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Climate change may disrupt plant-pollinator mutualisms by generating phenological asynchronies and by altering traits that shape interaction costs and benefits. Our knowledge is limited to studies that manipulate only one partner or focus on either phenological or trait-based mismatches. We assembled communities of three annual plants and a solitary bee prior to flowering and emergence to test how springtime warming affects phenologies, traits, interactions and reproductive output. Warming advanced community-level flowering onset, peak and end but did not alter bee emergence. Warmed plant communities produced fewer and smaller flowers with less, more-concentrated nectar, reducing attractiveness, and warmed bees were more generalized in their foraging, reducing their effectiveness. Plant-bee interactions were less frequent, shorter and peaked earlier under warming. As a result, warmed plants produced fewer, lighter seeds, indicating pollinator-mediated fitness costs. Climate change will perturb plant-pollinator mutualisms, causing wide-ranging effects on partner species and diminishing the ecosystem service they provide.

International audience; Cuckoo bumblebees are a monophyletic group within the genus Bombus and social parasites of free-living bumblebees, upon which they rely to rear their offspring. Cuckoo bumblebees lack the worker caste and visit flowers primarily for their own sustenance and do not collect pollen. Although different flower-visiting behaviours can be expected between cuckoo and free-living bumblebees due to different biological constraints, no study has yet quantified such differences. Here, we provide the first empirical evidence of different flower-visiting behaviours between cuckoo and free-living bumblebees. We recorded the flower-visiting behaviour of 350 individual bumblebees over two years in a wild population of the entomophilous plant Gentiana lutea, of which they are among the main pollinators. In cuckoo bumblebees (28.9% of the total), we only found males, while we found both workers and males in free-living bumblebees. Cuckoo bumblebees visited significantly more flowers for longer time periods than both free-living bumblebee workers and males within whorls, while differences at the whole-plant level were less marked. Free-living bumblebee males visited more flowers and performed slightly longer flower visits than workers. Behavioural differences between cuckoo male bumblebees and free-living bumblebee workers are likely related to different foraging needs, while differences between cuckoo and free-living bumblebee males may be caused by differences in colony development and a delayed mating period of free-living bumblebees. The longer visits made by cuckoo male bumblebees will likely negatively affect plant reproductive success through increased within-plant pollen flow.

International audience

Floral nectar is the primary reward directly consumed by floral visitors and its chemical composition affects their behaviour and fidelity. In turn, floral visitors are expected to alter floral nectar composition directly or indirectly through the introduction of external contaminants, such as pollen grains and microorganisms. To understand the effect of exogenous factors on nectar chemistry, we investigated the modifications of nectar sugar and amino acid composition in relation to floral visitors in the perennial herb Gentiana lutea. We quantified nectar contamination by floral visitors through visitor exclusion experiments in the field, estimating pollen and yeast concentration in visited flowers and in uncontaminated nectar at two different flower stages (flower bud and older open flowers). We then assessed changes in the composition and concentration of sugars and both protein and non-protein amino acid in the nectar. We found clear differences in the chemical composition of flower nectar in relation to flower stage and floral visitation. Nectar sugar and amino acid concentrations were significantly higher in older flowers than in flower buds. In addition, nectar sugar concentration was significantly higher in older flowers where visitors were excluded than in visited flowers. On the contrary, amino acid concentration was comparable between visited and non-visited older flowers. We also found that pollen contamination enriched the amino acid profile of the host nectar both quantitatively and qualitatively. Finally, nectar exposed to floral visitors showed a higher number of yeast cells than unvisited flowers although too low to cause the observed changes in the glucose:fructose ratio, suggesting the presence of fructose-related bacteria. Our results show that the chemical composition of floral nectar is altered by several endogenous and exogenous factors in a complex process of ecological relations, and suggest that the modulation of floral visitation through nectar is not solely related to the plant itself.

