Identification of Quantitative Trait Loci and candidate genes influencing ethanol sensitivity in honey bees

Preliminary Analysis of Genetic Markers for Functional Ethanol Tolerance in Honey Bees (Apis mellifera) Using a Free-Flying Paradigm

Honey bees are a commonly used species for alcohol research due to their genome being fully sequenced, their behavioral changes following consumption, and their preference for alcohol. The purpose of this article is to provide a preliminary examination of the genetic expression of heat shock protein 70 (HSP70) and big potassium ion channel protein (BKP) in honey bees following the consumption of either 0%, 2.5%, 5%, or 10% ethanol (EtOH) solutions. The foraging behaviors of the bees were observed and recorded through their return and drinking times. There were significant differences in the return and drinking times between some of the groups. The bees in the 10% condition took significantly longer to return compared to the other groups. Additionally, the bees in the 5% group spent significantly more time drinking compared to the bees in the control (0%) group. There were no significant differences in HSP70 or BKP between the different ethanol groups. Cumulatively, these findings suggest that, while bees may exhibit behavioral differences, the differences in gene expression may not be observed at the transcriptional level.

Association of Amine-Receptor DNA Sequence Variants with Associative Learning in the Honeybee

Octopamine- and dopamine-based neuromodulatory systems play a critical role in learning and learning-related behaviour in insects. To further our understanding of these systems and resulting phenotypes, we quantified DNA sequence variations at six loci coding octopamine-and dopamine-receptors and their association with aversive and appetitive learning traits in a population of honeybees. We identified 79 polymorphic sequence markers (mostly SNPs and a few insertions/deletions) located within or close to six candidate genes. Intriguingly, we found that levels of sequence variation in the protein-coding regions studied were low, indicating that sequence variation in the coding regions of receptor genes critical to learning and memory is strongly selected against. Non-coding and upstream regions of the same genes, however, were less conserved and sequence variations in these regions were weakly associated with between-individual differences in learning-related traits. While these associations do not directly imply a specific molecular mechanism, they suggest that the cross-talk between dopamine and octopamine signalling pathways may influence olfactory learning and memory in the honeybee.

Conservation of the Ethanol-Induced Locomotor Stimulant Response among Arthropods

Ethanol-induced locomotor stimulation has been variously described as reflective of the disinhibitory, euphoric, or reinforcing effects of ethanol and is commonly used as an index of acute ethanol sensitivity in rodents. The fruit fly Drosophila melanogaster also shows a locomotor stimulant response to ethanol that is believed to occur via conserved, ethanol-sensitive neurobiological mechanisms, but it is currently unknown whether this response is conserved among arthropod species or is idiosyncratic to D. melanogaster. The current experiments surveyed locomotor responses to ethanol in a phylogenetically diverse panel of insects and other arthropod species. A clear ethanol-induced locomotor stimulant response was seen in 9 of 13 Drosophilidae species tested, in 8 of 10 other species of insects, and in an arachnid (wolf spider) and a myriapod (millipede) species. Given the diverse phylogenies of the species that showed the response, these experiments support the hypothesis that locomotor stimulation is a conserved behavioral response to ethanol among arthropod species. Further comparative studies are needed to determine whether the specific neurobiological mechanisms known to underlie the stimulant response in D. melanogaster are conserved among arthropod and vertebrate species.

A genetic analysis of the stinging and guarding behaviors of the honey bee

In order to identify genes that are influencing defensive behaviors, we have taken a new approach by dissecting colony-level defensive behavior into individual behavioral measurements using two families containing backcross workers from matings involving European and Africanized bees. We removed the social context from stinging behavior by using a laboratory assay to measure the stinging response of individual bees. A mild shock was given to bees using a constant-current stimulator. The time it took bees to sting in response to this stimulus was recorded. In addition, bees that were seen performing guard behaviors at the hive entrance were collected. We performed QTL mapping in two backcross families with SNP probes within genes and identified two new QTL regions for stinging behavior and another QTL region for guarding behavior. We also identified several candidate genes involved in neural signaling, neural development and muscle development that may be influencing stinging and guarding behaviors. The lack of overlap between these regions and previous defensive behavior QTL underscores the complexity of this behavior and increases our understanding of its genetic architecture.

A verification of previously identified QTLs for cocaine-induced activation using a panel of B6.A chromosome substitution strains (CSS) and A/J x C57Bl/6J F2 mice

BACKGROUND

The objective of this study was to confirm provisional quantitative trait loci (QTL) for cocaine-induced locomotor activation, on chromosomes 1, 5, 6, 9, 12, 15, 16, 17, and 18, previously identified in the AXB/BXA recombinant inbred (RI) and AcB/BcA recombinant congenic (RC) strains of mice derived from A/J (A) and C57BL/6J (B6) progenitors. This was accomplished through a genetic analysis of cocaine-induced activity in an AxB6 F2 cross and a phenotypic survey across a panel of B6.A chromosome substitution strains (CSS) mice. Mice were tested for cocaine-induced activity, following administration of saline and cocaine (20 mg/kg), utilizing an open-field procedure.

RESULTS

Among AxB6 F2 mice, differences in cocaine-induced activity were associated with loci on chromosome 1 (D1Mit305), 5 (D5Mit409), 16 (D16Mit131), and 18 (D18Mit189). A survey of the CSS panel confirmed cocaine QTLs on chromosomes 5 and 15, previously identified in RI or RC strains. Overall, the regions on chromosomes 5 and 18 represent verification of QTL previously identified in both the RC and RI strains. Additionally, the B6 allele for these QTL was consistently associated with greater relative cocaine activation.

CONCLUSIONS

Collectively, chromosome 5 and 18 QTL have now been replicated in multiple independent crosses derived from the A/J and C57BL/6J progenitors. The use of an in silico analysis highlighted potential candidate genes on chromosomes 5 and 18. The present results complement the targeted gene approach currently prevalent in the study of cocaine and provide a broader empirically based focus for subsequent candidate gene studies.

Characterization of quantitative trait loci for the age of first foraging in honey bee workers

Identifying the basis of quantitative trait loci (QTL) remains challenging for the study of complex traits, such as behavior. The honey bee is a good model combining interesting social behavior with a high recombination rate that facilitates this identification. Several studies have focused on the pollen hoarding syndrome, identifying multiple QTL as the genetic basis of its behavioral components. One component, the age of first foraging, is central for colony organization and four QTL were previously described without identification of their genomic location. Enabled by the honey bee genome project, this study provides data from multiple experiments to scrutinize these QTL, including individual and pooled SNP mapping, sequencing of AFLP markers, and microsatellite genotyping. The combined evidence confirms and localizes two of the previous QTL on chromosome four and five, dismisses the other two, and suggests one novel genomic region on chromosome eleven to influence the age of first foraging. Among the positional candidates the Ank2, PKC, Erk7, and amontillado genes stand out due to corroborating functional evidence. This study thus demonstrates the power of combined, genome-based approaches to enable targeted studies of a manageable set of candidate genes for natural behavioral variation in the important, complex social trait "age of first foraging".