Molecular insights on the taxonomic position of the paternal ancestor of the Squalius alburnoides hybridogenetic complex.

Many hybrid Wsh lineages result from intrageneric crosses and are often asexual, being considered as “evolutionary dead-ends” (Vrijenhoek, 1998). This seems not to be true in the Squalius alburnoides (Iberian minnow) Steindachner 1866 complex. This complex, that seems to have originated in a cross between distant species, has a remarkable variability in ploidy level and genomic composition, includes fertile Wsh of both sexes and some of its forms retain meiosis and recombination (Alves et al., 2001). The S. alburnoides complex probably originated from crosses between S. pyrenaicus females and males from an unknown species. The complex includes 2nD50, 3nD75, and 4nD100 hybrid forms (reviewed in Alves et al., 2001) with varying proportions of the two parental genomes (denoted by P and A, corresponding to the S. pyrenaicus and paternal ancestor genomes, respectively). Reconstituted diploid non-hybrids (AA genome) are also produced and are morphologically distinct from the diploid hybrid form of the complex (PA). These non-hybrid Wsh, normally males (females seem to be extremely rare), exhibit the nuclear genome of the paternal ancestor (AA) and S. pyrenaicus-like mtDNA. In the absence of an identiWed paternal species this suggests that they are reconstituted from the hybrids (Alves et al., 2002). The oogenesis of triploid females with PAA genomes frequently involves discarding the Squalius (P genome), followed by normal meiosis and recombination, generating A gametes. When these gametes fuse with the sperm of AA males, which also undergo normal meioses, new AA male progeny is generated. In the absence of S. pyrenaicus, such as in the northern basins of