Labial Gland Secretions Research Articles

Evolution of Acquired Perfumes and Endogenous Lipid Secretions in Orchid Bees.

Male orchid bees are unique in the animal kingdom for making perfumes that function as sex pheromone. Males collect volatile chemicals from the environment in the neotropical forests, including floral and non-floral sources, creating complex but species-specific blends. Male orchid bees exhibit several adaptations to facilitate perfume collection and storage. When collecting volatile compounds, males apply lipid substances that they secrete from cephalic labial glands onto the fragrant substrate. These lipids help dissolve and retain the volatiles, similar to the process of 'enfleurage' in the traditional perfume industry. We investigated how the chemical composition of acquired perfume and labial gland secretions varied across the phylogeny of orchid bees, including 65 species in five genera from Central and South America. Perfumes showed rapid evolution as revealed by low overall phylogenetic signal, in agreement with the idea that perfume compounds diverge rapidly and substantially among closely related species due to their role in species recognition. A possible exception were perfumes in the genus Eulaema, clustering closely in chemospace, partly mediated by high proportions of carvone and trans-carvone oxide. Labial gland secretions, in contrast, showed a strong phylogenetic signal at the genus level, with secretions of Eufriesea and Exaerete dominated by fatty acids and Eulaema dominated by saturated acetates of chain lengths 12 to 16 C-atoms. Secretions of the majority of Euglossa were heavily dominated by one unsaturated long chain diacetate, (9Z)-Eicosen-1,20-diyldiacetate. However, we also identified few highly divergent species of Euglossa in four subclades (11 species) that appear to have secondarily replaced the diacetate with other compounds. In comparison with environment-derived perfumes, the evolution of labial gland secretion is much slower, likely constrained by the underlying biochemical pathways, but perhaps influenced by perfume-solvent chemical interactions.

Anticholinergic burden of medications is associated with dry mouth and reflected in minor labial gland secretion

ObjectiveMedications with anticholinergic potential inhibit saliva secretion. Polypharmacy potentiates anticholinergic burden, causing dry mouth symptoms and chronic deterioration of oral health. Patients of any age can be affected by anticholinergic medication-triggered hyposalivation (the objective measure of dry mouth); therefore, seeking predictions of hyposalivation to screen dry mouth is needed. DesignIn our prospective, cross-sectional clinical study, 55 middle-aged adult patients participated. We examined whether the anticholinergic burden calculated from anticholinergic medications (anticholinergic drug score; ADS) and blood serum anticholinergic activity (SAA; the gold standard measure of anticholinergic burden) is associated with hyposalivation. As no prior studies measured minor salivary glands regarding the quantifiable anticholinergic burden, we assessed hyposalivation by the minor saliva flow (MSF) and unstimulated whole saliva (UWS) secretion. ResultsOur data showed a negative linear relationship between SAA and UWS (p < 0.05); when SAA increases by one pmol/ml unit, the saliva flow decreases by 0.058 ml/min. MSF showed a linear correlation (p < 0.005) with UWS. In a multivariate logistic regression model (including age, gender, race, smoking status, xerostomia severity, ADS, and BMI), we identified SAA and age as predictors of hyposalivation (p < 0.05). ConclusionsWe provide evidence for the significant relationship between measurable anticholinergic burden and saliva flow. The correlation between UWS and MSF suggests that both saliva flow rate measurement methods could reflect anticholinergics-induced changes in salivary health.

A Gland of Many Uses: a Diversity of Compounds in the Labial Glands of the Bumble Bee Bombus impatiens Suggests Multiple Signaling Functions.

Communication in social insect colonies depends on signals accurately reflecting the identity and physiological state of the individuals. Such information is coded by the products of multiple exocrine glands, and the resulting blends reflect the species, sex, caste, age, task, reproductive status, and health of an individual, and may also contain caste-specific pheromones regulating the behavior and physiology of other individuals. Here we examined the composition of labial gland secretions in females of the bumble bee Bombus impatiens, of different castes, social condition, age, mating status, and ovarian activation. We show that active queens, gynes, and workers each produce caste-specific compounds that may serve different communicative functions. The composition and amounts of wax esters, mostly octyl esters produced by active queens, differed significantly between castes, mating, and social conditions, suggesting a social signaling role. Farnesyl esters were predominant in gynes and peaked at optimal mating age (6-10days), suggesting their possible roles as sex pheromone components. Reproductive status of females and age across castes was reflected by the ratio between short- and long-chain hydrocarbons, suggesting that these compounds may serve as fertility signals. Our findings overall suggest that the labial gland composition in B. impatiens reflects different facets of female physiology. While further bioassays are required to determine the functions of these compounds, they are likely to have important roles in communication between individuals.

