Sean O'Donnell

• PhD
• Professor at Drexel University

We report field observations of the cosmopolitan terrestrial isopod species Porcellionides pruinosus both inside the nest and following foraging trails of the seed harvester ant Messor ebeninus in the spring of 2022 and 2023. The isopods inside the nest either traveled to deeper tunnels or joined foraging trails. The density of isopods along foragi...

We report field observations of the cosmopolitan terrestrial isopod species Porcellionides pruinosus both inside multiple nests and following foraging trails of the seed harvester ant Messor ebeninus in the spring of 2022 and 2023. To our knowledge, this is the first observation of P. pruinosus in association with any ant species. Isopods inside th...

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 microb...

Solitary, size‐variable bees are adapted to a wide range of thermal environments (e.g., through critical thermal maxima, or CT max ) and are important, understudied subjects for research on species' vulnerability to climate change. Centris pallida are solitary, ground‐nesting desert bees with females varying two‐fold in body mass. We hypothesized t...

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...

Incoming solar radiation (wavelengths 290–2500 nm) significantly affects an organism’s thermal balance via radiative heat gain. Species adapted to different environments can differ in solar reflectance profiles. We hypothesized that conspecific individuals using thermally distinct microhabitats to engage in fitness-relevant behaviors would show int...

The transmission of microbial symbionts across individuals and generations can be critical for animal development and survival. Likewise, the transmission of microbes across closely interacting species could also affect host biology. Army ants (Formicidae: Dorylinae) and their hundreds of closely associated insect species (myrmecophiles) can provid...

Isodontia auripes [Fernald] females nested in fourteen 12-mm diameter artificial trap nests at two locations in New York State (Geneseo and Rensselaerville). We report broods of up to 14 pupae in a single chamber with an average of 5.8 pupae per chamber (previously reported range 2 - 6 pupae/chamber). Nest architecture, with plugs of finely shredde...

Species' mean relative head size decreases with increasing species mean body size in paper wasps, which may have important implications for biomechanics in these flying animals. Here we quantify the allometric relationship (log/log slope) of head size to body size in paper wasps. We sampled species in two genera (Agelaia and Polybia) to test whethe...

Neuroecology theory predicts relative investment in brain regions will vary to match differences in behavior. Social insect castes provide exceptional opportunities to test for adaptive brain investment because castes differ in behavior and in cognitive demands. Caste development in dampwood termites (genus Zootermopsis) is complex, providing multi...

Incoming solar radiation (wavelengths 290 – 2500 nm) significantly impacts an organism's thermal balance via radiative heat gain. Species adapted to different environments can differ in solar reflectance profiles. We hypothesized that conspecific individuals using thermally distinct microhabitats to engage in fitness-relevant behaviors would show i...

Reproductive castes are a defining characteristic of eusocial insects. The developmental timing of reproductive caste differentiation is important to shaping individual opportunities for reproductive flexibility. Because hard-part body size (e.g., wing length) is fixed for insects upon adult emergence, morphology can be used to assess pre-adult eff...

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 behav...

Individual heterogeneity within societies provides opportunities to test hypotheses about adaptive neural investment in the context of group cooperation. Here we explore neural investment in defense specialist soldiers of the eusocial stingless bee (Tetragonisca angustula) which are age sub-specialized on distinct defense tasks and have an overall...

Hypotheses for adaptive brain investment predict associations between the relative sizes of functionally distinct brain regions and the sensory/cognitive demands animals confront. We measured developmental differences in the relative sizes of visual processing brain regions (optic lobes) among dampwood termite castes to test whether optic lobe inve...

Synonyms Central nervous system The field of neuroecology focuses on adaptive evolutionary changes in the central nervous system , particularly in the brain. Brains are excellent organs for exploring the limits of adaptive evolution , as they combine immediate payoffs (such as effective decision-making and behavioral regulation) with elevated costs...

Individual heterogeneity within societies provides opportunities to test hypotheses about adaptive neural investment in the context of group cooperation. Here we explore neural investment in defense specialist soldiers of the eusocial stingless bee (Tetragonisca angustula) which are age sub-specialized on distinct defense tasks, and have an overall...

