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Abstract PremiseCo‐occurring plant species that share generalist pollinators often exchange pollen. This heterospecific pollen transfer (HPT) impacts male and female reproductive success through pollen loss and reductions in seed set, respectively. The resulting fitness cost of HPT imposes selection on reproductive traits (e.g., floral color and shape), yet we currently lack strong predictors for the post‐pollination fate of heterospecific pollen, especially within community and phylogenetic contexts. MethodsWe investigated the fate of heterospecific pollen at three distinct stages of plant reproduction: (1) pollen germination on the stigma, (2) pollen tube growth in the style, and (3) fertilization of ovules. We experimentally crossed 11 naturally co‐flowering species in the subalpine meadows of the Colorado Rocky Mountains, across a spectrum of phylogenetic relatedness. Using generalized linear mixed models and generalized linear models, we evaluated the effect of parental species identity and phylogenetic relatedness on pollen tube growth at each reproductive stage. ResultsWe found that heterospecific pollen tubes can germinate and grow within pistils at each reproductive stage, even when parental species are >100 My divergent. There was no significant effect of phylogenetic distance on heterospecific pollen success, and no evidence for a mechanism that suspends heterospecific pollen germination or pollen tube growth within heterospecific stigmas or styles. ConclusionsOur results show that even in communities where HPT is common, pre‐zygotic post‐pollination mechanisms do not provide strong barriers to interspecific fertilization. HPT can result in the loss of ovules even between highly diverged plant species.
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This content will become publicly available on August 13, 2025
Co-flowering richness has variable effects on pollen quantity and quality limitation in four Clarkia species
Abstract Background and AimsPollination failure occurs from insufficient pollen quantity or quality. However, the relative contributions of pollen quantity vs. quality to overall pollen limitation, and how this is affected by the co-flowering context, remain unknown for most plant populations. Here, we studied patterns of pollen deposition and pollen tube formation across populations of four predominately outcrossing species in the genus Clarkia to evaluate how the richness of co-flowering congeners affects the contribution of pollen quantity and quality to pollen limitation. MethodsWe partition variation in pollen deposition and pollen tube production across individuals, populations and species to identify the main sources of variation in components of reproductive success. We further quantify the relative contribution of pollen quantity and quality limitation to the reproductive success of the four Clarkia species using piecewise regression analyses. Finally, we evaluate how variation in the number of co-flowering Clarkia species in the community affects the strength of pollen quality and quality limitation. ResultsAcross all contexts, pollen deposition and the proportion of pollen tubes produced varied greatly among individuals, populations and species, and these were not always correlated. For instance, C. xantiana received the smallest pollen loads yet produced the highest proportion of pollen tubes, while C. speciosa exhibited the opposite pattern. Yet, co-flowering richness had variable effects on the strength of pollen quantity and quality limitation among populations. Specifically, breakpoint values, which are an indicator of overall pollen limitation, were two-fold higher in the four-species community compared with one- and two-species communities for two Clarkia species, suggesting that pollen limitation can increase with increasing richness of co-flowering congeners. ConclusionsOur results reveal a complex interplay between the quantity and quality of pollen limitation and co-flowering context that may have different evolutionary outcomes across species and populations.
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- Award ID(s):
- 1754299
- PAR ID:
- 10554492
- Publisher / Repository:
- Annals of Botany
- Date Published:
- Journal Name:
- Annals of Botany
- ISSN:
- 0305-7364
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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