A novel diagnostic technique of measuring labial minor salivary gland secretions using sodium fluorescein dye: Implications for patients with dry eyes

ABSTRACT Purpose: To evaluate the lower labial minor salivary glands (MSGs) flow rate using fluorescein dye in healthy individuals and patients with Sjögren’s syndrome (SS) and Stevens–Johnson syndrome (SJS). Methods: Thirty consecutive patients with SS (N = 15; mean age 35.7 years) and SJS (N = 15; 57.7 years), and their age- and sex-matched healthy controls (N = 40; mean ocular surface disease index (OSDI) = 6.1) had ocular examination and whole lower labial mucosa evaluation after ophthalmic fluorescein strip application under cobalt blue light. Analyzed parameters include average labial distribution of functional MSGs, their secretory flow rate, and comparison between healthy and diseased groups. Results: The mean salivary flow rate from the lower labial MSGs of normal individuals showed decade-wise decline (2.7 ± 0.29 l/min, 2.6 ± 0.39 l/min, 2.3 ± 0.6 l/min, 1.9 ± 0.95 l/min) with similar trend for the number of secreting MSG openings (38.7, 37.2, 30, 22). The mean OSDI score was 45.3 in SJS and 28.2 in SS group. Thirty eyes in each SS and SJS group had mean Schirmer I value of 1.5 ± 2.2 mm and 5.1 ± 4.4 mm. The mean lower labial salivary flow rate in SS group was 0.5 ± 0.28 l/min, and 2.0 ± 0.95 l/min in SJS group. When compared to normal, SS patients had a significant reduction in the flow rate (p < .00001); however, it was not significant for the SJS group (p = .28). The mean number of secreting MSG openings was reduced in both the groups compared to normal (SJS, 20.5; p = .01 and SS, 12; p < .0001). There was a significant difference between SS and SJS groups in terms of flow rate (p < .00001) and number of MSG openings (p = .001). The MSG flow rate and Schirmer values did not show any correlation in SS or SJS patients. Conclusion: The fluorescein-assisted evaluation of the lower lip can be used as a quantitative method for measuring the labial salivary flow rate in SS and SJS patients.

Resolving the species status of overlooked West‐Palaearctic bumblebees

AbstractMultisource approaches in taxonomy gather different lines of evidence in order to draw strongly supported taxonomic conclusions and constitute the basis of integrative taxonomy. In the case of overlooked taxa with disjunct distributions for which sampling is more challenging, integrative approaches help to propose stable hypotheses at the species and subspecies levels. Here, based on genetic and semio‐chemical traits, we performed an integrative taxonomic analysis to evaluate species delimitation hypotheses within a monophyletic group of bumblebees (Hymenoptera, Apidae, Bombus) including the formerly recognised subgenera Eversmannibombus, Laesobombus and Mucidobombus which are now included in the subgenus Thoracobombus. Our results demonstrate the conspecificity of several polytypic taxa, and we formally recognise the subspecies Bombus laesus aliceae comb. nov. Cockerell, 1931, endemic to North Africa, based on its allopatry, unique mitochondrial haplotype and divergent cephalic labial gland secretions. This highlights the need to maintain studying polytypic complexes of bumblebee taxa for which phylogenetic relationships could be still entangled and eventually implement conservation strategies for taxonomically differentiated lineages.

