Patterns and effects of heterospecific pollen transfer between an invasive and two native plant species: the importance of pollen arrival time to the stigma

Abstract

Premise Invasive plant species can integrate into native plant–pollinator communities, but the underlying mechanisms are poorly understood. Competitive interactions between invasive and native plants via heterospecific pollen (HP) and differential invasive HP effects depending on HP arrival time to the stigma may mediate invasion success, but these have been little studied. Methods We evaluated patterns and effects of HP receipt on pollen tube growth in two native and one invasive species in the field. We also used hand‐pollination experiments to evaluate the effect of invasive HP pollen and its arrival time on native reproductive success. Results Native species receive smaller and less‐diverse HP loads (5–7 species) compared to invasive species (10 species). The load size of HP had a negative effect on the proportion of pollen tubes in both native species but not in the invasive, suggesting higher HP tolerance in the latter. Invasive HP arrival time differentially affected pollen tube success in native species. Conclusions Our results highlight the need to study reciprocal HP effects between invasive and native species and the factors that determine differential responses to HP receipt to fully understand the mechanisms facilitating invasive species integration into native plant–pollinator communities.

Effect of heterospecific pollen deposition on pollen tube growth depends on the phylogenetic relatedness between donor and recipient

“…Hence, HP can germinate even in phylogenetically distant species and have neutral ( Fuchsia species) or even positive ( S. wettsteinii ) effects on recipient post-pollination success (pollen tubes in style end). A similar result was reported for Cakile edentula that when received HP of Bidens pilosa also increased CP tube growth, which was suggested to be stimulated by the release of biochemical compounds and result in a herd effect ( Suárez-Mariño et al 2019 ). In the context of pollination, the herd effect can be interpreted as the greater CP growth when in the presence of foreign pollen ( HP in our case); however, this is an idea that has yet to be formally tested ( Ashman et al 2020 ).…”

“…that exploit a wide variety of pollinators; Ollerton et al 2007 ) might not be impaired as much by HP as specialist-pollinated ones, because the former were presumably exposed more often and to higher and more diverse loads of HP over generations ( Fang and Huang 2013 ; Arceo-Gómez et al 2016 ; Fang et al 2019 ). Donor traits like HP size and apertures ( Ashman and Arceo-Gómez 2013 ), as well as extrinsic factors such as HP arrival time on stigmas ( Suárez-Mariño et al 2019 ), abiotic conditions ( Celaya et al 2015 ) and HP load diversity and identity ( Arceo-Gómez and Ashman 2011 ) also are known to contribute on recipient’s post-pollination outcomes.…”

Pollen transfer networks reveal alien species as main heterospecific pollen donors with fitness consequences for natives

“…Alien species represent around 30% of total plant richness (Parra‐Tab la et al., 2018) and a high percentage of all the flowers available to pollinators in these communities (76% ± 30, M ± SD ), but with high variability among sites (12%–99%; Table 1). Alien plant species also share a high proportion of the primary insect pollinators with native plant species (Albor et al., 2019; Suárez‐Mariño et al, 2019; Parra‐Tab la et al., 2019). Following Parra‐Tab la et al.…”

“…Pollen grains were photographed with an optical microscope equipped with a digital camera that allowed for the morphological characterization of pollen grains (Motic BA310). This pollen library was then used as a reference to identify pollen loads on stigmas and to record CP and HP abundance on each stigma (Suárez‐Mariño et al., 2019). A total of 4,500 styles were collected (average per site: 498.22 ± 348.32, ± SD ) corresponding to 1,273 individual plants.…”

“…pollen tube and seed production; e.g. Suárez‐Mariño et al., 2019). This latter step is imperative if we aim not only to determine the overall effects of plant invasion on co‐flowering communities but also to uncover the mechanisms that underlie such effects.…”