Ant Pheidole Dentata Research Articles

Age, worksite location, neuromodulators, and task performance in the ant Pheidole dentata.

Social insect workers modify task performance according to age-related schedules of behavioral development, and/or changing colony labor requirements based on flexible responses that may be independent of age. Using known-age minor workers of the ant Pheidole dentata throughout 68% of their 140-day laboratory lifespan, we asked whether workers found inside or outside the nest differed in task performance and if behaviors were correlated with and/or causally linked to changes in brain serotonin (5HT) and dopamine (DA). Our results suggest that task performance patterns of individually assayed minors collected at these two spatially different worksites were independent of age. Outside-nest minors displayed significantly higher levels of predatory behavior and greater activity than inside-nest minors, but these groups did not differ in brood care or phototaxis. We examined the relationship of 5HT and DA to these behaviors in known-age minors by quantifying individual brain titers. Both monoamines did not increase significantly from 20 to 95 days of age. DA did not appear to directly regulate worksite location, although titers were significantly higher in outside-nest than inside-nest workers. Pharmacological depletion of 5HT did not affect nursing, predation, phototaxis or activity. Our results suggest that worker task capabilities are independent of age beyond 20 days, and only predatory behavior can be consistently predicted by spatial location. This could reflect worker flexibility or variability in the behavior of individuals collected at each location, which could be influenced by complex interactions between age, worksite location, social interactions, neuromodulators, and other environmental and internal regulators of behavior.

Nest relocation in the ant Pheidole dentata

We studied nest relocation in the ant Pheidole dentata, a common species in the southern US, by following colonies for 6 weeks. We correlated probability of relocation with several abiotic and biotic environmental factors, such as air temperature, humidity, leaf litter depth (LLD), nest type and presence of phorid fly parasitoids. Colonies moved often, on average every 16.2 days. By the end of our study, fewer than 5 % of colonies marked at the start remained in their original nests. Only 3.1 % of colonies returned to a previously used nest. The mean distance of relocation was 0.76 ± 0.73 m. Colonies nested in a variety of locations, such as in the ground, by tree trunks, under rocks and inside wood. Several factors affected probability of relocation. Higher LLD and vapor pressure deficit (VPD) increased probability of relocation. Probability of relocation varied by nest type, by plot and week of study. We found no evidence that surface cover or rain affected relocation behavior. Colonies appear to avoid nests that become dry by nesting against tree trunks. Phorid fly abundance correlated negatively with VPD, yet it had no effect on colonies’ likelihood of relocation. We discuss other implications of frequent nest relocations.

Brood-care experience, nursing performance, and neural development in the ant Pheidole dentata

Social insect workers mature behaviorally and physiologically with increasing age, generally transitioning from or adding new tasks to their existing repertoire of within-nest nursing tasks. As adult minor workers of the ant Pheidole dentata age, they attend to brood more frequently and nurse more efficiently, perform a broader array of tasks, and undergo myological and neural development. Because these factors covary, the causal relationships among age, task experience, and neural and physiological maturation are not understood. We compared brood-care performance and efficiency by 10-day-old P. dentata minors that had acquired nursing experience to that of equal-age minors experimentally deprived of brood contact. We found the frequency and efficiency of nursing did not significantly differ between experimental and control worker groups, suggesting experience is not required for age-related improvement in nursing efficiency. Workers with and without prior nursing experience did not significantly differ macroscopically in brain anatomy or in brain serotonin content, although workers from the two treatments had slightly, but significantly, different levels of brain dopamine. These results suggest experience with brood is not required for P. dentata minor workers to develop nursing proficiency or undergo a substantial degree of the age-related neural development identifiable by our assessments, which could underscore the ontogeny of brood-care efficiency.

