Breaking the rules: modifications of sexual reproduction pathways in vertebrates.

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Sexual reproduction, prevailing in most eukaryotes, involves meiosis with recombination, reduced gametes, fertilization, karyogamy, and development of a new organism. Breaking this rule, hybridization in vertebrates may alter the canonical gametogenic and fertilization pathways: the emergence of rare "asexuality". Such vertebrates allow to address fundamental questions about the persistence of sexuality, gametogenesis and fertilization. However, causes and mechanisms of switches from sexuality to "asexuality" are poorly examined. In four diploid and triploid "asexual" anuran (Pelophylax) and fish complexes (two in Cobitis; Poecilia formosa), we compare different "asexual" modes, triggers and key pathways. Using integrative approaches (cytogenetics, cell biology, genomics), we will elucidate: 1) modifications of gametogenesis by premeiotic genome elimination or endoreplication, or failure of meiosis; 2) sperm elimination after fertilization, 3) identity of sex chromosomes in parental bisexual species and "asexual" hybrids including 4) a potential role to initiate of "asexuality".