The Vibration Signal and Juvenile Hormone Titers in Worker Honeybees, Apis mellifera

We examined the association between the vibration signal and juvenile hormone (JH) titers of honeybees by comparing vibrated recipients and non‐vibrated control workers that had been matched for age, colony of origin, and time of collection. Recipients collected at the moment they received vibration signals (0‐min bees) did not have higher JH titers compared with controls, which suggests that a worker's initial JH level did not influence its likelihood of receiving signals. In contrast, JH titers in workers collected 15–30 min after receiving vibration signals were slightly, but significantly higher than those of controls monitored for the same amount of time. These trends were consistent among colonies, despite the fact that we collected different age ranges of workers and observed pronounced variation in JH titers within and between the 0‐ and 15–30‐min groups of bees. Thus, over a broad age range of workers the vibration signal may contribute to elevated JH levels, and this effect does not occur because recipients have higher titers at the moment they receive signals. Because JH affects response thresholds in honeybees, increased titers elicited by the vibration signal may allow the signal to influence the performance of a variety of tasks in different worker age groups.     

Physiological correlates of division of labor among similarly aged honey bees

Hormone analyses and exocrine gland measurements were made to probe for physiological correlates of division of labor among similarly aged adult worker honey bees (Apis mellifera L.). Middle-age bees (ca. 2 weeks old) performing different tasks showed significant differences in both juvenile hormone (JH) biosynthesis rates and hemolymph titers; guards and undertakers had high JH, and wax producers and food storers, low JH. Guards and undertakers had similar hormone levels to foragers, even though they were 10 days younger than foragers. No differences in JH were detected among young bees (1-week-old queen attendants and nurses) or older bees (3–4 week-old pollen foragers, non-pollen foragers, and soldiers). Hypopharyngeal gland size was inversely correlated with worker age and rate of JH biosynthesis, but soldiers had significantly larger hypopharyngeal glands than did foragers, despite their similar age and JH level. Results from soldiers indicate that exocrine gland development is not always linked with age-related behavior and endocrine development; they also support the recent claim that soldiers constitute a group of older bees that are distinct from foragers. Hormonal analyses indicate that the current model of JH's role in honey bee division of labor needs to be expanded because high levels of JH are associated with several other tasks besides foraging. JH may be involved in the regulation of division of labor among similarly aged workers in addition to its role in age-related division of labor.Abbreviations JH Juvenile hormone - RIA radioimmunoassay - CA corpora allata - HPLC high performance liquid chromatography - TLC thin layer chromatography     

Intraspecific aggression in rosyside dace, a drift-feeding stream cyprinid

Individual rosyside dace Clinostomus funduloides in a semi-natural, artificial stream displayed substantial differences in their aggressiveness and could be classified as: (1) non-aggressive (NA, 18 of 30 rosyside dace), (2) moderately aggressive (MA, 9 of 30) and (3) highly aggressive (HA, 3 of 30). Rosyside dace groups, however, did not exhibit linear dominance hierarchies and fish size was only weakly correlated with the number of aggressive acts performed per individual. Small rosyside dace (<56 mm L_F) were always non-aggressive, but larger fish were present in all three aggression classes. The difference in size between the contestants was significantly, although not very strongly, correlated with the probability of winning an agonistic interaction (r ²=0·39). Aggressive rosyside dace may have ultimately gained higher fitness than less aggressive ones. HA individuals occupied the upstream-most position within foraging groups significantly more often than other rosyside dace. This location should be the most profitable one because its occupant will be the first to encounter prey. HA rosyside dace also occupied significantly higher focal velocities that were closer to energetic optima than MA and NA ones. They also had greater foraging rates and were less solitary than less aggressive fish, but these differences only were significant at the P=0·066 and P=0·081 level, respectively. Finally, HA fish performed significantly more aggressive acts and feedings backwards than other individuals. Despite these differences, the effects of intraspecific aggression in rosyside dace appeared less substantial than those that have been observed in stream salmonids.     

Dominance,Age and Aggression among Female Pronghorn,Antilocapra americana (Family: Antilocapridae)

The relationships among dominance, age and aggressive behaviour of marked, female pronghorn (Antilocapra americana; Family Antilocapridae) were studied in north central Colorado. Females formed dominance hierarchies with few circular relationships. Unlike other female ungulates, dominance rank was not correlated with age. Dominance rank was negatively correlated with rate of aggression initiated in summer and winter; however, aggressiveness as an individual trait was not related to dominance. Older females received higher rates of aggression than younger females in summer and winter. During the rut, dominance rank was correlated with rate of aggression received but not with rate of aggression initiated. Patterns of aggression that differ by season within a given hierarchy of dominance relationships suggest a different cause or function of aggressive behaviour in different seasons.     

