Behavioral and Neurogenomic Responses to Acoustic and Visual Sexual Cues are Correlated in Female Torrent Frogs

Diverse a nimal species use multimodal communica tion signals to coordina te reproductive behavior.Despite active research in this field,the brain mechanisms underlying multimodal communication remain poorly understood.Similar to humans and many mammalian species,anurans often produce auditory signals accompanied by conspicuous visual cues(e.g.,vocal sac inflation).In this study,we used video playbacks to determine the role of vocal-sac inflation in little torrent frogs(Amolops torrentis).Then we exposed females to blank,visual,auditory,and audiovisual stimuli and analyzed whole brain tissue gene expression changes using RNAseq.The results showed that both auditory cues(i.e.,male advertisement calls)and visual cues were attractive to female frogs,although auditory cues were more attractive than visual cues.Females preferred simultaneous bimodal cues to unimodal cues.The hierarchical clustering of differentially expressed genes showed a close relationship between neurogenomic states and momentarily expressed sexual signals.We also found that the Gene Ontology terms and KEGG pathways involved in energy metabolism were mostly increased in blank contrast versus visual,acoustic,or audiovisual stimuli,indicating that brain energy use may play an important role in response to these stimuli.In sum,behavioral and neurogenomic responses to acoustic and visual cues are correlated in female little torrent frogs.     

Characterizing the vibratory and acoustic signals of the “purring” wolf spider,Gladicosa gulosa (Araneae: Lycosidae)

Both airborne acoustic signals and substrate-borne vibrations are prevalent modes of animal communication, particularly in arthropods. While a wide variety of animals utilize one or both of these modalities, the connection between them is still ambiguous in many species. Spiders as a group are not known for using, or even perceiving, acoustic signals, despite being well-adapted for vibratory communication. Males of the “purring” wolf spider Gladicosa gulosa are reported to produce audible signals during courtship, although the literature on this species is largely anecdotal. Using a laser Doppler vibrometer and an omnidirectional microphone in controlled conditions, we recorded and characterized the visual and mechanical (both substrate-borne and airborne) signals of this species in an attempt to provide a qualitative and quantitative overview of its signal properties. We found that the vibratory signal is composed of two primary repeating and alternating elements, consisting of pulses of stridulation and percussive strikes, as well as a less common, but repeatable, third element. We also characterized a measurable airborne component to the signal that is significantly correlated with the amplitude of the vibratory signal, which we suggest is a by-product of the strong vibration. Neither modality correlated significantly with male body size or condition. Although the exact role of the acoustic component is unclear, we speculate that the unique properties of signalling in this species may have value in answering new questions about animal communication.     

Manipulation of colony environment modulates honey bee aggression and brain gene expression

The social environment plays an essential role in shaping behavior for most animals. Social effects on behavior are often linked to changes in brain gene expression. In the honey bee (Apis mellifera L.), social modulation of individual aggression allows colonies to adjust the intensity with which they defend their hive in response to predation threat. Previous research has showed social effects on both aggression and aggression‐related brain gene expression in honey bees, caused by alarm pheromone and unknown factors related to colony genotype. For example, some bees from less aggressive genetic stock reared in colonies with genetic predispositions toward increased aggression show both increased aggression and more aggressive‐like brain gene expression profiles. We tested the hypothesis that exposure to a colony environment influenced by high levels of predation threat results in increased aggression and aggressive‐like gene expression patterns in individual bees. We assessed gene expression using four marker genes. Experimentally induced predation threats modified behavior, but the effect was opposite of our predictions: disturbed colonies showed decreased aggression. Disturbed colonies also decreased foraging activity, suggesting that they did not habituate to threats; other explanations for this finding are discussed. Bees in disturbed colonies also showed changes in brain gene expression, some of which paralleled behavioral findings. These results show that bee aggression and associated molecular processes are subject to complex social influences .     

Conservation in Mammals of Genes Associated with Aggression-Related Behavioral Phenotypes in Honey Bees

The emerging field of sociogenomics explores the relations between social behavior and genome structure and function. An important question is the extent to which associations between social behavior and gene expression are conserved among the Metazoa. Prior experimental work in an invertebrate model of social behavior, the honey bee, revealed distinct brain gene expression patterns in African and European honey bees, and within European honey bees with different behavioral phenotypes. The present work is a computational study of these previous findings in which we analyze, by orthology determination, the extent to which genes that are socially regulated in honey bees are conserved across the Metazoa. We found that the differentially expressed gene sets associated with alarm pheromone response, the difference between old and young bees, and the colony influence on soldier bees, are enriched in widely conserved genes, indicating that these differences have genomic bases shared with many other metazoans. By contrast, the sets of differentially expressed genes associated with the differences between African and European forager and guard bees are depleted in widely conserved genes, indicating that the genomic basis for this social behavior is relatively specific to honey bees. For the alarm pheromone response gene set, we found a particularly high degree of conservation with mammals, even though the alarm pheromone itself is bee-specific. Gene Ontology identification of human orthologs to the strongly conserved honey bee genes associated with the alarm pheromone response shows overrepresentation of protein metabolism, regulation of protein complex formation, and protein folding, perhaps associated with remodeling of critical neural circuits in response to alarm pheromone. We hypothesize that such remodeling may be an adaptation of social animals to process and respond appropriately to the complex patterns of conspecific communication essential for social organization.     

