Geographic and temporal genetic structure in Lepeophtheirus salmonis from four salmon farms along the northwest and west coasts of Ireland: results from a microsatellite analysis

Abstract

The marine ectoparasitic copepod of salmonids, Lepeophtheirus salmonis (Krøyer), is a major pest of farmed Atlantic salmon (Salmo salar L.) causing great economic impact. The spatial scales over which L. salmonis populations in different salmon farms are typically connected, and the temporal scales over which L. salmonis from the same farm typically undergo genetic change are largely unknown. These questions were posed in a small-scale geographic study of population structure in L. salmonis from four salmon farms, along the northwest and west coasts of Ireland, using two outgroups from Norway and Canada. The temporal stability of genetic composition was also studied in samples collected quarterly during one year from one salmon farm in Ireland. Genetic composition in L. salmonis was characterised using four nuclear microsatellites. Significant but low genetic differentiation was observed between all sites (F ST = 0.08), with no evidence that differentiation was correlated with geographic distance. Temporal genetic differentiation was also evident (F ST = 0.07). An analysis of all L. salmonis samples except the ones from Norway detected two separate clusters. Each cluster contained both geographical and temporal samples. These results are consistent with a population model in which L. salmonis in salmon farms along the northwest and west coasts of Ireland are not isolated, but are potentially subject to (i) localised ecological factors at the particular farm sites or (ii) selection post-settlement or a combination thereof.

Genetic diversity of pacu for restocking programs in the Tietê and Grande rivers, Brazil

“…The difference (P<0.01) between Ho and He in all WPs was characterized by heterozygote deficiencies in the HWE. This difference (typical in fish populations) might have occurred from population fragmentation, the Wahlund effect (WILSON et al, 2004), endogamy (O'CONNELL; WRIGHT, 1997), or the bottleneck effect (AGOSTINHO et al, 2007). Based on these concepts, the difference in the average Ho in the 2011 and 2012 WPs might have resulted from the Wahlund effect, thus indicating a population structure in which random mating occurred (WILSON et al, 2004).…”

“…Genetic diversity of pacu for restocking programs in the Tietê and Grandes rivers, Brazil been useful for addressing questions relative to the population diversity and genetic structure of various fish species (NOLAN;POWELL, 2009;AUNG et al, 2010;HULAK et al, 2010;HORNE et al, 2013;MERANER et al, 2013). The objective of the current, unprecedented study was to evaluate the genetic diversity of P. mesopotamicus WPs and BSs using microsatellites markers for restocking programs in the Tietê and Grande rivers (Brazil).…”

Population genetic structure of the parasitic copepod Lepeophtheirus salmonis throughout the Atlantic

“…Sampling on these 5 farms was conducted prior to (T1) and post delousing (T2) with medicated treatments in order to investigate whether temporal and spatial genetic variation within a small geographic region may be affected by the process of delousing, as suggested previously (Nolan & Powell 2009). Details regarding the delousing history on these 5 farms were collected.…”

“…Each 96-well traycontained a minimum of 2 blank controls and Lepeophtheirus salmonis representing 1 sample. A total of 16 microsatellite loci were amplified in 3 multiplex reactions: Multiplex 1 included LsalSTA1, LsalSTA2, LsalSTA4, LsalSTA5 (Todd et al 2004) and LsNUIG14 adapted by Todd et al (2004); Multiplex 2 in clu ded Lsal103 EUVC,Lsal109EUVC,Lsal110EUVC, and LsNUIG09 (Nolan et al 2000);and Multiplex 3 included Lsal104 EUVC, Lsal105EUVC, Lsal106EUVC, Lsal108 EUVC (Messmer et al in press), LsalSTA3 (Todd et al 2004) and LsNUIG35B (Nolan & Powell 2009). Amplification conditions are available upon request from the authors.…”

“…Analysis of 4 mitochondrial DNA (mtDNA) genes (Tjensvoll et al 2006) and 6 microsatellite DNA markers (Todd et al 2004) revealed weak or no statistically significant genetic differentiation throughout the Atlantic, respectively. Conversely, studies conducted on lice from the Pacific using the cytochrome c oxidase subunit I (COI) mtDNA gene (Boulding et al 2009), in Scotland with random amplification of polymorphic DNA (RAPD) markers (Dixon et al 2004) and in Ireland with 4 microsatellite DNA markers (Nolan & Powell 2009) have identified highly significant spatial and temporal genetic structure. However, previous L. salmonis population genetic studies conducted in the Atlantic are characterised by small-to-modest sample sizes (Nolan et al 2000, Tjensvoll et al 2006, Nolan & Powell 2009), technical challenges (Todd et al 1997, Dixon et al 2004) and low numbers of polymorphic loci (Nolan et al 2000, Todd et al 2004, Nolan & Powell 2009.…”