The decline of pollinators may alter the complex system of interactions that they establish with flowering plants, with potential negative consequences on both partners. Within this context, network analysis may be a useful tool to study ecological properties of plant-pollinator interactions and to evaluate the outcomes of conservation actions. Three conservation measures were implemented within the European LIFE + PP-ICON project to support the local pollinator community of a population of the rare plant Dictamnus albus in a protected area near Bologna, Italy. Artificial nesting sites were installed to support solitary bees, populations of native plants were reinforced to increase foraging resources for pollinators, and colonies of bumblebees reared from wild queens were released in the study area. In this work we evaluate the effects of these conservation actions on plant-pollinator networks over a period of four years, comparing a pre- (2011–2012) and a post-conservation (2013–2014) action period. The overall network generalisation increased after the implementation of conservation measures and interactions were more evenly distributed. Module composition significantly changed between the two periods, showing a marked rewiring of interactions. D. albus was a module hub both before and after conservation actions, thus emerging as an important node within its own module. In addition, some plant and pollinator species directly targeted by conservation measures became module connectors, highlighting their increased importance in linking different modules. Finally, the reinforcement of plant and pollinator populations led to increased flower visitation. These results indicate that conservation actions affected species both directly and indirectly and that the network of interactions has potentially increased its robustness and resilience towards possible species loss. This study highlights ways in which network analysis can be used to measure changes in plant-pollinator interactions in response to conservation actions.

Thisfile contains the main text of the article "Cuckoo bumblebees perform slower and longer flower visits than true bumblebees".

Report of the catches made by the European bee determination training (COST Super-B Project) in the Calanques National Park.

International audience; Urbanization is one of the major threats to wild plants and pollinators, and its global increase demands a better understanding of the mechanism driving its negative impact. Urban warming and altered local environmental conditions have the potential to affect the timing of flowering and of pollinator activity. While previous evidence has shown that plant phenology tends to advance in urban areas, little is known about its effects on pollinator phenology. In this study we simultaneously assessed the response of the timing of flowering of native plants and of the flight period of wild pollinators to increased urbanization. We collected data from 12 sites along an urbanization gradient in northern France, a region under strong anthropogenic pressure. Overall, we recorded more than 70 plant species, and we sampled more than 4300 wild bees and hoverflies belonging to 154 species. Plant flowering showed a strong response to urbanization at the community level with a striking advancement of the flowering peak in sites at high urbanization. On the contrary, pollinator communities did not show any clear shift of their flight phenology along the gradient, neither regarding abundance nor diversity. Our results indicate that phenologies of plant and pollinator communities can respond differently along the same urbanization gradient. These asymmetric responses can drive modifications in the structure of plant–pollinator networks, and potentially negatively affect the fitness of both mutualistic partners.

Gentiana lutea L. (yellow gentian, Gentianaceae) is a protected orophyte of central and southern Europe, mainly threatened by the uncontrolled collection of its rhizome, used in traditional medicine and for liquor production. The species is self-compatible, but outcrossing mediated by pollinators is needed to obtain a viable progeny. In this study, we considered five natural populations belonging to the four subspecies of G. lutea. We performed controlled pollinations in the field (self- versus cross-pollination) followed by seed germination tests in laboratory conditions, adding a solution of gibberellic acid, in order to evaluate the seed performance. A cumulative index of inbreeding depression was calculated considering maternal reproductive output as well as seed performance traits. Seed weight and seed germination performance was similar between seeds resulting from naturally pollinated and pollen-augmented flowers and higher compared to selfed flowers, highlighting a disadvantage of selfing and the importance of cross-pollen transfer in natural conditions. However, in the small and isolated population of G. lutea subsp. symphyandra on Mt Grande we found a general reduction in seed germination rate, likely due to increased selfing or mating among close relatives as a consequence of a severe bottleneck. We discuss our results with regards to implications for conservation practices.

