H. Carl Gerhardt
Curators’ Distinguished Professor Emeritus of Biological Sciences
PhD, 1970 University of Texas at Austin
Evolution and neurobiology of acoustic communication in amphibians
Research descriptionMy research involves both evolutionary and neurobiological approaches to acoustic communication in frogs and toads. The system is particularly suitable for quantitative and experimental studies: males produce complex but stereotyped acoustic signals, whereas females respond phonotactically to playbacks of both natural and synthetic (computer-generated) sounds. By systematically varying the acoustic properties of synthetic sounds, I identify the pertinent properties used in mate choice and can thus make predictions about the direction, if any, of change in acoustic signal structure through evolutionary time. Knowledge about the pertinent properties of communication sounds also serves as a framework for studying the underlying neural mechanisms. Specifically, this research guides searches for auditory neurons or networks that selectively respond to acoustic features of known biological significance in mate choice.
One main focus of research is the gray treefrog complex. Two species of gray treefrog (Hyla chrysoscelis and H. versicolor) females have a hierarchy of preferences. Strong stabilizing preferences are based on properties that serve to identify the species of the calling male; weak directional preferences are based on properties that correlate with the energetic cost of producing the call. Females prefer the calls that are the most energetically expensive for the males to produce, and thereby may be assuring that the male they choose is at least in good physical condition, if not genetically superior to its neighbors. However, the relative importance of features used in mate choice varies geographically. Females from areas where both species occur weigh static, species-identifying properties more strongly than do females from populations where only one species occurs.
There are also striking differences in the mate-choice criteria of the two species, one of which (H. versicolor) has arisen multiple times by alloploidy resulting from hybridization between (H. chrysoscelis) and other, extinct species. The change in cell size that correlates with polyploidy has contributed to some of the species differences in advertisement calls and might also have affected female sensory mechanisms and preferences. Other explanations may be discovered from an on-going comparative study of preference-criteria in close relatives within the group: the bird-voiced treefrog (Hyla avivoca) and canyon treefrog (Hyla arenicolor). A recent study of gray treefrogs also showed that, even though males do not produce complex calls, females prefer complex calls in which the established advertisement call is followed by a novel acoustic appendage consisting of the calls of other species or even a burst of noise. When the same appendages led the advertisement call, however, the complex call was at best equivalent and sometimes less attractive than the advertisement call alone.
Reichert, M.S., Gerhardt, H.C., 2014. Behavioral strategies and signaling in interspecific aggressive interactions in gray tree frogs. Behavioral Ecology, 25:520-530.
Welch, A.M., Smith, M.J., Gerhardt, H.C., 2014. A multivariate analysis of genetic variation in the advertisement call of the gray treefrog, hyla versicolor. Evolution, 68:1629-1639.
Gerhardt, H.C., 2014. Predation reduces visual communication distance in an Anolis lizard. Proceedings of the National Academy of Sciences of the United States of America, 111: 9026-9027.
Reichert, M. S., & Gerhardt, H. C. 2013. Gray tree frogs, hyla versicolor, give lower-frequency aggressive calls in more escalated contests. Behavioral Ecology and Sociobiology, 67(5), 795-804
Gerhardt, H. C., & Humfeld, S. C. 2013. Pre-existing sensory biases in the spectral domain in frogs: Empirical results and methodological considerations. Journal of Comparative Physiology A: Neuroethology, Sensory, Neural, and Behavioral Physiology, 199(2), 151-157.
Reichert, M.S. and H.C. Gerhardt. 2013. Socially mediated call timing in the gray treefrog, Hyla versicolor. Behavioral Ecology 24: 393-401.
Henderson, J.J. and H. C. Gerhardt 2013. Restoration of call attractiveness by novel acoustic appendages in gray treefrogs. Animal Behaviour 86: 537-543.
Gerhardt, H.C., 2013. Geographic variation in acoustic communication: Reproductive character displacement and speciation. Evolutionary Ecology Research, 15:605-632.
Klymus, K. E., Humfeld, S.C. and H. C. Gerhardt. 2012. Geographic variation in male advertisement calls and female preference of the wide-ranging canyon treefrog Hyla arenicolor. Biological Journal of the Linnean Society 107: 219-232.
Reichert, M.S. and H.C. Gerhardt. 2012. Trade-offs and upper limits to signal performance during close-range vocal competition in gray treefrogs, Hyla versicolor. The American Naturalist 180: 425-437.
Klymus, K. E. and H.C. Gerhardt. 2012. ALFP markers resolve intra-specific relationships and Infer genetic structure among lineages of the canyon treefrog, Hyla arenicolor. Molecular Phylogenetics and Evolution 65: 654-667.
Gerhardt, H. C. (2012). Evolution of acoustic communication: A multi-level analysis of signal variation. Bioacoustics, 21(1), 9-11.
Honors & Awards
Selected honors and awards
Thomas Jefferson Award, The University of Missouri 2012
Hanse Wissenschaftskolleg (Institute for Advanced Study) fellowship, Delmenhorst, Germany 2012
Distinguished Herpetologist Award, The Herpetologist League 2006
Quest Award - Animal Behavior Society 2005
Frank Beach Award 2001
Elected Fellow - AAAS 1998
Senior Humboldt Award 1995
Presidential Award for Research and Creativity, University of Missouri 1992
Elected Fellow - Animal Behavior Society 1991
Aug. 5, 2016
Symposium in Honor of Prof. Carl Gerhardt
July 15, 2014
Nov. 19, 2012
DBS alumnus Mark Bee talks about research on vocal communication in frogs
Nov. 2, 2012
Five Biology Professors Celebrated at Faculty Recognition Banquet
April 10, 2012
Carl Gerhardt Recipient of Thomas Jefferson Award
Dec. 27, 2011
Frogs Use Calls to Find Mates with Matching Chromosomes