Evolution and maintenance of stigma-height dimorphism in Narcissus. I. Floral variation and style-morph ratios.

An unusual stylar dimorphism occurs in Narcissus, a plant genus of insect-pollinated Mediterranean geophytes. To determine the characteristics of the sexual polymorphism, we investigated floral variation in 46 populations of N. assoanus (section Jonquillae) and 21 populations of N. dubius (section Tazettae) in SW France. Flowers possess two stamen levels in each morph that occupy slightly different positions within the floral tube. In long-styled plants (L-morph), the stigma is located within or slightly above the upper-level stamens, whereas in short-styled plants (S-morph) the stigma is placed well below the lower-level stamens. The stigma-height dimorphism is distinct from heterostyly because the reciprocity of stigma and anther positions in the two style morphs is only weakly developed and there are no differences between the style morphs in pollen size or production. In both species, mean stigma-anther separation is much greater in the S-morph than the L-morph. In N. assoanus, population style-morph ratios vary from isoplethy (1L:1S) to L-biased, whereas in N. dubius they are usually strongly L-biased or occasionally contain only the L-morph. Populations fixed for the S-morph, or with S-biased morph ratios, were not observed. In N. assoanus, style-morph ratios were associated with population size: large continuous populations always exhibited 1:1 morph ratios, whereas smaller, fragmented populations were often L-biased. This pattern was not evident in N. dubius. We argue that biased style-morph ratios largely result from morph-specific differences in assortative mating.

Evolution and maintenance of stigma-height dimorphism in Narcissus. II. Fitness comparisons between style morphs.

Populations of the insect-pollinated geophytes Narcissus assoanus and N. dubius (Amaryllidaceae) are commonly dimorphic for stigma height. An extensive survey of populations of the two species in SW France revealed a wide range of style-morph frequencies, particularly populations with significantly more long-styled than short-styled plants. Here we employ experimental and theoretical approaches to investigate potential selective mechanisms governing the variation in style-morph frequencies. Controlled pollination of both species demonstrated that N. assoanus is moderately self-sterile whereas N. dubius is highly self-compatible. Both intra- and intermorph crosses of N. assoanus were equally fertile, indicating that the species does not exhibit heteromorphic incompatibility. Estimates of female fertility (fruit- and seed-set) and multilocus estimates of outcrossing using allozyme markers provided no evidence of morph-specific differences in maternal components of reproductive success in natural populations of the two species. This result suggested that differences between the morphs in male fertility may be largely responsible for the observed morph-ratio variation. To investigate this hypothesis we developed a mating model that incorporates the genetics of stigma-height dimorphism and contrasting rates of assortative and disassortative mating in the style morphs. Simulation results demonstrated that stigma-height dimorphism will always be maintained when levels of disassortative mating are greater than assortative mating, and that the observed L-biased populations in Narcissus spp. probably result from greater levels of assortative mating in this morph in comparison with the S-morph.

Availability of phosphorus in bone meal.

Two commercially available bone meal products (grades 0-12-0 and 6-12-0) were examined. Samples were prepared according to AOAC method 2.007, and total and available phosphorus contents were determined. Portions of these preparations were reground to pass through successively smaller sieves, and subsequent analyses indicated the availability of phosphorus to be directly proportional to fineness of grind. A quantity of the citrate-insoluble fraction of the bone meal was obtained by following AOAC extraction procedures. Agronomic studies were conducted that compared this insoluble fraction with the original bone meal material and with reagent grade Ca(H2PO4)2.H2O. The data indicated poor correlation between the analytically defined and agronomically determined availability of phosphorus.