Laboratory crosses and genetic analysis of natural populations demonstrate sexual viability of invasive hybrid watermilfoils (Myriophyllum spicatum × M. sibiricum)

• We investigated invasive hybrid watermilfoil ability to reproduce sexually.
• Hybrid artificial crosses produced viable seeds.
• Genetic evidence for advanced generation hybrids was found in natural populations.
• Sexual reproduction may impact management.

The hybrid offspring of invasive Eurasian watermilfoil (Myriophyllum spicatum) and native northern watermilfoil (Myriophyllum sibiricum) are highly invasive and have recently been considered to be of special management concern. Hybrid watermilfoils can reproduce asexually via fragmentation, but it is unknown if they can reproduce sexually. Here, we use laboratory crosses of hybrid watermilfoil genotypes to demonstrate that they can be sexually viable. In addition, a Bayesian analysis of Amplified Fragment Length Polymorphism (AFLP) data from natural populations of parental and hybrid watermilfoils was used to determine whether there was evidence for sexual reproduction by hybrid watermilfoils in natural populations. While many hybrid genotypes were estimated to be first generation hybrids, we found strong evidence for sexual reproduction in the form of later generation hybrids (F2 backcrosses, or later generation hybrids). Our study provides strong evidence that hybrids can, and frequently do, reproduce via sexual reproduction in natural populations. The capacity for sexual reproduction by hybrid watermilfoils has important management implications. The production of viable seeds may serve as an important source for the recolonization of previously treated lakes or areas within lakes. In addition, seeds may provide opportunities for colonization of new lakes (e.g., through water fowl). Thus, managers may consider practices that limit the production of seeds. In addition, sexual reproduction by hybrids may provide opportunities for the generation of unique genotypes through genetic recombination, some of which may be more invasive than their parental genotypes. Therefore, further consideration of sexual reproduction by hybrid watermilfoils is warranted.