doing the science
What are the functions of socially exchanged fluids?
Many organisms pass fluids between individuals of the same species that exert serious physiological effects on recipients. While the functions and physiological mechanism of these fluids are well known in some cases (e.g., for seminal fluids or maternal milk), much less know for others (e.g., saliva). The intimacy and context specific transmission of some of these fluids indicates that this type of chemical exchange might mediate a private means of communication and/or manipulation.
In my research, I have explored the contents of a fluid passed orally amongst social insects during trophallaxis, a behaviour wherein liquids are exchanged mouth-to-mouth between adults and between adults and larvae. Since its first description over a hundred years ago, trophallaxis has been widely thought of as a simple food-sharing mechanism, yet this behaviour has been observed in non-food related contexts, leading me to hypothesise that it might underlie a novel type of chemical communication. To test this hypothesis I've conducted a comprehensive analysis of this social fluid, using the ant Camponotus floridanus as a model organism. The findings are published here at eLife.
How can the individual change the collective?
One of the coolest things I found in this social fluid is abundant quantities of an important insect hormone - 'juvenile hormone.' Why is this so cool? This hormone is well known for it's ability to shift the development of larvae from worker fate to queen fate in bees, or from small worker to big worker in some ants. People have always simply thought that different larvae have different amounts of this hormone, perhaps because they are fed more or less nutritious food, but no one guessed that the workers were feeding them this hormone directly!
I found that when I supplement the food of the care-taking worker ants with more of this hormone, double the number of larvae get raised to metamorphosis. Given this, here we have a way for worker ants to control the maturation and development of their community.
Implications for democracy
While it seems very far from politics, we can think of this as a form of ant democracy. When the ants feed the larvae they aren't just feeding them food, they are casting quantitative ballots by administering a variable quantity of juvenile hormone. When more juvenile hormone is fed to larvae by the care-taking ants, those larvae are more likely to develop into adults, rather than end up as lunch (yes, there is a lot of cannibalism in social insects!).
How does this differ from our current systems of representation? The most notable difference is that in the ant system, voting is quantitative. If an individual invests a lot of time and resources in trying to make change, she can have an effect, but there are limits. She is limited physiologically by how much juvenile hormone she personally can produce (there are no hormone multi-billionaires), but also, she is limited by diffusion. If she is not highly involved in the rearing of the larvae, her effect will be muted by those more closely involved and more time-invested.
ONGOING: quantitative analysis of control of larval development through feeding
Most organisms (including us) have time-limited development. We develop for a more or less fixed amount of time before emerging as functional creatures. Ants are different. The same group of eggs can be reared to adulthood in three weeks or three months! Working with Ofer Feinerman's group at the Weizmann, I’ve been quantitatively measuring larval feeding and larval growth.
Ongoing: neofunctionalization of proteins involved in social exchange
One of the most abundant proteins I've found in this fluid seems to have undergone a number of recent duplications as it's shifted from an ancestral localization pattern to the trophallactic fluid. In collaboration with the Privman group at University of Haifa, I've explored this neofunctionalization both biochemically and bioinformatically. See LeBoeuf et al. 2018 for the details!
Friction & adhesion in the vertebrate auditory system
During my PhD work in the Hudspeth Lab (Rockefeller University), I explored the electrostatic and hydrodynamic forces that play upon the hair bundle, the mechanosensory organelle of the vertebrate inner ear and vestibular system. Addressing this system necessitated building a piconewton-sensitive high-resolution force-measuring microscope and development of experimental preparations to measure these minute forces. I found that the glycocalyx––the sugars emerging from the stereociliary membranes of the hair bundle––mediate elastic divalent-cation-sensitive interactions between stereocilia. These forces, along with hydrodynamic forces are likely to mediate the hair bundle cohesion that so important in staving off hearing-loss.
Tau, microtubule dynamics & neurodegeneration
In close collaboration with a graduate student, I developed a model of how tau-binding causes a shift in microtubule protofilament number, which in turn alters microtubule growth rate. Our predictions were born out in later studies! We also developed a novel structure-function cassette-binding model based on our results and the microtubule-binding repeats present in different isoforms of tau. While this model has not yet been further tested, the etiology of Alzheimer’s disease is again shifting toward the importance of tau function.