Department of Biological Sciences

Jeffrey Walker Ph.D.

Professor of Biology and Graduate Coordinator
Jeff Walker

Office Location

476C Science ("C" wing)

Phone

207.228.8166

Academic Degrees

  • Ph.D., Anatomy, SUNY Stony Brook, 1995
  • B.A., Geology, University of Pennsylvania, 1988

Profile

Dr. Walker joined the Biology Department at USM in 2000 after postdoctoral work at the Field Museum in Chicago. He is a physiologist with expertise in the evolution of functional systems, and his research combines computational and empirical approaches.

Dr. Walker regularly teaches Human Physiology (BIO 221, 223). He also occasionally teaches the organismal biology course (BIO 107) and the plant and animal physiology course (BIO 109) in the introductory biology sequence, as well as courses in Applied Biostatistics (BIO 413/513) and Research Methods (BIO 601).

Research Interests

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.

Recent Publications

My Google Scholar page

Some of my papers are available at ResearchGate

Walker, J.A. 2016. Monte Carlo simulation of OLS and linear mixed model inference of phenotypic effects on gene expression. PeerJ 4:e2575 https://doi.org/10.7717/peerj.2575.

Diamond, K.M., Schoenfuss, H.L., Walker, J.A., and Blob, R.W. 2016. Flowing water affects fish fast-starts: escape performance of the Hawaiian stream goby, Sicyopterus stimpsoni. Journal of Experimental Biology 219: 3100-3105.

Conradsen, C., Walker, J.A., Perna, C., and McGuigan, K. 2016. Repeatability of locomotor performance and morphology–locomotor performance relationships. Journal of Experimental Biology 219: 2888-2897.

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.