Evolutionary “Bet-Hedgers” under Cultivation: Investigating the Domestication of Erect Knotweed (Polygonum erectum L.) using Growth Experiments
Evolutionary “bet-hedging” refers to situations in which organisms sacrifice mean fitness for a reduction in fitness variance over time. Germination heteromorphism is the quintessential and most well understood bet-hedging strategy. It has evolved in many different plants, including the wild progenitors of some crops. Erect knotweed (Polygonum erectum L.), an annual seed crop, was cultivated in Eastern North America between c. 3000–600 BP. By c. 900 BP, cultivation had produced a domesticated subspecies with greatly reduced germination heteromorphism. Field observations and greenhouse experiments suggest that cultivation eliminated the selective pressures that maintain the bet-hedging strategy in erect knotweed, while humans also directly selected for seeds that germinated reliably and for seedlings with rapid early growth. The protection provided to erect knotweed under cultivation explains the domestication syndrome that has been observed in some archaeological assemblages. Dormancy provides seeds a means of escaping adverse conditions in time, while dispersal provides an escape in space. Farmers relaxed selective pressures that maintained dormancy in erect knotweed by acting as seed dispersers, spreading disturbance-adapted plants to predictable and protected environments, and by saving and exchanging seed stock. Experimental data also indicate that adaptive transgenerational plasticity may have been working against the expression of domestication syndrome in this case.
KeywordsDomestication Evolutionary bet-hedging Erect knotweed Experimental archaeology Eastern agricultural complex North America
I would like to acknowledge and thank the many people who contributed to this project by helping me access collections or populations under their care: Alan Brant, Paul and Nancy Krautman, Michelle Berg Vogel, Jim Solomon, George Yatskievych, Rusty Russell, Bruce Smith, Mary Suter, Mary Simon, George Crothers, David Pollack, Jack Rosen, Jane Buikstra, Jason King, Kris Gremillion, Wayna Adams, Neal Lopinot, Michael Meinkoth, Dee Ann Watt, John Kelly, Bill Green, Caitlin Rankin; and by sharing their knowledge with me and discussing these ideas: Michael Dyer, Gayle Fritz, Logan Kistler, Liz Horton, Kelsey Nordine, and Andrew Flachs. I would also like to acknowledge Nancy Asch Sidell, David Asch, and Sonia Sultan, three researchers whom I have never met but whose meticulous research inspired and greatly improved this project, and Marti Mueller for her careful editing and thoughtful questions. Support for this project was provided by the National Science Foundation, the Wenner-Gren Foundation, and the Lynne Cooper Harvey Fellowship in American Culture Studies at Washington University.
Compliance with Ethical Standards
This research was funded by US National Science Foundation Doctoral Dissertation Improvement Grant #58292.
Conflict of Interest
The author declares that she had no conflict of interest.
- Adams K. R. (2014). Little barley grass (Hordeum pusillum Nutt.): a Prehispanic new world domesticate lost to history. In New Lives for Ancient and Extinct Crops. P.E. Minnis, The University of Arizona Press, Tuscon, pp. 139–179.Google Scholar
- Anderson E. (1952). Plants, Man and Life, Missouri Botanical Garden, St. Louis.Google Scholar
- Asch, David L., and Nancy B. Asch. 1985a Archaeobotany. In The Hill Creek Homestead and the Late Mississippian Settlement in the Lower Illinois River Valley. M.D. Conner (ed.), Kampsville Archaeological Center, Vol. 1. Kampsville, The Center for American Archaeology, pp. 115–170.Google Scholar
- Asch, D. L., and Asch, N. B. (1985b). Prehistoric Plant Cultivation in West Central Illinois. In Prehistoric Food Production in North America. Ford, R.I. (ed.), pp. 149–203, Vol. 75. Ann Arbor, Museum of Anthropology, University of Michigan.Google Scholar
- Brenkle J. F. (1946). Notes on avicularia II. Phytologia 2(5): 169–171.Google Scholar
- Childs D. Z., Metcalf C. J. E., and Rees M. (2010). Evolutionary bet-hedging in the real world: empirical evidence and challenges revealed by plants. Proceedings of the Royal Society of London B: Biological Sciences rspb20100707: 1–10.Google Scholar
- Costea M., and Tardif F. J. (2004). The biology of Canadian weeds: Polygonum aviculare L. Canadian Journal of Plant Science 131: 481–506.Google Scholar
- Costea, M., Tardif, F. J., and Hinds, H. H. (2005). Polygonum L. In Flor of North America North of Mexico. F.o.N.A.E. Committee, (ed.), Vol. 5. New York and Oxford, eFloras.org.
