Extensive interlineage hybridization in the predominantly clonal Hydrilla verticillata

Area of Science:

• Botany and Plant Science
• Molecular Biology
• Ecology

Background:

• Hydrilla verticillata (hydrilla) is an ecologically and economically significant aquatic plant known for aggressive growth.
• Morphological variations, including monoecious and dioecious biotypes, exist within hydrilla populations.
• Previous studies utilized plastid DNA but lacked nuclear DNA phylogenetic analysis for intraspecific diversity.

Purpose of the Study:

• To evaluate the genetic diversity and phylogenetic relationships of native and introduced hydrilla populations.
• To analyze nuclear and plastid DNA sequences phylogenetically.
• To compare leaf morphologies among identified clades.

Main Methods:

• Phylogenetic analysis of nuclear (ITS, PDS) and plastid (trnL-F) DNA sequences using likelihood and Bayesian methods.
• Comparison of leaf morphologies to distinguish biotypes.
• Evaluation of genetic markers for intraspecific diversity.

Main Results:

• Nuclear markers (ITS and PDS) revealed significant polymorphic sequences and multiple lineages, including invasive American biotypes.
• Leaf morphology data supported distinct lineages and differentiated monoecious and dioecious biotypes in the U.S.
• Nuclear data indicated greater genetic diversity than plastid markers, suggesting hybridization events.

Conclusions:

• Invasive monoecious and dioecious hydrilla in the Americas are genetically distinct, arising from admixture of Eurasian progenitors.
• Nuclear gene data suggest hybridization between divergent lineages as a source of genetic diversity.
• Populations from India and South Korea are implicated as likely origins for the dioecious and monoecious biotypes, respectively.