Sean O'DOnnell

Families are the basic units of most animal societies, yet collaborative parental care is rare. Brain structure can change to accommodate the cognitive requirements of new behaviors such as the onset of parental care in fish, rodents, and primates. I asked whether similar patterns in neural and behavioral plasticity hold in arthropods. Hemilepistus reaumuri is a terrestrial isopod that exhibits bi-parental care by guarding the burrow and providing food for its offspring, making it an ideal model for investigating brain plasticity. To describe the neuroanatomical structure of H. reaumuri, I used traditional histology, immunohistochemistry, and nanoCT imaging. I focused on the localization of the antibody "anti-DC0", which is the diagnostic tool for describing insect and crustacean mushroom bodies because it is known to target and visualize regions that support learning and memory. I also described the structure of the central complex which supports parental behaviors such as foraging through the integration of first order sensory inputs into navigation and motor control. To characterize brain plasticity associated with the onset of parental care, I sampled isopods throughout development and found that their central body increased in volume relative to body size from immature to adult phases, associated with changes in body size. There was further body-size independent expansion of the central body in fully grown adults, associated with the transitions between young adult, gestation, and parental provisioning. To compare the behavior of bi-parental isopods to a missing partner, I conducted a field manipulation in which pairs of isopod parents were either left and observed as pairs or manipulated by the removal of one partner. The number of foraging trips decreased at a faster rate for unpaired males than for paired males; this pattern was not seen in females. Females started and ended foraging at the same time regardless of the manipulation and throughout the entire experiment, while unpaired males started foraging later in the day over time, and paired males started earlier. These results indicated some flexibility, mostly on the part of males, to adjust their behavior in response to the loss of a partner. In a final chapter, I provide a published natural history note describing the tendency of other xeric-adapted isopods to follow ant trails and spend time inside their nests.

