SYNAPTONEMAL COMPLEX-ANALYSIS OF INTERSPECIFIC HYBRIDS OF POECILIA (TELEOSTEI, POECILIDAE)

The pattern of chromosome pairing at meiotic prophase in males of the guppy (Poecilia reticulatus), black molly (P. sphenops), marble molly (P. velifera) and hybrids between these species was examined by means of electron microscopy of surface spread synaptonemal complexes. Meiot ic chromosomes of the pure species and P. sphenops x P. velifera hybri d showed complete pairing at pachytene. No indication of heteromorphis m for any chromosomes was found. The vast majority of pachytene cells of the P. velifera x P. reticulatus hybrid demonstrated various signs of pairing failure: univalents, interlocks, multiple non-homologous pa iring and end-to-end associations. However, a few cells were found to contain all completely paired homomorphic bivalents. These findings im ply that: (1) genetic divergence between these species was not accompa nied by gross chromosomal rearrangements; (2) pairing failure in the P . velifera x P. reticulatus hybrid is apparently determined by a diffe rence in the species-specific mechanism controlling meiotic prophase, rather than chromosome divergence.