DIVERSITY IN THE REPRODUCTIVE MODES OF FEMALES OF THE RUTILUS ALBURNOIDES COMPLEX (TELEOSTEI, CYPRINIDAE) - A WAY TO AVOID THE GENETIC CONSTRAINTS OF UNIPARENTALISM

Hybrid minnows collectively known as the Rutilus alburnoides complex a re found throughout much of the Iberian Peninsula and include diploid and polyploid forms with female-skewed sex ratios. Previous studies ha ve suggested that diploid and triploid females from the northern Douro Basin reproduce by hybridogenesis. The present study, which is based on experimental crosses and uses allozyme and minisatellite markers, r eveals that diploid females from the Tejo Basin exhibit a different fo rm of reproduction, transmitting the hybrid genome intact to the egg, which, upon fertilization, yields triploid progeny. Reproduction by tr iploid females from the southern Guadiana and Tejo basins resembles hy bridogenesis in that one genome is discarded in each generation withou t recombination, but the remaining two homospecific genomes are not tr ansmitted clonally. Elimination of the unmatched genome permits ready synapsis and meiosis between the homospecific genomes, and genetically distinct haploid eggs are produced (''meiotic hybridogenesis''). In s ome females, some sexual cells undergo an altered nonreductional meios is, resulting in genetically diverse diploid eggs. In contrast to most hybrid vertebrate complexes, in which diploids and triploids are evol utionarily independent, in the R. alburnoides complex, there is a bidi rectional movement of genes between diploid and triploid hybrids. Repr oduction by the types of diploid and triploid females discussed here i ntroduces high genotypic diversity into hybrid populations, and allows purging of deleterious genes and incorporation of beneficial mutation s in the same genome, characteristics believed to be major advantages of sexual reproduction.