IBRG hosts informal meetings
where members of affiliated lab groups in Princeton University's
Department of Ecology and
Evolutionary Biology or their guests give presentations on their current research. The overarching theme of talks and discussions for IBRG is behavior, and in practice this means that topics range from proximate studies of behavior itself to behavioral and evolutionary ecology. Common themes include cooperation, competition, signaling, foraging, and mimicry, to name but a few. If behavior is implicitly or explicitly involved, we are excited to discuss! Topics also run the gamut from theoretical to empirical and foundational/basic to applied.
These talks are usually about 20-30 minutes long followed by
30 minutes of discussion. We meet during the academic year on
Fridays from 3-4pm in Guyot 100.
All are welcome to attend!
The speaker schedule and mailing list for the 2023-24
academic year are being maintained by
Josh LaPergola, Qwahn Kent, Bre Bennett, and Katja Kochvar.
Please contact any of us if you are interested in presenting your research or would like to add
your name to the group's mailing list.
Title: Exploring Natural History From a Standing Start
This brainstorming chalk-talk provides an informal summary of insights gained from the Friday "EEB Natural History Walks" that Henry started in the Fall of 2017. It also shares Henry's tentative plans to write a guide on how to become a self-sufficient naturalist with the help of a companion who is a tyro like oneself.
Title: Plasticity and evolution in social insect brains: how sociality, caste, and body size shape CNS architecture
Social insects provide excellent opportunities for comparative tests of hypotheses for the adaptive evolution of brain tissue investment and nervous system architecture. Our lab uses social paper wasps and their solitary relatives in the family Vespidae to test some predictions of neuroecological theory. The family includes solitary species as well as representatives of most of the known grades or levels of social complexity. Within social colonies, queens and workers differ in behavior and ecology. Underappreciated is the fact that social Vespidae have also undergone dramatic transitions in body size. I will present results of comparisons of brain size and brain structure between reproductive castes (queens vs. workers: are queens brain-challenged?), solitary vs. social species (are social brains better?), and I will explore the importance of body size as a driver of complex brain allometry.
Title: Natural history of colonial nesting in the Hispaniolan Woodpecker
Explaining intra- and interspecific variation in sociality requires understanding the underlying ecological factors that promote or preclude grouping and the fitness consequences of group living. Colonial nesting, the dense concentration of individuals during breeding, offers an excellent opportunity for testing hypotheses to explain sociality and its variation. I studied the Hispaniolan Woodpecker (Melanerpes striatus), a facultative colonial breeder, in the Dominican Republic with the following goals: (1) test for the effects of colony size on reproductive success with the goal of distinguishing the hypotheses of grouping for socially derived benefits from aggregations that form due to the spatiotemporal clustering of resources; (2) identify the ecological resources that explain colony size variation; and (3) determine whether coloniality impacts the genetic mating system by increasing the incidence of conspecific brood parasitism and extra-pair paternity. I will present results pertaining to all three goals, with the over-arching objective of attempting to understand colonial nesting in a lineage (Aves: Picidae) where this phenomenon is exceptionally rare.
Title: Implications of diverging media in polarized societies: A model of information cascades and their effect on social network structure
Cascades are ubiquitous phenomena in biological and social systems. Information cascades occur in social systems when individuals base their behavior on the social information provided by the behavior of others. In essence, these cascades are the rapid spread of a behavior through a group. Common examples include startle cascades in fish schools or the spread of fads in human groups. While cascades are theoretically and experimentally well explored, most approaches ask how the social organization (i.e., social network structure) affects the likelihood and size of cascades. In this talk, I'll present very preliminary work on a cascade model that will ask the opposite: how might cascades reshape social networks? Particularly, I am interested in how cascades might reshape social networks when the information sources that individuals depend upon begin to become uncorrelated and say the opposite of one another. I will frame this model within the context of contemporary politics, where cascades take place among ideologically-polarized individuals reliant on increasingly divergent, partisan media sources. While this project is in very early stages, I hope to gather feedback and suggestions on the model, the approach/conceptual framing, and possible experiments to pair with the theory.
Title: Socio-ecological interactions amid cultural change: two fisheries case studies in Mongolia
Rivers in northern Mongolia have historically served as refuge habitat for endangered endemic fish like taimen (Hucho taimen), the largest salmonid in the world, because the country possessed limited culture of fishing and eating fish. This is changing rapidly, to the point where dozens of recreational angling groups now cater to Mongolian fishing hobbyists, and international tourism companies bring hundreds of foreign anglers to Mongolia every year to fish for taimen. The rise of recreational fishing is creating new socio-ecological interactions at the interface of human decision-making and fish population dynamics. In my talk, I will present two case studies of human-ecological interactions within this new setting. In the first, I explore what motivates foreign recreational anglers to travel to remote northern Mongolia to catch and release an endangered fish. Mixed qualitative-quantitative data gathered during ethnographic fieldwork suggests that foreign anglers are highly motivated by encountering large trophy-sized fish in an "exotic" setting, but that the quality of fish they encounter mostly does not influence future participation. In the second, I propose an experimental design to investigate whether commonly targeted salmonids in Mongolia exhibit hook learning behavior on different angling gears.
