Do Silene species with exposed stigmas tolerate interference by heterospecific pollen?

Pollen plays a key role in plant reproductive biology. Despite the long history of research on pollen and pollination, recent advances in pollen-tracking methods and statistical approaches to linking plant phenotype, pollination performance, and reproductive fitness yield a steady flow of exciting new insights. In this introduction to the Special Issue "Pollen as the Link Between Phenotype and Fitness," we start by describing a general conceptual model linking functional classes of floral phenotypic traits to pollinationrelated performance metrics and reproductive fitness. We use this model as a framework for synthesizing the relevant literature, highlighting the studies included in the Special Issue, and identifying gaps in our understanding and opportunities for further development of the field. The papers that follow in this Special Issue provide new insights into the relationships between pollen production, presentation, flower morphology, and pollination performance (e.g., pollen deposition onto stigmas), the role of pollinators in pollen transfer, and the consequences of heterospecific pollen deposition. Several of the studies demonstrate exciting experimental and analytical approaches that should pave the way for continued work addressing the intriguing role of pollen in linking plant phenotypes to reproductive fitness.

Section: Discussionmentioning

confidence: 99%

Section: Heterospecific Pollen Transfermentioning

confidence: 99%

Section: Heterospecific Pollen Transfermentioning

confidence: 99%

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Pollen as the link between floral phenotype and fitness

Opedal

Pérez‐Barrales

Brito

et al. 2023

“…Interestingly, the L. suffruticosum locality where L. tenue was used as pollen donor is a single‐species locality; these plants experienced a stronger reduction of conspecific‐pollen performance than did plants from coflowering localities, which were pollinated with L. narbonense and L. viscosum pollen (see Material and Methods, Appendix S2). Variation in the tolerance to interspecific pollen based on a previous history of pollen exposure has been identified as an adaptive mechanism to reduce reproductive costs (Grant, 1966; Arceo‐Gómez et al, 2016; Fang et al, 2019; Moreira‐Hernández et al, 2019; Streher et al, 2020; Hao et al, 2023 [in this issue]).…”

Section: Discussionmentioning

confidence: 99%

Incomplete partitioning of pollinators byLinum suffruticosumand its coflowering congeners

Pérez‐Barrales

Armbruster

2023

Premise: Linum suffruticosum shows variations in pollinator fit, pollen pickup, and local pollinators that predict pollen deposition rates. The species often coflowers with other Linum species using the same pollinators. We investigated whether L. suffruticosum trait variation could be explained by local patterns of pollinator sharing and associated evolution to reduce interspecific pollen transfer. Methods: Pollinator observations were made in different localities (single species, coflowering with other congeners). Floral traits were measured to detect differences across populations and from coflowering species. Reproductive costs were quantified using interspecific hand pollinations and measures of pollen-tube formation, combined with observations of pollen arrival on stigmas and pollen-tube formation after natural pollination in allopatric and sympatric localities. Results: The size and identity of the most important pollinator of L. suffruticosum and whether there was pollinator sharing with coflowering species appeared to explain floral trait variation related to pollinator fit. The morphological overlap of the flowers of L. suffruticosum with those of coflowering species varied, depending on coflowering species identity. A post-pollination incompatibility system maintains reproductive isolation, but conspecific pollen-tube formation was lower after heterospecific pollination. Under natural pollination at sites of coflowering with congeners, conspecific pollen-tube formation was lower than at single-species localities. Conclusions: Trait variation in L. suffruticosum appears to respond to the most important local pollinator. Locally, incomplete pollinator partitioning might cause interspecific pollination, imposing reproductive costs. These reproductive costs may generate selection on floral traits for reduced morphological overlap with coflowering congeners, leading to the evolution of pollination ecotypes.

“…The accumulation of pollen–pistil incompatibilities underlying post‐pollination isolation mechanisms also require evolutionary time, and thus efficiency of these barriers is expected to increase with phylogenetic distance between the interacting species (Ashman and Arceo‐Gómez, 2013; Moreira‐Hernández and Muchhala, 2019; Streher et al 2020). However, tolerance to heterospecific pollen deposition conferred by post‐pollination barriers among congeneric species has been observed in a few cases (e.g., Clarkia , Arceo‐Gómez et al, 2016; Burmeistera , Moreira‐Hernández et al, 2019; Silene , Hao et al, 2023 [in this issue]), suggesting that it might evolve more rapidly under some circumstances. In particular, cases where such barriers are present in sympatry but are absent between allopatric populations (e.g., Kay and Schemske, 2008; Arceo‐Gómez et al, 2016) suggest that pollen transfer dynamics in sympatry might favor the evolution of post‐pollination barriers to limit reproductive interference or prevent hybridization (Moreira‐Hernández and Muchhala, 2019).…”

mentioning

confidence: 99%

Limited reproductive interference despite high rates of heterospecific pollen transfer among co‐occurring bat‐pollinated Burmeistera

Moreira‐Hernández,

Ghai,

Terzich

et al. 2023

Premise: Many tropical plants are bat-pollinated, but these mammals often carry copious, multispecific pollen loads making bat-pollinated plants susceptible to heterospecific pollen deposition and reproductive interference. We investigated pollen transfer between sympatric bat-pollinated Burmeistera species and their response to heterospecific pollen deposition from each other. Methods: We quantified conspecific and heterospecific pollen deposition for two populations of B. ceratocarpa, a recipient species in heterospecific pollen transfer interactions, that co-occur with different donor relatives (B. borjensis and B. glabrata). We then used a cross-pollination scheme using pollen mixtures to assess the species' responses to heterospecific pollen deposition in terms of fruit abortion and seed production. Results: Burmeistera ceratocarpa received significantly more heterospecific pollen from its relatives at both sites than its own pollen was deposited on its relatives. However, heterospecific pollen deposition only affected seed production by B. borjensis and B. glabrata, but not by B. ceratocarpa, suggesting that early acting post-pollination barriers buffer the latter against reproductive interference. Crosses between sympatric and allopatric populations suggest that the study species are fully isolated in sympatry, while isolation between allopatric populations is strong but incomplete. Conclusions: We did not observe evidence of reproductive interference among our study species, because either heterospecific pollen deposition did not affect their seed production (B. ceratocarpa) or they receive heterospecific pollen only rarely (B. borjensis and B. glabrata). Frequent heterospecific pollen deposition might favor the evolution of barriers against foreign pollen (as in B. ceratocarpa) that alleviate the competitive costs of sharing low fidelity pollinators with cooccurring species.