Evidence of hybridity in invasive watermilfoil ( Myriophyllum ) populations

Abstract

Invasions of nonindigenous species have caused ecological devastation to natural communities worldwide, yet the biological bases for invasiveness remain poorly understood. Our studies of invasive watermilfoil (Myriophyllum) populations revealed widespread polymorphisms in biparentally inherited nuclear ribosomal DNA sequences, which were not detected in populations of native North American species. Subclones of the polymorphic regions revealed the occurrence of distinct sequences matching those acquired from both nonindigenous and native North American species. Molecular data demonstrate clearly that invasive watermilfoil populations in North America have resulted from hybridization between nonindigenous and native species. These observations suggest that invasiveness in these aggressive aquatic weeds may be linked to heterosis maintained by vegetative propagation.

Evidence for the hybrid origin of Nymphoides montana Aston (Menyanthaceae)

“…Evidence of relatively recent hybridisation is apparent in the often-sequenced nrITS region, which exists as tandem repeats that tend (in non-hybrid lineages) to be uniform across all copies, owing to the process of concerted evolution (Álvarez & Wendel 2003). However, in many recently derived hybrids, where concerted evolution has not had sufficient time to assimilate all copies of nrITS, the differences appear as sequence polymorphisms that then can be separated by molecular cloning (e.g., Moody & Les 2002). In some situations the ongoing process of concerted evolution is evidenced by the existence of chimeric sequences, i.e., nrITS sequences that exist as various recombinant copies of the two parental sequences (e.g., Les et al 2009), or by copies that are intermediate between the parental sequences, i.e., the result of crossingover followed by gene conversion (Álvarez & Wendel 2003).…”

Potential for Introduction of Invasive Species into Louisiana from Illinois River Dredged Material

“…The history of the spread of Eurasian watermilfoil in the United States is made unclear by the existence of herbarium specimens that were mislabeled and by the confusion with the native species, northern watermilfoil (M. sibiricum Kom.). Its history is further confounded by reports of hybridization between the nonindigenous Eurasian watermilfoil and the native northern watermilfoil (Moody and Les 2002). The molecular data suggest that invasiveness into new regions may be related to hybridization.…”

A DNA Fingerprinting Approach for Distinguishing Native and Non-native Milfoils

“…To accomplish this, we first visually inspected the electropherograms of our milfoil sequences with Sequencher (version 4.0.5) to double check base calling at nucleotide positions where sequences differed. Next, we aligned the DNA sequences from our milfoil samples with the Myriophyllum sequences available on GenBank (accessions AF513822-AF513850) from Moody and Les (2002) using ClustalX (version 1.81, Thompson et al 1997) to identify species genetically based on their phylogenetic relationships with respect to those on GenBank.…”

“…-Phylogenetic relationships among ITS alleles found in our samples (bold) and GenBank accessions (non-bold). "het x pin" samples refer to heterophyllum or pinnatum alleles found in hybrid plants in Moody and Les (2002). Numbers in parentheses refer to the number of lakes each allele was found in and the total number of individuals across all samples with each allele, respectively.…”

“…Milfoils are often identified based on floral characters, but these are not always available for inspection due to short flowering duration and the propensity for vegetative propagation. Morphologically based identification of milfoil species can be further complicated by hybridization (Aiken 1981, Ceska andCeska 1985), which has been reported for fieldcollected samples from some New England lakes (Moody and Les 2002). Accurate, reliable and year-round diagnostic characters are therefore needed to distinguish native milfoils from non-native M. heterophyllum.…”