Cabbage looper (Trichoplusia ni Hübner) labial glands contain unique bacterial flora in contrast with their alimentary canal, mandibular glands, and Malpighian tubules

In recent years, several studies have examined the gut microbiome of lepidopteran larvae and how factors such as host plant affect it, and in turn, how gut bacteria affect host plant responses to herbivory. In addition, other studies have detailed how secretions of the labial (salivary) glands can alter host plant defense responses. We examined the gut microbiome of the cabbage looper (Trichoplusia ni) feeding on collards (Brassica oleracea) and separately analyzed the microbiomes of various organs that open directly into the alimentary canal, including the labial glands, mandibular glands, and the Malpighian tubules. In this study, the gut microbiome of T. ni was found to be generally consistent with those of other lepidopteran larvae in prior studies. The greatest diversity of bacteria appeared in the Firmicutes, Actinobacteria, Proteobacteria, and Bacteriodetes. Well‐represented genera included Staphylococcus, Streptococcus, Corynebacterium, Pseudomonas, Diaphorobacter, Methylobacterium, Flavobacterium, and Cloacibacterium. Across all organs, two amplicon sequence variants (ASVs) associated with the genera Diaphorobacter and Cloacibacterium appeared to be most abundant. In terms of the most prevalent ASVs, the alimentary canal, Malpighian tubules, and mandibular glands appeared to have similar complements of bacteria, with relatively few significant differences evident. However, aside from the Diaphorobacter and Cloacibacterium ASVs common to all the organs, the labial glands appeared to possess a distinctive complement of bacteria which was absent or poorly represented in the other organs. Among these were representatives of the Pseudomonas, Flavobacterium, Caulobacterium, Anaerococcus, and Methylobacterium. These results suggest that the labial glands present bacteria with different selective pressures than those occurring in the mandibular gland, Malpighian tubules and the alimentary canal. Given the documented effects that labial gland secretions and the gut microbiome can exert on host plant defenses, the effects exerted by the bacteria inhabiting the labial glands themselves deserve further study.

The arctic and alpine bumblebees of the subgenus Alpinobombus revised from integrative assessment of species’ gene coalescents and morphology (Hymenoptera, Apidae, Bombus)

The bumblebees of the subgenus Alpinobombus of the genus Bombus are unusual among bees for specialising in many of the most northerly vegetated arctic habitats on Earth. Most named taxa in this group (37 available names from a total of 67 names) were described originally from differences in the colour patterns of the hair. Previous revisions have shown unusually little agreement, recognising a range of 6‒9 species, in part because of pronounced intraspecific variation in both skeletal morphology and in the colour patterns of the hair. Here we examine variation among 4622 specimens from throughout the group's global range. Bayesian inference of the gene tree for the fast evolving mitochondrial COI gene combined with Poisson-tree-process analysis of this tree shows support for 10 gene lineages as candidates for being putative species lineages. Integrative assessment shows that the interpretation of these results is not straightforward. Evidence from the fast evolving mitochondrial 16S ribosomal RNA gene supports two of the COI gene alleles (from the samples B. kluanensis s. str. and 'unnamed2') as being associated with just one 16S allele. Double COI bands on the PCR gels for these individuals and double peaks on sequence traces (in one case with both COI alleles sequenced from one individual) identifies this as a likely case of COI paralogy that has resulted in mitochondrial heteroplasmy. Evidence from morphology also supports only the remaining nine lineages as separate. Evidence from extracts of cephalic labial gland secretions (CLGS, with components believed to function as sex pheromones) reported by others shows small diagnostic differences between all of the candidate species examined (although B. kluanensis s. l. was not examined) and shows larger differences between all of the species pairs that we find are likely to have co-occurred at least in the past, revealing a likely limitation to the CLGS approach in cases of recent and continuously allopatric species. Consequently we infer nine species in the subgenus Alpinobombus (so that B. kluanensis s. str. and 'unnamed2' are interpreted as conspecific, as B. kluanensis s. l.). We provide distribution maps and identification keys for the nine species. The morphology of the male of B. kluanensis is described for the first time, including a unique, unusually dense pad of short hair on the mandible that may have a function involving CLGS in mate-searching behaviour. In seeking to identify the valid names for these species, seven new lectotypes are designated and support is provided for synonymizing 10 names as proposed in a recent summary table of names. The prevailing usage of Bombus balteatus Dahlbom is maintained as valid by proposing Bombus nivalis Dahlbom and Bombus tricolor Dahlbom as nomina oblita and by proposing Bombus balteatus Dahlbom as a nomen protectum. The prevailing usage of Bombus hyperboreus Schönherr is maintained as valid by supporting Apis arctica Quensel as a nomen oblitum and by supporting Bombus hyperboreus Schönherr as a nomen protectum. We then use sequence data from COI and 16S together with nuclear PEPCK and opsin genes to estimate dated phylogenetic relationships among the nine species, allowing for incongruent gene trees with *BEAST. If crown-group divergence within the subgenus Alpinobombus coincided with the global climate cooling and with the growth of the northern ice sheets at the end of the Miocene at ca 7.2 Ma, then divergences between each of the three pairs of sister species are likely to have coincided with fluctuations in vegetated land connections across the Bering Strait after ca 2.5 Ma.

