Just Cerfing Vol. 7, Issue 8, August 2016 Volume 5, Issue 4, April, 2014 | Page 34

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Invasive Potential of a Newly Introduced Species Vitex rotundifolia
of a species may help identify characteristics that contribute to the transition
from lag phase to an invasive species of concern.
In plants, invasion potential is influenced by the mating system, availability of pollinators in outcrossing or mixed-mating species, high seed viability,
and dispersal ability (Sakai et al., 2001). For example, species that exhibit
rapid vegetative reproduction rather than rely on successful fruit set can
transition more quickly from lag phase to exponential growth (log) phase
(Forseth and Innis, 2004; Hinman, 2011). For species that reproduce only
sexually and require pollinators for successful fruit set, transition from lag
phase may differ in length compared with selfing species (e.g., van Kleunen
et al., 2008). Although it is easy to determine the point of transition from
lag to log phases after the fact, management of an invasive species after
this transition is much more difficult and often much less effective (Groves,
2006; Larkins, 2012). The ability to predict invasion potential accurately
from ecological, genetic, and reproductive biology would greatly assist management practices (Humle, 2012; Quinn et al., 2013).
The mating system (whether outcrossing, selfing, or mixed mating) can
play a critical role in the introduction of new genetic material (Sakai et al.,
2001). In mixed or outcrossing species, introgression will play a more important role than in selfing species, where line sorting (selection and/or random sampling among distinct selfing lines) is more important in establishing genetic patterns in populations. The degree to which reproduction is
asexual also may be critical to invasion success because local establishment
and spread can occur more rapidly through lateral vegetative reproduction
as opposed to sexual reproduction (Speek et al., 2011). Furthermore, in littoral or aquatic environments, vegetative reproduction may be an important mode of long-distance dispersal because these species can spread by
seeds and ramets washed into water-bodies by storms or other disturbance
events, and remaining plants can recolonize recently disturbed areas quickly
(Schamp and Aarssen, 2010; Wang et al., 2011). For example, in the clonal
aquatic plant, Butontus ubellatus, 95% of sampled populations contained
a widespread genotype, suggesting an important role of clonal reproduction
(Kilber and Eckert, 2005).
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Although genetic factors intrinsic to the potential invader may be important (Prinzing et al., 2002), extrinsic factors can also play a leading
role (e.g., Lambrinos, 2004; Richards et al., 2006). Important examples of
such extrinsic factors are the availability and efficiency of pollinators, particularly in outcrossing species, and adequate environmental conditions
for germination (e.g., Parker and Haubensak, 2002). Therefore, changes
in adaptive genetic variation, relative allocation among modes of reproduction, and overall environment each contribute to the launch of a species into invasiveness.
Anthropogenic effects may be important on both ecological and genetic fronts in the transition from lag to exponential phase (Groves, 2006;
Keller and Taylor, 2008). Repeated planting may result in the introduction of new germplasm and thus the introduction of novel genetic information (Bossdorf et al., 2005; Lavergne and Molofsky, 2007; Roman
and Darling, 2007). But even without the introduction of new genetic
variation, planting in many new locations exposes the species to a wider
range of environments, which selects for certain suites of traits based on
novel environmental conditions, and can contribute to spread. Therefore
investigating the effects of introduction site on performance of a variety
of populations, thus genetic source materials will be critical to develop
an understanding of invasion potential across geography. The most important concern regarding transitions from introduced to invasive phases
may be the interactions between genetic factors intrinsic to invaders and
the variable environments in which they are introduced combined with
stochastic events that occur during the invasion (Keller and Taylor, 2008).
Our study investigates invasion potential of V. rotundifolia,a woody vine
or subshrub that employs both sexual and asexual reproduction strategies. Populations in North and South Carolina, initially introduced via
horticulture, primarily grow on coastal dunes. The introduction history
of V. rotundifolia is not completely resolved (see Olsen and Bell, 2005).
The introduction that led to its current distribution likely tran-spired in
the mid-1980s or early 1990s (Olsen and Bell, 2005). Additionally, after
Hurricane Hugo (1989), V. rotundifolia was increasingly used horticul-

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