The evolutionary history of an invasive species: alligator weed, Alternanthera philoxeroides

A.J. SOSA; E. GREIZERSTEIN; M.V. CARDO; M.C. TELESNICKI; M.H. JULIEN

La Grand Motte

Simposio; XII International Symposium on Biological Control opf Weeds; 2007

The eco-evolutionary mechanisms of biological invasions are still not thoroughly understood. Alligator weed, Alternanthera philoxeroides (Martius) Gisebach (Amaranthaceae), is a plant native to South America and a weed in Australia and other countries. To better understand its success as an invader, we assessed the morphologic and cytogenetic variability of 12 Argentinean populations and the cytogenetic variability of seven Australian populations. We found differences in leaf shape (width to length ratio) and stem architecture in the Argentinean populations, reproduction (sexual with regular meiosis in two Argentinean populations to completely asexual with irregular meiosis and low pollen viability in all other populations), and polyploid degree (tetraploids with sexual reproduction and seed production to hexaploids with or without sexual reproduction). We propose a hypothesis about the mechanism that drove alligator weed to form highly invasive hybrid populations with vegetative reproduction from diploid ancestors. We consider the implications for plant-herbivore interactions and biological control of this weed.