An unusual case of seed dispersal in an invasive aquatic; yellow flag iris (Iris pseudacorus)

Authors: Gaskin, John; POKOMY, MONICA - Montana State University; MANGOLD, JANE - Montana State University

Submitted to: Biological Invasions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/25/2016
Publication Date: 5/1/2016
Publication URL: https://handle.nal.usda.gov/10113/62764
Citation: Gaskin, J.F., Pokomy, M.L., Mangold, J.M. 2016. An unusual case of seed dispersal in an invasive aquatic; yellow flag iris (Iris pseudacorus). Biological Invasions. 18(7):2067-2075. doi:10.1007/s10530-016-1151-0.

Interpretive Summary: Understanding how invasive plants reproduce can help managers plan efficient control efforts. Invasive aquatic weeds typically reproduce primarily through vegetative means. Yellow flag iris is an invasive aquatic plant species. There have been contradictory reports of it dispersing primarily by seed vs. pieces of roots breaking off and floating to new locations. We performed genetic analysis of 20 aquatic populations across the Pacific Northwest of USA. We never found genetically identical plants from different populations. We also found that 99.1% of seed tested was viable. This evidence suggests that this invasive disperses almost entirely by seed, not root fragmentation. These findings are unusual for an aquatic invasive plant, and inform managers of two things: 1) to limit dispersal, development of mature seed in the field should be prevented; and 2) if classical biological control is proposed, an agent type that limits seed would be effective for managing further dispersal.

Technical Abstract: Understanding reproductive mode of invasive plants can help managers plan more efficacious control. Invasive aquatics typically reproduce primarily through vegetative means. Yellow flag iris is an invasive plant species often growing as an emergent aquatic. There have been contradictory reports of it dispersing primarily by seed vs. rhizome. We performed genetic analysis of transect collections in 20 aquatic populations across the Pacific Northwest of USA. We found 167 unique genotypes in 171 plants, and we never found genetically identical plants from different populations. We also found that 99.1% of seed tested was viable. This evidence suggests that this invasive disperses almost entirely by seed, not clonal fragmentation, when we consider plants that are at least 2 m apart. The presence of 10 genotypic clusters suggests multiple founding events from distinct genetic sources. No significant relationship between genetic and geographic distance also suggests multiple founding events, randomized across the landscape, rather than spread from one or a few founding sources. In all, the current genetic structuring of the yellow flag iris invasion is determined by a lack of vegetative propagule movement by water, high amounts of local seed movement by water, and perhaps occasional new establishment of populations via movement of propagules by humans or other animal mediated transport from diverse founding sources. These factors lead to genetically distinct populations that can be geographically close. These findings are unusual for an emergent aquatic, and inform managers of two things: 1) to limit dispersal, development of mature seed in the field should be prevented; and 2) if classical biological control is proposed, an agent guild that limits seed would be effective for managing further dispersal.