Chimpanzee insectivory is predominantly focused on social insects (e.g., termites and ants), as they have higher ratio of potential prey yield relative to predation effort. Chimpanzees invest considerable effort into cognitively complex, socially transmitted behaviors focused on acquiring social insects. Many of these behaviors include the modification and implementation of tools made from plant materials, though the methods for utilizing these tools and material preferences of these tools appear to vary culturally between chimpanzee communities, meaning that variation in the same type of tool use between communities is not explained by ecological differences. It has been suggested that insectivory and the complex behaviors used to acquire insect prey have contributed significantly to hominin evolution and encephalization, which implies social insects are a meaningful dietary resource for chimpanzees despite the relatively low proportion of their diets dedicated to insects (~5%). Given the potential importance of social insects as valuable diet items, the high degree of seasonally variability seen in chimpanzee insectivory is perplexing. Social insects are consumed in highly seasonal periods across many chimpanzee communities, and even among communities that consume social insects year-round there are pronounced seasonal peaks. This thesis explores patterns of variation in a common tool-use insectivorous behavior, termite fishing, as well as seasonal patterns of insect prey diversity in the unhabituated Ganga community of Nigeria-Cameroon chimpanzees (Pan troglodytes ellioti) in central Cameroon. To accomplish this, I used camera traps placed at 8 termite mounds near Ganga Research Station in Mbam & Djerem National Park from February 2020 to April 2023, a termite survey conducted at each of the 8 termite mounds from April 2022 to April 2023, and other biomonitoring data (fruit availability and fecal samples) collected at this site monthly from 2016 to 2023. I then combined quantitative ethnographic, quantitative ecological, and molecular methods to characterize behavioral and seasonal variation in the consumption of termites and other insect prey. I used these indirect methods of chimpanzee behavior and diet as the chimpanzees at Ganga are not habituated to human presence. Further, Ganga is an important community in which to study termite fishing, as the majority of studies on this behavior originate from chimpanzee communities inhabiting dense rainforest habitats, with a more recent push to characterize termite fishing in savanna chimpanzee communities as well. Ganga chimpanzees live in a complex savanna-forest ecotone in central Cameroon, and therefore may possess similarities with both rainforest and savanna chimpanzee communities. The first aim of this study was to identify termite fishing techniques and explore inter-individual variation in personal repertoires of P. t. ellioti at Ganga, and to situate patterns of termite fishing behavior at Ganga among that of other more well-studied chimpanzee communities. I identified 29 different termite fishing techniques in the Ganga community whose acquisition is consistent with trial-and-error development via social transmission. A combination of ecological similarity and geographic distance appear to contribute to cultural similarity in termite fishing between Ganga and other chimpanzee communities. The second aim of this study was to examine ecological correlates of termite fishing seasonality at Ganga. P. t. ellioti at Ganga have a highly seasonal period of termite fishing that occurs predominantly during the little rainy season from March to June. Seasonal exploitation of termites in this community appears mediated by termite accessibility in the upper portion of the soil surface. This accessibility appears to be related to termite reproductive behavior and is related to rainfall. Intermediate rainfall levels during the transition from the dry season to the little rainy season may cue termites to prepare for mating flights, which leads to greater presence in the soil surface and greater accessibility to predators. The third aim of this study employs molecular methods to explore seasonal consumption of social insects and insect prey diversity at Ganga using chimpanzee fecal samples. Results suggest infrequent, seasonal consumption of termites as well as frequent consumption of hymenopterans with seasonal peaks primarily in the dry season. Additionally, I found evidence of considerable indirect predation of other insect taxa whose lifecycles are strongly associated with plants or fruits that may be eaten by P. t. ellioti at Ganga. Finally, there was considerable inter-individual variation in arthropod prey between samples, but there is evidence of a more homogenous distribution of arthropod prey among samples from the dry season. The results of this thesis suggests a complex series of associations between environmental factors, insect consumption, and chimpanzee behavior. At Ganga, social insect consumption may be driven in part by opportunistic consumption of insects that are readily available, such as termites during the little rainy season. Environmental factors further appear associated with cultural elements of termite fishing tool use, given similarities in termite fishing between Ganga and distant communities with similar habitats. This suggests that chimpanzee habitats could contribute to chimpanzee cultural complexity. Finally, the high degree of potential secondary predation on a number of arthropod taxa points to an invisible source of nutrition available to chimpanzees, for which the degree of dietary contributions remains unknown. Altogether, insectivory at Ganga appears highly variable both between individuals and between seasons, which can ultimately have implications for nutrition and health in this community.

John Heinz National Wildlife Refuge (JHNWR) is an urban wetland in southeast Philadelphia, Pennsylvania that stretches over 1,000 acres. Its unique habitats are home to a large diversity of flora and fauna, including bees. Not much is known about the true diversity of the bee populations that inhabit JHNWR, but given the global decreases in insect population and the ecological importance of this wildlife refuge surrounded by urbanization, it is important to establish a baseline of what bee species occur there. In collaboration with the Pennsylvania Bee Monitoring Program, a survey was conducted at various locations across the Refuge from April to September, 2022, to document the diversity of bees present. In addition to compiling a species list for JHNWR, this survey was also used to explore three hypotheses: 1) The different microhabitats will have different bee populations, 2) Species will be found that have not previously been recorded to occur at JHNWR or in Philadelphia, and 3) A combination of Blue Vane Traps, Bee Bowls, and Aerial Netting is best to document bee diversity. Using these three collection methods, 2,977 bee specimens were caught and identified to 97 species, 39 of which are new Philadelphia County records. Through statistical analyses in R, it was concluded that the different microhabitats in the Refuge only had slightly similar bee populations, as well as that each of the three collection methods yielded unique bee populations. This shows that to effectively begin to measure the diversity of bee populations in a specific location, a variety of collection methods are needed across several different sites to capture the diversity of unique bee populations so we can monitor and work to conserve them amidst widespread pollinator declines.

