Differential Pollen‐tube Growth Rates and Nonrandom Fertilization in Hibiscus Moscheutos (Malvaceae)

Abstract

The prevalence of nonrandom fertilization due to postpollination events has rarely been studied in natural populations, despite important implications for outcrossing rates, mate choice, and plant fitness. Nonrandom paternity within fruits can be caused by both unequal fertilization and unequal embryo abortion. Using self‐compatible Hibiscus moscheutos, we studied the potential for nonrandom fertilization by comparing growth rates of pollen‐tubes from different donors. The branched style of Hibiscus allowed within‐flower comparisons between pollen donors. Relative pollen‐tube growth rates were determined by applying pollen from pairs of donors to different stigmas on adjacent stylar branches. We then measured the number of callose plugs per tube in cross‐sectional transects across the style after 3 hr. We demonstrate that rates of callose plug formation can be used as a sensitive indicator of relative pollen‐tube growth rate. Differences between pollen donors were common and repeatable. Self‐pollen‐tubes grew slower than outcross pollen‐tubes in some crosses and faster in others. Allozyme variation in glucose phosphate isomerase was used to show that individuals with fast‐growing pollen‐tubes sired a disproportionate number of seeds following mixed pollinations (up to 72%). Since seed abortion was negligible, we conclude that variation in pollen‐tube growth rates leads to nonrandom paternity within fruits.

Individual Variation in the Vigor of Self Pollen and Selfed Progeny in Hibiscus moscheutos (Malvaceae)

“…Details of the reproductive ecology of H. moscheutos are given in Spira (1989), Snow and Spira (1991a, b), and Spira et al (1992). Briefly, the large, one-day flowers are pollinated by solitary anthophorid bees (Ptilothrix bombiformisi and by bumblebees (Bombus spp.).…”

“…Pollen tube growth rates -Pollen tube "races" were conducted by applying self and outcross pollen to separate stigmas on separate, labeled stylar branches of the same flower (details in Snow and Spira, 1991a, b). The plants in this study were part of a collection of over 60 haphazardly chosen genotypes that were taken from a natural population and grown outdoors in Edgewater, Maryland (Snow and Spira, 1991 a).…”

“…This incubation period was appropriate for determining the number of callose plugs per tube in a standardized midstylar region, providing a good estimate of relative pollen tube growth rates (faster tubes produce callose plugs sooner than slower tubes; Snow and Spira, 1991a). This incubation period was appropriate for determining the number of callose plugs per tube in a standardized midstylar region, providing a good estimate of relative pollen tube growth rates (faster tubes produce callose plugs sooner than slower tubes; Snow and Spira, 1991a).…”

“…Self-compatibility was demonstrated in two previous experiments, which showed no differences in the number of seeds per fruit from self vs. outcross pollen (Spira, 1989;Snow and Spira, 1991a). Self-compatibility was demonstrated in two previous experiments, which showed no differences in the number of seeds per fruit from self vs. outcross pollen (Spira, 1989;Snow and Spira, 1991a).…”

Callose plug deposition patterns vary in pollen tubes of Arabidopsis thalianaecotypes and tomato species

“…For example, the number of callose plugs was used as an indicator of pollen tube growth rate in Hibiscus moscheutos [6,7]. In tomato, antisense lines for the pollen receptor kinase LePRK2 showed abnormal callose plug deposition and slower pollen tube growth than in wild type [8].…”