Origin of the Fittest and Survival of the Fittest: Relating Female Gametophyte Development to Endosperm Genetics

For more than a century, most biologists have viewed the structural diversity of angiosperm female gametophytes as trivial variants of the reproductive process. However, analysis of variation among angiosperm female gametophytes from an evolutionary developmental perspective can provide new insights into patterns of reproductive innovation and evolution among flowering plants. The key is to link the developmental and structural diversity of angiosperm female gametophytes to evolutionary innovations (perhaps even adaptations) associated with endosperm genetics and ploidy. Selection has been hypothesized to favor endosperms with higher ploidy, higher heterozygosity, higher maternal‐to‐paternal genome ratios, and reduced opportunity for genetic (interparental and/or parent‐offspring) conflict. We evaluate these hypotheses for the seven basic genetic types of endosperm known among flowering plants and interpret their relative importance when mating system is considered. We demonstrate that variation in female gametophyte developmental patterns represents the source material that ultimately creates variation in endosperm genetics. Evolutionary transitions in female gametophyte development are therefore a function of selection directly acting on the resultant phenotypes of endosperms. Thus, the relation between variation in female gametophyte development and variation in endosperm genetic constitution should be seen as one between the origin of structural novelties (origin of the fittest) and its downstream consequences on the relative fitness (survival of the fittest) of these novelties, as expressed in the biology of endosperm.