Alternative reproductive tactics (ARTs) occur when there is categorical variation in the reproductive strategies of a sex within a population. These different behavioral phenotypes can expose animals to distinct cognitive challenges, which may be addressed through neuroanatomical differentiation. The dramatic phenotypic plasticity underlying ARTs p...

Social aggression is a pervasive feature of insect societies. In eusocial Hymenoptera, aggression among females can affect task performance and competition over direct reproduction (egg laying); in most species males participate in social interactions relatively rarely. Males of the independent-founding paper wasp Mischocyttarus mastigophorus are e...

Subterranean foraging army ants (Labidus coecus) preyed on eggs and hatchlings of three species of Amazon River turtles (genus Podocnemis) in northeastern Peru. The raided nests were in a hatchery constructed atop the soil surface of a beach on the Tapiche River. The ant raid persisted across at least 9 days, and ant foraging impacted nests over an...

Social insects are well known for their aggressive (stinging) responses to a nest disturbance. Still, colonies are attacked due to the high-protein brood cached in their nests. Social wasps have evolved a variety of defense mechanisms to exclude predators, including nest construction and coordinated stinging response. Which predatory pressures have...

• Temporal segregation of species' activity periods may lessen interspecific competition. • e tested for temporal segregation among Neotropical army ants (Formicidae: Dorylinae). Co‐occurring species overlap on prey resources, and regular colony movements and long‐distance raiding increase interspecific interference. • We hypothesised interspecific...

Extreme temperatures can constrain foraging behavior, and individual differences in thermal tolerances may affect foraging performance within and among species. Ambient temperatures may thus mediate competitive interactions among species that share resources. Different species of desert seed-harvesting ants (genus Messor) forage for similar food re...

The dominance-nutrition hypothesis predicts that nutritional intake and energetic costs in adulthood interact to drive behavioral and physiological differences between females in primitively eusocial insects, and thereby affect reproductive caste. We tested predictions of this hypothesis in independent-founding Mischocyttarus pallidipectus paper wa...

Ants are significant structural and agricultural pests, generating a need for human-safe and effective insecticides for ant control. Erythritol, a sugar alcohol used in many commercial food products, reduces survival in diverse insect taxa including fruit flies, termites, and mosquitos. Erythritol also decreases longevity in red imported fire ants;...

Tests of hypotheses for the evolution of thermal physiology often rely on mean temperatures, but mounting evidence suggests geographic variation in temperature extremes is also an important predictor of species’ thermal tolerances. Although the tropics are less thermally variable than higher latitude regions, rain shadows on the leeward sides of mo...

Sex-biased dispersal occurs when one sex disperses more frequently or farther than the opposite sex. In ants, dispersal is often male biased and males typically contribute more strongly to gene flow within and among ant populations. However, army ants may offer an exceptional case of female-biased dispersal, because army ant colonies (particularly...

The ability of polyols to disrupt holometabolous insect development has not been studied and identifying compounds in food that affect insect development can further our understanding of the pathways that connect growth rate, developmental timing and body size in insects. High-sugar diets prolong development and generate smaller adult body sizes in...

Evolutionary transitions in social behavior are often associated with changes in species’ brain architecture. A recent comparative analysis showed that the structure of brains of wasps in the family Vespidae differed between solitary and social species: the mushroom bodies, a major integrative brain region, were larger relative to brain size in the...

Damage from termite infestations is economically significant and control can be costly when requiring the widespread use of conventional insecticides. Erythritol, a polyalcohol sweetener that is safe for human consumption, causes increased mortality when ingested by some insects, indicating potential as a safe alternative insecticide. Here, we inve...

Species of wasps in the Vespidae family range widely in body size. Vespid wasp species’ mean brain size increases relative to head capsule size in smaller species. In this study, I tested whether head capsule size varied allometrically with overall body size. I compared species ranging in body size from some of the largest to the smallest species....

