Andreas Jürgens

A framework for comparing pollinator performance: effectiveness and efficiency

Measuring pollinator performance has become increasingly important with emerging needs for risk assessment in conservation and sustainable agriculture that require multi‐year and multi‐site comparisons across studies. However, comparing pollinator performance across studies is difficult because of the diversity of concepts and disparate methods in use. Our review of the literature shows many unresolved ambiguities. Two different assessment concepts predominate: the first estimates stigmatic pollen deposition and the underlying pollinator behaviour parameters, while the second estimates the pollinators contribution to plant reproductive success, for example in terms of seed set. Both concepts include a number of parameters combined in diverse ways and named under a diversity of synonyms and homonyms. However, these concepts are overlapping because pollen deposition success is the most frequently used proxy for assessing the pollinators contribution to plant reproductive success. We analyse the diverse concepts and methods in the context of a new proposed conceptual framework with a modular approach based on pollen deposition, visit frequency, and contribution to seed set relative to the plants maximum female reproductive potential. A system of equations is proposed to optimize the balance between idealised theoretical concepts and practical operational methods. Our framework permits comparisons over a range of floral phenotypes, and spatial and temporal scales, because scaling up is based on the same fundamental unit of analysis, the single visit.

Flower scent composition in night-flowering Silene species (Caryophyllaceae)

Abstract Floral scent of 13 night-flowering Silene species (Caryophyllaceae) was collected by headspace adsorption and analysed via gas chromatography and mass spectrometry. Benzenoids together with isoprenoids dominated the scent in all species. Among the benzenoids, benzaldehyde ( Silene subconica 35.5%, Silene succulenta 23.1%, Silene sericea 15.6%, Silene vulgaris 12.2%, and Silene nutans 9.9%), methylbenzoate ( Silene saxifraga 96.1%, S. succulenta 15.2%), benzyl acetate ( Silene dichotoma 37.8%, S. nutans 30.1%, Silene italica 9.0%, and Silene latifolia 5.5%), or benzyl alcohol ( Silene viscosa 36.1%) occur in the largest amounts. p -Cresol is only found in the floral scent of S. dichotoma (28.5%). Among the isoprenoids, monoterpenes occur in the largest amounts (myrcene 23% in Silene chlorantha , trans -β-ocimene 27.2% in S. nutans and 34.9% in S. sericea , fenchyl acetate 12.7% in S. chlorantha , β-linalool 40.5% in S. chlorantha and 14.5% in S. italica ). Relatively high amounts of lilac compounds occur in S. latifolia (49.1%), Silene otites (35.7%), S. subconica (15.2%), and S. vulgaris (59.6%). Higher amounts of sesquiterpenes (isoprenoids) were only found in Silene vallesia with β-bourbonene and γ-muurolene. The vast majority of chemicals identified are common components of a wide array of scented angiosperm flowers. Nevertheless, the results conform most strongly with the findings in other night-blooming and/or moth-pollinated flowers. All investigated Silene species follow the general trend of floral scent compounds typical for moth-pollinated flowers, i.e. flowers having acyclic terpene alcohols (e.g. linalool), aromatic alcohols (benzyl alcohol, 2-phenylethanol) and esters derived from them, and small amounts of nitrogen-containing compounds.

Floral scent compounds of Amazonian Annonaceae species pollinated by small beetles and thrips.

Chemical analysis (GC-MS) yielded a total of 58 volatile compounds in the floral scents of six species of Annonaceae distributed in four genera (Xylopia, Anaxagorea, Duguetia, and Rollinia), Xylopia aromatica is pollinated principally by Thysanoptera and secondarily by small beetles (Nitidulidae and Staphylinidae), whereas the five other species were pollinated by Nitidulidae and Staphylinidae only. Although the six Annonaceae species attract a similar array of pollinator groups, the major constituents of their floral scents are of different biochemical origin. The fragrances of flowers of Anaxagorea brevipes and Anaxagorea dolichocarpa were dominated by esters of aliphatic acids (ethyl 2-methylbutanoate, ethyl 3-methylbutanoate), which were not detected in the other species. Monoterpenes (limonene, p-cymene, alpha-pinene) were the main scent compounds of Duguetia asterotricha, and naphthalene prevailed in the scent of Rollinia insignis flowers. The odors of X. aromatica and Xylopia benthamii flowers were dominated by high amounts of benzenoids (methylbenzoate, 2-phenylethyl alcohol).

