Biology subjects

Amsalem, E.

Publications and source records attributed to Amsalem, E..

12 recordsLinked to original sources

bioRxiv2025

Male attraction to short-range multimodal gyne signals in bumble bees

Mating is a crucial event in animal life, with significant implications for individual fitness. Insects have evolved complex mating systems and behaviors, such as pheromone signaling and elaborate courtship rituals, that convey vital information about mates species, quality, and receptiveness, to optimize reproductive success. These signals are especially critical in social species where a single female found a colony following a single event of mating. In this study, we investigate the short-range signals produced by gynes (newly emerged queens) and their role in mating in Bombus impatiens. Mating in bumble bees is facilitated by males marking mating sites with long-range labial gland pheromones, which attract gynes. It is assumed that gynes produce short-range signals necessary to initiate mating. While male bumble bee sex pheromones have been extensively studied across many species, the short-range signals produced by gynes remain poorly understood. Our findings show that males rely on multimodal signals, composed of visual, vibrational, and context-dependent sex pheromones produced by gynes. Choice bioassays designed to isolate the different signals produced by gynes indicate that visual cues are essential but not sufficient for successful mating, and compounds from the labial and dufour glands likely play a role in attracting males. Our results also highlight the importance of vibrational signals for male attraction. Together, these findings underscore the role of gynes in regulating mating and the significance of context in eliciting male responses and mate selection through various signals.

animal behavior and cognition↗

bioRxiv2025

A social bee can learn a novel queen pheromone

Many pheromone responses are hardwired into the insects nervous system and are essential for critical behaviors such as mating, alarm signaling, and trail following. Workers of social species are assumed to respond innately to queen pheromones, affecting their behavior and reproductive physiology. However, accumulating evidence suggests that learning and experience may also shape responses to social chemical cues. To examine if the response to queen-associated odors can be learned, we exposed Bombus terrestris workers to a novel odor by treating the queen daily with unfamiliar floral scents, either anisyl alcohol or methyl anthranilate. We allowed perfumed queens to establish colonies and examined worker attraction and egg laying following exposure to these odors in the absence of the queen either with or without brood as context. In a two-choice olfactometer, workers preferred the queen odor they learned during colony development. Exposure of workers to the queen-associated odor in the absence of the queen influenced worker egg laying only in the presence of brood, surprisingly resulting in increased egg laying. Our study demonstrates that workers can learn novel odors that are associated with their queen or nest, which in turn function as context-dependent social cues that modify their social and reproductive behavior.

evolutionary biology↗

bioRxiv2024

Sublethal pesticide exposure decreases mating and disrupts chemical signaling in a beneficial pollinator

Pesticides provide vital protection against insect pests and the diseases they vector but are simultaneously implicated in the drastic worldwide decline of beneficial insect populations. Convincing evidence suggests that even sublethal pesticide exposure has detrimental effects on both individual- and colony-level traits, but the mechanisms mediating these effects remained poorly understood. Here, we use bumble bees to examine how sublethal exposure to pesticides affects mating, a key life history event shared by nearly all insects, and whether these impacts are mediated via impaired sexual communication. In insects, mate location and copulation are primarily regulated through chemical signals and rely on both the production and perception of semiochemicals. We show through behavioral bioassays that mating success is reduced in bumble bee gynes after exposure to field-relevant sublethal doses of imidacloprid, and that this effect is likely mediated through a disruption of both the production and perception of semiochemicals. Semiochemical production was altered in gyne and male cuticular hydrocarbons (CHCs), but not in exocrine glands where sex pheromones are presumably produced (i.e., gyne mandibular glands and male labial glands). Male responsiveness to gyne mandibular gland secretion was reduced, but not the queen responsiveness to the male labial secretion. In addition, pesticide exposure reduced queen fat body lipid stores and male sperm quality. Overall, the exposure to imidacloprid affected the fitness and CHCs of both sexes and the antennal responses of males to gynes. Together, our findings identify disruption of chemical signaling as the mechanism through which sublethal pesticide exposure reduces mating success.

