Biomedical subjects

Gro V Amdam

Publications and source records attributed to Gro V Amdam.

18 recordsLinked to original sources

PubMed2006

Behavioral genomics of honeybee foraging and nest defense.

The honeybee has been the most important insect species for study of social behavior. The recently released draft genomic sequence for the bee will accelerate honeybee behavioral genetics. Although we lack sufficient tools to manipulate this genome easily, quantitative trait loci (QTLs) that influence natural variation in behavior have been identified and tested for their effects on correlated behavioral traits. We review what is known about the genetics and physiology of two behavioral traits in honeybees, foraging specialization (pollen versus nectar), and defensive behavior, and present evidence that map-based cloning of genes is more feasible in the bee than in other metazoans. We also present bioinformatic analyses of candidate genes within QTL confidence intervals (CIs). The high recombination rate of the bee made it possible to narrow the search to regions containing only 17-61 predicted peptides for each QTL, although CIs covered large genetic distances. Knowledge of correlated behavioral traits, comparative bioinformatics, and expression assays facilitated evaluation of candidate genes. An overrepresentation of genes involved in ovarian development and insulin-like signaling components within pollen foraging QTL regions suggests that an ancestral reproductive gene network was co-opted during the evolution of foraging specialization. The major QTL influencing defensive/aggressive behavior contains orthologs of genes involved in central nervous system activity and neurogenesis. Candidates at the other two defensive-behavior QTLs include modulators of sensory signaling (Am5HT(7) serotonin receptor, AmArr4 arrestin, and GABA-B-R1 receptor). These studies are the first step in linking natural variation in honeybee social behavior to the identification of underlying genes.

Animals↗

PubMed2006

Cellular senescence in honey bee brain is largely independent of chronological age.

Accumulation of oxidative stress-induced damage in brain tissue plays an important role in the pathogenesis of normal aging and neurodegenerative diseases. Neuronal oxidative damage typically increases with age in humans, and also in the invertebrate and vertebrate model species most commonly used in aging research. By use of quantitative immunohistochemistry and Western blot, we show that this aspect of brain senescence is largely decoupled from chronological age in the honey bee (Apis mellifera). The bee is a eusocial insect characterized by the presence of a reproductive queen caste and a caste of functionally sterile female workers that performs various alloparental tasks such as nursing and foraging. We studied patterns of oxidative nitration and carbonylation damage in the brain of worker bees that performed nurse tasks as 8- and 200-day-olds and foraging tasks as 20- and 200-day-olds. In addition, we examined 180-day-old diutinus bees, a stress-resistant temporal worker form that survives unfavorable periods. Our results indicate that nitration damage occurs only at low levels in vivo, but that a 60-kDa protein from honey bee brain is selectively nitrated by peroxynitrite in vitro. Oxidative carbonylation is present at varying levels in the visual and chemosensory neuropiles of worker bees, and this inter-individual variation is better explained by social role than by chronological age.

Age Factors↗

PubMed2006

Downregulation of vitellogenin gene activity increases the gustatory responsiveness of honey bee workers (Apis mellifera).

In the honey bee (Apis mellifera), young workers usually perform tasks in the nest while older workers forage in the field. The behavioral shift from nest-task to foraging activity is accompanied by physiological and sensory changes so that foragers can be characterized by a higher juvenile hormone (JH) level, a lower vitellogenin protein titer, and an increased responsiveness to water and sucrose stimuli. JH was hypothesized to be the key mediator of behavioral development, physiology, and sensory sensitivity in honey bee workers. Recent research, however, has shown that JH is controlled by the hemolymph vitellogenin level, which implies that the fat body specific vitellogenin gene can be a key regulator of behavioral change. Here, we show that downregulation of vitellogenin activity by RNA interference (RNAi) causes an increase in the gustatory responsiveness of worker bees. Our observations suggest that vitellogenin is an important regulator of long-term changes in honey bee behavior.

Animals↗

PubMed2006

Reproductive protein protects functionally sterile honey bee workers from oxidative stress.

