University of Vermont

The College of Arts and Sciences

Department of Biology

Faculty - Sara Helms Cahan, Chair

Sara Helms Cahan

Sara Helms Cahan, Assoc. Professor, Chair

  • Ph.D., Arizona State University, Department of Zoology, 1999
  • Texas A&M; Postdoctoral 1999-2000, Department of Entomology
  • University of Lausanne 2000-2004, Institute of Ecology
  • University of Vermont 2004-2010, Assistant Professor
  • University of Vermont 2010-2015, Associate Professor
  • University of Vermont 2015- , Associate Professor and Chair
  • C.V. (PDF)
Area of expertise

Social Insect Ecology

Contact Information
Email: Sara Helms Cahan

Office Hours: Monday and Tuesday from 1:00-2:00
Location: Marsh Life Science Building, Rm 120B
Phone: (802) 656-2962

Website for LAB



The research in my lab focuses on the consequences of sociality on the evolution of individual, population, and species characteristics. The evolution of social groups is a fundamental transition that has occurred in a diverse array of organisms, from bacteria to primates. I use the tools of ecology, ethology, and genetics to understand how social life affects the evolution and dynamics of ant populations, primarily in the southwestern and southern US. Ants are obligately social animals, organized into highly structured colonies containing one or more reproductive queens and a large number of female but reproductively sterile workers. The only component of the ant life cycle in which solitary life is possible is when young queens leave their parent nests to found their own new colonies, yet even at this stage queens of many species choose to join forces with other queens to form group nests rather than live solitarily. By living together, ants interact with their environment as a group, which can dramatically change their ability to tolerate environmental extremes, their interactions with members of their own and other species, and their patterns of dispersal and reproductive behaviors.

Our investigations focus on two main study systems. The first is the desert harvester ant Messor pergandei, in which the behavior of queens switches abruptly from solitary colony founding to group colony founding across its range in southern California. Current projects include: 1) quantifying gene flow across the behavioral transition zone, 2) measuring the types and strength of natural selection acting on queen behavior, both between regions and within the transition zone, and 3) the effects of social behavior on queen body size, morphology, and physiology.

Our second project is social insect hybrid zones, where the interaction between social structure and interspecific hybridization has led to some surprising and unique forms of interspecific interactions. We study two hybrid zones, one in the harvester ant genus Pogonomyrmex and the other between two North American fire ant species in the genus Solenopsis. In both these cases, hybrid offspring almost always become sterile workers, while non-hybrids are invariably reproductive offspring. Ongoing projects include the evolutionary origin and geographic distribution of genetic caste determination, how differences in caste fate of genetically different offspring are mediated within the colony, the role of selection in maintaining genetic caste systems, and the current and historical genetic relationships between hybridizing populations.

