Genetic homogeneity coupled with morphometric variability suggests high phenotypic plasticity in the sea louse Caligus rogercresseyi (Boxshall and Bravo, 2000), infecting farmed salmon (Salmo salar) along a wide latitudinal range in southern Chile

Abstract

The sea louse Caligus rogercresseyi is the most important pathogen causing “caligidosis” in the Chilean salmon industry. In this study, using cox1 gene, we evaluate the genetic variation of C. rogercresseyi from farmed Salmo salar along a latitudinal range (40°–52°S) in south Chile to determine whether morphological differences are explained by genetic or environmental factors. Female parasites were randomly collected from S. salar at five farms. Body variation was examined using multivariate analyses and genetic heterogeneity was explored with AMOVA. C. rogercresseyi exhibited significant morphometric variability among sites and parasites collected from >54°S were the longest ones. Parasites did not show genetic structure among farms. Thus, C. rogercresseyi infesting salmons is panmictic along an extensive latitudinal range in south Chile. The same genetic pattern can be explained by the frequent movement of parasitized S. salar among farms in that region. Phenotypic plasticity in parasites could be explained by natural or aquaculture‐mediated environment variability. C. rogercreseyi from 54°S could favor the local spread of this disease, suggesting an immediate health risk for the recent salmon industry in that region. Further research is required to confirm genetic homogeneity of this parasite along its geographical distribution using more powerful markers (e.g. SNPs).

The management of the sea lice in Chile: A review

“…Bravo et al 42 reported that at low temperature the adult lice are longer than at higher temperature. The same observations were made by Gonzalez et al 54 who reported that C. rogercresseyi exhibited significant morphometric variability among sites and that the lice collected from southern regions (>54 LS) were longer than lice collected in Region X (42 LS). Larger lice have been also reported during colder temperature for L. salmonis.…”

“…The same situation could have occurred with C. rogercresseyi in southern Chile, as resistance has developed against most of the medicines used for its control. The lice have shown a big plasticity and adaption to adverse environmental conditions 25,54 …”

Morphological and genetic variability in cosmopolitan tardigrade species - Paramacrobiotus fairbanksi Schill, Förster, Dandekar & Wolf, 2010

“…Cytochrome oxidase subunit I gene (COI) sequences are one of the most reliable among multiple other DNA barcodes to investigate genetic variation with phenotypic plasticity since it is a genetic marker with a high genetic variation 51 . Various studies combining COI variation and phenotypic plasticity were conducted throughout different invertebrates' phyla including tardigrades 9,21,52,53,54,55 , proving the markers accuracy in this groups of organisms. In the result, high genetic homogeneity has been observed for organisms with wide geographical distribution altogether with well visible morphological differences i.e., phenotypic plasticity 53 .…”

“…Various studies combining COI variation and phenotypic plasticity were conducted throughout different invertebrates' phyla including tardigrades 9,21,52,53,54,55 , proving the markers accuracy in this groups of organisms. In the result, high genetic homogeneity has been observed for organisms with wide geographical distribution altogether with well visible morphological differences i.e., phenotypic plasticity 53 .…”

Epidemiological Factors Associated With Caligus rogercresseyi Infection, Abundance, and Spatial Distribution in Southern Chile

“…Space–time patterns suppose parasitic aggregation across the geographic area occupied by salmon farming, with an increase in risk around predetermined sites. Also, the genetic analysis of C. rogercresseyi along a latitudinal range (40°-52°S) in southern Chile proposes genetic homogeneity, morphometric variability among sites, and longest parasites from >52°S ( 20 ). However, location areas associated with different infestation levels of C. rogercresseyi throughout three regions of Chile had not been investigated yet.…”