University of Pennsylvania, B.A. 1988
SUNY Stony Brook, Ph.D., 1995
See a few of my lab videos of animal swimming and flying at my lab YouTube channel
Work in the Walker lab focuses on how functional systems evolve. The evolution of naturally engineered functional systems and human engineered systems are both constrained by trade-offs. For example, kayaks that track well aren't much fun in the surf or white water because of a trade-off between yaw stability and maneuverability. Trade-offs can be mitigated with modular designs. This would be tough with kayaks but the multiple gears of a bike is a good example of a modular design. Modular designs, of course, come with costs. This interplay between costs of modularity v. costs of trade-offs is what makes the evolution of functional systems an interesting focus of study.
The heart of the work is a "general model of functional constraints on phenotypic evolution", whose inchoate form appeared in an NSF dissertation improvement award proposal in about 1991. The vortex of work around this model has spun off side projects in a number of different directions including morphometric modeling, biomechanical modeling of locomotion in fish and fruit flies, and lots of Monte-Carlo simulations to discover best practices.
The core of the "functional constraints model" is the mapping from phenotype to performance (or "form-function mapping"). This mapping requires two things: 1) functionally relevant measures of morphology, which we satisfy with a combination of geometric morphometric variables and biomechanical shape indices, and 2) measures of the ability of organisms to perform fitness-related tasks such as acquiring prey, avoiding predators, and attracting mates. The empirical work in the lab, then, tends to resemble an animal Olympiad. We use Trinidadian guppies, threespine sticklebacks, and, of course, the fruit fly, Drosophila melanogaster, to test various aspects of the functional constraints model.
Pre-prints are available at (soon to be added!)
Some of my papers are available at ResearchGate
Walker, J.A. and Caddigan, S. P. 2015. Performance trade-offs and individual quality in decathletes. Journal of Experimental Biology. DOI: 10.1242/jeb.123380.
Walker, J.A. 2014. The effect of unmeasured confounders on the ability to estimate a true performance or selection gradient (and other partial regression coefficients). Evolution. DOI: 10.1111/evo.12406.
Walker, J.A., Alfaro, M.E., Noble, M.M., and Fulton, C.J. 2013. Body fineness ratio as a predictor of maximum prolonged-swimming speed in coral reef fishes. PLOS One. 8: e75422. DOI: 10.1371/journal.pone.0075422.
Hendry, A.P., Hudson, K., Walker, J.A., Räsänen, K., and Chapman, L.J. 2011. Genetic divergence in morphology-performance mapping between Misty Lake and inlet stickleback. Journal of Evolutionary Biology, 24: 23–35.