Representative Publications

  • Stanton-Geddes, J.,  A. Nguyen, L. Chick, J. Vincent, M. Vangala, R. R. Dunn, A. M. Ellison, N. J. Sanders, N. J. Gotelli, and S. Helms Cahan 2016.  Thermal reactionomes reveal divergent responses to thermal extremes in warm and cool-climate ant species. BMC Genomics DOI: 10.1186/s12864-016-2466-z.
  • Nguyen, A., N. Gotelli and S. Helms Cahan, 2016. Sequence, cis-regulatory evolution and expression profile of ant heat shock proteins. BMC Evolutionary Biology DOI: 10.1186/s12862-015-0573-0.
  • Muscedere, M., S Helms Cahan, K. R. Helms, and J. F. Traniello, 2016.  Geographic and life-history variation in ant queen colony founding correlate with brain amine levels.  Behavioral Ecology 27:271-278.
  • Smith, C. R., S. Helms Cahan, C. Kemena, S. G. Brady, W. Yang, E. Bornberg-Bauer, T. Eriksson, J. Gadau, M. Helmkampf, D. Gotzek, M. O. Miyakawa, A. Suarez, and A. Mikheyev, 2015.  How do genomes create novel phenotypes? Insights from the loss of the worker caste in ant social parasites.  Molecular Biology and Evolution 32:2919-2931.
  • Gotzek, D., H. J. Axen, A. Suarez, S. Helms Cahan, and D. Shoemaker, 2015.  Global invasion history of the Tropical Fire Ant, Solenopsis geminata: A stowaway on the first global trade routes. Molecular Ecology 24:374-388.
  • Herrmann, M. and S. Helms Cahan 2014. Inter-genomic sexual conflict drives antagonistic coevolution in harvester ants.  Proceedings of the Royal Society of London B 281:20141771.
  • Helms Cahan, S and K. R. Helms 2014.  Variation in social structure alters queen body mass and productivity in the desert seed-harvester ant Messor pergandeiInsectes Sociaux 61:153-161.
  • Axen, H. J., A. Wildermuth and S. Helms Cahan 2014.  Environmental filtering of foraging strategies mediates patterns of coexistence in the fire ants Solenopsis geminata, Solenopsis xyloni, and their interspecific hybrids.  Ecological Entomology 39:290-299.
  • Helms, K.R., N. J. Newman and S. Helms Cahan 2013.  Regional variation in queen and worker aggression in incipient colonies of the desert ant Messor pergandeiBehavioral Ecology and Sociobiology 67:1563-1573.
  • Helms Cahan, S. and  E. Gardner-Morse 2013.  Emergence of reproductive division of labor in forced queen groups of the ant Pogonomyrmex barbatusJournal of Zoology 291:12-22.
  • Abbott, R. et al., (I am one of 40 co-authors), 2013.  Hybridization and Speciation.  Journal of Evolutionary Biology 26:229-246.
  • Zhou, Y. and S. Helms Cahan 2012.  A novel family of terminal-repeat retrotransposon in miniature (TRIM) in the genome of the red harvester ant, Pogonomyrmex barbatus. PLoS One 7:e53401.
  • Helms Cahan, S. and K. R. Helms 2012.  Relatedness does not explain geographic variation in queen cooperation in the seed-harvester ant Messor pergandei. Insectes Sociaux 59:579-585.
  • Helms, K. R. & S. Helms Cahan 2012.  Large scale regional variation in cooperation, conflict, group size, and cooperative breeding among queens of the desert ant Messor pergandeiAnimal Behaviour 84:499-507.
  • Helms Cahan, S., Graves, C. J., Brent, C. S., 2011. Intergenerational effect of maternal juvenile hormone on offspring in Pogonomyrmex harvester ants.  Journal of Comparative Physiology B.181:991-999.
  • Helms Cahan, S., Daly, A. M., Schwander, T., Woods, H. A. 2010.  Genetic caste determination does not reduce colony growth rates in Pogonomyrmex harvester ants.  Functional Ecology 24:301-309.
  • Helms Cahan, S., Julian, G. E. 2010.  Shift in frequency-dependent selection across the life-cycle in obligately interbreeding harvester ant lineages.  Evolutionary Ecology 24:359-374.
  • Helms, K. R. and S. Helms Cahan, 2009.  Divergence in mating flight patterns of the seed-harvester ant Pogonomyrmex rugosus Emery, (1895) in the western Mojave Desert.  Myrmecological News 13:15-17.
  • Schwander, T., Helms Cahan, S., S. Suni, Keller, L. 2008. Mechanisms of reproductive isolation between an ant species of hybrid origin and its parents. Evolution 62:1635-1643.
  • Schwander, T., Humbert, J.-Y., Brent, C. S., Helms Cahan, S., Chapuis, L., Renai, E., Keller, L. 2008. Maternal effect on female caste determination in a social insect. Current Biology 18:265-269.
  • Schwander, T., Keller, L., Helms Cahan, S. 2007. Two alternate mechanisms contribute to the persistence of interdependent lineages in Pogonomyrmex harvester ants. Molecular Ecology 16:3533-3543.
  • Schwander, T., Helms Cahan, S., Keller, L. 2007. Characterization and distribution of Pogonomyrmex harvester ant lineages with genetic caste determination. Molecular Ecology 16:367-387.
  • Helms Cahan, S. Julian, G.E., Schwander, T., Keller, L. 2006. Reproductive isolation between the harvester ant Pogonomyrmex rugosus and two lineages with genetic caste determination. Ecology 87:2160-2170.
  • Julian, G.E., Helms Cahan, S. 2006. Behavioral differences between Pogonomyrmex rugosus and two dependent lineages (H1/H2). Ecology 87:2207-2214.
  • Schwander, T., Helms Cahan, S., Keller, L. 2005. Genetic caste determination in Pogonomyrmex harvester ants imposes costs during colony founding. Journal of Evolutionary Biology 19:402-409.
  • Helms Cahan, S., Rissing, S.W. 2005. Variation in queen size across a behavioral transition zone in the ant Messor pergandei. Insectes Sociaux 52:84-88
  • Helms Cahan, S., Julian, G. E, Rissing, S. W., Schwander, T, Parker, J. D., Keller, L. 2004. Loss of phenotypic plasticity explains genotype-caste association in harvester ants. Current Biology 14:2277-2282.
  • Helms Cahan, S., Keller, L. 2003. Complex hybrid origin of genetic caste determination in harvester ants. Nature 424:306-309.
  • Helms Cahan, S., Vinson, S. B. 2003. Reproductive division of labor between hybrid and non-hybrid offspring in a fire ant hybrid zone. Evolution 57:1562-1570.
  • Helms Cahan, S., Parker, J. D., Rissing, S. W., Johnson, R. A., Polony, T. S., Weiser, M.D., Smith, D.R. 2002. Extreme genetic differences between queens and workers in hybridizing Pogonomyrmex harvester ants. Proceedings of the Royal Society of London, Series B 269:1871-1877.
  • Helms Cahan, S., Blumstein, D.T., Sundstrom, L., Liebig, J. and Griffin, A. 2002. Social trajectories and the evolution of social behavior. Oikos 96:206-216.
  • Helms Cahan, S., 2001. Ecological variation across a behavioral transition zone in the ant Messor pergandei. Oecologia 129:629-635.
  • Helms Cahan, S. 2001. Co-operation and conflict in ant foundress associations: insights from geographical variation. Animal Behaviour 61:819-825.