Research on aging shows that regulatory pathways of fertility and senescence are closely interlinked. However, evolutionary theories on social species propose that lifelong care for offspring can shape the course of senescence beyond the restricted context of reproductive capability. These observations suggest that control circuits of aging are remodeled in social organisms with continuing care for offspring. Here, we studied a circuit of aging in the honey bee (Apis mellifera). The bee is characterized by the presence of a long-lived reproductive queen caste and a shorter-lived caste of female workers that are life-long alloparental care givers. We focus on the role of the conserved yolk precursor gene vitellogenin that, in Caenorhabditis elegans, shortens lifespan as a downstream element of the insulin/insulin-like growth factor signaling cascade. Vitellogenin protein is synthesized at high levels in honey bee queens and is abundant in long-lived workers. We establish that vitellogenin gene activity protects worker bees from oxidative stress. Our finding suggests that one mechanistic explanation for patterns of longevity in bees is that a reproductive regulatory pathway has been remodeled to extend life. This perspective is of considerable relevance to research on longevity regulation that builds largely on inference from solitary model species.

Age Factors↗

PubMed2006

Complex social behaviour derived from maternal reproductive traits.

A fundamental goal of sociobiology is to explain how complex social behaviour evolves, especially in social insects, the exemplars of social living. Although still the subject of much controversy, recent theoretical explanations have focused on the evolutionary origins of worker behaviour (assistance from daughters that remain in the nest and help their mother to reproduce) through expression of maternal care behaviour towards siblings. A key prediction of this evolutionary model is that traits involved in maternal care have been co-opted through heterochronous expression of maternal genes to result in sib-care, the hallmark of highly evolved social life in insects. A coupling of maternal behaviour to reproductive status evolved in solitary insects, and was a ready substrate for the evolution of worker-containing societies. Here we show that division of foraging labour among worker honey bees (Apis mellifera) is linked to the reproductive status of facultatively sterile females. We thereby identify the evolutionary origin of a widely expressed social-insect behavioural syndrome, and provide a direct demonstration of how variation in maternal reproductive traits gives rise to complex social behaviour in non-reproductive helpers.

Aging↗

PubMed2006

Order, disorder, death: lessons from a superorganism.

Animal models contribute to the understanding of molecular mechanism of cancer, revealing complex roles of altered cellular-signaling networks and deficient surveillance systems. Analogous pathologies are documented in an unconventional model organism that receives attention in research on systems theory, evolution, and aging. The honeybee (Apis mellifera) colony is an advanced integrative unit, a "superorganism" in which order is controlled via complex signaling cascades and surveillance schemes. A facultatively sterile caste, the workers, regulates patterns of growth, differentiation, homeostasis, and death. Workers differentiate into temporal phenotypes in response to dynamic social cues; chemosensory signals that can translate into dramatic physiological responses, including programmed cell death. Temporal worker forms function together, and effectively identify and terminate abnormal colony members ranging from embryos to adults. As long as this regulatory system is operational at a colony level, the unit survives and propagates. However, if the worker phenotypes that collectively govern order become too few or change into malignant forms that bypass control mechanisms to replicate aberrantly; order is replaced by disorder that ultimately leads to the destruction of the society. In this chapter we describe fundamental properties of honeybee social organization, and explore conditions that lead to states of disorder. Our hope is that this chapter will be an inspirational source for ongoing and future work in the field of cancer research.

Animals↗

PubMed2006

8. The development and evolution of division of labor and foraging specialization in a social insect (Apis mellifera L.).

How does complex social behavior evolve? What are the developmental building blocks of division of labor and specialization, the hallmarks of insect societies? Studies have revealed the developmental origins in the evolution of division of labor and specialization in foraging worker honeybees, the hallmarks of complex insect societies. Selective breeding for a single social trait, the amount of surplus pollen stored in the nest (pollen hoarding) revealed a phenotypic architecture of correlated traits at multiple levels of biological organization in facultatively sterile female worker honeybees. Verification of this phenotypic architecture in "wild-type" bees provided strong support for a "pollen foraging syndrome" that involves increased senso-motor responses, motor activity, associative learning, reproductive status, and rates of behavioral development, as well as foraging behavior. This set of traits guided further research into reproductive regulatory systems that were co-opted by natural selection during the evolution of social behavior. Division of labor, characterized by changes in the tasks performed by bees, as they age, is controlled by hormones linked to ovary development. Foraging specialization on nectar and pollen results also from different reproductive states of bees where nectar foragers engage in pre-reproductive behavior, foraging for nectar for self-maintenance, while pollen foragers perform foraging tasks associated with reproduction and maternal care, collecting protein.

