Biology Reference
In-Depth Information
Box 12.1
Twomain approaches are used to identify the source of NIMS. The first relies on
the assumption that the vector of introduction (e.g., ballast waters of cargo ships
along a specific route) is known. Knowledge of the target species' distribution
range and the navigation routes can be combined to identify the likely source
regions for that species. Vector management can then prevent further
introductions (Ruiz and Carlton
2003
). Most importantly, biogeoclimatic
models can forecast potential zones vulnerable to invasion and predict the
range expansion of invasive NIMS by combining information gathered from
species distribution, transport vectors, local ecophysiological conditions, and
the species-known ecophysiological tolerance ranges (Arrontes
2005
).
A second method deploys DNA sequencing markers and geographical
information (phylogeographic approach). Specimens are collected, DNA is
extracted, and the same (one or more than one) DNA region is sequenced
from multiple individuals to infer the genealogical relationships among
introduced and putative native populations of the invasive species and recon-
struct the spatial history of the invasion (Fig.
12.1
). A variety of DNA
sequencing markers have been today developed from mitochondrial, plastid,
and nuclear genomes (see case studies); however, the successful use of the
approach relies on the resolution of the marker and an adequate sampling
strategy. Less applied in seaweed invasion biology is the population genetic
approach based on allele frequencies of microsatellite markers to assign
individuals to a specific population (for reviews of both approaches, see
Wares et al.
2005
; Muirhead et al.
2008
).
extent of the introduced range. This information can be immediately available
where algal floras are well described and survey programs for early detection are
in place (Anderson
2007
). In geographical regions, however, where local seaweed
species are poorly explored and historical records such as species lists are limited, a
presumably introduced species may either be native or cryptogenic. Visual surveys
and identifications based on gross morphology are often sufficient to detect
introductions since many NIMS are conspicuous and genetic discontinuities do
not always occur within species (O'Doherty and Sherwood
2007
; Castelar et al.
2009
). However, many algal genera have extreme levels of phenotypic plasticity
and species can potentially hybridize with close relatives (e.g., introduced and
native populations of
Fucus evanescens
and
F. serratus
; Coyer et al.
2007
). For
many introduced seaweeds only multidisciplinary approaches, which take into
account molecular, morphological, reproductive, and ecophysiological evidence,
are able to characterize the introduced taxonomic units. Such approaches provide
sound information on the origins and the geographical trajectory of the invasion and
are able to predict persistence and expansion potential of introduced populations
(Flagella et al.
2010
; Pang et al.
2010
).
