|FRANKS, S - Fordham University|
|GOODNIGHT, C - University Of Vermont|
Submitted to: Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/30/2011
Publication Date: 1/12/2012
Citation: Franks, S., Wheeler, G.S., Goodnight, C. 2012. Genetic variation and evolution of secondary compounds in native and introduced populations of the invasive plant Melaleuca quinquenervia. Evolution. DOI: 10.1111/j.1558-5646.2011.01524.x.
Interpretive Summary: Invasive weeds introduced in a new range can show large evolutionary change from strong selective forces in their new habitat. This change can be manifested in more rapid growth and greater reproduction and decreased chemical defenses intended to protect the plant from herbivory. These changes can explain the successful establishment of many species in their introduced range. Such changes can be manifested in greater plant size and seed production. Also, invasive plants may be more susceptible to damage from generalist herbivores. It is critical to understand the changes that have occurred and that can potentially occur when designing long-term sustainable management programs of these invasive weeds. Often the habit of the plant in its invasive range differs greatly from that of its native range. Moreover the insects that consume these plants are confronted with very different nutritional challenges. This is especially important for programs that are developing insects as biological control agents against these invasive weeds. The results of this research shows that the invasive Everglades weed, Melaleuca has decreased many of its natural chemical defenses in Florida compared with those in its native Australia. Therefore these invasive plants should be more nutritious for herbivores introduced as biological control agents.
Technical Abstract: Evolution of introduced species can be rapid in their invaded range but can also be constrained by loss of genetic variation. We used quantitative genetic analyses to examine multivariate evolution of secondary compounds in an invasive plant. Seeds of Melaleuca quinquenervia from its native range in Australia and introduced range in Florida were planted in common field plots. Of 20 leaf terpenoids quantified using gas chromatography, most had greater concentrations in herbivore damaged plants, indicating that they are associated with herbivory response. Most of the compounds showed lower concentrations in the introduced populations. This is consistent with an evolutionary decrease in defense, as predicted by the evolution of increased competitive ability (EICA) hypothesis. Three compounds (1,8-Cineole, E-nerolidol, and Viridiflorol) used for quantitative genetic analyses all showed positive linear selection, and there were negative genetic correlations between nerolidol and both other compounds. Genetic variances and covariances were significantly reduced in the introduced range. It appears that evolution in defensive compounds occurred despite a loss of quantitative genetic variation following introduction and genetic correlations opposing selection. Selection patterns and G-matrix comparisons also indicate that selection is more likely than drift as the mechanism of the evolutionary change.