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Hybridization can often lead to the formation of novel taxa which can have traits that resemble either or both parental species. Determining the similarity of hybrid traits to parental taxa is particularly important in plant conservation, as hybrids that form between rare and common taxa may more closely resemble a rare parental species, thereby putting the rare parental taxon at further risk of extinction via increased backcrossing and introgression. We investigated the floral (morphological and chemical) traits and orchid mycorrhizal (OrM) fungal associations of the endangered orchid Orchis patens, its more common sister species O. provincialis, and their natural hybrid O. × fallax in natural sympatric populations. We found that both morphological and chemical floral traits of O. × fallax are shared by the parents but are more similar to O. patens than O. provincialis. OrM fungi were shared among all three taxa, indicating that the availability of OrM fungi should not represent a barrier to establishment of individuals of any of these taxa. These results suggest that O. × fallax may be able to expand its distribution within a similar niche to O. patens. This highlights the importance of quantifying differences between hybrids and parental taxon in species conservation planning.

AIM: Interactions with mycorrhizal fungi are increasingly recognized as an important factor underlying the distribution and abundance of orchid species. However, the geographical distribution of orchid mycorrhizal fungi (OMF) and how their communities vary over large geographical areas are less well understood. Because climatic and environmental similarity may decrease with geographical distance or because some OMF have limited dispersal capabilities, similarities in orchid mycorrhizal communities can be expected to decrease with increasing distances separating orchid populations. However, up till now empirical evidence is largely lacking. LOCATION: Eurasia. TAXA: Gymnadenia conopsea (L.) R. Brown and Epipactis helleborine (L.) Crantz. METHODS: High‐throughput sequencing was used to perform a cross‐continental comparison of OMF that associate with two widespread Eurasian terrestrial orchids, Epipactis helleborine and Gymnadenia conopsea. Both phylogenetic and nonphylogenetic measures of community dissimilarity and their components were calculated and related to geographical distances using Mantel tests. RESULTS: Our results showed that in both orchid species similarity in mycorrhizal communities decreased significantly with geographical distance. Decomposing the contribution of spatial turnover and nestedness to overall dissimilarity showed that the observed dissimilarity was mainly the result of species replacement between regions, and not of species loss. Similarly, a strong relationship was observed between phylogenetic community dissimilarity and geographical distance. Decomposing PCD values into a nonphylogenetic and phylogenetic component showed that orchid populations located closely next to each other were likely to contain the same operational taxonomic units (OTUs), but that the non‐shared taxa came from different phylogenetic clades. Species indicator analyses showed that the majority of OMF OTUs were restricted to particular geographical areas. However, some OTUs occurred in both continents, indicating that some fungi have very wide distributions. MAIN CONCLUSIONS: Overall, these results demonstrate that orchid mycorrhizal communities differ substantially across large geographical areas, but that the distribution of orchids is not necessarily restricted by the distribution of particular OMF. Hence, widespread orchid species can be considered mycorrhizal generalists that are flexible in the OMF with which they associate across large geographical areas. ispartof: JOURNAL OF BIOGEOGRAPHY vol:47 issue:2 pages:421-433 status: published

Pollinator taxa may vary in their contribution to plant outcrossing rates and hence differ in their influence on plant fitness. In plants that have ornithophilous floral traits (large, deep-tubed orange-red flowers with dilute nectar), it is expected that birds should be the most effective agents of outcrossing. However, bees often pollinate plants with ornithophilous floral traits and may contribute to their outcrossing. To assess the contribution of bees to outcrossing rates and inbreeding in the rare self-compatible treelet Aloe thraskii, we compared outcrossing rates (t) and adult inbreeding coefficients (F), in bird-excluded and open-pollinated plants. We then tested whether outcrossing rates, and inbreeding depression (δ) estimated using Ritland’s genetic marker-based approach, varied according to bee and bird visitation rates, plant height, flowering population size, population density, and isolation distance across eight populations. Outcrossing rates did not differ between progeny from open-pollinated and bird-excluded inflorescences. Outcrossing rates increased with bee visitation, but not bird visitation. Adult inbreeding coefficients were low (F = 0–0.1), and inbreeding depression estimates were high (δ = 0.59–1). Estimates of inbreeding depression did not vary according to population aggregation. These results highlight the contribution to outcrossing that insect pollinators can make to outcrossing rates of rare plant species that are seemingly adapted for bird pollination.

