Quantitatively determined self-incompatibility. IV. Pollination and seed set in Borago officinalis

Sexual selection: an evolutionary force in plants?

Sexual selection has traditionally been used to explain exaggerated sexual traits in male animals. Today the concept has been developed and various other sexually related traits have been suggested to evolve in the same manner. In nearly all new areas where the theory of sexual selection has been applied, there has been an intense debate as to whether the application is justified. Is it the case that some scientists are all too ready to employ fashionable ideas? Or are there too many dogmatic researchers refusing to accept that science develops and old ideas are transformed? Maybe the controversies are simply a reflection of the difficulty of defining a theory under constant re-evaluation. Thus, we begin by summarizing the theory of sexual selection in order to assess the influence of sexual selection on the evolution of plant morphology. We discuss empirical findings concerning potentially affected traits. Although we have tried to address criticisms fairly, we still conclude that sexual selection can be a useful tool when studying the evolution of reproductive traits in plants. Furthermore, by including the evidence from an additional kingdom, a fuller understanding of the processes involved in sexual selection can be gained.

Quantitatively determined self-incompatibility. 5. Detection of multi-locus systems

Multi-locus self-incompatibility systems may be distinguished from single-locus systems by reciprocal differences in backcrosses and between crossed progeny of individual clearly compatible crosses. Such crosses are extremely laborious, so other methods have been suggested. In this note, it is shown that the coefficient of crossability is not a useful discriminant of self-incompatibility, as indeed should be expected from the properties of multi-locus systems, and that linkage methods are also unlikely to be successful. Until more self-incompatibility genes have had their sequences characterised, there is no substitute for the traditional genetical methods.