Hagai Y. Shpigler

Endocrine Influences on the Organization of Insect Societies

We review evidence for endocrine influences on division of labor in insect societies. Juvenile hormone (JH) has been studied most extensively. JH is involved in control of four forms of division of labor: division of labor for reproduction among adults, division of labor for reproduction via caste differentiation, division of labor for colony growth and development among adults, and division of labor for colony growth and development via physical castes. Ecdysteroids, biogenic amines, and insulin have begun to be studied in these contexts as well. Ecdysteroids are implicated in the control of caste determination and reproductive maturation in bees. Octopamine influences the division of labor among workers, octopamine and serotonin exert neurohormonal influences on the production of JH by the corpora allata, and octopamine and dopamine levels are correlated suggestively with aspects of reproductive development in bumblebees, honeybees, and paper wasps. Insulin signaling is involved in caste determination and division of labor among workers. Vitellogenin, best known as a yolk protein, may also have hormone-like functions in the regulation of division of labor among workers. We present a verbal model that proposes that evolutionary changes in endocrine function play key roles in the evolution of division of labor.

Susceptibility to chronic pain following nerve injury is genetically affected by CACNG2

Chronic neuropathic pain is affected by specifics of the precipitating neural pathology, psychosocial factors, and by genetic predisposition. Little is known about the identity of predisposing genes. Using an integrative approach, we discovered that CACNG2 significantly affects susceptibility to chronic pain following nerve injury. CACNG2 encodes for stargazin, a protein intimately involved in the trafficking of glutamatergic AMPA receptors. The protein might also be a Ca(2+) channel subunit. CACNG2 has previously been implicated in epilepsy. Initially, using two fine-mapping strategies in a mouse model (recombinant progeny testing [RPT] and recombinant inbred segregation test [RIST]), we mapped a pain-related quantitative trait locus (QTL) (Pain1) into a 4.2-Mb interval on chromosome 15. This interval includes 155 genes. Subsequently, bioinformatics and whole-genome microarray expression analysis were used to narrow the list of candidates and ultimately to pinpoint Cacng2 as a likely candidate. Analysis of stargazer mice, a Cacng2 hypomorphic mutant, provided electrophysiological and behavioral evidence for the genes functional role in pain processing. Finally, we showed that human CACNG2 polymorphisms are associated with chronic pain in a cohort of cancer patients who underwent breast surgery. Our findings provide novel information on the genetic basis of neuropathic pain and new insights into pain physiology that may ultimately enable better treatments.

pain2: A neuropathic pain QTL identified on rat chromosome 2

&NA; We aimed to locate a chronic pain‐associated QTL in the rat (Rattus norvegicus) based on previous findings of a QTL (pain1) on chromosome 15 of the mouse (Mus musculus). The work was based on rat selection lines HA (high autotomy) and LA (low autotomy) which show a contrasting pain phenotype in response to nerve injury in the neuroma model of neuropathic pain. An F2 segregating population was generated from HA and LA animals. Phenotyped F2 rats were genotyped on chromosome 7 and chromosome 2, regions that share a partial homology with mouse chromosome 15. Our interval mapping analysis revealed a LOD score value of 3.63 (corresponding to p = 0.005 after correcting for multiple testing using permutations) on rat chromosome 2, which is suggestive of the presence of a QTL affecting the predisposition to neuropathic pain. This QTL was mapped to the 14–26 cM interval of chromosome 2. Interestingly, this region is syntenic to mouse chromosome 13, rather than to the region of mouse chromosome 15 that contains pain1. This chromosomal position indicates that it is possibly a new QTL, and hence we name it pain2. Further work is needed to replicate and to uncover the underlying gene(s) in both species.