Limits on volume changes in the mushroom bodies of the honey bee brain

The behavioral maturation of adult worker honey bees is influenced by a rising titer of juvenile hormone (JH), and is temporally correlated with an increase in the volume of the neuropil of the mushroom bodies, a brain region involved in learning and memory. We explored the stability of this neuropil expansion and its possible dependence on JH. We studied the volume of the mushroom bodies in adult bees deprived of JH by surgical removal of the source glands, the corpora allata. We also asked if the neuropil expansion detected in foragers persists when bees no longer engage in foraging, either because of the onset of winter or because colony social structure was experimentally manipulated to cause some bees to revert from foraging to tending brood (nursing). Results show that adult exposure to JH is not necessary for growth of the mushroom body neuropil, and that the volume of the mushroom body neuropil in adult bees is not reduced if foraging stops. These results are interpreted in the context of a qualitative model that posits that mushroom body neuropil volume enlargement in the honey bee has both experience-independent and experience-dependent components.     

Methoprene does not affect juvenile hormone titers in honey bee (Apis mellifera) workers

Methoprene, a juvenile hormone (JH) analog, is a widely used insecticide that also accelerates behavioral development in honey bees (Apis mellifera). JH regulates the transition from nursing to foraging in adult worker bees, and treatment with JH or methoprene have both been shown to induce precocious foraging. To determine how methoprene changes honey bee behavior, we compared JH titers of methoprene‐treated and untreated bees. Behavioral observations confirmed that methoprene treatment significantly increased the number of precocious foragers in 3 out of 4 colonies. In only 1 out of 4 colonies, however, was there a significant difference in JH titers between the methoprene‐treated and control bees. Further, in all 4 colonies, there was no significant differences in JH titers between precocious and normal‐aged foragers. These results suggest that methoprene did not directly affect the endogenous JH secreted by corpora allata. Because methoprene caused early foraging without changing workers’ JH titers, we conclude that methoprene most likely acts directly on the JH receptors as a substitute for JH.     

Social Modulation of Stress Reactivity and Learning in Young Worker Honey Bees

Alarm pheromone and its major component isopentylacetate induce stress-like responses in forager honey bees, impairing their ability to associate odors with a food reward. We investigated whether isopentylacetate exposure decreases appetitive learning also in young worker bees. While isopentylacetate-induced learning deficits were observed in guards and foragers collected from a queen-right colony, learning impairments resulting from exposure to this pheromone could not be detected in bees cleaning cells. As cell cleaners are generally among the youngest workers in the colony, effects of isopentylacetate on learning behavior were examined further using bees of known age. Adult workers were maintained under laboratory conditions from the time of adult emergence. Fifty percent of the bees were exposed to queen mandibular pheromone during this period, whereas control bees were not exposed to this pheromone. Isopentylacetate-induced learning impairments were apparent in young (less than one week old) controls, but not in bees of the same age exposed to queen mandibular pheromone. This study reveals young worker bees can exhibit a stress-like response to alarm pheromone, but isopentylacetate-induced learning impairments in young bees are suppressed by queen mandibular pheromone. While isopentylacetate exposure reduced responses during associative learning (acquisition), it did not affect one-hour memory retrieval.     

Juvenile hormone levels are increased in winners of cockroach fights

In lobster cockroach (Nauphoeta cinerea) adult males, concomitant expression of attack behavior and an increase in juvenile hormone (JH) III titer can be induced by contact with an isolated antenna [Chou et al., 2007. Antenna contact and agonism in the male lobster cockroach, Nauphoeta cinerea. Horm. Behav. 52, 252–260]. In the present study, socially naïve N. cinerea males that were either aggressive posture-adopting (i.e., “ready-for-fight”) or not (i.e., “non-ready-for-fight”) were paired to ask if status was determined by JH III levels before the encounter and if JH III levels were altered in dominants and subordinates after the encounter. The results showed that, although in the non-aggressive posture-adopting male pairs, the one with higher JH titers before the encounter was more likely to become the dominant, this was not the case in pairs formed between aggressive posture-adopting males or between non-aggressive posture-adopting and aggressive posture-adopting males. In all types of male pairs combined, JH III levels in the dominant were significantly increased after the encounter compared with before the encounter and were significantly higher than those in the subordinates, suggesting that the JH III increase in the dominants may serve to sustain aggression. JH III application before rank formation had a significant effect on establishment of dominant status in non-aggressive posture-adopting, but not aggressive posture-adopting, males. After rank formation, JH III application to subordinates had no effect on rank switch. These results indicate that the relationship between JH and aggression in this cockroach species is broadly consistent with the vertebrate challenge hypothesis, which predicts that testosterone levels increase in response to social stimuli to modulate aggression.     