Division of labor and structural plasticity in an extrinsic serotonergic mushroom body neuron in the ant Pheidole dentata

Worker polyphenisms in ants enable insightful analyses of neuronal underpinnings of division of labor, a crucial aspect of animal social organization. In the ant Pheidole dentata, which has a dimorphic worker caste, serotonin titer increases in the brain with age, modulating pheromonal recruitment communication and foraging, behaviors characteristic of mature individuals. Serotonin-immunoreactive (5HT-IR) neurons are found in the mushroom bodies (MB) and may modulate multi-sensory information processing associated with cues and social signals guiding task performance. The volume of this neuropil correlates with worker subcaste and age in P. dentata, but the role of structural variation in individual extrinsic MB neurons in division of labor in ants is poorly understood. We tested the hypothesis that branching complexity in a 5HT-IR calyx input neuron (CIN) in the MBs increases with age in minor workers of P. dentata in association with task repertoire expansion. We further predicted that major workers, which are defense specialists, have less elaborate CIN axonal arbors at any age in comparison to minor workers, which are task generalists. Contrary to our predictions, immunohistochemical and morphometric analyses revealed significantly greater CIN branching in both newly eclosed and mature major workers, and identified an effect of worker age on branching complexity only in majors. Our results indicate a modulatory role of the CIN in subcaste-specific behaviors and suggest behavioral specialization may be associated with the elaboration of specific MB neurons.

Morphine addiction in ants: visualizing a neurochemical pathway of drug reward

Morphine addiction in ants: visualizing a neurochemical pathway of drug reward

Aging brains and social behavior in an invertebrate model: neuromodulation and neuroanatomy of task attendance across the worker lifespan of the ant Pheidole dentata

Aging brains and social behavior in an invertebrate model: neuromodulation and neuroanatomy of task attendance across the worker lifespan of the ant Pheidole dentata

Serotonin modulates worker responsiveness to trail pheromone in the ant Pheidole dentata

As social insect workers mature, outside-nest tasks associated with foraging and defense are typically performed at higher frequencies. Foraging in ants is often a pheromonally mediated collective action performed by mature workers; age-dependent differences in olfactory response thresholds may therefore proximately regulate task repertoire development. In the ant Pheidole dentata, foraging activity increases with chronological age in minor workers, and is chemically controlled. The onset of foraging in minor workers is accompanied by marked neuroanatomical and neurochemical changes, including synaptic remodeling in olfactory regions of the brain, proliferation of serotonergic neurons, and increased brain titers of monoamines, notably serotonin. We examined the linkage of serotonin and olfactory responsiveness by assaying trail-following performance in mature P. dentata minor workers with normal serotonin levels, or serotonin levels experimentally lowered by oral administration of the serotonin synthesis inhibitor α-methyltryptophan (AMTP). By assessing responsiveness to standardized pheromone trails, we demonstrate that trail-following behaviors are significantly reduced in serotonin-depleted workers. AMTP-treated individuals were less likely to initiate trail following, and oriented along pheromone trails for significantly shorter distances than untreated, similar-age workers. These results demonstrate for the first time that serotonin modulates olfactory processes and/or motor functions associated with cooperative foraging in ants.

Coming of age in an ant colony: cephalic muscle maturation accompanies behavioral development in Pheidole dentata

Although several neurobiological and genetic correlates of aging and behavioral development have been identified in social insect workers, little is known about how other age-related physiological processes, such as muscle maturation, contribute to task performance. We examined post-eclosion growth of three major muscles of the head capsule in major and minor workers of the ant Pheidole dentata using workers of different ages with distinct task repertoires. Mandible closer muscle fibers, which provide bite force and are thus critical for the use of the mandibles for biting and load carrying, fill the posterio-lateral portions of the head capsule in mature, older workers of both subcastes. Mandible closer fibers of newly eclosed workers, in contrast, are significantly thinner in both subcastes and grow during at least the next 6days in minor workers, suggesting this muscle has reduced functionality for a substantial period of adult life and thus constrains task performance capability. Fibers of the antennal muscles and the pharynx dilator, which control antennal movements and food intake, respectively, also increase significantly in thickness with age. However, these fibers are only slightly thinner in newly eclosed workers and attain their maximum thickness over a shorter time span in minors. The different growth rates of these functionally distinct muscles likely have consequences for how adult P. dentata workers, particularly minors, develop their full and diverse task repertoire as they age. Workers may be capable of feeding and interacting socially soon after eclosion, but require a longer period of development to effectively use their mandibles, which enable the efficient performance of tasks ranging from nursing to foraging and defense.