Deep evolutionary conservation of autism-related genes

Significance Sociobiological theory proposed that similarities between human and animal societies reflect similar evolutionary origins. We used comparative genomics to test this controversial idea by determining whether superficial behavioral similarities between humans and honey bees reflect shared molecular mechanisms. We found unique and significant enrichment for autism spectrum disorder-related genes in the neurogenomic signatures of a high-level integration center of the insect brain in bees unresponsive to two different salient social stimuli. These results demonstrate deep conservation for genes implicated in autism spectrum disorder in humans and genes associated with social responsiveness in honey bees. Comparative genomics thus provides a means to test theory on the biology of social behavior. E. O. Wilson proposed in Sociobiology that similarities between human and animal societies reflect common mechanistic and evolutionary roots. When introduced in 1975, this controversial hypothesis was beyond science’s ability to test. We used genomic analyses to determine whether superficial behavioral similarities in humans and the highly social honey bee reflect common molecular mechanisms. Here, we report that gene expression signatures for individual bees unresponsive to various salient social stimuli are significantly enriched for autism spectrum disorder-related genes. These signatures occur in the mushroom bodies, a high-level integration center of the insect brain. Furthermore, our finding of enrichment was unique to autism spectrum disorders; brain gene expression signatures from other honey bee behaviors do not show this enrichment, nor do datasets from other human behavioral and health conditions. These results demonstrate deep conservation for genes associated with a human social pathology and individual differences in insect social behavior, thus providing an example of how comparative genomics can be used to test sociobiological theory.

Behavioral, transcriptomic and epigenetic responses to social challenge in honey bees

Understanding how social experiences are represented in the brain and shape future responses is a major challenge in the study of behavior. We addressed this problem by studying behavioral, transcriptomic and epigenetic responses to intrusion in honey bees. Previous research showed that initial exposure to an intruder provokes an immediate attack; we now show that this also leads to longer‐term changes in behavior in the response to a second intruder, with increases in the probability of responding aggressively and the intensity of aggression lasting 2 and 1 h, respectively. Previous research also documented the whole‐brain transcriptomic response; we now show that in the mushroom bodies (MBs) there are 2 waves of gene expression, the first highlighted by genes related to cytoskeleton remodeling, and the second highlighted by genes related to hormones, stress response and transcription factors (TFs). Overall, 16 of 37 (43%) of the TFs whose cis‐motifs were enriched in the promoters of the differentially expressed genes (DEGs) were also predicted from transcriptional regulatory network analysis to regulate the MB transcriptional response, highlighting the strong role played by a relatively small subset of TFs in the MBs transcriptomic response to social challenge. Whole brain histone profiling showed few changes in chromatin accessibility in response to social challenge; most DEGs were ‘ready’ to be activated. These results show how biological embedding of a social challenge involves temporally dynamic changes in the neurogenomic state of a prominent region of the insect brain that are likely to influence future behavior.

Social influences on body size and developmental time in the bumblebee Bombus terrestris

In many social insects, including bumblebees, the division of labor between workers relates to body size, but little is known about the factors influencing larval development and final size. We confirmed and extend the evidence that in the bumblebee Bombus terrestris the adult bee body size is positively correlated with colony age. We next performed cross-fostering experiments in which eggs were switched between incipient (before worker emergence) and later stage colonies with workers. The introduced eggs developed into adults similar in size to their unrelated nestmates and not to their same-age full sisters developing in their mother colony. Detailed observations revealed that brood tending by the queen decreases, but does not cease, in young colonies with workers. We next showed that both worker number and the queen presence influenced the final size of the developing brood, but only the queen influence was mediated by shortening developmental time. In colonies separated by a queen excluder, brood developmental time was shorter in the queenright compartment. These findings suggest that differences in body size are regulated by the brood interactions with the queen and workers, and not by factors inside the eggs that could vary along with colony development. Finally, we developed a model showing that the typical increase in worker number and the decrease in brood contact with the queen can account for the typical increase in body size. Similar self-organized social regulation of brood development may contribute to the optimization of growth and reproduction in additional social insects.

Laboratory Assay of Brood Care for Quantitative Analyses of Individual Differences in Honey Bee (Apis mellifera) Affiliative Behavior

Care of offspring is a form of affiliative behavior that is fundamental to studies of animal social behavior. Insects do not figure prominently in this topic because Drosophila melanogaster and other traditional models show little if any paternal or maternal care. However, the eusocial honey bee exhibits cooperative brood care with larvae receiving intense and continuous care from their adult sisters, but this behavior has not been well studied because a robust quantitative assay does not exist. We present a new laboratory assay that enables quantification of group or individual honey bee brood “nursing behavior” toward a queen larva. In addition to validating the assay, we used it to examine the influence of the age of the larva and the genetic background of the adult bees on nursing performance. This new assay also can be used in the future for mechanistic analyses of eusociality and comparative analyses of affilative behavior with other animals.