Ingestion of the polyol mannitol caused sex-biased mortality in adult Drosophila melanogaster, but larval mortality was not sex-biased. High-sugar diets prolong development and generate smaller adult body sizes in D. melanogaster. We hypothesized that mannitol ingestion would generate similar developmental phenotypes as other high-carbohydrate diet...

Mannitol, a sugar alcohol used in commercial food products, has been previously shown to induce sex-biased mortality in female Drosophila melanogaster when ingested at a single concentration (1 M). We hypothesized that sex differences in energy needs, related to reproductive costs, contributed to the increased mortality we observed in females compa...

Mannitol, a sugar alcohol used in commercial food products, induced sex-specific mortality in the fruit fly Drosophila melanogaster when ingested at a single concentration (1M), and female mortality was greater than male mortality. We hypothesized that sex differences in energy needs, related to reproductive costs, contribute to increased mortality...

Endothermic animals do not always have a single adaptive internal temperature; some species exhibit plastic homeostasis, adaptively allowing body temperature to drop when thermoregulatory costs are high. Like large-bodied endotherms, some animal societies exhibit collective thermal homeostasis. We tested for plasticity of thermoregulation in the se...

In social insects, group members can differ in thermal physiology, and these differences may affect colony function. Upper thermal tolerance limits (CTmax) generally increase with body size among and within ant species, but size effects on lower thermal tolerances (CTmin) are poorly known. To test whether CTmin co-variation with body size matched p...

Eciton burchellii is a Neotropical army ant that influences the ecology of many associated animal species, including their prey and species that attend the ant's foraging raids. At least 29 bird species are obligate specialists on foraging at army ant raid fronts, and additional species across diverse avian orders follow army ant raids in a faculta...

Background In eusocial animal colonies, individuals from different castes often play divergent behavioral roles and confront distinct cognitive demands. Neuroecology theory predicts variation in cognitive demands will correspond to differences in brain investment because brain tissue is energetically expensive. We hypothesized colony-level selectio...

The yellow fever mosquito Aedes aegypti Linnaeus is a major vector of several viruses that cause disease in humans and other animals. Conventional insecticides have been used for vector control, but can be problematic because Ae. aegypti and other mosquitoes can evolve resistance to them and they can negatively impact non‐target insect species. The...

The climatic variability hypothesis (CVH) is a cornerstone of thermal ecology, predicting the evolution of wider organismal thermal tolerance ranges in more thermally variable environments. Thermal tolerance ranges depend on both upper and lower tolerance limits (critical thermal maxima [CTmax] and critical thermal minima [CTmin]), which may show d...

Division of labor in social groups can be influenced by differential nutrition. Consumption of more food or higher-quality food often affects individuals’ capacities for reproduction. In social insects, nutrients consumed during immature (e.g., larval) stages often affect adult reproductive capacity, but adult nutrition may also impact reproductive...

Previous feeding studies showed the polyalcohol erythritol was toxic when ingested by adult laboratory fruit flies (Drosophila melanogaster). We asked whether erythritol could additionally affect fly population growth either through larval toxicity or through effects on adult reproduction. Females did not avoid laying on food substrates with 1M ery...

Directional climate change (global warming) is causing rapid alterations in animals’ environments. Because the nervous system is at the forefront of animals’ interactions with the environment, the neurobiological implications of climate change are central to understanding how individuals, and ultimately populations, will respond to global warming....

Body size limits brain volume, but size may also differentially constrain the volumes of brain regions. Size variation and compartmentalized brains of swarm-founding paper wasps (Epiponini) make them good models for the study of size-related brain allometry. We analysed the relative volumes of brain regions that process different sensory inputs: th...

The performance of integrated biological systems can often be described by the behavior of component subunits: the proportion of subunits performing an activity, and the rate of recruitment to the activity, can be relevant to system performance. We develop a model for activation of subunits (receivers) to a task when activation requires repeated si...

The performance of integrated biological systems can often be described by the behavior of component subunits: the proportion of subunits performing an activity, and the rate of recruitment to the activity, can be relevant to system performance. We develop a model for activation of subunits (receivers) to a task when activation requires repeated si...