The influence of drone physical condition on the likelihood of receiving vibration signals from worker honey bees, <Emphasis Type="Italic">Apis mellifera</Emphasis>

Honey bee workers will perform vibration signals on adult drones, which respond by increasing the time spent receiving trophallaxis. Because trophallaxis provides the proteins for sexual maturation, workers could direct vibration signals towards drones showing certain physical characteristics, potentially influencing drone development and colony reproductive output. We examined the influence of drone condition on the likelihood of receiving vibration signals by comparing body weight, protein concentrations, and hemolymph juvenile hormone (JH) titers between drones that received the vibration signal and same-age, non-vibrated controls. Vibrated and control drones did not differ in total body weight, abdomen weight, abdomen-to-body weight ratio, total protein concentrations, or hemolymph JH titers. In contrast, vibrated drones had significantly lower thorax weight and smaller thorax-to-body weight ratios compared with controls. Because relative thorax weight may affect flight ability and mating success, workers could use the vibration signal to increase the care received by less developed drones, potentially contributing to the production of greater numbers of competitive males. However, the differences in thorax weights, while significant, were very small, and it is unknown how such slight differences might be assessed by workers or affect drone performance. Nevertheless, vibration signals performed on drones may provide opportunities for exploring the effect of the quality of reproductive individuals on caste interactions in honey bees.     

Iterative evolution of increased behavioral variation characterizes the transition to sociality in spiders and proves advantageous

Abstract The evolution of group living is regarded as a major evolutionary transition and is commonly met with correlated shifts in ancillary characters. We tested for associations between social tendency and a myriad of abiotic variables (e.g., temperature and precipitation) and behavioral traits (e.g., boldness, activity level, and aggression) in a clade of spiders that exhibit highly variable social structures (genus Anelosimus). We found that, relative to their subsocial relatives, social species tended to exhibit reduced aggressiveness toward prey, increased fearfulness toward predators, and reduced activity levels, and they tended to occur in warm, wet habitats with low average wind velocities. Within-species variation in aggressiveness and boldness was also positively associated with sociality. We then assessed the functional consequences of within-species trait variation on reconstituted colonies of four test species (Anelosimus eximius, Anelosimus rupununi, Anelosimus guacamayos, and Anelosimus oritoyacu). We used colonies consisting of known ratios of docile versus aggressive individuals and group foraging success as a measure of colony performance. In all four test species, we found that groups composed of a mixture of docile and aggressive individuals outperformed monotypic groups. Mixed groups were more effective at subduing medium and large prey, and mixed groups collectively gained more mass during shared feeding events. Our results suggest that the iterative evolution of depressed aggressiveness and increased within-species behavioral variation in social spiders is advantageous and could be an adaptation to group living that is analogous to the formation of morphological castes within the social insects.     

Larval juvenile hormone treatment affects pre-adult development,but not adult age at onset of foraging in worker honey bees (Apis mellifera)

Previous research has shown that juvenile hormone (JH) titers increase as adult worker honey bees age and treatments with JH, JH analogs and JH mimics induce precocious foraging. Larvae from genotypes exhibiting faster adult behavioral development had significantly higher levels of juvenile hormone during the 2nd and 3rd larval instar. It is known that highly increased JH during this period causes the totipotent female larvae to differentiate into a queen. We treated third instar larvae with JH to test the hypothesis that this time period may be a developmental critical period for organizational effects of JH on brain and behavior also in the worker caste, such that JH treatment at a lower level than required to produce queens will speed adult behavioral development in workers. Larval JH treatment did not influence adult worker behavioral development. However, it made pre-adult development more queen-like in two ways: treated larvae were capped sooner by adult bees, and emerged from pupation earlier. These results suggest that some aspects of honey bee behavioral development may be relatively insensitive to pre-adult perturbation. These results also suggest JH titer may be connected to cues perceived by the adult bees indicating larval readiness for pupation resulting in adult bee cell capping behavior.     

