Geitonogamous Selfing Research Articles

Genetic constraints on mating system evolution in the cleistogamous annual Impatiens pallida: inbreeding in chasmogamous flowers

Each Impatiens pallida individual has both a selfing mode of reproduction (cleistogamy) and a potentially outcrossing mode of reproduction (chasmogamy). The persistence of such a mating heteromorphism is in direct contrast to the theoretical expectation that mixed-mating strategies are evolutionarily unstable. Studies designed to detect fitness advantages of chasmogamous reproduction find only slight differences in the fitness of seed from the two reproductive modes. Inbreeding in chasmogamous flowers could cause these results. This hypothesis was tested by estimating the parameters of the correlated matings model for each of three generations in a natural population of I. pallida using multilocus electrophoretic data from 8934 chasmogamous seed sampled from 1080 individuals. Effective selfing in chasmogamous flowers averaged more than 0.50, changing from 0.66 to 0.54 to 0.48 over three generations. Geitonogamous selfing comprised approximately 80 per cent of this inbreeding in each generation: the remainder was mating among relatives. The correlation of selfing and the correlation of outcrossed paternity within and among the chasmogamous flowers of individuals were moderate in each generation, ranged within +0.11 to +0.21 and changed little over three generations. Individuals that were further from their nearest neighbour or were shorter produced a greater proportion of inbred chasmogamous seed. Those that produced more chasmogamous flowers had higher rates of geitonogamous selfing. Taken together these results are strong evidence that substantial inbreeding occurred in chasmogamous flowers through both geitonogamous selfing and biparental inbreeding, that this inbreeding caused the genetic correlation of chasmogamous sibs to be more similar to the genetic correlation among completely selfed sibs than to the genetic correlation among completely outcrossed sibs, that effective selfing within chasmogamous flowers can change over generations and be influenced by plant architecture and pollinator behaviour, and that chasmogamous flowers of I. pallida have a stable, partially selfing mating strategy.

SEX EXPRESSION, BREEDING SYSTEM, AND POLLEN BIOLOGY OF RICINOCARPOS PINIFOLIUS: A CASE OF ANDRODIOECY?

A population of 54 Ricinocarpos pinifolius (Euphorbiaceae) plants contained male plants, which produced only staminate flowers, and hermaphrodites, which produced staminate and pistillate flowers. The fraction of pistillate flowers ranged continuously from 0 to 0.68. Insect pollination was effective and fruit set virtually complete except for losses to herbivores. Self pollen, outcross pollen from male plants, and outcross pollen from hermaphrodites were all equivalent in viability, germination, tube growth, ovule penetration, and fruit setting ability. Inbreeding depression was manifested as late abortion of some selfed seeds. Geitonogamous selfing is largely prevented by temporal separation of male and female functions within plants. This temporal separation, combined with population‐wide synchrony of flowering, may create unusual conditions allowing male plants at low frequency to match hermaphrodites in reproductive success.

Floral protogyny, self-compatibility and the pollination ofOurisia macrocarpa(Scrophulariaceae)

Abstract The simple gullet flowers of Ourisia macrocarpa are borne in sequentially blooming whorls. They are pollinated primarily by small halictids and syrphids. The plants are self-compatible. Hemisynchronous, multi-cycle, incomplete proto-gyny allows both autogamous and geitonogamous selfing. Autogamy is infrequent due to movements of stamens and styles, and to allogamous pollination during the female stage. Minimum and maximum estimates of the frequency of geitonogamous pollinations are 2.4 and 31.2%. Avoidance of self-pollination is probably the most important selective force that has favoured floral protogyny.

Expression of Andromonoecy and Pollination of Tuberous Lomatiums (Umbelliferae)

Tuberous lomatiums (Lomatium, Umbelliferae) constitute a well-de- fined infrageneric group that is characterized by adaptation to a short, early spring growing season followed by a long summer drought. All tuberous lomatiums are andromonoecious and all exhibit 'a pattern of increasing ratios of hermaphroditic to staminate flowers in successively maturing inflorescences. Floral visitation by a variety of Diptera, Hymenoptera, and Coleoptera effects outcrossing and may also mediate geitonogamous selfing. Xenogamy is promoted by protogyny of hermaphroditic flowers, the arrangement of staminate and perfect flowers, and the sequence of floral maturation. Geitonogamy is favored by the morphology of the inflorescences, overlap of the staminate and pistillate stages of different flowers on the same indi- vidual, and the behavior of pollinators. Andromonoecy and high pollen production favor both xenogamy and geitonogamy. The floral features of tuberous lomatiums ensure relatively high levels of seed production even though abundance and activity of pollinators may be limited by harsh environmental conditions. The characteristic and comparatively uniform inflorescences of the Umbelliferae undoubtedly contributed to early recognition of this nat- ural family. Apparent uniformity may account, in part, for what until recently has been a paucity of investigations into the biological impor- tance of floral features of umbellifers. Studies by Bell (1971), Bell and Lindsey (1978), Brehm (1979), Cruden (1976), Cruden and Hermann- Parker (1977), Lindsey (1982), Lloyd (1973, 1980a, b), Schlessman (1978, 1980), and Webb (1979, 1980) have revealed considerable variation with