- Delcourt, Paul A, et al. (1986). Holocene ethnobotanical and Paleoecological record of human impact on vegetation in the little Tennessee River valley, Tennessee. Quaternary Research 25(3):330–349.Google Scholar
- Delcourt, P. A, et al. (1998). Prehistoric human use of fire, the eastern agricultural complex, and Appalachian oak-chestnut forests: paleoecology of cliff palace pond, Kentucky. American Antiquity 63(3):263–278.Google Scholar
- Ford, R. I., ed. (1985). Prehistoric food production in North America. Volume 75. Ann Arbor, Museum of Anthropology, University of Michigan.Google Scholar
- Fritz, G. J. (1986). Prehistoric ozark agriculture: The University of Arkansas Rockshelter Collections. Dissertation, University of North Carolina.Google Scholar
- Fritz G. J. (1993). Early and middle woodland period Paleoehtnobotany. In Scarry C. M. (ed.), Foraging and farming in the eastern woodlands, University Press of Florida, Gainesville, pp. 39–56.Google Scholar
- Fritz G. J. (2014). Maygrass: its role and significance in native Easern North American. In Minnis P. E. (ed.), New lives for ancient and extinct crop, Universtiy of Arizona Press, Tuscon, pp. 12–43.Google Scholar
- Fritz G. J., and Smith B. D. (1988). Old collections and new technology: documenting the domestication of Chenopodium in Eastern North America. Midcontinental Journal of Archaeology 13(1): 3–27.Google Scholar
- Gremillion K. J. (1993b). The evolution of seed morphology in domesticated Chenopodium: an archaeological case study. Journal of Ethnobiology 13: 149–169.Google Scholar
- Gremillion K. J. (1993c). Plant husbandry at the archaic/woodland transition: evidence from the cold oak shelter, Kentucky. Midcontinental Journal ofArchaeology 18: 161–189.Google Scholar
- Gremillion K. J. (1998). Changing roles of wild and cultivated plant resources among early farmers of Eastern Kentucky. Southeastern Archaeology 17(2): 140–157.Google Scholar
- Hunter, A. A. (1992). Utilization of Hordeum pusillum (Little Barley) in the Midwest United States: Applying Rindos' Co-evolutionary Model of Domestication. Dissertation, University of Missouri-Columbia.Google Scholar
- Mueller, N. G. (2017a). An extinct domesticated subspecies of erect knotweed in Eastern North America: Polygonum erectum L. ssp. watsoniae (POLYGONACEAE). Novon 25(2).Google Scholar
- Mueller, N.G. (2017b). Documenting domestication in a lost crop (Polygonum erectum L.): Evolutionary bet-hedgers under cultivation. Vegetation History and Archaeobotany 26(1).Google Scholar
- Mueller N. G (2017c). Seeds as artifacts of communities of practice: the domestication of erect knotweed in Eastern North America. Dissertation, Washington University in St. Louis.Google Scholar
- Murray P. M., and Sheehan, M. C. (1984). Pehistoric polygonum use in the Midwestern United States. In Experiments and Observations on Aboriginal Wild Plant Food Utilization in Eastern North America. Munson, P.J. (ed.), Prehistory Research Series, Vol. VI. Indianapolis, Indian Historical Society.Google Scholar
- Sauer C. O. (1952). Seeds, spades, hearths, and herds: the domestication of animals and foodstuffs, MIT Press, Cambridge.Google Scholar
- Simon M. L., and Parker K. E. (2006). Prehistoric plant use in the American bottom: new thoughts and interpretations. Southeastern Archaeology 25(2): 212–257.Google Scholar
- Slatkin M. (1974). Hedging one's evolutionary bets. Nature 250: 704–705.Google Scholar
- Smith B. D. (1992). The floodplain weed theory of plant domestication in eastern North America. In Smith B. D. (ed.), Rivers of change: essays on early agriculture in North America, Smithsonian Institution Press, Washington.Google Scholar
- Wymer D. A. (1993). Cultural change and subsistence: the middle woodland and late woodland transition in the Mid-Ohio Valley. In Scarry C. M. (ed.), Foraging and farming in the eastern woodlands, University Press of Florida, Gainesville, pp. 138–156.Google Scholar
- Yarnell, R. A. (1978). Domestication of sunflower and sumpweed in Eastern North America. In The Nature and Status of Ethnobotany. Ford, R.A. (ed.), Anthropological Papers No. 67. Ann Arbor, Museum of Anthropology, Univerity of Michigan, pp. 289–299.Google Scholar
- Yarnell R. A. (1993). The importance of native crops during the late archaic and woodland periods. In Scarry C. M. (ed.), Foraging and farming in the eastern woodlands, University Press of Florida, Gainesville, pp. 13–26.Google Scholar