Title: Digitally draining the oceans (so we can see what’s inside)
The way light travels underwater differs fundamentally from that in the atmosphere, which affects how an image is formed on the sensor of the camera. Compared to images taken in air, underwater images are covered in thick, colored "fog", and the brightness and color of objects get distorted with even short distances from the camera. This degradation due to water poses a huge barrier to scientific progress at a time when our oceans are under increasing pressure from pollution, overfishing, and climate change: we routinely collect large underwater image datasets that capture important information regarding the state of our oceans, but we cannot analyze them efficiently. Traditional computer vision and machine learning algorithms do not work consistently on underwater images, and consequently the analysis of most underwater imagery requires expensive manual effort. On average, a human expert spends over 2 hours identifying and counting fish in a video that is one hour long.
Recovery of lost colors and contrast in underwater images remains an unsolved problem. In this talk, bridging optical oceanography and underwater computer vision, I will show that a fundamental reason for the lack of a robust color reconstruction method is the prevalent use of an underwater image formation equation that was originally derived for the atmosphere. Then, based on a new physically accurate equation I proposed and validated, I will introduce the Sea-thru algorithm that successfully removes water from underwater images, revealing the underwater world in a way we have never seen before. Finally, I will discuss the applications of this updated underwater image formation equation in visual ecology, ranging from software tailored for finding camouflaged octopus, to the design of multispectral cameras that mimic the visual systems of aquatic animals.
Title: Sociality and Communication in the Plains Zebra: A case study of the social complexity hypothesis
Equids are a small taxon of closely related species that display great diversity in the number and stability of social bonds and associations they possess. This makes equids a potentially valuable case study for investigating the social complexity hypothesis, which posits that animals living in complex social environments require more complex communicative abilities. However, despite the complexity displayed in some equid social systems, little comparative work has been done on how they use their communication to navigate their social environments, or how their social structure may interact with their communicative complexity. Furthermore, there has been little work on how these species may integrate and combine signals from multiple modalities to overcome the limitations of any given modality and generate more complex and informative signaling repertoires. I have begun to address these questions by focusing on the Plains zebra. Plains zebras live in complex, multi-level societies, forming long term social bonds that are similar to many primate societies in interesting ways. By studying the Plains zebra, a species that is phylogenetically unrelated to primates and yet occupies a similar social niche, I hope to gain a better understanding of how and why complex communication evolved in animals, including humans. As the first step of this project, I am building a vocal repertoire of the Plains zebra. Inspired by how naive human infants use statistical learning to learn what words are in a constant stream of sound, I will be utilizing machine learning to remove the human perceptual biases that may interfere with our ability to distinguish potentially meaningful distinctions in acoustic units. Only after the machine learning algorithm has identified possible units in the repertoire will I return to the field and try to connect these units to their communicative context. Using this method, I will hopefully be able to assemble a more ecologically relevant categorization of their acoustic signals and gain insights into how different species with different computational strengths and weaknesses encode and parse acoustic information.
Title: Persistent state drives female receptivity and aggression in Drosophila
During social interactions animals dynamically shape their behavior based on both immediate sensory cues, such as acoustic signals from a partner, and internal states. These internal states can last for extended periods of time (e.g., hunger) and can modulate neural activity, and consequently behavior, over similarly long timescales. Recently, genetic tools in mice and flies have facilitated identification of neurons that promote a persistent change in behavioral state. In male mice, a small population of hypothalamic neurons control both mating and aggression by promoting persistent internal states. Similarly, in male flies, activating a small group of central brain neurons (called P1) promote persistent singing and aggression. Similar neurons in females, that induce a persistent behavioral state, have not yet been identified in either mice or flies. To address this gap, we focused on pC1 neurons (of which P1 neurons are a male-specific subset) in female Drosophila melanogaster. Previous studies showed that activating pC1 neurons in females promotes receptivity, and stronger neural activation can drive male-like behaviors such as song production. Here, we investigate if and how pC1 activation persistently affects female interactions with a courting male. We activated pC1 neurons in a solitary female for 5 minutes before introducing a male. We quantified male and female behavior by recording acoustic signals, tracking the motion and orientation of both flies, and applying both unsupervised and supervised clustering methods. We discovered that pC1 activation induces high levels of female-male aggression (including shoving and head-butting), male-like behaviors (including chasing and wing-extension) and simultaneously increased receptivity and altered responses to male courtship song, all over timescales of minutes following activation. We then imaged Calcium activity throughout the brain to identify areas with persistent activity over timescales that matched our behavioral observations. These experiments identified several persistently active neural clusters. Our results indicate that activation of pC1 neurons in females can drive a persistent behavioral state affecting several sensorimotor pathways simultaneously, including circuits not normally activated during courtship.
Title: Iridescent bird plumage - does diversity of nanostructure drive diversity in color?
