In the light of evolution IX: Clonal reproduction: Alternatives to sex.

Evolutionary studies of clonal organisms have advanced considerably in recent years, but are still fledgling. Although recent textbooks on evolution or genetics might give the impression that nonsexual reproduction is an anomaly in the living world, clonality is the rule rather than the exception in many viruses, bacteria, and parasites that undergo preponderant asexual evolution in nature. Asexual reproduction is also common in insects, pathogenic helminthes, crustacea, and plants, and is found even in vertebrates. Clonality is thus of crucial importance in basic biology as well as in studies dealing with transmissible diseases. The primary focus of the Colloquium is on the balance between sexuality and clonality, because many so-called clonal organisms benefit from both evolutionary modes. Apart from its classic advantage of generating new genetic variants, sexual reproduction (genetic exchange between two different cells) plays a major role in DNA repair, which could represent its ancestral function. Clonal evolution, by contrast, permits the proliferation of high-fitness, multilocus associations and the avoidance of recombinational load (generation of low-fitness recombinants). Moreover, clonal evolution plays a crucial role in cancer biology, where the propagation of cancer cells displays striking analogies with that of microparasites. The study of clonal reproduction raises many theoretical, experimental, and technological challenges that may yield considerable pay-offs in microbiology and parasitology (e.g., in human medicine, veterinary medicine, and agronomy), artificial cloning, and the study of cancer. This “In the Light of Evolution” Colloquium made it possible to bring together specialists in various disciplines, including genetics, evolution, statistics, bioinformatics, and medicine. A balance is sought between the various disciplines, including clonal animals and plants, animal and human cloning, pathogens, and cancer studies. Active cross-fertilization is expected among scientists who have previously worked mostly separately. The Colloquium publication should be of considerable interest to the scientific community, including graduate students and postdoctorates.