occurrence of apomictic parthenogenesis combined with polyploidy in a few species of Melanoides. One of these species, Melanoides tuberculatus, includes a diploid race with 2n = 32 chromosomes and a polyploid race with 90–94 chromosomes, which thus appears to be more or less at the hexaploid level when compared to the former. Both these races are parthenogenetic, but in the latter there occur exceptional males which are sterile, constituting about 3 per cent of the population. The males show evidence of structural and numerical hybridity in the occurrence of bridge and fragment in the meiotic divisions and in the presence of non-pairing univalents with irregular distribution in the first meiotic metaphase and anaphase.