Submitted to: Biodiversity Issues
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/20/2006
Publication Date: 7/20/2006
Citation: BIODIVERSITY SCIENCE 2006, 14(3):232-240
Interpretive Summary: The knowledge of the invasion mechanism of an alien species is considered primordial to design control strategies. To determine if the invasiveness of alligator weed Alternanthera philoxeroides is explained by advantages of ecological differences between the native and introduced regions or rapid adaptive evolution in the exotic range in China, we compared 19 morphological and anatomical traits of alligator weed collected in native (Argentina) and invasive (China and USA) regions. The results show that native populations from Argentina had significant morphological variation in nine traits, whereas populations from introduced regions showed no significant variations in any of the 19 traits. From these morphological characterizations we suggest that one population from Argentina (Santa Fé, 59°49'W, 29°16'S) seems to be similar to the one that originated the invasion in China and also in USA. Hence, we encourage control programs that considered this feature as important for any future decisions.
Technical Abstract: The damage caused by biological invasions has traditionally been thought to result from alien species taking advantage of ecological differences between the native and introduced regions. In contrast, evidence is increasing that invasive plants can undergo rapid adaptive evolution during the process of range expansion. Using a common garden approach, we compared 19 morphological and anatomical traits of Alternanthera philoxeroides collected in native (Argentina) and invasive (China and USA) regions. The results show that native and invasive A. philoxeroides have become genetically differentiated. Populations from Ar-gentina had significant morphological variation in nine traits, with heritability varying from 49% to 89%. The nine traits are stomatal density, stomatal index, diameter of stem, diameter of pith cavity, thickness of vascular cylinder, thickness of cortex, area ratio of vascular cylinder, area ratio of pith cavity, and leaf index. However, populations from introduced regions showed no significant variations in any of the 19 traits, indicating that the morphological differences within introduced regions might be based on phenotypic plasticity. Based on the result of PCA (primary component analysis), all five introduced populations and one population from Argentina (Santa Fé, 59°49'W, 29°16'S) can be clustered as one group, implying that the Santa Fé population may have similar genotypes with the lineage introduced to China. The existence of genetically differentiation of A. philoxeroides between native and introduced regions should be considered in any program that attempts management or utilization of this plant.