Acceptance by Honey Bee Guards of Non‐Nestmates is not Increased by Treatment with Nestmate Odours

Honey bee, Apis mellifera, entrance guards use chemical cues to discriminate nestmates from non‐nestmates. Previous research has shown that when wax combs are reciprocally swapped between two colonies, guards become more accepting of workers from the swap partner. However, when combs were transferred only one way, guards in the comb‐receiver colony became more accepting of bees from the comb‐donor colony, but not vice versa. Hence, the increased acceptance of non‐nestmates caused by reciprocal comb swapping was not because of introduced bees acquiring odours from the transferred combs, which was surprising because comb wax was known to affect the odour of bees. In the current experiment, we caused workers to acquire either nestmate or non‐nestmate odours by holding them for 15 min in a tube, which had previously held nestmates or non‐nestmates and then measured their acceptance by entrance guards of nestmate or non‐nestmate hives. When transferred workers had acquired odours of non‐nestmates, acceptance by their own colony’s guards significantly decreased to 66% from 91%. Conversely, the acceptance of non‐nestmates that had acquired odours of the guards’ own nestmates was unchanged, 25% vs. 25%. These results show that when equivalent changes in the odour of introduced bees are made, guards are more sensitive to changes that cause nestmates to acquire non‐nestmate odours than vice versa. These results are also a likely explanation for the earlier and surprising results from the unidirectional comb swap experiment ( Couvillon et al. 2007 ). We make a hypothesis for the underlying mechanism in terms of a multidimensional recognition cue space.     

Changes in weight of the pharyngeal gland and haemolymph titres of juvenile hormone,protein and vitellogenin in worker honey bees

Four physiological parameters (haemolymph-juvenile hormone titre, protein concentration, vitellogenin concentration, and pharyngeal gland dry weight) were examined in the following categories of queenright adult worker bees: summer bees 1–40 days old, winter bees 80–130 days old, 12–100-day old bees at the beginning of winter, 100–195-day old bees at the end of winter, and 1–100-day old bees experimentally induced to live longer in summer.In contrast to the continuously increasing titre of juvenile hormone in ageing summer bees, winter bees kept a constant low level. In bees at the beginning of winter, the hormone titre never reached high values. However, at the end of winter it rose from a low to a high level, comparable with the high titre of 24–40-day old summer bees. In experimentally induced longlived bees in summer, the juvenile hormone titre did not increase as in normal summer bees but remained low as in bees at the beginning of winter. Among the known natural juvenile hormones, only juvenile hormone III was present in the haemolymph of winter bees.The results support the hypothesis of polyphenism being regulated by the titre of juvenile hormone in the haemolymph.     

Seasonal changes in juvenile hormone titers and rates of biosynthesis in honey bees

Honey bee colonies can respond to changing environmental conditions by showing plasticity in age related division of labor, and these responses are associated with changes in juvenile hormone. The shift from nest taks to foraging has been especially well characterized; foraging is associated with high juvenile hormone titers and high rates of juvenile hormone biosynthesis, and can be induced prematurely in young bees by juvenile hormone treatment or by a shortage of foragers. However, very few studies have been conducted that study plasticity in division of labor under naturally occurring changes in the environment. To gain further insight into how the environment and juvenile hormone influence foraging behavior, we measured juvenile hormone titers and rates of biosynthesis in workers during times of the year when colony activity in temperate climates is reduced: late fall, winter, and early spring. Juvenile hormone titers and rates of biosynthesis decreased in foragers in the fall as foraging diminished and bees became less active. This demonstration of a natural drop in juvenile hormone confirms and extends previous findings when bees were experimentally induced to revert from foraging to within-hive tasks. In addition, endocrine changes in foragers in the fall are part of a larger seasonally related phenomenon in which juvenile hormone levels in younger, pre-foraging bees also decline in the fall and then increase the following spring as colony activity increases. The seasonal decline in juvenile hormone in foragers was mimicked in summer by placing a honey bee colony in a cold room for 8 days. This suggests that seasonal changes in juvenile hormone are not related to photoperiod changes, but rather to changes in temperature and/or colony social structure that in turn influence endocrine and behavioral development. We also found that active foragers in the late winter and early spring had lower juvenile hormone levels than active foragers in late spring. In light of recent findings of a possible link between juvenile hormone and neuroanatomical plasticity in the bee brain, these results suggest that bees can forage with low juvenile hormone, after previous exposure to some threshold level of juvenile hormone leads to changes in brain structure.     

Juvenile hormone profiles of worker honey bees,Apis mellifera,during normal and accelerated behavioural development

Juvenile hormone III (JH) haemolymph titres were quantified in adult worker honey bees under colony conditions conducive to either typical or accelerated behavioural development. JH titres of bees under conditions of accelerated behavioural development were significantly higher than same-aged bees under more typical conditions, even before the onset of foraging. These results are consistent with previous findings indicating that JH plays a causal role in timing the onset of foraging behaviour in honey bees. We also detected a peak of JH in 2-3 day old adult bees, the significance of which is unknown.     