Generalist flowers are visited by a broad variety of insects that function as pollinators, occasional visitors and as pollen and/or nectar robbers. Moreover, among legitimate pollinators the pollination efficiency can be different. Nectar greatly affects visitor behaviour and fidelity to a certain species, influencing plant reproductive effort. In this study we have investigated a generalist system (Gentiana lutea L.), examining the role of flower visitors and quantifying the contribution of each pollinating taxon in three natural populations. In order to verify the level of generalization, we introduce an index of Pollinator Performance (PoP), based on insect visitation rate and cross-pollen transport efficiency. Our results confirm the high degree of pollinator-generalization of the study species. Nevertheless, flower visitors show various degree of pollinating performance, mainly defined by their sedentary versus dynamic behaviour. Sedentary insects enhance geitonogamous pollen transfer, which results in reduced seed set and pollen limitation. In particular, an unusual sluggish behaviour was observed in bumblebees feeding on nectar. The hexose-rich abundant nectar offered by G. lutea flowers is remarkably rich in proline and β-alanine amino acids: this composition presumably influences feeding choice and insect dynamism, likely exerting a narcotic effect on pollinators. The consequences on plant fitness are discussed in an evolutionary perspective.

International audience; Understanding the population dynamics of rare and endangered plant species is essential to elaborate correct management plans for their conservation. Demographic monitoring of individual species provides valuable information here. However, demographic studies are limited to species for which one can follow individuals through their life history. They are also time consuming, making it difficult to make simultaneous studies of several species with different populations in order to have a more general assessment of rare species dynamics in a given region. In this paper, we illustrate how the use of an approach based on transition frequencies allows for the simultaneous study and comparison of trends in 32 populations of six species with very different life histories and growth forms in the Mediterranean region of the South of France. The results show significant effects of spring rainfall deficit on annual population dynamics but not for perennial species that show a delayed response, and illustrate population declines due to direct human impacts on populations in the study region. Our study illustrates the alarming overall vulnerability of populations and is simple and rapid to apply in a multi-population and multi-species context. It could thus be used by conservation management staff to construct assessments of population vulnerability elsewhere.

Background: Taxonomic analysis provides a basic understanding for taxon identification and contributes to preliminary information for several branches of applied biology, while studies on reproductive strategies and plant fitness are essential to interpret population status and dynamics. Aims: We tested the reliability of diagnostic characters for identification and to characterise sexual resource allocation, the breeding system and seed predation among subspecies of Gentiana lutea. Methods: We analysed morphological characters in 70 herbarium specimens. In five natural populations we counted pollen and ovule numbers, assessed reproductive output after pollination treatments and evaluated pre-dispersal predation. Results: Taxonomic traits previously indicated as diagnostic were not sufficient to discriminate among subspecies. The pollen number and pollen:ovule (P:O) ratio varied strongly among subspecies; self-pollinated flowers produced a significantly lower number of seeds than open-pollinated flowers. Retention of empty fruits and high levels of pre-dispersal seed predation were observed in every case. Conclusions: The variation of P:O ratios among subspecies suggests different efficiency in pollen transfer. The species is self-compatible, nevertheless all subspecies require pollen vectors to enhance cross pollination and viable seed production. Fruit retention may have evolved as a strategy to reduce predation, ensuring higher plant fitness.

International audience; Urbanisation is one of the main drivers of landscape modification, as vegetation andopen lands are replaced by paved surfaces, roads and buildings. These changes imply thephenomenon of urban heat islands – urban and suburban areasshow increased temperaturescompared to their rural surroundings. However, its influences on flowering period and polli-nator activity remains poorly investigated.We surveyed 12 meadows managed by local practitioners with standardised native seed mixesin the M ́etropole Europ ́eenne de Lille (northern France). Sites were selected according to anurban gradient (three urbanisation levels, based on the proportion of impervious areas withina 500m radius), and were visited bi-weekly from April 4th to June 29th 2017.We estimatedthe flowering abundance at all sites at any given observation period. At the same time, wesampled pollinators (bees and hoverflies) using pan traps and hand net. We estimated theeffects of sampling day and urbanisation level on flower cover and pollinator activity usingGLMMs.Urbanisation had a strong effect on average flowering phenology of the whole plant commu-nity. In medium and high urbanisation sites, flowering peak occurred respectively 7 and 30days earlier, compared to rural areas. Similar patterns were found for the most commonflowering species. Our results also suggest that flowering duration has increased in urbanareas. We observed phenological shifts of pollinators as urbanisation increased. Bumblebeesexperienced a similar advance of activity in moderately and highly urbanised sites, comparedto rural sites. Likewise, we observed an advancement of the activity of some solitary bees(Halictidae) in urban areas. We are currently analysing data regarding the other bee andhoverfly taxa found during the study. We will discuss the possible effects of phenology shiftson plants and pollinators, and their consequences in relation to temporal mismatches amongspecies