Thoracobombus from Mexico: a description of the male species-specific cephalic labial gland secretions

The male cephalic labial gland secretions of bumblebees are known to be species-specific semiochemicals. These secretions that are involved in bumblebee pre-mating recognition provide efficient diagnostic characters for species delimitation. The subgenus Thoracobombus is the largest group of bumblebees and is found in the Palearctic, Nearctic, and Neotropical regions. Here, the cephalic labial gland secretion (CLGS) composition of six Mexican Thoracobombus bumblebee species are analyzed: Bombus diligens, B. medius, B. mexicanus, B. pensylvanicus, B. trinominatus, and B. weisi. Our results suggest the presence of two new potential species into the formerly recognized B. weisi as well as one new potential species in the taxon presently identified as B. pensylvanicus. Moreover, the male of B. pensylvanicus, known to congregate at nest sites awaiting the emergence of virgin queens, is characterized by low concentrations of the C16 component. This observation raises the possibility that courtship behavior as well as environmental constraints could affect the role of the male bumblebees’ CLGS.

Adding attractive semio-chemical trait refines the taxonomy of Alpinobombus (Hymenoptera: Apidae)

Species taxonomy of bumblebees (Bombus Latreille, 1802) is well known to be problematic due to a potentially high intra-specific variability of morphological traits while different species can converge locally to the same color pattern (cryptic species). Assessing species delimitation remains challenging because it requires to arbitrarily select variable traits whose accuracy continues to be debated. Integrative taxonomic approach seems to be very useful for this group as different independent traits are assessed to propose a rational taxonomic hypothesis. Among operational criteria to assess specific status, the reproductive traits involved in the pre-mating recognition (i.e., the male cephalic labial gland secretions, CLGS) have been premium information. Since these secretions are supposed to be species-specific, these chemical traits can bring essential information where species delimitation is debated. Here, we describe and compare the CLGS of 161 male specimens of nine Alpinobombus taxa: alpinus, balteatus, helleri, hyperboreus, kirbiellus, natvigi, neoboreus, polaris, and pyrrhopygus. We aim also to test the congruence between this new information (reproductive traits) and published genetic dataset. Our results emphasized six distinct groups with diagnostic major compounds: (a) alpinus + helleri with hexadec-9-en-1-ol; (b) polaris + pyrrhopygus with two major compounds hexadec-9-en-1-ol and hexadec-9-enal; (c) balteatus with tetradecyl acetate; (d) kirbiellus with geranyl geranyl acetate; (e) hyperboreus + natvigi with octadec-11-en-1-ol; (f) neoboreus with octadec-9-en-1-ol. Based on this new information, we can confirm the species status of B. alpinus, B. balteatus, B. hyperboreus, B. kirbiellus, B. neoboreus, and B. polaris. We also confirm the synonymy of helleri (Alps) with alpinus (Sweden). However, the specific status of natvigi (Alaska) and pyrrhopygus (Sweden) is questionable and these taxa do not have specific CLGS composition.

Explorative study on mucosal and major salivary secretion rates, caries and plaque microflora in head and neck cancer patients.