Nursery pollination is an unusual plant–insect interaction in which an insect is both pollinator and seed predator. Depending on the abundance of the nursery pollinator and of other pollinators, this interaction can range from mutualism to parasitism and it is thus likely to vary geographically. We investigated this mechanism in the widespread species Silene latifolia in a Mediterranean environment that is likely to offer a rich pollinator community to the plant, thus decreasing the dependence on the nursery pollinator. Surprisingly, we found that although generalist pollinators contribute significantly to plant fitness, the nursery pollinator is still the more efficient., Plants involved in specialized pollinator interactions, such as nursery pollination, may experience trade-offs in their female fitness, as the larvae of their pollinators may also consume seeds produced by the flowers they pollinate. These interactions could potentially shift between mutualism and parasitism, depending on the presence and abundance of both the nursery pollinator and of other pollinators. We investigated the fitness trade-off in a Mediterranean plant (Silene latifolia), which has a specialist nocturnal nursery pollinator moth (Hadena bicruris) and is also visited by several diurnal pollinators. We estimated the pollination rates and fecundity of S. latifolia in both natural and experimental populations in the Mediterranean. We estimated natural pollination rates in different flowering times and with presence/absence of the H. bicruis moth. Then by exposing plants to each pollinator group either during the day or at night, we quantified the contribution of other diurnal pollinators and the specialized nocturnal nursery pollinator to plant female fitness. We found no difference in plant fruit set mediated by diurnal versus nocturnal pollinators, indicating that non-specialist pollinators contribute to plant female fitness. However, in both natural and experimental populations, H. bicruris was the most efficient pollinator in terms of seeds produced per fruit. These results suggest that the female fitness costs generated by nursery pollination can be overcome through higher fertilization rates relative to predation rates, even in the presence of co-pollinators. Quantifying such interactions is important for our understanding of the selective pressures that promote highly specialized mutualisms, such as nursery pollination, in the Mediterranean region, a centre of diversification of the carnation family.

We demonstrate that invasive populations of Rhododendron ponticum in Ireland are genetically distinct from ancestral populations in Spain and produce flowers which have wider floral tubes. Although Irish populations are spreading and Spanish ones are declining, we found low genetic diversity among individual plants within populations in both regions, and limited between-population gene flow. Wider floral tubes may have evolved in response to novel pollinators in Ireland. Few studies examine invasive species in both their introduced and native habitats, but this approach is needed to understand invasive species evolution and ecology., Populations of introduced species in their new environments are expected to differ from native populations, due to processes such as genetic drift, founder effects and local adaptation, which can often result in rapid phenotypic change. Such processes can also lead to changes in the genetic structure of these populations. This study investigated the populations of Rhododendron ponticum in its introduced range in Ireland, where it is severely invasive, to determine both genetic and flower width diversity and differentiation. We compared six introduced Irish populations with two populations from R. ponticum's native range in Spain, using amplified fragment length polymorphism and simple sequence repeat genetic markers. We measured flower width, a trait that may affect pollinator visitation, from four Irish and four Spanish populations by measuring both the width at the corolla tip and tube base (nectar holder width). With both genetic markers, populations were differentiated between Ireland and Spain and from each other in both countries. However, populations displayed low genetic diversity (mean Nei's genetic diversity = 0.22), with the largest proportion (76–93 %) of genetic variation contained within, rather than between, populations. Although corolla width was highly variable between individuals within populations, tube width was significantly wider (>0.5 mm) in introduced, compared with native, populations. Our results show that the same species can have genetically distinct populations in both invasive and native regions, and that differences in floral width may occur, possibly in response to ecological sorting processes or local adaptation to pollinator communities.

The net effect of pollen production on fecundity in plants can range from negative – when self-pollen interferes with fecundity due to incompatibility mechanisms, to positive – when pollen availability is associated with increased pollinator visitation and fecundity due to its utilization as a reward. We investigated the responses of bees to pollen and nectar rewards, and the effects of these rewards on pollen deposition and fecundity in the hermaphroditic succulent shrub Aloe tenuior. Self-pollinated plants failed to set fruit, but their ovules were regularly penetrated by self-pollen tubes, which uniformly failed to develop into seeds as expected from ovarian self-incompatibility (or strong early inbreeding depression). Bees consistently foraged for pollen during the morning and early afternoon, but switched to nectar in the late afternoon. As a consequence of this differential foraging, we were able to test the relative contribution to fecundity of pollen- versus nectar-collecting flower visitors. We exposed emasculated and intact flowers in either the morning or late afternoon to foraging bees and showed that emasculation reduced pollen deposition by insects in the morning, but had little effect in the afternoon. Despite the potential for self-pollination to result in ovule discounting due to late-acting self-sterility, fecundity was severely reduced in artificially emasculated plants. Although there were temporal fluctuations in reward preference, most bee visits were for pollen rewards. Therefore the benefit of providing pollen that is accessible to bee foragers outweighs any potential costs to fitness in terms of gender interference in this species.

