Dominance behavior can regulate a division of labor in a group, such as that between reproductive and non-reproductive individuals. Manipulations of insect societies in a controlled environment can reveal how dominance behavior is regulated. Here, I examined how morphological caste, fecundity, group size, and age influence the expression of dominance behavior using the ponerine ant Harpegnathos saltator. All H. saltator females have the ability to reproduce. Only those with a queen morphology that enables dispersal, however, show putative sex pheromones. In contrast, those with a worker morphology normally express dominance behavior. To evaluate how worker-like dominance behavior and associated traits could be expressed in queens, I removed the wings from alate gynes, those with a queen morphology who had not yet mated or left the nest, making them dealate. Compared to gynes with attached wings, dealates frequently performed dominance behavior. In addition, only the dealates demonstrated worker-like ovarian activity in the presence of reproductive individuals, whereas gynes with wings produced sex pheromones exclusively. Therefore, the attachment of wings determines a gyne’s expression of worker-like dominance behavior and physiology. When the queen dies, workers establish a reproductive hierarchy among themselves by performing a combination of dominance behaviors. To understand how reproductive status depends on these interactions as well as a worker’s age, I measured the frequency of dominance behaviors in groups of different size composed of young and old workers. The number of workers who expressed dominance scaled with the size of the group, but younger ones were more likely to express dominance behavior and eventually become reproductive. Therefore, the predisposition of age integrates with a self-organized process to form this reproductive hierarchy. A social insect’s fecundity and fertility signal depends on social context because fecundity increases with colony size. To evaluate how a socially dependent signal regulates dominance behavior, I manipulated a reproductive worker’s social context. Reproductive workers with reduced fecundity and a less prominent fertility signal expressed more dominance behavior than those with a stronger fertility signal and higher fecundity. Therefore, dominance behavior reinforces rank to compensate for a weak signal, indicating how social context can feed back to influence the maintenance of dominance. Mechanisms that regulate H. saltator’s reproductive hierarchy can inform how the reproductive division of labor is regulated in other groups of animals.

The living world is replete with easily observed structural adaptations (e.g. teeth, claws, and stingers), but behavioral adaptations are no less impressive. Conspecific aggression can be defined as any harmful action directed by one animal at another of the same species. Because it is a potentially risky and costly behavior, aggression should be elicited only under optimal conditions. In honeybees, nestmate recognition is considered the driving factor determining whether colony guards will aggress against other honeybees attempting to gain entry to the colony. Models and empirical research support the conclusion that nestmate recognition should be favored over direct kin recognition. Thus, bees tend to use environmentally mediated cues associated with their colonies (e.g. colony odors) to recognize nestmates. The framework of nestmate recognition suggests that non-nestmates should always be aggressed against while nestmates should always be accepted. However, aggression towards nestmates and acceptance of non-nestmates are seen in a wide variety of eusocial insects, including honeybees. These are typically classified as rejection errors and acceptance errors, respectively. As such, they can be explained using signal detection theory and optimal acceptance threshold models, which postulate that recognition errors are inevitable if there is overlap in the cues used to distinguish “desirables” (fitness-enhancing) from “undesirables” (fitness-decrementing) conspecifics. In the context of social insects desirables are presumed to be nestmates and undesirables are presumed to be non-nestmates. I propose that honeybees may make more refined decisions concerning what conspecifics are desirable and undesirable, accounting for at least some of the phenomena previously reported as recognition errors. Some “errors” may be the result of guard bees responding to cues associated with threats and benefits beyond nestmate identity. I show that less threatening neighbors receive less aggression than highly threatening strangers. I show that well-fed colonies exhibit less aggression and that bees from well-fed colonies receive less aggression. I provide evidence that honeybees may decrease aggression towards nestmates and non-nestmate not involved in robbing while increasing aggression towards non-nestmate from a robber colony. Lastly, I show that pollen bearing foragers, regardless of nestmate identity, receive little to no aggression compared to non-pollen bearing foragers.

Social animals benefit from the aggregation of knowledge and cognitive processing power. Part of this benefit comes from individual heterogeneity, which provides the basis to group-level strategies, such as division of labor and collective intelligence. In turn, the outcomes of collective choices, as well as the needs of the society at large, influence the behavior of individuals within it. My dissertation research addresses how the feedback between individual and group-level behavior affects individuals and promotes collective change. I study this question in the context of seed selection in the seed harvester ant, Pogonomyrmex californicus. I use both field and laboratory studies to explore questions relating to individual behavior: how forager decision-making is affected through information available in the nest and at the seed pile; how workers interact with seeds in the nest; and how forager preferences diverge from each other’s and the colony’s preference. I also explore the integration between individual and colony behavior, specifically: how interactions between the foraging and processing tasks affect colony collection behavior; how individual behavior changes affect colony preference changes and whether colony preference changes can be considered learning behavior. To answer these questions, I provided colonies with binary choices between seeds of unequal or similar quality, and measured individual, task group, and colony-level behavior. I found that colonies are capable of learning to discriminate between seeds, and learned information lasts at least one month without seed interaction outside of the nest. I also found that colony learning was coordinated by foragers receiving updated information from seeds in the nest to better discriminate and make choices between seed quality during searches for seeds outside of the nest. My results show that seed processing is essential for stimulating collection of novel seeds, and that foraging and processing are conducted by behaviorally and spatially overlapping but distinct groups of workers. Finally, I found that foragers’ preferences are diverse yet flexible, even when colonies are consistent in their preference at the population level. These combined experiments generate a more detailed and complete understanding of the mechanisms behind the flexibility of collective colony choices, how colonies incorporate new information, and how workers individually and collectively make foraging decisions for the colony in a decentralized manner.