To analyse mucosal and major salivary secretion rates, caries and plaque microflora in connection with treatment for cancer in the head and neck region. Thirty-three patients were included and the number of teeth, filled surfaces and caries lesions registered. The labial and buccal gland secretion and stimulated whole salivary secretion rates were determined. Supragingival plaque microflora was analysed using cultivation technique. Data were collected pretreatment, during treatment and 6months, 1year and 2years post-treatment. Two years post-treatment, 36% had new caries lesions, which had been restored. The labial secretion was comparable with pretreatment, while the buccal secretion was lower (P<.001). The stimulated secretion rate was lower compared with pretreatment (P<.001) and was ≤0.7mL/minute for 50%. Growth of lactobacilli increased during treatment (P<.001) and remained increased (P<.001), while growth of mutans streptococci was decreased (P<.01) 2years post-treatment. Growth of Candida increased over time and was higher 2years post-treatment compared with pretreatment (P<.001) while growth of Prevotella was lower (P<.01). Two years post-treatment, the stimulated salivary secretion rate was substantially decreased, acid-tolerant lactobacilli and Candida increased, acid-sensitive microorganisms decreased, and the caries prevalence was low.

Variability in Sexual Pheromones Questions their Role in Bumblebee Pre-Mating Recognition System.

Sex-specific chemical secretions have been widely used as diagnostic characters in chemotaxonomy. The taxonomically confused group of bumblebees has reaped the benefit of this approach through the analyses of cephalic labial gland secretions (CLGS). Most of currently available CLGS descriptions concern species from the West-Palearctic region but few from the New World. Here, the CLGS of four East-Palearctic species Bombus deuteronymus, B. filchnerae, B. humilis, and B. exil (subgenus Thoracobombus) are analysed. Our results show high levels of variability in the major compounds in B. exil. In contrast, we describe a low differentiation in CLGS compounds between B. filchnerae and its phylogenetically closely related taxon B. muscorum. Moreover, the chemical profiles of B. filchnerae and B. muscorum are characterized by low concentrations of the C16 component, which is found in higher concentrations in the other Thoracobombus species. This raises the possibility that courtship behavior as well as environmental constraints could affect the role of the bumblebee males' CLGS.

An unusual recruitment strategy in a mass-recruiting stingless bee, Partamona orizabaensis.

Foragers of several stingless bee species deposit attractive scent marks on solid substrates to precisely recruit nestmates to food. Interestingly, Partamona workers quickly recruit large numbers of nest mates to resources, likely even without the deposition of attractive scent marks. However, systematic studies of the recruitment system of these bees are lacking. We now studied the recruitment behavior of P. orizabaensis. Our findings show that foragers of this species can recruit large numbers of nestmates to food sources at a particular location. The precise nestmate recruitment does not rely on attractive scent marks deposited on substrates. We never observed any scent marking behavior and feeders baited with labial or mandibular gland extracts were not attractive for the bees. Chemical analyses showed that the foragers' labial gland secretions exclusively contain long chain hydrocarbons, which render their role in recruitment communication unlikely. Whether mandibular gland secretions, which contain esters and alcohols that are known as attractive pheromones in other bee species, are used to guide recruits toward food during flight, remains elusive. We conclude that Partamona's quick recruitment system that does not rely on conspicuous scent marks has evolved as a strategy against competition with sympatrically occurring and more aggressive bee species.

Chemical reproductive traits of diploid Bombus terrestris males: Consequences on bumblebee conservation.

The current bumblebee decline leads to inbreeding in populations that fosters a loss of allelic diversity and diploid male production. As diploid males are viable and their offspring are sterile, bumblebee populations can quickly fall in a vortex of extinction. In this article, we investigate for the first time a potential premating mechanism through a major chemical reproductive trait (male cephalic labial gland secretions) that could prevent monandrous virgin queens from mating with diploid males. We focus our study on the cephalic labial gland secretions of diploid and haploid males of Bombus terrestris (L.). Contrary to initial expectations, our results do not show any significant differentiation of cephalic labial gland secretions between diploid and haploid specimens. Queens seem therefore to be unable to avoid mating with diploid males based on their compositions of cephalic labial gland secretions. This suggests that the vortex of extinction of diploid males could not be stopped through premating avoidance based on the cephalic labial gland secretions but other mechanisms could avoid mating between diploid males and queens.