Bees collect pollen as an important resource for offspring development while acting as pollen vectors for the plants visited. Foraging preferences of pollinators together with plant species availability shape the web of interactions at the local scale. In this study, we focused on the bee pollinator community of a population of the rare protected perennial herb Dictamnus albus, with the aim to characterise the pollen preferences and the foraging niche overlap among species through time. Bees were sampled during four consecutive years in a natural population of D. albus, throughout the blooming period of the plant species. We performed an analysis of insect pollen loads to investigate the interactions with the study species and the co-flowering plants in the area, and to evaluate the degree of foraging overlap among pollinators. Over the study years, all bee species showed a high fidelity to D. albus (60–80%), even if some taxa preferentially collected pollen from other flowering species. The foraging niche overlap in the pollinator community decreased together with an increased diversity of co-flowering plant species. The results obtained indicate that bees preferentially forage on D. albus in the studied area, but that co-flowering species contribute to complement their diet and likely reduce competition for foraging resources. It appears therefore important to maintain a high diversity of co-flowering plants to preserve the diversity in the studied pollinator community of D. albus.

International audience; AbstractInbreeding is caused by the mating of closely related individuals and may produce a decrease in the fitness of offspring and have deleterious consequences for adults. In haplodiploid social Hymenoptera inbreeding has a further negative effect due to the production of unviable or sterile diploid males. As a consequence, mechanisms of inbreeding avoidance would be expected to evolve. In this study, we investigated the mating choice between related (inbred) or unrelated (outbred) gynes and males of Bombus terrestris reared in laboratory conditions by performing cage and tunnel experiments. Not only did we find no mating preference for related or unrelated partners (mating success 41.55 ± 3.7 and 39.69 ± 4.4%, respectively), but the mating latency was even shorter in inbred (6.97 ± 0.6 min) than in outbred matings (8.74 ± 0.8 min). We hypothesize that in wild populations of B. terrestris, the lack of incest avoidance could be compensated by tolerance of high levels of inbreeding.

International audience; Diapause control and colony initiation are among the major problems encountered in the rearing of bumble bee colonies in small-scale rearing. In this study, we used Bombus terrestris queens obtained from commercial colonies to investigate (1) the diapause survival in virgin and mated queens, (2) the diapause and colony initiation performance of mated bumble bee queens in relation to the pre-diapause weight and (3) the effect of pupae’s sex on colony initiation. We found that diapause survival is negatively affected by mating and by the low pre-diapause weight, but first egg deposition and development of the first adult worker were delayed in heavy queens. We found no significant differences in the egg-laying success in relation to pupae’s sex; however, queens stimulated with queen pupae laid more eggs per cell and developed a first brood larger than those stimulated with male pupae. Our results can be useful in small-scale rearing, including the rearing of wild queens for conservation purposes.

Disassortative mating in distylous self-incompatible species should result in the equilibrium of morph types in natural populations. Deviation from isoplethy may affect pollen transfer, and in isolated populations it could lead to Allee effect and genetic drift. Pollen limitation has been found to occur in several distylous species, for which mating opportunities are actually reduced to half population. In this study, we investigated the reproductive features and pollination ecology of the narrow endemic Primula apennina. We recorded equilibrium of morph frequencies in the studied population, reflecting the comparable fecundity found in the two morphs. Long-styled flowers produce more pollen grains of smaller size than short-styled ones: we hypothesize that in thrum flowers, pollen is more easily removed by the insect pollinator Macroglossum stellatarum, resulting in equal pollen amounts carried to both short styles and long styles. This lower pollen transfer efficiency from long-styled to short-styled flowers is also reflected in legitimate pollen-ovule ratio values. Despite results show no evidence of imminent threats to population persistence at study site, the strict dependence on one or very few pollinator species, and ecological traits, may increase extinction risks in the long-term period.