Pollen grain numbers, ovule numbers and pollen-ovule ratios in Caryophylloideae: correlation with breeding system, pollination, life form, style number, and sexual system

Abstract. Pollen-ovule ratios (P/O) were measured for 79 species of Caryophylloideae (Agrostemma, Dianthus, Saponaria, Silene, and Vaccaria). We analyzed if these features are best correlated with (1) the breeding system (outcrossing or selfing), (2) diurnal or nocturnal pollination, (3) life form (annual versus perennial), (4) style number, (5) the sexual system (hermaphroditism, gynodioecism, dioecism), or (6) the taxonomy of species. According to the classification of Cruden [(1977) Evolution 31:32–46] most species in the subfamily Caryophylloideae are facultative autogamous or facultative xenogamous. Autogamous or cleistogamous species showed significantly lower P/Os than outcrossing species. We found no differences between night- and day-flowering species; thus from our data diurnal and nocturnal flower visitors may be considered as equally efficient in transferring pollen. However, other factors are also important for the interpretation of P/Os. Pollen grain numbers and ovule numbers were found to correlate with style number, life form, and breeding system. The low P/Os of some dioecious, and therefore obligate outcrossing, species are discussed in relation to morphological traits that improve pollen deposition by pollinators on the stigma, and in relation to different flower numbers of male and female plants.

Flower scent composition in Dianthus and Saponaria species (Caryophyllaceae) and its relevance for pollination biology and taxonomy

Abstract Floral fragrance compounds of seven Dianthus species ( D. arenarius , D. armeria , D. barbatus , D. deltoides , D. monspessulanus , D. superbus, and D. sylvestris ) and one Saponaria species ( S. officinalis ) (Caryophyllaceae) were studied using headspace adsorption technique followed by gas chromatography massspectrometry (GC-MS). The number of compounds (fatty acid derivatives, benzenoids, phenyl propanoids, isoprenoids, and nitrogen containing compounds) identified in the floral odors ranged from 18 to 51 but all were dominated by only 1–3 compounds. Most of the compounds identified in this study have been previously reported in floral scents from species of the closely related genus Silene L. However, the phenyl propanoids eugenol, methyleugenol, methylisoeugenol, cis -asarone, and trans -asarone have formerly not been found in Silene . Based on the measurement of Sorensen’s index of similarity ( I s ) nonmetric multidimensional scaling (MDS) was used to detect meaningful underlying dimensions and to visualize similarities between the investigated species. The MDS analysis showed three groups of species, (1) the diurnal D. armeria , D. barbatus , and D. deltoides are characterized by the predominance of fatty acid derivatives, (2) the closely related nocturnal D. monspessulanus , and D. superbus by high relative amounts of isoprenoids such as cis -β-ocimene and β-caryophyllene, and (3) the species D. arenarius , D. sylvestris and S. officinalis by a predominance of benzenoids, especially methylbenzoate. The results are discussed in relation to pollination, especially by butterflies, moths, and hawkmoths.

Chemical mimicry of insect oviposition sites: a global analysis of convergence in angiosperms

Floral mimicry of decaying plant or animal material has evolved in many plant lineages and exploits, for the purpose of pollination, insects seeking oviposition sites. Existing studies suggest that volatile signals play a particularly important role in these mimicry systems. Here, we present the first large-scale phylogenetically informed study of patterns of evolution in the volatile emissions of plants that mimic insect oviposition sites. Multivariate analyses showed strong convergent evolution, represented by distinct clusters in chemical phenotype space of plants that mimic animal carrion, decaying plant material, herbivore dung and omnivore/carnivore faeces respectively. These plants deploy universal infochemicals that serve as indicators for the main nutrients utilised by saprophagous, coprophagous and necrophagous insects. The emission of oligosulphide-dominated volatile blends very similar to those emitted by carrion has evolved independently in at least five plant families (Annonaceae, Apocynaceae, Araceae, Orchidaceae and Rafflesiaceae) and characterises plants associated mainly with pollination by necrophagous flies and beetles.

Chemical composition of anther volatiles in Ranunculaceae: genera-specific profiles in Anemone, Aquilegia, Caltha, Pulsatilla, Ranunculus, and Trollius species

Anther volatiles of 12 Ranunculaceae species distributed in six genera (Anemone, Aquilegia, Caltha, Pulsatilla, Ranunculus, and Trollius) were investigated by thermal desorption of anthers in quartz microvials inserted into a modified injector. Chemical analysis (GC-MS) yielded a total of 116 compounds from which 103 compounds could be identified. A great diversity of compounds was observed, including aliphatic compounds, aromatics, mono- and sesquiterpenoids, and nitrogen-bearing compounds. Intraspecific variation in the chemical profiles was significantly lower than interspecific variation. Eight compounds explained 96.1% of the observed total variation between the taxa: protoanemonin, octanal, (E,E)-α-farnesene, 2-phenyl ethanol, pentadecane, α-muurolene, phenyl acetaldehyde, and linalool oxide (pyranoid) were either present only in specific taxa or varied greatly in their relative amount between the taxa. An analysis of the scent data using the chord-normalized expected species shared (CNESS) distances of chemical profiles of the species, followed by visualization of the data with nonmetric multidimensional scaling (NMDS) showed that most species belonging to the same genus have similar chemical compositions. The differences in the chemical composition of anther volatiles are discussed with respect to the taxonomy and pollination biology of the species.