zoology↗

bioRxiv2022

The influence of the social environment on larval development and resulting caste in Bombus impatiens

The ability of a single genome to express multiple phenotypes is key to understanding social evolution, where individuals with different morphologies perform different tasks. In social insects, phenotypes are typically determined during larval development and depend on the social environment. Here, we used the bumble bee Bombus impatiens to examine the social regulation of body size variation and caste by manipulating the identity (queen/worker) and the number of caretakers tending for the brood. Eggs of females and males were kept in cages with (1) a single queen; (2) a single worker; (3) three workers; or (4) ten workers. We measured larval weight, developmental length, and the resulting caste (in females) throughout the brood development of >2000 individuals. We found differences in larval mass when reared by varying number of workers, but not when reared by a single worker compared to a queen. Additionally, in contrast with previous findings in B. terrestris, none of the female eggs reared by workers developed into gynes (new queens), indicating that the mechanisms regulating caste determination in B. impatiens is not solely dependent on the queen presence as in B. terrestris. Adult males were slightly larger than workers and developed for a longer period in the presence of the queen. Overall, we suggest that body size in B. impatiens is determined by the number of caretakers and is likely mediated by the amount of provision. The hypothesis that the queens presence manipulates female caste was not supported by our data.

ecology↗

bioRxiv2022

Sexual production is regulated by the brood in Bombus impatiens colonies

Sexual production in social insects marks the peak of colony development, yet the mechanisms regulating it remain unclear. We investigated the role of brood in colony development, worker reproduction, and sexual production in Bombus impatiens. While larvae are known to reduce worker egg-laying and enhance the queens reproductive inhibition, these effects were previously tested only in small groups. We manipulated brood size in full-sized, young colonies by doubling or removing brood and monitored development. Colonies with doubled brood produced significantly more gynes, independent of the number of workers, while reduced-brood colonies exhibited a non-significant increase in male production that was driven by colony size. Worker ovary activation was lower in double-brood colonies, with no change in aggression. A follow-up experiment directly testing the effect of colony size showed that higher worker density led to higher ovary activation in workers but did not affect sexual production. These results suggest that brood strongly influences colony development and sexual production, possibly reflecting an extended phenotype of the queen, whereas worker ovary activation appears to be a more flexible process influenced by either brood presence or colony size. Understanding brood dynamics may be key to understanding the evolution of female castes in social insects.

evolutionary biology↗

bioRxiv2022

Impacts and mechanisms of CO2 narcosis in bumble bees: Narcosis depends on dose, caste and mating status and is not induced by anoxia

Carbon dioxide (CO2) is commonly used to immobilize insects and to induce reproduction in bees. However, despite its wide use and potential off-target impacts, its underlying mechanisms are not fully understood. Here we used Bombus impatiens to examine whether CO2 impacts are mediated by anoxia and whether these mechanisms differ between female castes or following mating. We examined the behavior, physiology, and gene expression of workers, mated and virgin queens following exposure to anoxia, hypoxia, full and partial hypercapnia, and control. Hypercapnia and anoxia caused immobilization, but only hypercapnia resulted in behavioral, physiological, and molecular impacts in bees. Recovery from hypercapnia resulted in increased abdominal contractions and took longer in queens. Additionally, hypercapnia activated queens-but inhibited workers ovaries in a dose-dependent manner and caused a depletion of fat-body lipids in both. All responses of hypercapnia were weaker following mating in queens. Analysis of gene expression related to hypoxia and hypercapnia supported the physiological findings in queens, demonstrating that the overall impacts of CO2, excluding virgin queen ovaries, were unique and were not induced by anoxia. This study contributes to our understanding of the impacts and the mechanistic basis of CO2 narcosis in insects and its impacts on bees physiology.

biochemistry↗

bioRxiv2022

Differential gene expression underlying the biosynthesis of Dufour's gland signals in Bombus impatiens

