Outbreeding in Angiosperms: Floral Architecture and Sexuality

Abstract

Sexuality in flowering plants is distinctly correlated with mating systems. Maximum numbers of flowering plants are outbreeders, and cross-pollination is the predominant type of pollen transfer to increase genetic variation. Morphological traits that promote outbreeding include temporal (dichogamy) and spatial separation (herkogamy) of male and female functions of flowers, monoecy and dioecy. Monoecy permits both inbreeding and outbreeding, while outbreeding is the only means of reproduction in dioecious species. Outbreeding confers on plant an opportunity to ‘move’ its genes amongst conspecific populations and is largely influenced by the availability of pollinators. Though pollinator-driven mating is favoured by most plant species, certain populations may occasionally maximize their reproductive fitness under adverse conditions by adopting multiple strategies such as autonomous selfing, dichogamy, late and early selfing, prepotency and outbreeding. Sexual plasticity manifested through mixed-mating, multiple mating, biparental inbreeding and sex switching has helped plants not only reproduce sexually but also ‘move on’. In addition, pollination environment also alters the outcrossing rates in a population emphasizing the fact that mating systems are labile. How various populations maintain potential for such shifts needs to be investigated. This chapter focuses on the outbreeding strategies in plants and also discusses how mating systems may evolve over the next few decades in response to challenges presented by changing environment.