Hermaphroditism can lead to both intra- and intersexual conflict between male and female gender functions. However, the effect that such gender conflicts have on pollination efficiency has seldom been investigated. By artificially reducing the number of available male gametes on an individual, we quantified whether male interference with pollination efficiency occurs in the self-compatible, moth-pollinated orchid Satyrium longicauda. We partially emasculated S. longicauda inflorescences and compared pollination success and fecundity in these plants to intact controls. Pollen in both groups of plants was colour-labelled so that its dispersal by pollinators could be tracked directly in the field. Intact flowers on partially emasculated inflorescences exported more pollen and received more cross-pollen and less self-pollen than those on intact inflorescences. Proportion of fruit set per plant was similar between the two treatments; however, fruits on partially emasculated plants had proportionally more viable seeds than those on intact controls. These results provide empirical evidence that male interference with pollination efficiency can occur in a hermaphroditic plant and that such interference can compromise fecundity. The most likely mechanism for such male interference is competition for placement on the proboscis of hawkmoth pollinators. Consequently, male competition for siring success may influence the evolution of sexual systems in hermaphroditic pollinator-dependent plants.

Summary Factors underlying the Allee effect are still heavily debated in ecology. For plants that rely on pollinators for seed production, decreases in conspecific aggregation may reduce attractiveness to floral visitors and lead to an Allee effect. However, floral visitors often differ in their pollination effectiveness; hence, the likelihood of an Allee effect in plant fecundity may depend on how various flower visitors respond to plant aggregation. We tested for Allee effects on fecundity of individuals across two years in the self-incompatible perennial, Kniphofia linearifolia Baker (Xanthorrhoeaceae), which has two distinct types of pollinator, birds and native bees. For this, we used three measures of aggregation; population size, density and isolation. We made replicated pollinator observations in populations of various aggregations and quantified fecundity in these populations. To determine the differences in pollinator effectiveness and assess their contribution to fecundity, we selectively excluded bird visitors from K. linearifolia in these populations. We found that population size, but not density or isolation distance, was associated with increased bird abundance and seed set in one of the two years of the study. Bird visitation rate increased with increased plant aggregation within populations. Fruit set and seed set per flower were positively related to bird visitation rate. The difference in seed set per flower between bird-excluded and unmanipulated plants increased with increasing population size. Although birds were much less frequent visitors than bees (on average 2.1 visits plant−1 h−1 compared to 57.5 visits plant-1 h−1), selective exclusion experiments indicated that birds are consistently the more effective pollinators of this species, and therefore most likely to influence fecundity. Synthesis. In this system, characterised by an Allee effect on plant fecundity, birds were the most effective pollinators, responded positively to plant aggregation and were associated with increased fecundity. Therefore, the responses of effective pollinators to plant aggregation may be a factor that underlies Allee effects on plant fecundity.

Density can affect attraction of pollinators, with rare plants receiving fewer pollinating visits compared with more common co-flowering species. However, if a locally rare species is very attractive in terms of the rewards it offers pollinators, it may be preferentially visited. Spiranthes romanzoffiana is a nectar rewarding, geographically rare, endangered orchid species which forms small populations in Ireland, co-flowering with more common, florally rewarding species. We examined visitation rates to S. romanzoffiana and two nectar rewarding co-flowering species (Mentha aquatica and Prunella vulgaris) in the west of Ireland. These three plant species were visited by three bee species (Bombus pascuorum, B. hortorum and Apis mellifera). B. pascuorum was the most common visitor, while A. mellifera was least common. Our results suggest that individual S. romanzoffiana inflorescences compete intraspecifically for visitation from pollinators at high densities. The relationship between visitation to S. romanzoffiana and total floral density appeared to be positive, suggesting interspecific facilitation of pollinator visitation at high densities. Nectar standing crop varied through the season, among species and between open and bagged flowers. Nectar standing crop was not correlated with visitation in S. romanzoffiana. Despite relatively high visitation, S. romanzoffiana produced no mature fruit during this flowering season. The lack of fruit maturation in this species may be a major factor causing its rarity in Europe.