Iridescence produces some of the most striking color displays known in the animal world. They are produced by nanoscale arrays in the feather filaments which consist of keratin and melanosomes (melanin-filled organelles). Birds have evolved a surprising diversity of nanostructures, with some species incorporating air-filled hollow melanosomes, others flat melanosomes, and yet others hollow flat melanosomes. These derived melanosomes have evolved convergently in several bird lineages. The advantage of evolving hollow and/or flat melanosome morphologies is unknown, but some evidence suggests it allows birds to produce a broader range of colors. In this talk, I present my preliminary results from exploring this question. I use plumage data from museum bird skins, capturing the actual color diversity of different structures, and apply optical modelling to reconstruct the theoretically possible color diversity of each structure. I then ask whether birds with novel melanosome morphologies produce more colorful plumages, and whether this is due to an increase in the theoretical color range for novel structures.
The social intelligence hypothesis argues that social pressures have shaped the evolution of cognition in animals. What is social cognition and how might it be compared across species and individuals? I suggest that the building blocks of social cognition are a suite of skills, ordered roughly according to the cognitive demands they place upon individuals, that allow animals to recognize others, their relationships, and perhaps their mental states. Some skills are elementary and virtually ubiquitous, others are rarer. I treat these skills as the targets of selection and assume that more complex levels of social cognition evolve only when simpler methods are inadequate. All can be tested through field observations and experiments. Research on social cognition reveals how selection has favored the evolution of concepts and social classifications.
Title: Deciphering the molecular mechanism of toxin resistance of fireflies in vivo
Although conspicuous in the dark, fireflies are usually avoided by predators because they contain a group of potent bitter-tasting and toxic chemical compounds called lucibufagins (LBG). LBG inhibits Na+, K+-ATPase, an essential enzyme for a variety of cellular processes. LBG is either produced de novo (e.g. genus Photinus) or acquired via preying on the former (e.g. genus Photuris, a.k.a. "femme fatale"). One way the fireflies detoxify from LBG in their own body is through mutating and/or duplicating Na+, K+-ATPase to make it insensitive to LBG. We have identified four copies of Na+, K+-ATPase alpha subunit (ATPα1) in the predatory firefly Photuris where the most ancient copy remains the same as the sensitive ancestral state and three derived ones each carries putatively insensitivity-conferring substitutions. In the contrast, LBG-producer Photinus possesses only one copy of seemingly conserved ATPα1. However, through evolutionary analysis, we have identified an undocumented amino acid substitution that possibly renders the insensitivity. Furthermore, we have engineered the amino acid substitutions either alone or in combination, into fruit fly D. melanogaster. Therefore, we can evaluate the impact of the substitutions in a clear background, and at multiple levels, from the biochemistry attributes of altered enzyme to behavior and overall fitness.
Title: The Evolution of Looking and Seeing: New Insights from Colorful Jumping Spiders
Insects and spiders face an important challenge: their lifestyles often rely heavily on vision and yet their small size imposes severe spatial constraints on their visual systems. As a result, these tiny animals offer a number of inventive solutions for miniaturized visual sensing, with jumping spiders arguably at the apex. In this seminar, Dr. Morehouse will highlight his recent work to understand how jumping spiders see the world, how these visual capabilities have evolved over time, and how their unusual visual systems have shaped the ways that they communicate with each other.
Title: Parasitism in Hybrids: Nature & Nurture in the Zebra-Nematode Arms Race
Host hybridization can throw a wrench into host-parasite evolutionary dynamics as the parasites encounter potential hosts with diverse allele combinations. Studies comparing the infection statuses of hybrids and their parent taxa have yielded mixed results that depend not only on the particular natural histories of the species in question, but also on the genetic, behavioral, and environmental context for their interactions. Evidence for a heterozygote advantage in a key antigen-recognizing locus against nematodes in equids led us to predict enhanced resistance to gastrointestinal nematodes in equid hybrids. In a study of the host-parasite relationship in hybrids of the Grevy's and plains zebra in central Kenya, we found evidence for hybrid vigor but only in specific environmental contexts. Our results shed light on how genes and the environment tip the scales in this complicated system and have implications for conservation management as several lines of evidence suggest that macroparasites exhibit a major selection pressure on equids in particular.
Title: Testing hypotheses for the evolutionary origins of behavioral traits using artificial neural networks: the "number sense" as a case study.
Humans and many non-human animals have the "number sense:" an ability to estimate the number of items in a set without counting. Most hypotheses of the evolutionary origins of the number sense are adaptationist, suggesting that the number sense arises from an intrinsic fitness benefit. Here I tested the plausibility of an alternative hypothesis: that the number sense might initially arise as a byproduct of selection for other neural functions. To this end, I examined whether animals share the number sense with a deep convolutional neural network (DCNN) trained for object recognition. I found that the DCNN demonstrates three hallmarks of the number sense: numerosity-selective units, the behavioral ratio effect, and ordinality. The DCNN was not trained to enumerate, and so these are emergent properties of the network. By analogy the number sense in animals was not necessarily the result of direct selective pressure to enumerate but might have "come for free" with the evolution of a complex visual system.