In our exponentially expanding world, the knowledge of a group versus that of an individual is more relevant than ever. Social insects have evolved to rely on the information from the collective, and in the case of harvester ants, their choice revolves around the best seeds to collect.
The objective of this experiment is to study a colony’s seed preference following previous exposure to a seed type in the seed harvester ant Pogonomyrmex californicus. It was hypothesized that foragers would demonstrate a measurable preference for the seed type they had previously experienced over the novel seed type. The cuticular hydrocarbon profile is suspected to be an influence in the foragers’ seed selection. Following an incubation period with the designated seed type, a series of preference trials were conducted over the course of two days for two experiments in which each colony fragment was given a seed pile with a 1:1 ratio of niger and sesame, after which any seeds moved off the seed pile were determined to be chosen, as well as if the workers were observed moving the seeds off the pile from the video recordings. Using video recordings, the seed selections of individual foragers were also tracked. The results partially support the hypothesis, however, in some cases, the ants did not collect enough seeds for the preference to be significant, and not all colony fragments had preferences that lined up with what they had previously experienced according to their treatment. Familiarity with the hydrocarbon profile of the seed type the colony had experienced is a possible proximal explanation for why colonies had seed preferences that aligned with their treatment, the seed they were designated to experience. Due to the low quantity of seeds collected during preference trials, seed preference amongst individual foragers remains unclear due to many different foragers selecting a seed during only one trial, with very few foragers returning to forage for seeds over the course of the experiment.

Studies of cooperation remain an important aspect in understanding the evolution of social cues and interactions. One example of cooperation is pleometrosis, an associative behavior of forming a colony with two unrelated, fertile queens. However, most ant species display haplometrosis, the founding of a colony by a single queen. In these associations, the queen typically rejects cooperation. In populations of Pogonomyrmex californicus, both pleometrosis and haplometrosis exists. It is not clear how associative -metrosis became a practiced behavior since haplometrotic queens tend to fight. However, as fighting in pleometrotic queens became less frequent, this induces benefit, in terms of cost savings, in having associative behaviors. The hypothesis tested was nest excavation of pleometrotic queens show sociality, while haplometrotic queens show association independence. Isolated pleometrotic queens (P) showed low excavation rate at 2.72cm2/day, compared to the rate when the task was shared in (PP) nests, 4.57cm2/day. Nest area of the (P) queens were also affected during days 3 and 4 of the experiment, where there was presence of nest area decrease. Furthermore, the excavation session of (P) was the only one determined as significant between all other nests. Although the (P) queens have low values, they eventually reach a similar point as the other nests by day 6. However, the lack of haste in excavation leads to longer exposure to the elements, substituting the risk of losing cuticles in excavation for the risk of predation. For the haplometrotic queens, nests of (H) and (HH) displayed no significant difference in excavation values, leading to having social effect in their association.

Persistent cooperation between unrelated conspecifics rarely occurs in mature eusocial insect societies. In this dissertation, I present evidence of non-kin cooperation in the Nearctic honey ant Myrmecocystus mendax. Using microsatellite markers, I show that mature colonies in the Sierra Ancha Mountain of central Arizona contain multiple unrelated matrilines, an observation that is consistent with primary polygyny. In contrast, similar analyses suggest that colonies in the Chiricahua Mountains of southeastern Arizona are primarily monogynous. These interpretations are consistent with field and laboratory observations. Whereas cooperative colony founding was observed frequently among groups of Sierra Ancha foundresses, founding in the Chiricahua population was restricted to individual foundresses. Furthermore, Sierra Ancha foundresses successfully established incipient laboratory colonies without undergoing queen culling following emergence of the first workers. Multi-queen laboratory Sierra Ancha colonies also produced more workers and repletes than haplometrotic colonies, and when brood raiding was induced between colonies, queens of those with more workers had a higher survival probability.

