Genotyping of 262 <i>Crassostrea gigas</i> individuals using six microsatellite loci in two multiplex PCR.

<p>Genotyping of 262 <i>Crassostrea gigas</i> individuals using six microsatellite loci in two multiplex PCR.</p

Simulation of larval dispersal.

<p>The spatial distribution of the 369 landed Pacific oyster (<i>Crassostrea gigas</i>) larvae in Swedish and Norwegian coastal waters in total for the simulated years (1990, 1998, 2002, 2006, 2007, 2010), summed per coastal grid cell (50x50 km). Number of landed larvae (super-individuals) per grid cell is shown (see legend). The location and names of the sampled DNA stations in this study are indicated (black circles, cf. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0177481#pone.0177481.t001" target="_blank">Table 1</a>). For simulation details see [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0177481#pone.0177481.ref050" target="_blank">50</a>]. Reprinted from Rinde et al. 2016 under a CC BY license, with permission from NIVA, original copyright 2016. The map is produced using ESRIs GIS software ArcMap v 10.4.1 (<a href="http://www.esri.com" target="_blank">www.esri.com</a>), and the country dataset GISCO NUTS 2010.</p

Rapid expansion of the invasive oyster <i>Crassostrea gigas</i> at its northern distribution limit in Europe: Naturally dispersed or introduced?

<div><p>The Pacific oyster, <i>Crassostrea gigas</i>, was introduced to Europe for aquaculture purposes, and has had a rapid and unforeseen northward expansion in northern Europe. The recent dramatic increase in number of <i>C</i>. <i>gigas</i> populations along the species’ northern distribution limit has questioned the efficiency of Skagerrak as a dispersal barrier for transport and survival of larvae. We investigated the genetic connectivity and possible spreading patterns between Pacific oyster populations on the southern Norwegian coast (4 localities) and Swedish and Danish populations by means of DNA microsatellite analysis of adult oysters, and by simulating larvae drift. In the simulations we used a 3D oceanographic model to explore the influence of recent climate change (1990–2010) on development, survival, and successful spreading of Danish and Swedish Pacific oyster larvae to Norwegian coastal waters. The simulations indicated adequate temperature conditions for development, survival, and settlement of larvae across the Skagerrak in warm years since 2000. However, microsatellite genotyping revealed genetic differences between the Norwegian populations, and between the Norwegian populations and the Swedish and Danish populations, the latter two populations being more similar. This patchwork pattern of genetic dissimilarity among the Norwegian populations points towards multiple local introduction routes rather than the commonly assumed unidirectional entry of larvae drifted from Denmark and Sweden. Alternative origins of introduction and implications for management, such as forecasting and possible mitigation actions, are discussed.</p></div

Summary statistics of the six genotyped microsatellites loci in the six analysed sampling locations.

<p>Summary statistics of the six genotyped microsatellites loci in the six analysed sampling locations.</p

Sampling overview and simplified introduction history.

<p><i>Crassostrea gigas</i> aquaculture introduction pathways in Europe (^A[<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0177481#pone.0177481.ref023" target="_blank">23</a>], ^B[<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0177481#pone.0177481.ref017" target="_blank">17</a>], ^C[<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0177481#pone.0177481.ref003" target="_blank">3</a>], ^D[<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0177481#pone.0177481.ref024" target="_blank">24</a>], ^E[<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0177481#pone.0177481.ref009" target="_blank">9</a>] & ^F[<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0177481#pone.0177481.ref007" target="_blank">7</a>]) and the genetic differenciation boundary between a documented southern and northern genetic group delineated by a dotted line (^B[<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0177481#pone.0177481.ref017" target="_blank">17</a>], ^G[<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0177481#pone.0177481.ref015" target="_blank">15</a>] & ^H[<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0177481#pone.0177481.ref001" target="_blank">1</a>]). The six <i>C</i>. <i>gigas</i> collection sites used in this study are indicated by the oyster symbole (See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0177481#pone.0177481.t001" target="_blank">Table 1</a> for details). For Norway, valid and withdrawn aquaculture licenses for <i>Ostrea edulis</i> (<a target="_blank">http://www.fiskeridir.no/register/akvareg/?m=utl_lok&s=1</a>; 20. May 2014) and <i>C</i>. <i>gigas</i> (Directorate of Fisheries) are indicated by open circles and stars, respectively. The map is produced using ESRIs GIS software ArcMap v 10.4.1 (<a href="http://www.esri.com" target="_blank">www.esri.com</a>), and the country dataset GISCO NUTS 2010.</p

Discriminant Analysis of Principal Components (DAPC).

<p>Scatter plot with (a) and without (b) location N_B in the analysis. Sampling locations are internally connected with lines to the center of each ellipses. The Danish and Swedish samples are indicated by blue colors (D_A, dark blue and S_S, light blue), the Norwegian outlier location (N_B, green) is differentiated from the remaining Norwegian samples (N_I, N_O, and N_G) represented by red color.</p