Plants with multiple flowers could be prone to autonomous self-pollination and insect-mediated geitonogamy, but physiological and ecological features have evolved preventing costs related to autogamy. We studied the rare perennial herb Dictamnus albus as a model plant, with the aim of describing the plant-pollinator system from both plant and pollinator perspectives and analysing features that promote outcrossing in an entomophilous species. The breeding system and reproductive success of D. albus were investigated in experimental and natural conditions, showing that it is potentially self-compatible, but only intra-inflorescence insect-mediated selfing is possible. Nectar analysis showed gender-biased production towards the female phase, which follows the male phase, and during flowering, full blooming is found in flowers at the bottom of the raceme. Among a wide spectrum of insect visitors, three genera (Bombus, Apis, Megachile) were found to be principal pollinators. A study of insect behaviour showed a tendency towards bottom-to-top flights for the most important pollinators Bombus spp. and Apis mellifera: upward movements on the racemes could be explained by foraging behaviour, from more to less rewarding flowers. In accordance with the 'declining reward hypothesis', bumblebees and honeybees leave the plant when gain of reward is low, after which few flowers are visited, reducing the chance of self-pollen transfer among flowers. Intra-flower self-pollination is prevented in D. albus by protandry and herkogamy, while the nectar-induced sequential pattern of pollinator visits avoids geitonogamy and tends to maximise pollen export, promoting outcrossing. All these features for preventing selfing benefit plant fitness and population genetic structure.

Knowledge about mixed mating systems can improve our understanding of the evolutionary dynamics of reproductive systems. Here we report a study of the floral and reproductive biology of Hypericum elodes, an Atlantic-European soft-water pools specialist which shows a floral architecture consistent with both self- and cross-pollination. Controlled pollination experiments were performed in a natural population during three consecutive years. Marked flowers were monitored until fruit production, and laboratory germination experiments were conducted with the seeds produced. Plants were self-compatible (SCI>0.75), however, compared with selfing, cross-pollination enhanced fruit-set, seed-set and seedling growth, but not seed germination. Inbreeding depression (δ) was mild in the pre-dispersal stages (δ = 0.22 for fruit set, 0.18 for seed set and 0.13 for seed mass), low for germination percentage (δ = 0.003) and mild for seedling growth (δ = 0.23). The breeding system of H. elodes promotes outcrossing and assures reproductive success by means of competitive autogamy. Our results suggest a mixed mating strategy for the studied population, characterized by mild inbreeding depression (cumulative δ = 0.57), highlighting the benefit of this reproductive mode in unpredictable habitat, as the typical shallow-water meadows where H. elodes grows.

The interplay between insect and plant traits outlines the patterns of pollen transfer and the subsequent plant reproductive fitness. We studied the factors that affect the pollination efficiency of a pollinator community of Dictamnus albus L. by evaluating insect behaviour and morphological characteristics in relation to flowering phenology. In order to extrapolate the pollinator importance of single taxa and of the whole pollinator guild, we calculated an index distinguishing between potential (PPI) and realized (RPI) pollinator importance. Although the pollinator species spectrum appeared rather constant, we found high intra- and inter-annual variability of pollinator frequency and importance within the insect community. Flower visitation rate strictly depended on insect abundance and on the overlap between their flying period and flower blooming. All the pollinators visited flowers from the bottom to the top of the racemes, excluding intra-plant geitonogamous pollination, and most of them showed high pollen fidelity. Only medium large-sized bees could contact the upward bending stiles while feeding on nectar, highlighting a specialisation of the plant towards bigger pollinators. Moreover, we found evidence of functional specialisation, since all pollinators were restricted to a single taxonomic group (order: Hymenoptera; superfamily: Apoidea). Both the PPI and RPI indices indicate Habropoda tarsata as the most important pollinator of D. albus. Following hand cross-pollination experiments we revealed the presence of pollination limitation in 1 of the 3 years of field study. We discuss this result in relation to flowering abundance and to possible mismatches of phenological periods between plants and insects.