Pheromones regulating social behavior are one of the most explored phenomena in social insects. However, compound identity, biosynthesis and their genetic regulation are known in only a handful of species. Here we conducted chemical and RNA-seq analyses of the Dufours gland in the bumble bee Bombus impatiens and examined the signals and the pathways regulating signal production in queens and workers. Across Hymenopterans, the Dufours gland contains mostly long-chained hydrocarbons and esters that signal reproductive and social status in several bee species. In bumble bees, the Dufours gland contains queen- and worker-specific esters, in addition to terpenes and terpene-esters only found in gynes and queens. These compounds are assumed to be synthesized de novo in the gland, however, their genetic regulation is unknown. A whole transcriptome gene expression analysis of the gland in queens, gynes, queenless and queenright workers showed distinct transcriptomic profiles, with thousands of differentially expressed genes between the groups. Workers and queens express genes associated with key enzymes in the biosynthesis of wax esters, while queens and gynes preferentially express key genes in terpene biosynthesis. In contrast, no genes were differentially expressed in queenless and queenright workers, despite differences in their Dufours gland chemistry and reproductive state, suggesting the quantitative differences in worker secretion are not regulated at the level of production. Overall, our data demonstrate gland-specific regulation of chemical signals associated with social behavior and identifies genes and pathways regulating caste-specific chemical signals in social insects.

genomics↗

bioRxiv2020

Built to change: dominance strategy changes with life stage in a primitively eusocial bee

Access to reproduction is determined by an individual dominances rank in many species and is achieved through aggression and/or dominance signalling. In eusocial insects one or several dominant females (queens) monopolize reproduction but to what extent queens rely on aggression and signalling remains obscure. Aggression is costly and its efficiency depends on the group size, whereas signalling may reduce the risks and costs of aggression. Both strategies are used to regulate reproduction in social taxa, with aggression being more common in small social groups, compared to signalling in larger societies. Here, we examine the use of aggression and chemical signalling in a social species (Bombus impatiens) where the dominant queen interacts with increasing numbers of workers as she ages. We found that the queens strategy to monopolize reproduction changes with life stage, shifting from overt aggression to chemical signalling as the queen gets older. Particularly, old queens exhibited a higher ratio of short to long cuticular hydrocarbons compared to young queens, an endogenous shift that was attributed to age, as all egg-laying queens were fecund and kept with the same number of workers. Our findings contribute to the understanding of reproductive dominance in the context of an individuals life history.

evolutionary biology↗

bioRxiv2020

Show me your Dufour's gland and I'll tell you who you are: caste and physiology specific signals in Bombus impatiens

Reproductive division of labor in insect societies is regulated through multiple concurrent mechanisms, primarily chemical and behavioral. Here, we examined if the Dufours gland secretion in the primitively eusocial bumble bee Bombus impatiens signals information about caste, social condition, and reproductive status. We chemically analyzed Dufours gland contents across castes, age groups, social and reproductive conditions, and examined worker behavioral and antennal responses to gland extracts. We found that workers and queens each possess caste-specific compounds in their Dufours glands. Queens and gynes differed from workers based on the presence of diterpene compounds which were absent in workers, whereas four esters were exclusive to workers. These esters, as well as the total amounts of hydrocarbons in the gland, provided a separation between castes and also between fertile and sterile workers. Olfactometer bioassays demonstrated attraction of workers to Dufours gland extracts that did not represent a reproductive conflict, while electroantennogram recordings showed higher overall antennal sensitivity in queenless workers. Our results demonstrate that compounds in the Dufours gland act as caste- and physiology-specific signals and are used by workers to discriminate between workers of different social and reproductive status.

physiology↗

bioRxiv2020

High thermal plasticity and vulnerability in extreme environments at the warm distributional edge: the case of a tidepool shrimp

