The potential of alien Solidago × niederederi Khek (Asteraceae) to compete for insect pollinators with its parental species

Abstract Interspecific competition for pollinators is a common and widely studied phenomenon, but in the case of spontaneous hybrids between alien and native plant species, it is poorly understood. Morphological similarity of hybrids to their parents may result in attracting the same pollinators, and thus increase the risk of introgression in mixed populations, which in turn may cause genetic erosion and even the extinction of pure populations of native parental species. To persist in the environment, animal-pollinated hybrids must maximize their reproductive success by effectively competing for pollinators, especially if they show reduced pollen viability. We tested the potential for competition for insect pollinators in Solidago × niederederi , a natural hybrid between the invasive S . canadensis and the native S . virgaurea , including three mixed populations in north-eastern Poland. We collected and video recorded flower visitors as well as measured selected morphological traits of the hybrid and its parental species, in August 2022. We also performed comparative biochemical analyses of volatile compounds emitted by inflorescences (capitula), using headspace solid-phase microextraction and gas chromatography with mass spectrometry (HS-SPME/GC–MS). The hybrid and its parental species were visited mostly by Diptera (Syrphidae) and they produced a complex scent with the dominance of α- and ß-pinene, myrcene, limonene, and germacrene D. However, a competitive hierarchy may be established between the three Solidago taxa, depending on the site, with stronger competition from S . canadensis . Moreover, the differences in insect visitation numbers between the hybrid and its parental species were strongly attributed to morphological variations. We assumed that visit duration may be more closely related to successful pollen transfer than the sheer number of insect visits, potentially increasing evolutionary pressure on the hybrid and its native parental species. Furthermore, the similarity of the floral scent between the hybrid and its parental species may enhance interspecific exchange of pollen and thus increase introgression, which may be particularly dangerous for the gene pool and persistence of native populations of S . virgaurea .