Evidence for human-caused founder effect in populations of Solanum jamesii found at archaeological sites: I. Breeding experiments and the geography of sexual reproduction

Authors: PAVLIK, BRUCE - University Of Utah; BAKER, MARGARET - University Of Utah; Bamberg, John; DEL RIO, ALFONSO - University Of Wisconsin; KINDER, DAVID - Ohio Northern University; LOUDERBACK, LISBETH - University Of Utah

Submitted to: American Journal of Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/17/2021
Publication Date: 9/29/2021
Citation: Pavlik, B.M., Baker, M., Bamberg, J.B., Del Rio, A.H., Kinder, D., Louderback, L.A. 2021. Evidence for human-caused founder effect in populations of Solanum jamesii found at archaeological sites: I. Breeding experiments and the geography of sexual reproduction. American Journal of Botany. 108(9):1808-1815. https://doi.org/10.1002/ajb2.1737.
DOI: https://doi.org/10.1002/ajb2.1737

Interpretive Summary: Potato is the top vegetable crop in the USA and world, with many wild related species available for breeding. One of these is Solanum jamesii (jam), native to the southwest USA. This jam potato has a lot of valuable traits. We would like to know how it lives in the wild and how ancient native Americans moved it and used it for food. We collected several populations of jam, some from sites inhabited by ancient native Americans, some not, and examined differences in how well they were able to reproduce by seeds. Populations from ancient inhabited sites appear to have less seed reproduction, suggesting early humans spread them to habitation sites north beyond their natural range, and cultivated them to survive and reproduce mainly as tubers. This kind of information impacts our sense of the relative genetic diversity of jam populations from different geographic sites, and thus will help the US Potato Genebank manage the collection, preservation, and use of these stocks in breeding to improve the crop.

Technical Abstract: Plant domestication can be detected when transport, use and manipulation of propagules impact reproductive functionality, especially in species with self-incompatible breeding systems. Evidence for human-caused founder effect in the Four Corners potato (Solanum jamesii Torr.) was examined by conducting 526 controlled matings between archaeological and non-archaeological populations from field-collected tubers grown in a greenhouse. In addition, specimens from 24 major herbaria, along with collection records from >160 populations were examined to determine which have been observed to produce fruits. Archaeological populations did not produce any fruits when self-crossed or out-crossed between individuals from the same source. A weak ability to self- or out-cross within populations was observed in non-archaeological populations. Out-crossing between archaeological and non-archaeological populations, however, produced fully formed, seed-containing fruits, especially with a non-archaeological pollen source. Fruit formation has been observed in 51 of 162 occurrences, probably constrained in some locations by monsoonal drought, lack of pollinators, and spatial separation of suitable partners. Some archaeological populations (especially those along ancient trade routes) had records of fruit production (Chaco Canyon, Mesa Verde) while others (those in northern Arizona and southern Utah) did not. The present study suggests that archaeological populations could have different origins at different times – some descending directly from large gene pools to the south and others derived from gardens already established around occupations. The latter experienced a chain of founder events, further reducing genetic diversity and mating capability. Consequently, some archaeological populations lack the genetic ability to sexually reproduce, likely as the result of human-caused founder effect.