Animals↗

PubMed2005

Social reversal of immunosenescence in honey bee workers.

A striking example of immunosenescence is seen in the honey bee (Apis mellifera) worker caste. The bees' age-associated transition from hive duties to more risky foraging activities is linked to a dramatic decline in immunity. Explicitly, it has been shown that an increase in the juvenile hormone (JH) level, which accompanies onset of foraging behavior, induces extensive hemocyte death through nuclear pycnosis. Here, we demonstrate that foragers that are forced to revert to hive-tasks show reversal of immunosenescence, i.e. a recovery of immunity with age. This recovery, which is triggered by a social manipulation, is accompanied by a drop in the endogenous JH titer and an increase in the hemolymph vitellogenin level. Vitellogenin is a zinc binding glycolipoprotein that has been implicated in the regulation of honey bee immune integrity. We also establish that worker immunosenescence is mediated by apoptosis, corroborating that reversal of immunosenescence emerges through proliferation of new cells. The results presented here, consequently, reveal a unique flexibility in honey bee immunity--a regulatory plasticity that may be of general biological interest.

Aging↗

PubMed2005

Vitellogenin regulates hormonal dynamics in the worker caste of a eusocial insect.

Functionally sterile honey bee workers synthesize the yolk protein vitellogenin while performing nest tasks. The subsequent shift to foraging is linked to a reduced vitellogenin and an increased juvenile hormone (JH) titer. JH is a principal controller of vitellogenin expression and behavioral development. Yet, we show here that silencing of vitellogenin expression causes a significant increase in JH titer and its putative receptor. Mathematically, the increase corresponds to a dynamic dose-response. This role of vitellogenin in the tuning of the endocrine system is uncommon and may elucidate how an ancestral pathway of fertility regulation has been remodeled into a novel circuit controlling social behavior.

Animals↗

PubMed2005

Bivoltinism as an antecedent to eusociality in the paper wasp genus Polistes.

To learn the evolutionary trajectories of caste differentiation in eusocial species is a major goal of sociobiology. We present an explanatory framework for caste evolution in the eusocial wasp genus Polistes (Vespidae), which is a model system for insect eusocial evolution. We hypothesize that Polistes worker and gyne castes stem from two developmental pathways that characterized the bivoltine life cycle of a solitary ancestor. Through individual-based simulations, we show that our mechanistic framework can reproduce colony-level characteristics of Polistes and, thereby, that social castes can emerge from solitary regulatory pathways. Our explanatory framework illustrates, by specific example, a changed perspective for understanding insect social evolution.

Animals↗

PubMed2005

Intergenerational transfers may have decoupled physiological and chronological age in a eusocial insect.

Life-history theory generally predicts that there should be no selection for longevity beyond the limit of reproductive capacity. However, the capacity to increase fitness may not end when individuals reach a state of functional sterility. Recent studies show that intergenerational transfers of resources from post-reproductive parents can increase the offspring's fitness, and analytical theory shows that age-trajectories of transfers may shape the course of senescence in social organisms. In eusocial insects, female roles are partitioned so that one phenotype or "caste" reproduces while another is responsible for resource transfers: the reproductive "queens" are arrested in a continuous reproductive mode, while transfer-activities such as hygienic behaviors, guarding, foraging and further food processing ("nursing") that increases the nutritional value of provisions are conducted by sterile "workers". Worker honey bees normally perform these tasks in a sequence so that nursing inside the protected nest is conducted prior to more risky exterior hive activities such as guarding and foraging. However, foragers may revert to nurse-activity in response to demographic changes, and worker bees can also develop into a stress resistant survival form with a 10-fold increase in lifespan. This elastic division of parental functions is believed to increase colony fitness. Further, it generates a stage-dependent trajectory of senescence that is difficult to address with established theories of aging. In the following, we show how a recent theory that includes resource transfers can be used to elucidate patterns of senescence in eusocial, non-reproducing individuals like the honey bee worker.

