I investigate a social parasitism by examining the lives the parasite involved. I use a variety of techniques to understand the population genetics, host acquisition behaviors, and space-use of an obligate parasitic ant (Polyergus mexicanus) that conducts raids to steal the brood of its host species (several Formica spp.) and makes them “slave” workers in the parasite’s nest. I consider the interacting roles of intraspecific competition, kinship, and host specialization on each of these topics.

In Chapter 1, I use microsatellite loci to characterize the genetic structure of the parasite population at three scales: subpopulations, neighboring nests, and among nestmates. I find that there are three very distinct subpopulations that often predict host-use patterns, but not always. Neighboring nests are sometimes closely related, enabling potential kin selection. Lastly, parasite nestmates are overwhelmingly full siblings, yet there were numerous nestmates that must have come from different parents, suggesting that raiding parasites may also steal conspecific brood for enslavement.

In Chapter 2, I characterize raids from an optimal foraging perspective. I found that parasitic colonies that send more raiders further distances obtain more brood on their raids. Nests that are capable of larger raids in general had a higher success rate, and more variability in raid sizes, but not distances. These findings suggest that raids are tailored to the expected quality of the host nest target, and that larger nests have more flexibility in their raiding tactics.

In Chapter 3, I investigate intraspecific competition, aggression, and territoriality among parasites by looking at the spatial arrangement of P. mexicanus nests and raids relative to their conspecific neighbors and their host species. I found that nests were often overdispersed, a classic sign of intraspecific competition. However, contrary to my predictions, raids from neighboring nests that shared host species overlapped more than those that used different host species. Overall, these spatial results suggest that competition among parasites may play out at different life stages, and that the specific identity of host species might determine the nature of conspecific parasitic interactions.

This work documents the complexity and far-reaching implications of parasite-parasite interactions.

All organisms must allocate limited resources to reproduction and survival, producing life history trade-offs. One such trade-off is maternal care, which balances a female’s current reproduction against her future survival. Alternative reproductive tactics have evolved as a way of maximizing lifetime reproductive success by balancing the costs of parental care against the benefits that care provides to current offspring. Conspecific brood parasitism (CBP) is an alternative reproductive tactic where females lay eggs in the nest of a conspecific, providing no further care to those offspring. Some parasitic females may have their own nest in addition to laying parasitically. This results in three possible seasonal reproductive options: nesting and parasitizing, nesting without parasitizing, and parasitizing without nesting. While CBP is taxonomically widespread, it occurs at remarkably high rates in waterfowl. Detecting CBP is challenging, and historically researchers have relied on behavioral and morphological evidence to identify it. Recently, genetic methods of maternity assignment have allowed researchers to detect parasitism directly. However, genetic methods have not been examined under conditions common in waterfowl, where parasitic females may be highly related to their hosts and the candidate parent pool is often incomplete. Additionally, while females can flexibly transition between CBP reproductive options between years, the reproductive success of CBP reproductive options are often quantified by single-season estimates and are rarely considered in the context of the entire lifespan of the females that engage in this behavior.

My dissertation focuses on testing accuracy of both genetic and non-genetic methods of detecting CBP and quantifying long-term patterns of CBP in the wood duck (Aix sponsa) in California. In Chapter 1, I assessed the accuracy of detecting CBP using genetic assignments with simulated wood duck populations. Genetic methods of maternity assignment in the context of CBP in wood ducks rarely make assignment errors given a diverse set of microsatellite markers and a largely complete sample of candidate mothers, but the risk of false exclusion and misassignment does increase with related females in the candidate parent pool. In Chapter 2, I compared field-based genetic and non-genetic estimates of CBP. Non-genetic methods produced underestimates of CBP as compared to genetic estimates. However, in combination with genetic estimates of CBP, non-genetic methods uncovered CBP patterns in wood ducks that genetic methods alone would not have revealed. In Chapter 3, I used genetic assignments to quantify the frequency of CBP in wood ducks at the population level over five years, calculated single-season reproductive success of individual females’ reproductive options, and determined long-term patterns of CBP behavior of individual and their individual lifetime fitness estimates. The frequency of non-parasitic nesting females declined as density of breeding females and nest sites increased. Females that nested and parasitized had the highest reproductive success by single season measurements, while parasites that did not nest had the lowest reproductive success. Nesting parasitism contributed the most offspring to lifetime reproductive success but parasitism alone or nesting without parasitism could result in large fitness gains. Females nested more frequently as they aged, with or without parasitism, and continued to do so until they exited the population. Collectively, the results of my thesis suggest that genetic methods of maternity assignment are robust in CBP waterfowl, and female wood ducks flexibly transition into nesting reproductive options as they age, which ultimately results in higher reproductive success over the course of their lifetimes. My research is one of the first studies to assess lifetime reproductive success in a CBP system and highlights the importance of taking a long-term perspective in studies of alternative reproductive options to fully understand the costs and benefits of engaging in these behaviors.