Age and task efficiency in the ant Pheidole dentata: young minor workers are not specialist nurses

Age-related task performance, or temporal polyethism, is a prominent characteristic of labour organization in most social insects. In many species, including almost all ants, young workers perform within-nest tasks such as brood rearing and queen attendance and transition to tasks outside the nest as they age. We examined temporal polyethism in the ant Pheidole dentata by constructing single-age cohort subcolonies and directly determining the ability of young and old minor workers to care for the queen and developing brood. In contrast to the predictions of most temporal polyethism models, larvae reared by old workers gained significantly more mass than those reared by young workers, and did not differ significantly in mass from larvae reared by groups of workers of intermediate age. Additionally, old workers were more responsive to brood care and queen care needs than young workers: old workers approached, cared for and retrieved brood more frequently than young workers, and engaged in more queen-directed behaviours even though young workers tended to remain in closer proximity to the queen. These results do not support the traditional characterization of young workers as a discrete temporal caste specialized to respond to queen and brood needs. Although brood and queen care are performed earlier in development than foraging, older workers retain the ability to perform these tasks and do so with high efficiency. Our study suggests that the apparent specialization of young P. dentata minor workers on nursing may be an artefact of their age-related repertoire expansion and development of task proficiencies.

Age‐ and subcaste‐related patterns of serotonergic immunoreactivity in the optic lobes of the ant Pheidole dentata

Serotonin, a biogenic amine known to be a neuromodulator of insect behavior, has recently been associated with age-related patterns of task performance in the ant Pheidole dentata. We identified worker age- and subcaste-related patterns of serotonergic activity within the optic lobes of the P. dentata brain to further examine its relationship to polyethism. We found strong immunoreactivity in the optic lobes of the brains of both minor and major workers. Serotonergic cell bodies in the optic lobes increased significantly in number as major and minor workers matured. Old major workers had greater numbers of serotonergic cell bodies than minors of a similar age. This age-related increase in serotonergic immunoreactivity, as well as the presence of diffuse serotonin networks in the mushroom bodies, antennal lobes, and central complex, occurs concomitantly with an increase in the size of worker task repertoires. Our results suggest that serotonin is associated with the development of the visual system, enabling the detection of task-related stimuli outside the nest, thus playing a significant role in worker behavioral development and colony-wide division of labor.

Age-related repertoire expansion and division of labor in Pheidole dentata (Hymenoptera: Formicidae): a new perspective on temporal polyethism and behavioral plasticity in ants

The controversy concerning the extent to which the organization of division of labor in social insects is a developmental process or is based on task allocation dynamics that emerge from colony need independent of worker age and endocrine or neural state has yet to be resolved. We present a novel analysis of temporal polyethism in the ant Pheidole dentata, demonstrating that task attendance by minor workers does not shift among spatially associated sets of behaviors that minimally overlap but rather expands with age. Our results show that the number of tasks performed by older minors increases through the addition and retention of behaviors, with up to a sixfold increase in repertoire size from day 1 to day 20 of adult life. We also show that older minors respond to colony needs by performing significantly more brood care as its demand increases, indicating that they can quickly upregulate nursing according to labor requirements. This level of plasticity was absent in younger siblings. The breadth of responsiveness to task-related olfactory stimuli increased with age. In a binary choice test in which young and old minor workers could orient toward odorants from brood or food, older workers responded to both brood and food, whereas young workers responded only to brood. These dissimilar responses to stimuli associated with nursing and foraging indicate age-related differences in sensory ability and provide a physiological basis for the age-related repertoire expansion model. We discuss repertoire expansion in P. dentata in light of behavioral development and caste flexibility in ants.

