Hybridization, cryptic diversity, and invasiveness in introduced variable-leaf watermilfoil

Area of Science:

• Ecology
• Evolutionary Biology
• Botany

Background:

• Invasive species evolution is often linked to hybridization.
• Variable-leaf watermilfoil (Myriophyllum heterophyllum) in the northeastern US comprises hybrid and pure lineages.
• Previous observations suggested hybrids are more invasive, but data were lacking.

Purpose of the Study:

• To quantitatively compare the ecological distinctiveness and invasiveness of hybrid and pure lineages of Myriophyllum heterophyllum.
• To test the hypothesis that hybridization enhances invasiveness in this species.
• To investigate the role of intraspecific hybridization in invasiveness.

Main Methods:

• Ecological traits (biomass, plant size, branching) were compared among distinct lineages.
• Field observations and quantitative measurements were employed.
• Lineage identification involved genetic and morphological assessments.

Main Results:

• Hybrids showed greater biomass, size, and branching than at least one pure M. heterophyllum lineage.
• Pure parental lineages also exhibited invasive traits, comparable to hybrids in some aspects.
• No evidence supported a role for intraspecific hybridization in invasiveness where lineages co-occurred.

Conclusions:

• Distinct lineages of Myriophyllum heterophyllum are ecologically different.
• Hybridization may contribute to invasiveness, but pure lineages can also be highly invasive.
• Identifying cryptic lineages is crucial for prioritizing rapid response and control efforts against invasive aquatic plants.