The Shaking Signal of the Honey Bee Informs Workers to Prepare for Greater Activity

One of the most conspicuous activities of worker bees inside a hive is the shaking of other workers. This shaking has long been suspected to be a communication behavior, but its information content and function have until recently remained mysterious. Prior studies of the colony-level patterns of the production of the shaking signal suggest strongly that this signal serves to arouse workers to greater activity, such as at times of good foraging. Data from our observations of individual bees bolster the hypothesis that the shaking signal informs workers to prepare for a higher level of activity. We followed foragers in a colony whose only source of ‘nectar’ was a sugar-water feeder and discovered that when the feeder was left empty for 1–3 d and then refilled, the first bees to find the food initially produced only shaking signals upon return to the hive. It was not until they had completed several trips to the feeder that they began to produce waggle dances. Evidently, the shaking signal and the waggle dance function together to stimulate a colony's foragers to activity.     

period expression in the honey bee brain is developmentally regulated and not affected by light, flight experience, or colony type

Changes in circadian rhythms of behavior are related to age-based division of labor in honey bee colonies. The expression of the clock gene period (per) in the bee brain is associated with age-related changes in circadian rhythms of behavior, but previous efforts to firmly associate per brain expression with division of labor or age have produced variable results. We explored whether this variability was due to differences in light and flight experience, which vary with division of labor, or differences in colony environment, which are known to affect honey bee behavioral development. Our results support the hypothesis that per mRNA expression in the bee brain is developmentally regulated. One-day-old bees had the lowest levels of expression and rarely showed evidence of diurnal fluctuation, while foragers and forager-age bees (> 21 days of age) always had high levels of brain per and strong and consistent diurnal patterns. Results from laboratory and field experiments do not support the hypothesis that light, flight experience, and colony type influence per expression. Our results suggest that the rate of developmental elevation in per expression is influenced by factors other than the ones studied in our experiments, and that young bees are more sensitive to these factors than foragers.     

Age- and behaviour-related changes in the expression of biogenic amine receptor genes in the antennae of honey bees (Apis mellifera)

We recently identified changes in amine-receptor gene expression in the antennae of the honey bee that correlate with shifts in the behavioural responsiveness of worker bees towards queen mandibular pheromone. Here we examine whether variations in expression of amine-receptor genes are related to age and/or to behavioural state. Colonies with a normal age structure were used to collect bees of different ages, as well as pollen foragers of unknown age. Single- and double-cohort colonies were established also to generate nurses and pollen foragers of the same age. Amdop1 was the only gene examined that showed no significant change in expression levels across the age groups tested. However, expression of this gene was significantly higher in 6-day-old nurses than in pollen foragers of the same age. Levels of expression of Amdop2 were very variable, particularly during the first week of adult life, and showed no correlation with nursing or foraging behaviour. Amdop3 and Amtyr1 expression levels changed dramatically with age. Interestingly, Amtyr1 expression was significantly higher in 15-day-old pollen foragers than in same-age nurses, whereas the opposite was true for Amoa1. While Amoa1 expression in the antennae was lower in 6- and 15-day-old pollen foragers than in nurses of the same age, differences in gene expression levels between nurses and pollen foragers could not be detected in 22-day-old bees. Our data show dynamic modulation of gene expression in the antennae of worker bees and suggest a peripheral role for biogenic amines in regulating behavioural plasticity in the honey bee.     

Modulation of motor behavior by dopamine and the D1-like dopamine receptor AmDOP2 in the honey bee

Determining the specific molecular pathways through which dopamine affects behavior has been complicated by the presence of multiple dopamine receptor subtypes that couple to different second messenger pathways. The observation of freely moving adult bees in an arena was used to investigate the role of dopamine signaling in regulating the behavior of the honey bee. Dopamine or the dopamine receptor antagonist flupenthixol was injected into the hemolymph of worker honey bees. Significant differences between treated and control bees were seen for all behaviors (walking, stopped, upside down, grooming, flying and fanning), and behavioral shifts were dependent on drug dosage and time after injection. To examine the role of dopamine signaling through a specific dopamine receptor in the brain, RNA interference was used to reduce expression levels of a D1-like receptor, AmDOP2. Injection of Amdop2 dsRNA into the mushroom bodies reduced the levels of Amdop2 mRNA and produced significant changes in the amount of time honey bees spent performing specific behaviors with reductions in time spent walking offset by increases in grooming or time spent stopped. Taken together these results establish that dopamine plays an important role in regulating motor behavior of the honey bee.