Effects of heterospecific pollen on stigma behavior in Campsis radicans: Causes and consequences

Abstract

Premise: Pollinator sharing of co-flowering plants may result in interspecific pollen receipt with a fitness cost. However, the underlying factors that determine the effects of heterospecific pollen (HP) are not fully understood. Moreover, the cost of stigma closure induced by HP may be more severe for plants with special touch-sensitive stigmas than for plants with non-touch-sensitive stigmas. Very few studies have assessed HP effects on stigma behavior. Methods: We conducted hand-pollination experiments with 10 HP donors to estimate HP effects on stigma behavior and stigmatic pollen germination in Campsis radicans (Bignoniaceae) at low and high pollen loads. We assessed the role of phylogenetic distance between donor and recipient, pollen size, and pollen aperture number in mediating HP effects. Additionally, we observed pollen tube growth to determine the conspecific pollen-tube-growth advantage. Results: Stigma behavior differed significantly with HP of different species. Pollen load increased, while pollen size decreased, the percentage of permanent closure and stigmatic germination of HP. Stigmatic HP germination increased with increasing aperture number. However, HP effects did not depend on phylogenetic distance. In addition, conspecific pollen had a pollen-tube-growth advantage over HP. Conclusions: Our results provide a good basis for understanding the stigma-pollen recognition process of plant taxa with touch-sensitive stigmas. We concluded that certain flowering traits drive the HP effects on the post-pollination period. To better understand the impact of pollinator sharing and interspecific pollen transfer on plant evolution, we highlight the importance of evaluating more factors that determine HP effects at the community level.

Incomplete partitioning of pollinators byLinum suffruticosumand its coflowering congeners

“…These observations were similar to the incompatibility reaction observed after self‐pollination, so the incompatibility system in L. suffruticosum may adaptively preclude pollen‐tube formation after interspecific pollinations (Grant, 1969; Broz and Bedinger, 2021). The lack of pollen‐tube formation could also be a non‐adaptive consequence of species divergence in that none of the interacting species are closely related or belong to the same subclade (Ruiz‐Martin et al, 2018, but see Zou et al, 2022). Our surveys did not reveal obvious hybrids, although hybrids between Linum species have been obtained experimentally (Ockendon, 1968; Seetharam, 1972).…”

“…Conspecific pollen‐tube performance might depend on the absolute or relative amounts of conspecific and heterospecific pollen reaching stigmas, the timing of the arrival of conspecific relative to heterospecific pollen, or the identity and diversity of heterospecific pollen donors (Armbruster and Herzig, 1984; Arceo‐Gómez and Ashman, 2011; Bruckman and Campbell, 2016; Tong and Huang, 2016; Cavalcante et al, 2020; Coetzee et al, 2020). Heterospecific pollen‐tube formation might depend on the phylogenetic distance between species or the presence of interspecific incompatibility systems that operate similarly to the self‐incompatibility reaction (Grant, 1966; Broz and Bedinger, 2021; Zou et al, 2022). Because interspecific pollination is generally costly, tolerance to receiving pollen from other species can reduce or mitigate fitness costs, allowing pollinator sharing and species coexistence (Arceo‐Gómez et al, 2016; Moreira‐Hernández et al, 2019; Streher et al, 2020).…”