HybHyp--hybridizing the host: the long reach of parasite genes. A new hypothesis to explain host-parasite interrelationships in plant hybrid complexes.

Ever since existence of sexuality in plants was accepted in around 1700, questions centred about the role and maintenance of sexual reproduction in general, leading to a number of hypotheses like the Vicar of Bray, the Ratchet or the Hitch-hiker theory. Bell (The masterpiece of nature. The evolution and genetics of sexuality. University of California Press, Berkeley, LA, 1982) formulated the Red Queen Hypothesis (RQH) which explains the persistence of sexual reproduction as an outcome of a coevolutionary arms race between hosts and parasites. By sexual recombination and genetic diversification hosts minimize the risk of pathogen infection. Since virulence of pathogens is genetically determined and often species specific, parasites are mostly adapted to common host genotypes, whereas rare and divergent genotypes are less infected and therefore have a selective advantage. Employing Dawkins (The extended phenotype. The long reach of the gene, 1999) central theorem of the extended phenotype to the RQH, mating systems in hosts might be a result of the long reach of the parasites genes. Here now the hypothesis is proposed, that evolution by hybridisation and polyploidy in host plants is an extended phenotype of parasites, a response of hosts triggered by the parasites genes to slow down the effects of the Red Queen strategy of plants. Thus, hybridisation and polyploidy might have evolved by parasite pressure and not by host strategy. This hypothesis is called the "hybridisation-of-the-host-hypothesis".