Interspecific chemical communication in raids of the robber bee Lestrimelitta limao

Most social bees collect floral resources to obtain proteins and carbohydrates. However, the obligate cleptoparasite stingless bee Lestrimelitta limao, the so-called robber bee, is a rare exception as it collects resources by raiding other stingless bee nests. The mechanisms these bees use to overcome host colony defenses are poorly understood. Many host species retreat inside the nest during L. limao attacks and the signals triggering this behavior require a better understanding. While some researchers have proposed that robber bees release chemical compounds that are responsible for host retreat, others have hypothesized that the observed behavior results from communication among host workers. In order to investigate the role of interspecific signals in raids, we tested the effects of robber bees’ mandibular and labial gland secretions on the behavior of Frieseomelitta varia workers. We combined behavioral assays with chemical and electrophysiological analyses. We found that citral and 9-nonacosene are major mandibular gland compounds and two esters, hexadecyl acetate and 9-hexadecenyl acetate, are major labial gland compounds. These three major compounds elicited electro-physiological responses on host worker antennae. Robber bee labial gland extracts repelled both foragers and guards, while mandibular gland content increased aggression. Our results suggest that interspecific communication plays a role during natural raids and that esters from L. limao labial glands, rather than citral, are more likely to trigger the host retreat. The results add to our knowledge about L. limao chemical communication and help to elucidate the mechanisms involved in their intriguing foraging strategy.

Complex alarm strategy in the most basal termite species

Studying basal taxa often allows shedding a light on the evolution of advanced representatives. The most basal termite species, Mastotermes darwiniensis, possesses unique morphological and behavioural traits, of which many remain scarcely studied. For these reasons, we conducted a comprehensive study of the alarm communication in this species and compared its components to behavioural modes described in other termites. In M. darwiniensis, the alarm is communicated by substrate-borne vibrations resulting from vertical vibratory movements. Another similar behaviour consists in longitudinal movements, by which the alarm is delivered to other termites in contact with alerted individual. Both these two behavioural modes could be used in synergy to create complex movements. M. darwiniensis also uses chemical alarm signals produced by labial gland secretion, in contrast to Neoisoptera in which this function is fulfilled exclusively by the frontal gland secretion. Moreover, we demonstrated in M. darwiniensis the presence of a positive feedback mechanism thought to occur exclusively in the crown group Termitidae. This positive feedback consists in both oscillatory movements of alerted individuals in response to alarm signals and release of alarm pheromone by excited soldiers. Our results confirm that M. darwiniensis is a remarkable example of mosaic evolution, as it combines many primitive and advanced features, and its alarm communication clearly belongs to the latter category.

First Chemical Analysis and Characterization of the Male Species-Specific Cephalic Labial-Gland Secretions of South American Bumblebees.

The evolution of signals and reproductive traits involved in the pre-mating recognition has been in focus of abundant research in several model species, such as bumblebees (genus Bombus). However, the most-studied bumblebee reproductive trait, the male cephalic labial gland secretions (CLGS), remains unknown among bumblebee species from South America. In this study, the CLGS of five South American bumblebees of the subgenera Thoracobombus (Bombus excellens and B. atratus) and Cullumanobombus (B. rubicundus, B. hortulanus, and B. melaleucus) were investigated, by comparing the chemical compositions of their secretions to those of closely related European species. The results showed an obvious interspecific differentiation in both subgenera. The interspecific differentiation among the species of the Thoracobombus subgenus involved different compounds present at high contents (main compounds), while those of the Cullumanobombus subgenus shared the same main components. This suggests that among the species of the Cullumanobombus subgenus, the differentiation in minor components could lead to species discrimination.

Methods for species delimitation in bumblebees (Hymenoptera, Apidae, Bombus): towards an integrative approach

Delimitation of closely related species is often hindered by the lack of discrete diagnostic morphological characters. This is exemplified in bumblebees (genus Bombus). There have been many attempts to clarify bumblebee taxonomy by using alternative features to discrete morphological characters such as wing shape, DNA, or eco‐chemical traits. Nevertheless each approach has its own limitations. Recent studies have used a multisource approach to gather different lines of speciation evidence in order to draw a strongly supported taxonomic hypothesis in bumblebees. Yet, the resulting taxonomic status is not independent of selected evidence and of consensus methodology (i.e. unanimous procedure, majority, different weighting of evidence). In this article, we compare taxonomic conclusions for a group of taxonomically doubtful species (the Bombus lapidarius‐group) obtained from the four commonly used lines of evidence for species delimitation in bumblebees (geometric morphometric of wing shape, genetic differentiation assessment, sequence‐based species delimitation methods and differentiation of cephalic labial gland secretions). We ultimately aim to assess the usefulness of these lines of evidence as components of an integrative decision framework to delimit bumblebee species. Our results show that analyses based on wing shape do not delineate any obvious cluster. In contrast, nuclear/mitochondrial, sequence‐based species delimitation methods, and analyses based on cephalic labial gland secretions are congruent with each other. This allows setting up an integrative decision framework to establish strongly supported species and subspecies status within bumblebees.