Endocrine Influences on Insect Societies

Insect societies are defined by an intricate division of labor among individuals. There is a reproductive division of labor between queens and workers, and a division of labor among workers for all activities related to colony growth and development. The different castes in an insect society and the diverse roles they play are extreme manifestations of phenotypic plasticity. This chapter reviews the roles that various hormones play in governing different forms of division of labor in the insect societies, including juvenile hormone (JH), the ecdysteroids, insulin, biogenic amines, and neuropeptides. We discuss how these endocrine systems regulate diverse physiological and molecular processes during development and adulthood by serving as key signal transducers to combine information about internal and external state. We also draw on the results of a burgeoning literature on transcriptomic studies to propose a theoretical framework for how hormones modulate brain transcriptomic architecture underlying social behavior to generate phenotypic plasticity. A key feature of this framework is the notion that there has been neofunctionalization of certain endocrine systems via the rewiring of ancestral transcriptional regulatory networks. We end this chapter by presenting a mechanistic model for the evolution of insect sociality based on the co-option of endocrine pathways to respond to and regulate social behavior, using JH as a model system. In particular, we explore the relationship between the degree of neofunctionalization in JH-related pathways, the life stage at which JH modulates social stimuli, and the degree of phenotypic plasticity exhibited by various species.

Quantifying the effects of pollen nutrition on honey bee queen egg laying with a new laboratory system

Honey bee populations have been declining precipitously over the past decade, and multiple causative factors have been identified. Recent research indicates that these frequently co-occurring stressors interact, often in unpredictable ways, therefore it has become important to develop robust methods to assess their effects both in isolation and in combination. Most such efforts focus on honey bee workers, but the state of a colony also depends on the health and productivity of its queen. However, it is much more difficult to quantify the performance of queens relative to workers in the field, and there are no laboratory assays for queen performance. Here, we present a new system to monitor honey bee queen egg laying under laboratory conditions and report the results of experiments showing the effects of pollen nutrition on egg laying. These findings suggest that queen egg laying and worker physiology can be manipulated in this system through pollen nutrition, which is consistent with findings from field colonies. The results generated using this controlled, laboratory-based system suggest that worker physiology controls queen egg laying behavior. Additionally, the quantitative data generated in these experiments highlight the utility of the system for further use as a risk assessment tool.

Honey bee neurogenomic responses to affiliative and agonistic social interactions.

Social interactions can be divided into two categories, affiliative and agonistic. How neurogenomic responses reflect these opposing valences is a central question in the biological embedding of experience. To address this question, we exposed honey bees to a queen larva, which evokes nursing, an affiliative alloparenting interaction, and measured the transcriptomic response of the mushroom body brain region at different times after exposure. Hundreds of genes were differentially expressed at distinct time points, revealing a dynamic temporal patterning of the response. Comparing these results to our previously published research on agonistic aggressive interactions, we found both shared and unique transcriptomic responses to each interaction. The commonly responding gene set was enriched for nuclear receptor signaling, the set specific to nursing was enriched for olfaction and neuron differentiation, and the set enriched for aggression was enriched for cytoskeleton, metabolism, and chromosome organization. Whole brain histone profiling after the affiliative interaction revealed few changes in chromatin accessibility, suggesting that the transcriptomic changes derive from already accessible areas of the genome. Although only one stimulus of each type was studied, we suggest that elements of the observed transcriptomic responses reflect molecular encoding of stimulus valence, thus priming individuals for future encounters. This hypothesis is supported by behavioral analyses showing that bees responding to either the affiliative or agonistic stimulus exhibited a higher probability of repeating the same behavior but a lower probability of performing the opposite behavior. These findings add to our understanding of the biological embedding at the molecular level.