Age-related changes in biogenic amines in individual brains of the ant Pheidole dentata

The behavioral development of minor workers of the ant Pheidole dentata involves a progression of tasks beginning with brood care and culminating in foraging as individuals age. To understand the role of brain neurochemistry in age-related division of labor, we measured the levels of serotonin, dopamine and octopamine in individual brains of minor workers of different age. Serotonin and dopamine levels were significantly correlated with worker age: both increased as minor workers matured, and serotonin rose significantly in the oldest ants. In addition, the serotonin:dopamine ratio was significantly higher in the oldest workers. Octopamine levels did not change with age, although the ratios of octopamine:serotonin and octopamine:dopamine were significantly higher in the youngest workers. These age-associated changes in biogenic amine levels suggest an involvement of neuromodulators in minor worker behavioral ontogeny and temporal polyethism in P. dentata.

Age-related changes in the number and structure of synapses in the lip region of the mushroom bodies in the antPheidole dentata

Behavioral development in the worker caste of many adult ants follows a pattern of task transitions that contribute to the division of labor within colonies. In the ant Pheidole dentata, the number of tasks that minor workers attend to increases as they progress from brood-care activities within the nest to acts outside the nest such as foraging and defense. In this study we investigated synapse maturation in the lip region of mushroom bodies in young and old minor workers because of its potentially crucial role in behavioral development, task performance, and repertoire expansion. As minor workers aged, individual presynaptic boutons enlarged and acquired more synapses and vesicles, but the total number of synapses in the lip region did not change significantly. Glial cell processes occupied less of the synaptic neuropil as ants matured. These findings indicate an expansion and enhancement of efficacy at specific sets of synaptic connections between the projection interneurons and Kenyon cell dendrites and a commensurate loss of other connections as minor workers age and expand their behavioral repertoire.

Behavioral flexibility in age castes of the antPheidole dentata

Division of labor among size and age classes in social insect colonies is a fundamental aspect of sociality, with such classes typically showing behavioral specialization and being associated with particular tasks for prolonged periods of time (i.e., forming castes). Theoretically, such specialization and division of labor enhance efficiency and, ultimately, reproductive success, and the ratios among members of those castes are hypothesized to be under selection and adaptive. However, our recent field study of the ant Pheidole dentatashowed no correlation between ecological factors which should affect colony growth and those caste ratios but implied flexibility in the association between minor worker age castes and their tasks. In laboratory experiments on behavioral flexibility in minor age castes of P. dentataold workers in colonies without young workers competently perform both old worker (caste“typical”) and young worker (“atypical”) tasks, and vice versa. The implications of these results for ergonomie theory are considered.

Social organization in the ant Pheidole dentata

Caste theory states that the proportions of individuals in different demographic classes of an insect society should vary with environmental factors, and are adaptive because they enhance colony-level efficiency. We examined the proportions of workers in different age and size classes (temporal and physical castes) in whole colonies of the ant Pheidole dentata collected in two different habitats. Despite significant ecological differences between the habitats in competition, resource availability and predation, we found no differences in the physical and temporal caste structures of colonies. Also, there was no correlation between physical or temporal caste ratios and the reproductive output of colonies. Because of topography, distance between sites, and apparent low vagility of Pheidole alates, we assume that gene flow between the sites is inadequate to account for the observed similarities. Although age- and size-related patterns of division of labor were observed, similarities in the behavioral profiles (the sum of the relative contributions of each age cohort to the performance of tasks) in colonies having different age caste structures suggests that worker, flexibility may be more important than rigidly programmed age- and size-correlated patterns of task performance.