In the tropics, daily temperature fluctuations can pose physiological challenges for ectothermic organisms, and upper thermal limits may affect foraging activity over the course of the day. Variation in upper thermal limits can occur among and within species, and for social insects such as ants, within colonies. Within colonies, upper thermal limit...

We describe an emigration of the Neotropical army ant Eciton mexicanum where the head of the emigration column was separated in time from previous raid column activity, and the emigration was not connected to the new bivouac site by a column of workers. Over 12 h elapsed between raid activity and the onset of emigration, suggesting the emigration f...

Eusocial insect reproductive castes (in Hymenoptera, female reproductive queens and sterile workers) differ dramatically in behavior. Castes may differ in the cognitive demands that affect patterns of brain tissue investment. Queens and workers diverge most strongly in the advanced eusocial, or swarm-founding species, where queens do not forage and...

Mixed-species assemblages can involve positive and negative interactions, but uncertainty about high-value patchy resources can increase the value of information sharing among heterospecific co-foragers. I sampled species composition of bird-flocks attending army-ant raids in three adjacent elevation zones in Costa Rica, across multiple years, to t...

Social insect nestmates often differ in thermal tolerance (the range of temperatures at which an individual functions). Worker thermal physiology can covary with body size, development, genetics and gene expression. Because colonies rely on the integration of diverse colony members, individual thermal tolerance differences can affect group performa...

We review research on brain development and brain evolution in the wasp family Vespidae. Basic vespid neuroanatomy and some aspects of functional neural circuitry are well-characterized, and genomic tools for exploring brain plasticity are being developed. Although relatively modest in terms of species richness, the Vespidae include species spannin...

Symbiotic bacteria play important roles in the biology of their arthropod hosts. Yet the microbiota of many diverse and influential groups remain understudied, resulting in a paucity of information on the fidelities and histories of these associations. Motivated by prior findings from a smaller scale, 16S rRNA-based study, we conducted a broad phyl...

Physiological constraints can limit thermal niche breadth in organisms, particularly for small-bodied ectotherms. Daily temperature fluctuations often surpass annual (seasonal) temperature variation in the tropics, suggesting diel temperature cycles could drive thermal specialization by individuals that are active at different times of the day. We...

Physiological constraints can limit thermal niche breadth in organisms, particularly for small-bodied ectotherms. Daily temperature fluctuations often surpass annual (seasonal) temperature variation in the tropics, suggesting diel temperature cycles could drive thermal specialization by individuals that are active at different times of the day. We...

Symbiotic bacteria play important roles in the biology of their arthropod hosts. Yet the microbiota of many diverse and influential groups remain understudied, resulting in a paucity of information on the fidelities and histories of these associations. Motivated by prior findings from a smaller scale, 16S rRNA-based study, we conducted a broad phyl...

Previous work showed the non-nutritive polyol sweetener Erythritol was toxic when ingested by Drosophila melanogaster (Meigen, 1930). This study assessed whether insect toxicity is a general property of polyols. Among tested compounds, toxicity was highest for erythritol. Adult fruit flies (D. melanogaster) fed erythritol had reduced longevity rela...

Active brood-warming in army ant nests (bivouacs) is well documented for surface-dwelling Eciton burchellii and E. hamatum colonies in lowland tropical forests. However, little is known about thermoregulation by the below-ground bivouacking army ants that comprise all other species in subfamily Dorylinae. Here we report the first observations of su...

Shifts to new ecological settings can drive evolutionary changes in animal sensory systems and in the brain structures that process sensory information. We took advantage of the diverse habitat ecology of Neotropical army ants to test whether evolutionary transitions from below- to above-ground activity were associated with changes in brain structu...

The occurrence of active brood-warming in army ant nests (bivouacs) is well documented among surface-dwelling Eciton burchellii colonies in the lowlands, but how this species interacts with the variety of conditions experienced across its expansive range remains understudied. Even less is known about if and how thermoregulation is achieved in other...

Temperature variation along elevational clines generates locally stable but spatially diverse temperatures in the tropics, potentially selecting for the evolution of thermally specialized animal populations. The Neotropical army ant Eciton burchellii parvispinum is distributed across a wide elevation range spanning 11°C mean annual temperature. The...