The transmission of microbial symbionts across animal species could strongly affect their biology and evolution, but our understanding of transmission patterns and dynamics is limited. Army ants (Formicidae: Dorylinae) and their hundreds of closely associated insect guest species (myrmecophiles) can provide unique insights into interspecific microbial symbiont sharing. Here, we compared the microbiota of workers and larvae of the army ant Eciton burchellii with those of 13 myrmecophile beetle species using 16S rRNA amplicon sequencing. We found that the previously characterized specialized bacterial symbionts of army ant workers were largely absent from ant larvae and myrmecophiles, whose microbial communities were usually dominated by Rickettsia , Wolbachia , Rickettsiella and/or Weissella . Strikingly, different species of myrmecophiles and ant larvae often shared identical 16S rRNA genotypes of these common bacteria. Protein‐coding gene sequences confirmed the close relationship of Weissella strains colonizing army ant larvae, some workers and several myrmecophile species. Unexpectedly, these strains were also similar to strains infecting dissimilar animals inhabiting very different habitats: trout and whales. Together, our data show that closely interacting species can share much of their microbiota, and some versatile microbial species can inhabit and possibly transmit across a diverse range of hosts and environments.

Differences in behaviour and physiology among social insect colonies provide opportunities for evolutionary responses to environmental selection. Colony differences in thermal physiology can indicate potential for social insect populations to accommodate temperature extremes and determine how populations will respond to changing climates. We tested whether army ant ( Eciton burchellii parvispinum ) colonies differed in their distributions of worker tolerances of extreme low temperatures (CT _min ) and extreme high temperatures (CT _max ). We sampled workers across a range of body sizes in each colony, and we collected data from colonies at both warmer low elevation sites and cooler high elevation sites. Colonies differed significantly in the distributions of both CT _min and CT _max ; colony mean CT _min and CT _max were not correlated. The colony differences were not associated with worker body size variation. Some thermal physiology differences were associated with local climates: colonies from warmer lower elevation sites had significantly higher CT _min and higher CT _max , but much of the inter‐colony variation was unexplained. If significant colony variation in thermal physiology is associated with genetic differences, thermal environments could drive evolutionary changes in thermal physiology.

Climate change is predicted to cause significant increases in global temperatures that will place many species under temperature-dependent selection. The consequences of climate change may be especially severe for ectothermic species, which rely heavily on their environment to maintain a non-lethal body temperature. Little attention has been paid to the potential effects of climate change on variable morphology, physiology, or behavior within a species. Alternative reproductive tactics (ARTs) occur when there is categorical variation in the mating-related behavior or morphology of individuals of one sex within a population, and are ideal for investigating the impacts of the thermal environment on behavioral, physiological, or morphological variation. Males of the Sonoran Desert bee Centris pallida use ARTs and are dimorphic in both behavior and morphology. Large-morph males use a fixed strategy that relies on scent to locate mates buried underground. Small-morph males are behaviorally flexible, generally using visual cues to locate females in the sky but sometimes using the scent-based strategy. First, I characterized variation in neuroanatomy between large and small morph C. pallida males, demonstrating that relative investment in visual and olfactory peripheral processing regions support the different mate-location tactics used by the morphs. Next, I demonstrated that small-morph males have increased relative investment in eye size and ommatidia density, but reduced total ommatidia numbers, eye surface areas, and visual acuities compared to large males. These data suggest that both allometric constraints associated with body size and mate location behaviors correlate with external visual investment. Finally, I investigated physiology and morphological adaptations to the microclimates used by the morphs: large-morph males use a hotter microclimate near the ground while small-morph males hover several feet above the surface. Small-morph males have increased thermal tolerance compared to large-morph males, despite a cooler microclimate, suggesting they use a physiological thermal adaptation to survive high environmental temperatures. Large-morph males have increased reflectance of solar radiation on their dorsal, but not ventral, surface as compared to small-morph males, representing a morphological thermal adaptation to the high solar radiation and ambient temperatures experienced in their microclimate. Together, these data suggest that individuals within a species may vary significantly in their adaptive potential under climate change. Variation in morphological/neuroanatomical systems may support different behaviors for individuals within the same species, sex, and population. Unique thermal adaptations, physiological or morphological, may cause differentiation in the intraspecific selective effects of climate change with important implications for range shifts, intraspecific behavioral diversity, and species' survival.