Disease Status and Population Origin Effects on Floral Scent: Potential Consequences for Oviposition and Fruit Predation in A Complex Interaction Between A Plant, Fungus, and Noctuid Moth

In the Silene latifolia–Hadena bicruris nursery pollination system, the Hadena moth is both pollinator and seed predator of its host plant. Floral scent, which differs among S. latifolia individuals and populations, is important for adult Hadena to locate its host. However, the success of moth larvae is strongly reduced if hosts are infected by the anther smut fungus Microbotryum violaceum, a pathogen that is transmitted by flower visitors. There were no qualitative differences between the scent of flowers from healthy and diseased plants. In addition, electroantennographic measurements showed that Hadena responded to the same subset of 19 compounds in samples collected from healthy and diseased plants. However, there were significant quantitative differences in scent profiles. Flowers from diseased plants emitted both a lower absolute amount of floral scent and had a different scent pattern, mainly due to their lower absolute amount of lilac aldehyde, whereas their amount of (E)-β-ocimene was similar to that in healthy flowers. Dual choice behavioral wind tunnel tests using differently scented flowers confirmed that moths respond to both qualitative and quantitative aspects of floral scent, suggesting that they could use differences in floral scent between healthy and infected plants to discriminate against diseased plants. Population mean fruit predation rates significantly increased with population mean levels of the emission rates of lilac aldehyde per flower, indicating that selection on floral scent compounds may not only be driven by effects on pollinator attraction but also by effects on fruit predation. However, variation in mean emission rates of scent compounds per flower generally could not explain the higher fruit predation in populations originating from the introduced North American range compared to populations native to Europe.

Inter- and Intraspecific Variation in Floral Scent in the Genus Salix and its Implication for Pollination

The floral scent composition of 32 European and two Asian Salix L. species (Salicaceae) was analyzed. Intra- and interspecific variation was compared for a subset of 8 species. All Salix species are dioecious and floral scent was collected from both male and female individuals by using a dynamic headspace MicroSPE method, and analyzed by GC-MS. A total of 48 compounds were detected, most of them being isoprenoids and benzenoids. Commonly occurring compounds included trans-β-ocimene, cis-β-ocimene, benzaldehyde, d-limonene, α-pinene, cis-3-hexenyl aceatate, linalool, 1,4-dimethoxybenzene, and β-pinene. Two compounds, 1,4-dimethoxybenzene and trans-β-ocimene, were responsible for most of the interspecific variation. In a subset of eight extensively sampled species, six had a characteristic floral scent composition; half of the pairwise species comparisons confirmed significant differences. In three of these eight species, intraspecific variability could be explained by sex differences. Variation in Salix floral scent may provide specific signals that guide pollinators and thus contribute to the reproductive isolation of compatible and cooccurring species.

Naïve and conditioned responses of Culex pipiens pipiens biotype molestus (Diptera: Culicidae) to flower odors

Abstract Flower odors are important signals for chemical communication between plants and flower visitors. Here, we studied the naïve responses of Culex pipiens pipiens biotype molestus Forskal 1775 (Diptera: Culicidae) to typical flower odors and assessed the learning capacity of mosquitoes to floral volatiles. The odor compounds used in the bioassay, phenyl acetaldehyde, veratrole, and 2-methoxyphenol, are typically found in the floral odor of Silene otites (L.) Wibel, a plant that is pollinated by nectar-drinking mosquitoes and moths, and/or in other closely related Silene species. Wind tunnel bioassays with a mixture of these compounds revealed that attraction of mosquitoes to odors was positively correlated with time passed since the last feeding. In single component bioassays, mosquitoes showed strong innate responses to phenyl acetaldehyde and only moderate or weak responses to veratrole and 2-methoxyphenol. Furthermore, in comparison with naïve mosquitoes, conditioned mosquitoes were significantly more attracted to the mixture and single volatiles. These results indicate that naïve mosquitoes are effectively attracted by appropriate floral scent compounds and that learning can increase the attractiveness of these compounds.