In self-incompatible clonal plants, the spread of individual plants can exacerbate mate limitation to the point that it becomes a serious constraint on long-term population persistence, especially in small, isolated populations. In such species, it may be necessary to introduce new genetic material from other populations to restore seed production, a strategy termed “genetic rescue”. In this study we assess the potential pertinence of such genetic rescue in the clonal perennial plant Convolvulus lineatus L., whose populations are often highly reduced in spatial extent and are currently being fragmented by land development projects in Mediterranean France. To do so, we quantify fruit production in a range of populations of different size over four years and perform a series of hand-pollination experiments in natural populations to assess whether fruit set is limited by mate availability. We found that C. lineatus is a self-incompatible species that shows extremely low values of fruit set in natural populations and that a principal cause of this low fruit set is a lack of compatible pollen. This may be primarily due to clonal spread that causes individual populations to be comprised of patches containing one or very few incompatibility types. In small populations fragmented by human activities and which show an absence of fruit production, we thus argue that genetic rescue represents a promising conservation management strategy to avoid inevitable long-term future population decline. We discuss how best to introduce new genetic material into the study populations.

none 6 no In many species, inbreeding avoidance mechanisms prevent mating between close relatives, but these mechanisms are poorly studied in bumble bees. The probability of inbred matings within a colony in eusocial insects may depend on the timing of gyne and male emergence and on their sex ratio. In this study, we compared the development of 35 colonies of the bumble bee Bombus terrestris from founding to the emergence of the last gyne, and we investigated the probability of inbred mating in colonies with fertile newborn gynes and males. We calculated a novel colony inbreeding risk index (IRI), which considers the overlap period between fertile gynes and males, their numbers, and the colony sex ratio. We found that the IRI values were strictly correlated with the time elapsed between the gyne point and the switch point (i.e., from the moment of deposition of the first diploid egg that produces a gyne to the first haploid egg). We separated the colonies into two groups based on the mean value of the IRI: colonies with low IRI produced more gynes (93.8 ± 9.4), for a longer period (32.1 ± 1.8 days) and with a lower percentage of overlapped gynes (69 ± 5%) than colonies with high IRI (57.1 ± 21 gynes, 23.3 ± 2.9 days, and 100% overlapped gynes, respectively). A low IRI is connected to a reduced risk of inbred mating, while colonies with a high IRI may be advantaged in conditions of isolation, in case of the absence of non-related reproducers. Inbreeding risk index proved to be a good indicator of the colony reproductive strategy. none Gherardo Bogo; Natasha de Manincor; Alessandro Fisogni; Marta Galloni; Laura Zavatta; Laura Bortolotti Gherardo Bogo; Natasha de Manincor; Alessandro Fisogni; Marta Galloni; Laura Zavatta; Laura Bortolotti

Several biotic and abiotic factors affect the seasonal and daily activities of flower-visiting insects, which, ultimately, influence the composition and abundance of a pollinator community and the extent of their pollination service. The aim of this four-year study was to assess the effect of some abiotic and biotic factors on the abundance and activity pattern of flower-visiting insects throughout the blooming of a locally rare plant species, Dictamnus albus L. (Rutaceae). We found a large inter-annual variation in the abundance and activity of flower visitors, with up to a six-fold variation in the total number of individual insects observed. Moreover, a similar fluctuation among years was also highlighted by biodiversity indices and by the changes in the relative frequency of each flower-visiting taxon. Annual, seasonal and daily variations were explained by a certain level of “response diversity” between flower-visiting taxa in relation to different environmental conditions during D. albus blooming. The foraging activity was related to ambient temperature in the tribe of Halictini and to relative humidity in four flower-visiting taxa (positive relation in the tribe Anthophorini; negative relation in the taxa Megachilini, Halictini and Syrphidae). The climate conditions during the winter might have also affected the phenology and the abundance of flower-visiting taxa with a large number of insects observed in warmer years. Among the biotic factors, flower availability did not affect the abundance of insects observed in the patch. Moreover, we did not find any significant negative associations (e.g. possible competition) in the co-occurrence of different flower visiting taxa, instead we found six significant positive associations probably related to similar preferences towards specific environmental conditions. In conclusion, our results show that the flower visitor community of D. albus is quite variable among years, seasons and daily hours, but the relative high visitor diversity and the different patterns of activity related to different environmental responses might guarantee a stable pollination service of this plant species in years with extreme environmental conditions.