Biosynthetic Studies of the Male Marking Pheromone in Bumblebees by Using Labelled Fatty Acids and Two-Dimensional Gas Chromatography with Mass Detection.

Two-dimensional comprehensive gas chromatography (GC×GC) coupled with mass detection was used as a tool for biosynthetic studies of bumblebee pheromones. Prior to biosynthetic experiments, the chromatographic behaviour of isotopically modified esters in the GC×GC system as well as their behaviour in mass detection was studied. The male marking pheromones of Bombus lucorum, Bombus lapidarius and Bombus terrestris were investigated. Main pheromonal components are ethyl tetradec-9-enoate (53 %) and ethyl dodecanoate (6 %) in B. lucorum, hexadec-9-en-1-ol (52 %) and hexadecan-1-ol (31 %) in B. lapidarius, and 2,3-dihydrofarnesol (58 %) and ethyl dodecanoate (15 %) in B. terrestris. The research strategy was based on 1) in vivo incubation of isotopically (2 H, 13 C) modified fatty acids (FAs) and analysis of their metabolites and 2) feeding experiments with 2 H- and 13 C-labelled FAs mixed with food. It was observed that labelled FAs were modified into the most abundant aliphatic compounds present in labial gland secretions. In feeding experiments, the labelled FAs were transformed into pheromone components. Transport of the FA precursors from the fat body through haemolymph was confirmed. The results show that FAs, stored in the form of triacylglycerols in the fat body, are likely to participate in the biosynthesis of some aliphatic pheromone components.

Subspecific differentiation in male reproductive traits and virgin queen preferences, in Bombus terrestris

Many species display local variations in pre-mating signals and in mating preferences. This may lead to discrimination against potential foreign mates that may ultimately lead to reproductive isolation. However, the extent to which population differentiation in mating cues affects the species recognition has received little empirical support. Here, we investigate the consequence of geographic differentiation in male reproductive traits on female preferences to these traits in Bombus terrestris. We characterise (1) the geographic differentiation in male cephalic labial gland secretions (CLGS), a key trait for mate attraction, and (2) the preference of virgin females to the CLGS of different subspecies. Our results show geographic CLGS differences parallel with divergences in female preferences for these secretions. This geographic CLGS differentiation in males, along with female preference for sympatric males, could lead to or reflect a pre-mating isolation among subspecies.

An integrative taxonomic approach to assess the status of Corsican bumblebees: implications for conservation

AbstractMany islands are biodiversity hotspots that host numerous endemic species. Unfortunately, insular faunas suffer from high rates of extinction and endangerment, and numerous conservation plans have been developed for their protection. These conservation plans are often assessed on the basis of occurrence and proportion of endemic taxa. However, delimitations of species and subspecies are still confusing and controversial. From a practical point of view, these disagreements make it difficult for government agencies and non‐governmental organizations to initiate conservation measures. The present study develops a pragmatic integrative taxonomic approach on the basis of molecular and eco‐chemical criteria. This method is applied to the insular bumblebee fauna of Corsica. For each taxon, the differentiation of Corsican taxa from the nearest related allopatric parents is characterized using genetic markers and the chemical composition of cephalic labial gland secretions. Phylogenetic analyses, Bayesian implementation of the general mixed Yule‐coalescent approach, and comparative chemical studies show that two Corsican taxa can be considered as endemic species while five others can be considered as subspecies. Regardless of the taxonomic assessment the method facilitates diagnosis of evolutionarily significant units and rank taxa according to their distinctiveness. International Union for Conservation of Nature red lists are reconsidered according to the new taxonomic hypothesis for Corsican bumblebees. Modifications in species assessments are proposed. The present approach provides useful data sets for policy‐makers and conservation organizations.