Long fascinated and puzzled researchers, eusociality and the evolutionary mechanisms selecting for and maintaining it are most easily observed within insect societies. In eusocial paper wasps, reproduction is limited to a small subset of females while the remainder forage and feed and care for the offspring. Some hypotheses in the field predict that female reproductive status is shaped by nutrition specifically ingested during larval development, while others predict that wasps emerge as adults with an equal opportunity to develop ovaries in adulthood, depending on their social position and nutrition acquisition within the colony. The goal of my work is to untangle the mechanisms maintaining reproductive caste within a primitively eusocial paper wasp species. Using social network analysis and stable isotope analysis, I found that aggressive female wasps were significantly enriched in nitrogen and spent more time on the nest than subordinate females (and were more likely to have developed ovaries), likely increasing their ability to store the nutrients necessary for building costly reproductive tissue in adulthood. Aggressive and reproductively developed females were also slightly larger in body size, although wing length was distributed normally across reproductive development, indicating that pre-adult body size is not the only factor affecting caste development. Finally, I found evidence that queens status is communicated to nestmates via cuticular hydrocarbons, providing further evidence that nestmate identification (essential to adult dominance interactions) is necessary for caste determination in this species. Taken together, it is likely that caste is shaped by both developmental and adult-stage factors, and further research is necessary in order to fully characterize the development of caste in primitively eusocial insects.

Chapter 1: Cognitive evolution research relies heavily on phylogenetic comparisons of cognitive traits between groups. However, there is no universal brain to body scaling relationship, and scaling relationships can differ significantly between even closely related groups. Thus, comparative research must be paired with investigations of scaling within the subject taxonomic group, in order to detect differences in cognitive traits that are indicative of differences in function. This study investigates allometric scaling relationships between cephalothorax volume, total central nervous system investment, and investment in specific brain regions in Anelosimus spiders. Brain scaling relationships in spiders have been previously understudied, and previous research has predominantly focused on miniaturized spiders. We found that in Anelosimus, total central nervous system size scaled positively with cephalothorax size, and that relative central nervous system investment decreased with increasing cephalothorax size, following Haller's rule in pattern of brain investment. Brain regions differed in scaling relationships; there was a negative relationship between relative arcuate body investment and supraesophageal ganglion size, while relative investment in the protocerebrum was not dependent on total central nervous system volume. Further, we identified sex-specific allometric relationships between relative arcuate body investment and supraesophageal ganglion investment, with females having relatively increased arcuate body investment compared to males. In total, these results lay the groundwork for future comparative work in Anelosimus by establishing scaling relationships. Chapter 2: The evolution of social systems can place novel selective forces on investment in expensive neural tissue by changing cognitive demands. Previous hypotheses about the impact of sociality on neural investment have received equivocal support when tested across diverse taxonomic groups and social structures. We suggest previous models for social behavior-brain relationships have overlooked important variation in social groups. Social groups vary significantly in structure and function, and the specific attributes of a social group may be more relevant to setting cognitive demands than sociality in general. We focus on three attributes of social groups that could influence cognitive demands in different ways: division of labor, including worker specialization and task redundancy, intragroup communication, including information sharing and behavioral coordination, and intragroup conflict, including competition and dominance hierarchy. We outline how variation in these attributes can affect selection for individual cognition, resulting in the possibility of selection for either increased or decreased cognitive investment with transitions to sociality in different taxa. Finally, we test some of the predictions generated using this framework in a phylogenetic comparison of neural tissue investment in Anelosimus social spiders. The social system of Anelosimus is distinct from previously tested social vertebrates and invertebrates because social spiders engage in task sharing and cooperative brood care but lack behavioral and reproductive caste. This decoupling allowed a direct assessment of the cognitive impact of task sharing and cooperative brood care. We hypothesized that in social spider species, these characteristics would reduce selection for cognitive ability relative to subsocial species. We found that social species had significantly decreased investment in the arcuate body, the higher-order cognitive center of the spider brain, supporting our predictions. Future comparative tests of brain evolution in social species should account for the special behavioral characteristics that accompany social groups in the subject taxa.