Microsatellite analyses of additional locations within the M. mendax range suggest that polygyny is also present in some other populations, especially in central-northern Arizona, albeit at lower frequencies than that in the Sierra Anchas. In addition, analyses of multiple types of genetic data, including microsatellites, the mitochondrial barcoding region, and over 2000 nuclear ultra-conserved elements indicate that M. mendax populations within the southwestern U.S. and northwestern Mexico are geographically structured, with strong support for the existence of two or more divergent clades as well as isolation-by-distance within clades. This structure is further shown to correlate with variation in queen number and hair length, a diagnostic taxonomic feature used to distinguish honey ant species.

Together, these findings suggest that regional ecological pressures (e.g. colony density , climate) may have acted on colony founding and social strategy to select for increasing workforce size and, along with genetic drift, have driven geographically isolated M. mendax populations to differentiate genetically and morphologically. The presence of colony fusion in the laboratory and life history traits in honey ant that are influenced by colony size, including repletism, brood raiding, and tournament, support this evolutionary scenario.

In order to survive, species must regulate their intake of nutrients. In desert leafcutter ant colonies, acquisition of nutrients is not only important for maintaining the health of the colony, but also for the survival of a fungus which the ants cultivate and then consume. This multi-trophic, symbiotic relationship is relatively unique to leafcutter ants and interesting to researchers due to the complexity of how the individual foragers supply nutrients to both the colony and the fungus. The objective of this experiment is to study foraging rates and variation in macronutrient preference among foragers from the same colony of the desert leafcutter ant Acromyrmex versicolor. This study asks if individual foragers vary in their preference of protein to carbohydrate ratios when compared to the overall nutrient content of the colony, and how do these individuals respond as the nutrient content of the available diets increasingly deviates from the previously determined nutritional intake target ratio between 1 Protein:6.3 Carbohydrates to 1 Protein:7.5 Carbohydrates. It was hypothesized that foragers express individualized nutritional preferences that in aggregate balance colony macronutrient consumption, and the number of individuals collecting the diets would decrease as the available nutritional diets deviated away from the colony-level intake target of approximately 1P:7C. The results show trends that support the hypothesis that the number of foraging instances and the number of foragers who exhibit individualized preference towards a certain protein to carbohydrate ratio is highest when the colony is presented with diets that are closest to the colony nutritional intake target.

This project aims to better understand aggression in a cooperative social system, specifically within the ant species Pogonomyrmex Californicus. The queens of some populations of these ants form cooperative associations of unrelated queens during nest foundation, while others prefer to form solitary nests and may show aggression towards unwanted nest mates. Because it is difficult to collect large amounts of data from a wild population and laboratory environments cannot capture the scale of nature, we created a computer simulation based on data collected in the lab and the field that emulates the life cycle of this species of ants. By manipulating behavioral and environmental conditions and observing the results we were able to better understand the advantages and disadvantages of showing aggression in this cooperative social system.

Division of Labor among social insects is frequently discussed in regards to the colony's worker population. However, before a colony achieves a worker population, a queen is required to perform all of the tasks necessary for her survival: foraging, building the colony, and brood care. A simple ODE model was developed through the use of a framework of replicator equations in dynamical environments to investigate how queen ants perform and distribute all of the tasks necessary for her and her colony's survival by incorporating individual internal thresholds and environmental stimulus. Modi�cations to the internal threshold, risk of performing the task, and the rate of increase of the environmental stimulus were also explored. Because of the simplicity of the model, it could also be used to measure the task performance of larger populations of social insects. However, the model has only been applied to the data collected from Pogonomyrmex barbatus single queen ants.

Pogonomyrmex Californicus, a species of harvester ants, have polyandrous queens, meaning that each queen mates with multiple males before starting a colony. Genetic diversity derived from polyandry can provide fitness benefits to a social insect colony in several ways including an increase in behavioral flexibility of the work force. In some cases, P.californicus colonies can even exhibit polygyny, meaning that multiple queens cooperate to produce workers in a colony. In previous studies, the colony size, worker age, and genotypes of Pogonomyrmex californicus colonies were all found to influence task division to varying degrees, with matrilines appearing to only have influence within their respective colonies. These studies on matrilineal or induced variation and division of labor do not consider the effects of naturally occurring patrilineal variation, and it is unclear how exactly these two traits interact to influence colony function. In order to explore the influence of patriline on task division we raised single-queen P. californicus colonies in the lab and tested the effect of patriline on task performance in the workforce. Behavioral observations, and then genotypic data was collected and analyzed for one focal colony in the lab. The microsatellite data revealed a total of five identified patrilines among the observed workers and a Pearson chi-square test of independence showed a significant relationship between patriline and task performance. This suggests that polyandry alone can provide at least some of the benefits of genetic diversity to colony function. Further testing is needed to determine if the addition of cooperative queens may further increase genetic diversity in a colony and could supplement benefits to workforce performance. The benefits of genetic diversity may not be additive, though, in which case extra matrilines would not provide further benefit for the colony and would not then be a main driver of queen cooperation in this and other systems where polyandry and polygyny co-occur.