Nest-mate recognition template of guard honeybees (Apis mellifera) is modified by wax comb transfer

In recognition, discriminators use sensory information to make decisions. For example, honeybee (Apis mellifera) entrance guards discriminate between nest-mates and intruders by comparing their odours with a template of the colony odour. Comb wax plays a major role in honeybee recognition. We measured the rejection rates of nest-mate and non-nest-mate worker bees by entrance guards before and after a unidirectional transfer of wax comb from a 'comb donor' hive to a 'comb receiver' hive. Our results showed a significant effect that occurred in one direction. Guards in the comb receiver hive became more accepting of non-nest-mates from the comb donor hive (rejection decreased from 70 to 47%); however, guards in the comb donor hive did not become more accepting of bees from the comb receiver hive. These data strongly support the hypothesis that the transfer of wax comb increases the acceptance of non-nest-mates not by changing the odour of the bees, but by changing the template used by guards.     

Juvenile hormone levels in honey bee (Apis mellifera L.) foragers: foraging experience and diurnal variation

A rising blood titer of juvenile hormone (JH) in adult worker honey bees is associated with the shift from working in the hive to foraging. We determined whether the JH increase occurs in anticipation of foraging or whether it is a result of actual foraging experience and/or diurnal changes in exposure to sunlight. We recorded all foraging flights of tagged bees observed at a feeder in a large outdoor flight cage. We measured JH from bees that had taken 1, 3-5, or >100 foraging flights and foragers of indeterminate experience leaving or entering the hive. To study diurnal variation in JH, we sampled foragers every 6h over one day. Titers of JH in foragers were high relative to nurses as in previous studies, suggesting that conditions in the flight cage had no effect on the relationship between foraging behavior and JH. Titers of JH in foragers showed no significant effects of foraging experience, but did show significant diurnal variation. Our results indicate that the high titer of JH in foragers anticipates the onset of foraging and is not affected by foraging experience, but is modulated diurnally.     

Territorial Behaviour and Social Organization as a Function of the Level of Aggressiveness in Male Mice

Territoriality and social organization were examined in relation to different genetic dispositions for aggressive behaviour. The animals used in the study were male mice of the 51st and 52nd generation of selection for high (Turku Aggressive, TA) and low (Turku Non-Aggressive, TNA) levels of aggressiveness. The level of aggressiveness of the animals was assessed by means of individual tests with non-aggressive standard opponents, after which they were allowed to form individual territories in a 102 times 204 times 90 cm enclosure. TA and TNA males were placed in different enclosures. After 2 wk, when the partitions between individual pens were removed, the behaviour of the animals was observed for a 7-d period. Excessive fighting between the highly aggressive TA males occurred, resulting in the formation of dominant-subordinate relationships. A great number of attacks inflicted were found to be associated with dominance in the colony, and correlated with a high level of aggressiveness when the animals were individually tested for aggression after having been in colony environments. The level of aggressiveness of the TA males that had become subordinates had significantly decreased. The TNA males fought less and were more often found to stay in their original territory for the entire period of observation. The results suggest that different genotypes for aggression arc related to differences in territoriality and social organization in mice.     

Endocrine mediated phenotypic plasticity: Condition-dependent effects of juvenile hormone on dominance and fertility of wasp queens

There has been increasing interest in the mechanisms that mediate behavioral and physiological plasticity across individuals with similar genotypes. Some of the most dramatic plasticity is found within and between social insect castes. For example, Polistes wasp queens can nest alone, dominate a group of cooperative queens, or act as worker-like subordinates who rarely reproduce. Previous work suggests that condition-dependent endocrine responses may play a role in plasticity between castes in the hymenoptera. Here, we test whether condition-dependent endocrine responses influence plasticity within castes in the wasp Polistes dominulus. We experimentally manipulate juvenile hormone (JH) titers in nest-founding queens and assess whether JH mediates variation in behavior and physiology. JH generally increased dominance and fertility of queens, but JH's effects were not uniform across individuals. JH had a stronger effect on the dominance and fertility of large individuals and individuals with facial patterns advertising high quality than on the dominance and fertility of small individuals and those advertising low quality. These results demonstrate that JH has condition-dependent effects. As such, they clarify how JH can mediate different behaviors in well nourished queens and poorly nourished workers. Many Polistes queens nest cooperatively with other queens, so condition-dependent hormonal responses provide a mechanism for queens to adaptively allocate energy based on their probability of successfully becoming the dominant queen. Research on the endocrine basis of plasticity often focuses on variation in endocrine titers alone. However, differential endocrine responses are likely to be a widespread mechanism mediating behavioral and physiological plasticity.