I am, fundamentally, an integrative, organismal biologist with broad interests related to phenotypic evolution and evolutionary ecology. I am particularly interested in the evolution of ecologically important, complex traits such as chemical defenses. My research is interdisciplinary and integrates molecular, organismal, and population analyses in a comparative framework.  I am particularly interested in the evolution, ecology, and physiology of tetrodotoxin (TTX) toxicity in the newt, Taricha granulosa and other TTX-bearing salamanders.

My current work as a NIH/NIGMS postdoctoral researcher seeks to understand the molecular biology, neurophysiology and evolution of tetrodotoxin (TTX) resistance in Taricha as well as other related Asian and European newt species (Family: Salamandridae). Because tetrodotoxic salamanders are exposed to their own toxins, they must also be resistant to those toxins. As a result the TTX bearing phenotype is best seen as a complex trait involving multiple, evolutionarily independent pathways (i.e., toxicity and resistance). Evolution of resistance, in turn, requires

adaptations in multiple paralogous genes with tissue-specific patterns of expression (voltage-gated sodium channels). Adaptation in these genes is also strongly constrained by functional requirements. My work examines the phenotypic effects, adaptive costs, and evolutionary history of TTX resistance in salamanders by looking at changes in these genes in salamanders. I use a combination of neurophysiology (heterologous channel expression and electrophysiology) and molecular biology (site-directed mutagenesis and RT cloning) to identify changes in region of the sodium channel where TTX binds (the ion-conducting pore) and, in turn, examine the effect of those changes on resistance (the phenotype). Because the pore governs the ion selectivity of the channel (e.g. preference for sodium ions over other cations), I can also quantify adaptive costs associated with these changes by looking at changes in the biophysical properties of channels modified to incorporate TTX resistance-conferring changes. Finally, I am using a comparative phylogenetic framework to examine the evolutionary history of these changes across multiple paralogs.

charlesh at stanford dot edu

I am also interested in large scale evolutionary and ecological processes such as coevolution. TTX levels of Taricha newts show high levels of geographic variability. This variation results, in part, from coevolution with a TTX resistant snake predator (Thanmnophis sirtalis). As a graduate student at Utah State University I worked with Edmund (Butch) D. Brodie Jr. and his son Edmund (Butch) D. Brodie III to document this effect of spatially structured coevolution on the evolution of TTX toxicity in Taricha This research explicitly explored patterns of geographic variation in the degree of phenotypic matching between newts and snake as well as spatially structured variation in the selection regime underlying this interaction and resulted in a publication in PLoS Biology and received coverage by the San Francisco Chronicle, The New Scientist, and Reuters New Service as well as being chosen as an editors picks of the week at PLoS Biology.

A basic goal of evolutionary biology is to understand how species interactions shape the evolution of phenotype. This work requires knowledge of the specific traits under selection in a given biotic interaction as well as the mode in which those traits can respond to selection. Understanding the chemical ecology of TTX toxicity in salamander is, thus, critically important to understanding its evolution. Much of my work is focused on elucidating the physiology and ecology underlying TTX toxicity in Taricha granulosa and other TTX-bearing salamanders.

Two major foci of this work include:

1) TTX Provisioning of Eggs in Taricha: The strong positive correlation between female Taricha granulosa TTX and mean clutch TTX suggests that this species is provisioning its eggs with TTX (Hanifin et al., 2003). TTX likely serves as a chemical defense against egg predation and there is evidence that egg predation from TTX-resistant caddis fly larvae may be ecologically important. Selection associated with egg predation could, in turn, drive the evolution of increased TTX levels in adult newts (i.e., selection favoring increases in egg TTX would result in increases in adult TTX levels because of the phenotypic correlation between these traits). I am exploring egg provisioning in multiple populations of T. torosa and T. granulosa to further examine this possibility. Although T. torosa lays its eggs in large exposed masses (as opposed to T. granulosa, which deposits eggs individually and cryptically), my results indicate that differences in TTX provisioning across populations of Taricha are not strongly associated with species level differences in egg laying ecology (Hanifin and Edgehouse, in prep). Instead, these differences appear to result from population specific ecological interactions that are, as yet, unclear.

2) The Chemical Ecology and Adaptive Role of 6-epiTTX in Salamanders: Studies of other chemically mediated attack-defense systems have revealed that toxic species can evolve multiple related defensive compounds in response to attack by exploiter species. Taricha and other TTX-bearing salamanders posses a unique stereoisomer of TTX: 6-epiTTX. Presence and levels of this toxin are geographically variable (Hanifin et al., 2003, Hanifin et al., in prep). I will explore the role of 6-epiTTX in the defensive ecology of newts with a multi-level study encompassing molecular, organismal, and population level analyses to examine the possibility that selection by resistant snake predators (or egg predation) has favored production of  6-epiTTX in populations of Taricha.

Hanifin, C. T., Brodie, E. D. Jr., and Brodie E. D. III. 2008. Phenotypic mismatches reveal escape from arms-race coevolution. Public Library of Science (PLoS) Biology 6(3) e60 (highlighted as a weekly editor’s pick: Gross, L, PLoS Biology Vol. 6, No. 3, e75 and in The New Scientist: McKenna, P., March 11 2008)

Brodie, E. D. III, Feldman, C., Hanifin, C. T., Motychak, J.,  Mulchahy, D., Williams, B., and Brodie, E. D., Jr. 2005. Evolutionary response of predators to dangerous prey: parallel arms races in multiple species pairs. Journal of Chemical Ecology. 31(2):343-356

Cardall, B. L., Brodie, E. D. III, Brodie, E. D. ,Jr., and Hanifin, C. T., 2004. Regeneration and secretion of tetrodotoxin in the rough-skin newt, Taricha granulosa. Toxicon. 44 (8):933-938.

Hanifin, C. T., Brodie, E. D. III, and Brodie, E. D., Jr.  2004.  A predictive model to estimate total skin tetrodotoxin in the newt Taricha granulosa. Toxicon. 43:243-249.

Hanifin, C. T., Brodie, E. D. III, and Brodie, E. D., Jr.  2003.  Tetrodotoxin levels in eggs of the rough-skin newt, Taricha granulosa, are correlated with female toxicity. Journal of Chemical Ecology. 29:1729-1739.

Hanifin, C. T., Brodie, E. D. III, and Brodie, E. D., Jr.  2002.  Tetrodotoxin levels of the rough-skin newt, Taricha granulosa, increase in captivity. Toxicon. 40:1149-1153.

Hanifin, C. T., Yotsu-Yamashita, M., Yasumoto, T., Brodie, E. D., III, Brodie, E. D., Jr.  1999. Variation of tetrodotoxin within and among populations of the newt Taricha granulosa. Journal of Chemical Ecology 25:2161-2175.

click for PDF of Curriculum Vitae

snake eating a toxic newt, Taricha granulosa