It is clear that Eurasian and hybrid watermilfoils exhibit genetic variation for growth and herbicide response, and this variation is of interest to managers charged with developing and evaluating control tactics. How genetic variation is structured within and among populations is unclear. For example, do populations consist largely of single genotypes that vegetatively (clonally) propagate, or are they genetically diverse? Similarly, do individual clones have widespread distributions indicative of extensive dispersal of asexual propagules, or do they have restricted, local distributions? These questions have important management implications regarding the adaptive potential of populations, and whether the same management tactics in different lakes will have similar efficacy. We studied patterns of within- and among-lake genetic variation in 80 lakes in Michigan and Minnesota using a combination of microsatellites, amplified fragment length polymorphisms, and single nucleotide polymorphisms generated from genotyping by sequencing.
Results/Conclusions
We found that within-lake genetic diversity was generally low for Eurasian and hybrid watermilfoil, indicating that the majority of reproduction within lakes occurs via vegetative (clonal) propagation. However, there were several notable exceptions to this pattern, suggesting that sexual reproduction occurs within at least some lakes some of the time. In contrast, among-lake genetic diversity was relatively high, meaning that lakes tended to harbor different genotypes from one another. However, several genotypes were shared among lakes, including one genotype with known herbicide response properties. This pattern of relatively low within-lake diversity and high among-lake diversity is common in aquatic plants, and may be related to seed dispersal and recruitment, colonization by one or a few genotypes, or adaptive responses to local selection pressures. As a practical matter for Eurasian and hybrid watermilfoil management, that lakes are commonly composed of different genotypes means that managers should explicitly consider and evaluate genetic variation as a potential explanation for variation in observed efficacy of the same control tactics in different lakes. At the same time, that some lakes share genotypes provides opportunities for efficiency in collecting and sharing genotype-specific growth and herbicide response information to inform management decisions.