Evolution of Asexual Reproduction in Plants

Asexual reproduction is found in many taxonomic groups and considerable effort has been directed by biologists towards understanding its mechanisms, evolution and ecological significance. This research monograph, which is the culmination of several years of research by the author, offers a though-provoking contribution to this debate. It is primarily aimed at biologists undertaking research into the evolution, genetic control and ecological costs and benefits of different patterns of reproduction, although it should also be of interest to senior undergraduates. The main aim of the book is to understand why asexual reproduction per se and its many different forms have very uneven distributions within and among different taxonomic groups. This is illustrated with reference to the major groups of extant land plants - the bryophytes, ferns, gymnosperms and angiosperms - although in his search for answers the author has made much use of insights gleaned from studies of asexuality in animals, and the arguments presented can be applied equally to both kingdoms. In a series of seven chapters, it is shown how major differences between taxa in the frequency and form of asexual reproduction are due to differences in ontogeny and in fundamental aspects of reproductive ecology. These combine to exert a major influence on the probability of asexuality, or a particular pattern of asexual reproduction, evolving and undergoing favourable selection in a taxon. The author highlights the important role the male function plays in the spread and maintenance of asexuality in cosexual taxa, and illustrates how this function can overcome many of the ecological costs hitherto associated with asexual reproduction by providing a gene for asexuality with the means to move from genome to genome. The arguments presented lead the author to challenge current concepts of the evolutionary and ecological consequences of asexuality, with this part of the discussion culminating in a reappraisal of the role, and the reasons for the maintenance, of genetic recombination in sexual organisms.