The social brain hypothesis assumes the evolution of social behaviour changes animals' ecological environments, and predicts evolutionary shifts in social structure will be associated with changes in brain investment. Most social brain models to date assume social behaviour imposes additional cognitive challenges to animals, favouring the evolution...

Models that predict organismal and population responses to climate change may be improved by considering ecological factors that affect species thermal tolerance. Species differences in microhabitat use can expose animals to diverse thermal selective environments at a given site and may cause sympatric species to evolve different thermal tolerances...

In social insects, both task performance (foraging) and dominance are associated with increased brain investment, particularly in the mushroom bodies. Whether and how these factors interact is unknown. Here we present data on a system where task performance and social behavior can be analyzed simultaneously: the small carpenter bee Ceratina austral...

We show that Erythritol, a non-nutritive sugar alcohol, was toxic to the fruit fly Drosophila melanogaster. Ingested erythritol decreased fruit fly longevity in a dose-dependent manner, and erythritol was ingested by flies that had free access to control (sucrose) foods in choice and CAFE studies. Erythritol was US FDA approved in 2001 and is used...

As small-bodied, ecologically dominant ectotherms, ants are important models for understanding animal responses to temperature variation and climate change. We took advantage of extreme variation in body size and species habitat use among Neotropical army ants (Ecitoninae) to explore how physiology and ecology affect thermal tolerance. The relation...

Brain investment is evolutionarily constrained by high costs of neural tissue. Several ecological factors favour the evolution of increased brain investment; we predict reduced brain region investment will accompany the evolution of organismal or social parasitism when parasites rely on host behaviour and cognition to solve ecological problems. To...

Army ant swarm raids in Neotropical montane forest are attended by diverse flocks of foraging birds that can include residents year-round and overwintering Nearctic migrants. We asked whether migrants and residents affect each other's ability to forage at army ant raids. We quantified variation in raid attendance by three guilds of birds: wintering...

Army ant swarm raids in Neotropical montane forest are attended by diverse flocks of foraging birds that can include residents year-round and overwintering Nearctic migrants. We asked whether migrants and residents affect each other's ability to forage at army ant raids. We quantified variation in raid attendance by three guilds of birds: wintering...

Insecticides have a variety of commercial applications including urban pest control, agricultural use to increase crop yields, and prevention of proliferation of insect-borne diseases. Many pesticides in current use are synthetic molecules such as organochlorine and organophosphate compounds. Some synthetic insecticides suffer drawbacks including h...

As small-bodied, ecologically dominant ectotherms, ants are important models for understanding animal responses to temperature variation and climate change. We took advantage of extreme body size variation and species habitat differences among army ants (Ecitoninae) to explore how physiology and ecology affect thermal tolerance. The relationship be...

Adaptive brain architecture hypotheses predict brain region investment matches the cognitive and sensory demands an individual confronts. Social hymenopteran queen and worker castes differ categorically in behavior and physiology leading to divergent sensory experiences. Queens in mature colonies are largely nest-bound while workers depart nests to...

Paper wasps are diverse in Neotropical rainforests but the factors that affect their abundance are poorly understood. Army ants (Ecitoninae) are generally thought to have the greatest predatory impact on populations of social wasps, but there is emerging evidence that predatory birds could also be a significant source of colony mortality. Our objec...

Inhibited dispersal, leading to reduced gene flow, threatens populations with inbreeding depression and local extinction. Fragmentation may be especially detrimental to social insects because inhibited gene flow has important consequences for cooperation and competition within and among colonies. Army ants have winged males and permanently wingless...

Red-throated Caracaras Ibycter americanus (Falconidae) are specialist predators of social wasps in the Neotropics. It had been proposed that these caracaras possess chemical repellents that allow them to take the brood of wasp nests without being attacked by worker wasps. To determine how caracaras exploit nests of social wasps and whether chemical...

Larvae of some species of ants in the subfamily Ponerinae have specilaized adhesive structures on the dorsum of the body.These adhesive structures appear to function to attach the larvae to the walls and roof of nest chambers. We show these structures vary in number, placement, and morphology. We use a recent molecular phylogeny of the Ponerinae...