Aging↗

PubMed2004

Reproductive ground plan may mediate colony-level selection effects on individual foraging behavior in honey bees.

The colony-level phenotype of an insect society emerges from interactions between large numbers of individuals that may differ considerably in their morphology, physiology, and behavior. The proximate and ultimate mechanisms that allow this complex integrated system to form are not fully known, and understanding the evolution of social life strategies is a major topic in systems biology. In solitary insects, behavior, sensory tuning, and reproductive physiology are linked. These associations are controlled in part by pleiotropic networks that organize the sequential expression of phases in the reproductive cycle. Here we explore whether similar associations give rise to different behavioral phenotypes in a eusocial worker caste. We document that the pleiotropic genetic network that controls foraging behavior in functionally sterile honey bee workers (Apis mellifera) has a reproductive component. Associations between behavior, physiology, and sensory tuning in workers with different foraging strategies indicate that the underlying genetic architectures were designed to control a reproductive cycle. Genetic circuits that make up the regulatory "ground plan" of a reproductive strategy may provide powerful building blocks for social life. We suggest that exploitation of this ground plan plays a fundamental role in the evolution of social insect societies.

Animals↗

PubMed2004

Epigenetic regulation of aging in honeybee workers.

Aging and longevity are complex life history traits that are influenced by both genes and environment and exhibit significant phenotypic plasticity in a broad range of organisms. A striking example of this plasticity is seen in social insects, such as ants and bees, where different castes can have very different life spans. In particular, the honeybee worker offers an intriguing example of environmental control on aging rate, because workers are conditionally sterile and display very different aging patterns depending on which temporal caste they belong to (hive bee, forager, or a long-lived caste capable of surviving for several months on honey alone). The ubiquitous yolk protein vitellogenin appears to play a key role in the regulatory circuitry that controls this variation. Here we outline the current understanding of the relation between vitellogenin and somatic maintenance in honeybee workers, and how this relation can be understood in a life history context.

Aging↗

PubMed2004

From genes to societies.

Research on model organisms has substantially advanced our understanding of aging. However, these studies collectively lack any examination of the element of sociality, an important feature of human biology. Social insects present a number of unique possibilities for investigating social influences on aging and potentially detecting new mechanisms for extremely prolonged, healthy life spans that have evolved naturally. Social evolution has led to life spans in reproductive females that are much longer (up to over 100-fold) than those of males or of nonreproductive worker castes. These differences are particularly dramatic because they are due to environmental influences, as all individuals develop from the same genomes. Social insect colonies consist of semi-autonomous individuals, and the relationship between the colony and the individual creates many interesting predictions in the light of the common theories of aging. Furthermore, the variety of lifestyles of social insects creates the potential for crucial comparative analyses across distinct social systems.

Animals↗

PubMed2004

Hormonal control of the yolk precursor vitellogenin regulates immune function and longevity in honeybees.

A striking example of plasticity in life span is seen in social insects such as ants and bees, where different castes may display distinct ageing patterns. In particular, the honeybee offers an intriguing illustration of environmental control on ageing rate. Honeybee workers display a temporal division of labour where young bees (or 'hive bees') perform tasks within the brood nest, and older bees forage for nectar, pollen propolis and water. When bees switch from the hive bee to the forager stage, their cellular defence machinery is down-regulated by a dramatic reduction in the number of functioning haemocytes (immunocytes). This study documents that the yolk precursor vitellogenin is likely to be involved in a regulatory pathway that controls the observed decline in somatic maintenance function of honeybee foragers. An association between the glyco-lipoprotein vitellogenin and immune function has not previously been reported for any organism. Honeybee workers are functionally sterile, and via the expression of juvenile hormone, a key gonotrophic hormone in adult insects, their vitellogenin levels are influenced by social interactions with other bees. Our results therefore suggest that in terms of maintenance of the cellular immune system, senescence of the honeybee worker is under social control.

