A genetic cline shapes population structure of the round sardinella along its West African distribution

Abstract

Small pelagic fishes play an important role in human-food security and marine food webs relationships. Among them, the round sardinella Sardinella aurita is an extremely valuable fish resource in West Africa. A suite of twelve microsatellite loci was developed ad hoc for this species using ddRADseq technology, and genotyped on some 1,300 individuals collected in the coastal area spanning from Morocco to Angola. The significant differentiation detected between the northernmost samples (from Morocco to Guinea) and the southernmost ones (from Liberia to Angola) was due to one single locus, which was strong and consistently flagged as a candidate outlier to positive selection, thus suggesting that local adaptation might be one of the drivers of the observed pattern. Furthermore, the signal due to this locus resided uniquely in the frequency of allele SauMS002_131, which displayed a remarkable latitudinal cline with the centre situated in the coastal waters off Sierra Leone. This allele frequency, starting around 47-63% in Morocco-Guinea and dropping to 0% in Gabon and southwards, accounts for the aforementioned North-South declining trend, and can be used as a meaningful tool to assist the outline of the population structure for this species in the West coast of Africa for management purposes.

The information deposited here consists of two excel files:

1. Sardinella aurita_Microsatellites.xlsx. A set of twelve microsatellites was isolated for Sardinella aurita through the analysis of ddRADsequencing fragments. Markers were developed ad hoc using individuals from Morocco, Gabon and Angola. The file contains two spreadsheets. a. Optimized microsatellites: Refers to the twelve microsatellites genotyped in the current study. Detailed information about forward and reverse primers, annealing temperature, MgCl2 concentration and arrangement in multiplex reactions is provided. b. Sequences for microsatellites: Consists of 49 sequences containing motif repeats that would allow the eventual isolation of some extra markers.

2. Sardinella aurita_Genotypes.xlsx: Genotypic data obtained from the mentioned twelve microsatellite loci, which were genotyped on 1294 individuals sampled along the NW coast of Africa, from Morocco to Angola. Individuals were collected by trawl onboard the R.V. “Dr. Fridtjof Nansen”. a. Geographic & genetic information: Contains: ID, sampling year, survey code, sampling station with geographic coordinates, name of the sample, country it belongs to, and genotypic information at 12 microsatellites per individual. b. GenAlEx_Format: File ready for exportation into different formats.