Social groups can range from cohesive and stable to fluid and temporary, with many variations of the two. Social structure can effect selection pressures on individuals, and in turn, feedback from how social groups are organized can affect selection on different traits and behaviors. Here, I focus on group organization and how individual traits may correlate with sociality, and ultimately, survivorship. The research here ties together multiple threads to understand how individual traits connect to each other to shed light on how stable groups are organized, and which traits are most important to help maintain this structure over time. In Chapter 1, I ask if golden-crowned sparrows have consistent behavior within a season and over multiple years, and if this consistent behavior correlates with behavior in the field and several morphological traits. I found that the sparrows do have consistent behaviors in short-term captivity, yet these are independent of the traits measured here, and may connect with other factors such as predation response or foraging methods. For Chapter 2, I quantified individual sociality using social network measures and asked if dominance, plumage badges of status, sex, age, or mass could predict a sparrows’ social measures. I found that older and smaller birds had more connections. Chapter 3 links the previous chapters as I determined which behaviors and traits affected survivorship over ten years. Higher dominance increased survivorship, while older birds had lower survivorship. However, survivorship only decreased in the oldest age classes, showing evidence of senescence. Chapter 4 builds on Chapter 2, and used GPS tracking to discover if golden-crowned sparrows which were in the same winter communities bred in the same area. I discovered that sparrows in the same social community went to separate breeding locations, showing long-term social memory across migration. This thesis demonstrates that age, size and dominance are important aspects in social behavior and survival. Older individuals had more connections, and in conjunction with previous research, had stronger connections over years. This shows that older individuals can play a keystone role in maintaining cohesiveness of social communities over time.

Stable social organization in a wide variety of organisms has been linked to kinship, which can minimize conflict due to the indirect fitness benefits from cooperating with relatives. In birds, kin selection has been mostly studied in the context of reproduction or in species that are social year round. Many birds however are migratory and the role of kinship in the winter societies of these species is virtually unexplored. A previous study detected striking social complexity and stability in wintering populations of migratory golden-crowned sparrows (Zonotrichia atricapilla)--individuals repeatedly form close associations with the same social partners, including across multiple winters.

In chapter one I test the possibility that kinship might be involved in these close and stable social affiliations. I examine the relationship between kinship and social structure for two of the consecutive wintering seasons from the previous study. I found no evidence that social structure was influenced by kinship--relatedness between most pairs of individuals was at most that of first cousins (and mostly far lower) and Mantel tests revealed no relationship between kinship and pairwise interaction frequency. Kinship also failed to predict social structure in more fine-grained analyses, including analyses of each sex separately (in the event that sex-biased migration might limit kin selection to one sex) and separate analyses for each social community. The complex winter societies of golden-crowned sparrows appear to be based on cooperative benefits unrelated to kin selection. Although the complex social structure detected in wintering golden-crowned sparrows is not predicted by kinship, genetic variation may play a role in variation of winter social traits.

In chapter two, I investigate the genetic causes of variation in fitness-related traits in a winter population of golden-crowned sparrows. Individuals show great variation in morphological and behavioral traits that may play a role in winter dominance and ultimately survival. I found that individuals that were more heterozygous--based on internal relatedness measures reflecting individual genetic variation--were more socially dominant, had larger gold crown patches (which predict social dominance in some contexts) and had stronger social connections within their social networks.

Although the underlying mechanism driving the HFCs detected in this study is unknown, the detection of moderate correlations between an individual's heterozygosity level and social dominance, winter plumage, and sociality is interesting. Theses traits connect in important ways to winter social behavior, suggesting that these HFC analyses detected true relationships. It is therefore feasible that more heterozygous individuals are more socially dominant because they may be, for example, better foragers and have energy to expend on aggressive behaviors. Another reasonable explanation for the relationship between heterozygosity and social dominance could be that more socially dominant birds could be older; heterozygosity might be linked to longevity. Although a physiological mechanism is unknown in sparrows, it is possible that plumage may reflect the general quality (e.g., better immune function) of the individual. As with social dominance, "core" individuals of a community (i.e., individuals that are more likely to be found flocking with other birds of their community) may also be older or higher quality individuals. "Core" individuals interact and have contact with others in the community and may therefore be at higher risk of encountering disease, parasite, and pathogens. If this measure of heterozygosity reflects immune function heterozygosity, then more heterozygous individuals may be more likely to be "core" individuals.

The recent focus on preparing students to pursue careers in science, technology, engineering, and mathematics (STEM) fields have resulted in educational researchers investigating how best to support this goal. Government and private funding has been directed to STEM internship programs (particularly at the undergraduate level). These internship programs are designed to provide workplace opportunities as well as provide support from the program to acquire skills needed by students to transition from school to the workforce. Most of this support has been developed (by internship programs and researchers) in the sciences. Engineers are in high demand and universities and internship programs are tasked with preparing more engineering students to be professional engineers. Our development of the Solution Articulation Framework (SAF), supports learners' (interns) acquisition of argumentation skills in engineering; engaging in argumentative practices promotes content knowledge and communication skills in many disciplines but has not been explored deeply in the engineering education literature. We focused our attention on improving learners' engineering argumentation practices with a particular emphasis on articulation of engineering solutions.

In chapter three, I identify a critical component (functional requirements) to effectively articulating a proposed engineering solution and offer an operational definition along with suggestions for implementing these ideas in engineering education. My findings were immediately used to revise our SAF and warrants further research on other components of the SAF. The research in this chapter advances the emerging research field in engineering education by highlighting the importance and difficulties associated with teaching argumentation skills in engineering.