1.Climate change threatens the resilience of species, especially at their warm distributional edge in extreme environments. However, not much is known about the thermal vulnerability of marine intertidal species at this edge. We investigated the thermal vulnerability of the tidepool shrimp, Palaemon elegans in the fast-warming southeastern Mediterranean, its warm distributional edge. Tidepool organisms experience strong and fast thermal fluctuations. This might make them more resilient to change, but also bring them closer to their thermal limits during extreme conditions. To test the shrimps resilience, we tested three hypotheses: (1) P. elegance in the southeast Mediterranean has higher critical thermal maximum (CTMax) than in cooler regions, (2) the shrimp possess seasonal acclimatization, but (3) long exposure to extreme summer temperatures might erode its thermal performance making it vulnerable to future climate change. We characterized the shrimps thermal environment and population dynamics, determined CTMax and tested diverse physiological performance attributes (respiration, digestion, activity, growth) under a wide range of temperatures during winter and summer. P. elegans has a wide optimum performance range between 20-30{degrees}C during summer and its CTMax is 38.1{degrees}C, higher than its Atlantic counterparts. However, its warming tolerance is only 0.3{degrees}C, indicating low capacity for dealing with further warming in pools compared to northeast Atlantic populations that have wider tolerance. Prolonged exposure to current mean summer values in open water ([~] 32{degrees}C) would also significantly reduce its performance and increase mortality. This suggests that its population viability may be reduced under continuous regional warming and intensification of extreme events.

ecology↗

bioRxiv2019

A small family business: synergistic and additive effects of the queen and the brood on worker reproduction in a primitively eusocial bee

The mechanisms that maintain reproductive division of labor in social insects are still incompletely understood. Most studies focus on the relationship between adults, overlooking another important stakeholder in the game - the juvenile offspring. Recent studies from various social species show that not only the queen, but also the brood regulates reproductive division of labor between females, but how the two coordinate to maintain reproductive monopoly remained unexplored.\n\nOur study aims at disentangling the roles of the brood and the queen in regulating worker reproduction in primitively eusocial bees. We examined the effects induced by the brood and queen, separately and together, on the behavioral, physiological and brain gene expression of Bombus impatiens workers. We found that young larvae induce a releaser effect in workers, decreasing egg laying and aggressive behaviors, while the queen induces both releaser and primer effects, modifying worker aggressive and egg laying behavior and reproductive physiology. The expression of reproduction- and aggression-related genes was altered in the presence of both queen and brood, but the effect was stronger or the same in the presence of the queen.\n\nWe identified two types of interactions between the queen and the brood in regulating worker reproduction: (1) synergistic interactions regulating worker physiology, where the combined effect of the queen and the brood was greater than each of them separately; (2) additive interactions regulating worker behavior, where the combined effects of the queen and the brood are the gross sum of their separated effects. In these interactions the brood acted in a manner similar to the queen but to a much smaller extent and improved the quality of the effect induced by the queen. Our results suggest that the queen and the brood of primitively eusocial bees coordinate synergistically, additively, and sometimes even redundantly to regulate worker behavior and reproduction, and the interaction between them exists in multiple regulatory levels.

animal behavior and cognition↗

bioRxiv2019

The role of insect diapause in the divergence of social female castes: Insights from primitively eusocial bumble bee workers

Insects maximize their fitness by exhibiting predictable and adaptive seasonal patterns in response to changing environmental conditions. These seasonal patterns are often expressed even when insects are kept in captivity, suggesting they are functionally and evolutionary important. In this study we examined whether workers of the eusocial bumble bee Bombus impatiens maintained a seasonal signature when kept in captivity. We used an integrative approach and compared worker egg-laying, ovarian activation, body size and mass, lipid content in the fat body, cold tolerance and expression of genes related to cold tolerance, metabolism, and stress throughout colony development. We found that bumble bee worker physiology and gene expression patterns shift from reproductive-like to diapause-like as the colony ages. Workers eclosing early in the colony cycle had increased egg-laying and ovarian activation, and reduced cold tolerance, body size, mass, and lipid content in the fat body, in line with a reproductive-like profile, while late-eclosing workers exhibited the opposite characteristics. Furthermore, expression patterns of genes associated with reproduction and diapause differed between early- and late-eclosing workers, partially following the physiological patterns. We suggest that a seasonal signature, innate to individual workers, the queen or the colony is used by workers as a social cue determining the phenology of the colony and discuss possible implications for understanding reproductive division of labor in bumble bee colonies and the evolutionary divergence of female castes in the genus Bombus.

evolutionary biology↗