Animals↗

PubMed2004

Altered physiology in worker honey bees (Hymenoptera: Apidae) infested with the mite Varroa destructor (Acari: Varroidae): a factor in colony loss during overwintering?

The ectoparasitic mite Varroa destructor (Anderson & Trueman) is the most destructive pest of the honey bee, Apis mellifera L., in Europe and the United States. In temperate zones, the main losses of colonies from the mites occur during colony overwintering. To obtain a deeper knowledge of this phenomenon, we studied the mites' impact on the vitellogenin titer, the total protein stores in the hemolymph, the hemocyte characteristics, and the ecdysteroid titer of adult honey bees. These physiological characteristics are indicators of long-time survival and endocrine function, and we show that they change if bees have been infested by mites during the pupal stage. Compared with noninfested workers, adult bees infested as pupae do not fully develop physiological features typical of long-lived wintering bees. Management procedures designed to kill V. destructor in late autumn may thus fail to prevent losses of colonies because many of the adult bees are no longer able to survive until spring. Beekeepers in temperate climates should therefore combine late autumn management strategies with treatment protocols that keep the mite population at low levels before and during the period when the winter bees emerge.

Acari↗

PubMed2003

Social exploitation of vitellogenin.

Vitellogenin is a female-specific glucolipoprotein yolk precursor produced by all oviparous animals. Vitellogenin expression is under hormonal control, and the protein is generally synthesized directly before yolk deposition. In the honeybee (Apis mellifera), vitellogenin is not only synthesized by the reproductive queen, but also by the functionally sterile workers. In summer, the worker population consists of a hive bee group performing a multitude of tasks including nursing inside the nest, and a forager group specialized in collecting nectar, pollen, water, and propolis. Vitellogenin is synthesized in large quantities by hive bees. When hive bees develop into foragers, their juvenile hormone titers increase, and this causes cessation of their vitellogenin production. This inverse relationship between vitellogenin synthesis and juvenile hormone is opposite to the norm in insects, and the underlying proximate processes and life-history reasons are still not understood. Here we document an alternative use of vitellogenin by showing that it is a source for the proteinaceous royal jelly that is produced by the hive bees. Hive bees use the jelly to feed larvae, queen, workers, and drones. This finding suggests that the evolution of a brood-rearing worker class and a specialized forager class in an advanced eusocial insect society has been directed by an alternative utilization of yolk protein.

Animals↗

PubMed2003

Disruption of vitellogenin gene function in adult honeybees by intra-abdominal injection of double-stranded RNA.

BACKGROUND: The ability to manipulate the genetic networks underlying the physiological and behavioural repertoires of the adult honeybee worker (Apis mellifera) is likely to deepen our understanding of issues such as learning and memory generation, ageing, and the regulatory anatomy of social systems in proximate as well as evolutionary terms. Here we assess two methods for probing gene function by RNA interference (RNAi) in adult honeybees. RESULTS: The vitellogenin gene was chosen as target because its expression is unlikely to have a phenotypic effect until the adult stage in bees. This allowed us to introduce dsRNA in preblastoderm eggs without affecting gene function during development. Of workers reared from eggs injected with dsRNA derived from a 504 bp stretch of the vitellogenin coding sequence, 15% had strongly reduced levels of vitellogenin mRNA. When dsRNA was introduced by intra-abdominal injection in newly emerged bees, almost all individuals (96%) showed the mutant phenotype. An RNA-fragment with an apparent size similar to the template dsRNA was still present in this group after 15 days. CONCLUSION: Injection of dsRNA in eggs at the preblastoderm stage seems to allow disruption of gene function in all developmental stages. To dissect gene function in the adult stage, the intra-abdominal injection technique seems superior to egg injection as it gives a much higher penetrance, it is much simpler, and it makes it possible to address genes that are also expressed in the embryonic, larval or pupal stages.

Abdomen↗