The mosaic brain evolution hypothesis predicts that the relative volumes of functionally distinct brain regions will vary independently and correlate with species' ecology. Paper wasp species (Hymenoptera: Vespidae, Polistinae) differ in light exposure: they construct open versus enclosed nests and one genus (Apoica) is nocturnal. We asked whether...

Here we report field observations of group hunting by two Neotropical species of paper wasps, Parachartergus apicalis in Costa Rica and Agelaia cf. angulata in Peru. In both cases, multiple workers simultaneously attacked live caterpillar prey. We describe the wasps' behavior and their interactions with the relatively large-bodied (>80 mm length) c...

Many members of the ant subfamily Ponerinae possess in larval form a variety of specialized sticky appendages to facilitate the attaching of brood to nest chamber walls. The presence of these structures has been documented for decades, but up until now the exact mechanism by which they produce adhesion has not been fully explored. In this project,...

Symbiotic microorganisms provide important services to their arthropod hosts, including digestion of dietary compounds, provisioning of nutrients deficient in their hosts’ diets, and defence against natural enemies and abiotic stressors. Such bacteria need to survive and compete against other microbes in internal environment of the host, which is k...

Tropical birds forage at army ant raids on several continents. Obligate foraging at army ant raids evolved several times in the Neotropical true antbird family (Thamnophilidae), and recent evidence suggests a diversity of bird species from other families specialize to varying degrees on army ant exploitation. Army ant raids offer access to high pre...

1. Sodium is often a limiting nutrient for terrestrial animals, and may be especially sought by herbivores. Leafcutter ants are dominant herbivores in the Neotropics, and leafcutter foraging may be affected by nutritional demands of the colony and/or the demands of their symbiotic fungal mutualists. We hypothesized that leafcutter colonies are sodi...

Tropical birds forage at army ant raids on several continents. Obligate foraging at army ant raids evolved several times in the Neotropical true antbird family (Thamnophilidae), and recent evidence suggests a diversity of bird species from other families specialize to varying degrees on army ant exploitation. Army ant raids offer access to high pre...

The rapid disruption of tropical forests probably imperils global biodiversity more than any other contemporary phenomenon. With deforestation advancing quickly, protected areas are increasingly becoming final refuges for threatened species and natural ecosystem processes. However, many protected areas in the tropics are themselves vulnerable to hu...

Army ant-following birds that inspect bivouacs (temporary nests of nomadic army ants) might provide a novel candidate for studying elements of mental time travel in animals, namely the ability to 1) remember the time and place of specific past events and 2) to use this memory to plan for future actions. Army ant colonies are a rich but unpredictabl...

Animal societies depend on effective defence of group resources. Defensive mechanisms can be costly and may constrain the evolution of social structure. We analysed how exocrine mechanisms of colony defence were affected by the evolution of social complexity and of nest architecture in paper wasps (Vespidae). Eusocial paper wasp species exhibit two...

Unlike most social insects, Eciton burchellii army ants cannot thermoregulate through nest construction. Instead, army ants thermoregulate behaviorally by creating a living nest (bivouac), shifting its position and structure, and potentially through nest site selection. We hypothesized that bivouac site selection is critical to E. burchellii colony...

Geographic and elevational variation in the local abundance of swarm-raiding army ants has implications for the population dynamics of their prey, as well as affecting the profitability of army-ant-following behavior for birds. Here, we analyze systematically collected data on E. burchellii and L. praedator raid rates from geographically and elevat...

Army ant-following birds that inspect bivouacs (temporary nests of nomadic army ants) might provide a novel candidate for studying elements of mental time travel in animals, namely the ability to 1) remember the time and place of specific past events and 2) to use this memory to plan for future actions. Army ant colonies are a rich but unpredictabl...

We compared species mean data on the size of functionally distinct brain regions to test the relative rates at which investment in higher-order cognitive processing (mushroom body calyces) versus peripheral sensory processing (optic and antennal lobes) increased with increasing brain size. Subjects were eusocial paper wasps from queen and worker ca...