Population Genetic Structure and Connectivity of the European Lobster Homarus gammarus in the Adriatic and Mediterranean Seas

Abstract

Highly selective fishing has the potential to permanently change the characteristics within a population and could drive the decline of genetic diversity. European lobster is an intensively fished crustacean species in the Adriatic Sea which reaches high market value. Since knowledge of population structure and dynamics is important for effective fisheries management, in this study, we used 14 neutral microsatellites loci and partial mitochondrial COI region sequencing to explore population connectivity and genetic structure by comparing samples from the Adriatic Sea and the adjacent basins of the Mediterranean Sea. The obtained results suggest that neutral genetic diversity has not been significantly affected by decrease in population size due to overfishing, habitat degradation and other anthropogenic activities. Global genetic differentiation across all populations was low (F _ST = 0.0062). Populations from the Adriatic Sea were panmictic, while genetic differentiation was found among populations from different Mediterranean basins. Observed gene flow for European lobster suggest that populations in the north eastern Adriatic act as a source for surrounding areas, emphasizing the need to protect these populations by establishing interconnected MPAs that will be beneficial for both fisheries and conservation management.

Keywords: fisheries; gene flow; genetic diversity; microsatellites; mtDNA; population structure.

FIGURE 1

Central and eastern Mediterranean Sea bathymetry with sampling locations of European lobster Homarus gammarus where the first two letters of location abbreviations denote the geographic origin of samples (AD, Adriatic Sea; IO, Ionian Sea; AE, Aegean Sea; LG, Ligurian Sea) and the second two letters denote the abbreviations for sampling sites (VE, Venice; UM, Umag; PU, Pula; LO, Lošinj; AN, Ancona; HV, Hvar; VI, Vis; BA, Bari; CO, Corsica; PA, Patras; AL, Alexandroupoli). Information on populations included and regional subdivisions are provided in Table 1. Isobaths indicate depths of 250, 500, 1000, and 1200 m. The colors represent different depths. The figure was prepared in MATLAB 2014a (www.mathworks.com) and GIMP 2.8.16 (www.gimp.org) software.

FIGURE 2

Bayesian clustering of European lobster Homarus gammarus populations in accordance to STRUCTURE assignment scores, where three (K = 3) inferred clusters were assumed. See Table 1 for additional information on sample names.

FIGURE 3

Isolation by distance plot showing the pairwise relationships of genetic distances in respect to the pairwise geographical distances in European lobster Homarus gammarus populations. Two-dimensional kernel density estimation in the MASS package in R was applied for the plot illustration, where the different colors present different correlation densities of genetic and geographic distances (red, high density; blue, low density).

FIGURE 4

Gene flow diagrams for European lobster Homarus gammarus populations presenting (A) contemporary gene flow estimates (m) from BayesAss, and (B) historical gene flow estimates (M) from Migrate-n. Grid width represents the total amount of incoming and outgoing gene flow estimated for each population. Arrows indicate the direction of gene flow among the populations while the width of arrows are proportional to the relative amount of gene flow observed among connected populations. The wider arrow is linked with higher gene flow. The threshold for graphical illustration of gene flow was set to 0.01 for BayesAss and 2.0 for Migrate-n estimates. Exact gene flow estimates are presented in Supplementary Table 3. Populations codes are showed in Table 1.

FIGURE 5

Median-joining network based on COI haplotypes (A) and geographical distribution of haplotypes (B) for European lobster Homarus gammarus. Colored circles represent haplotypes found in sampled populations whose sizes are proportional to the number of individuals. Missing haplotypes are indicated by small yellow dots. The pie charts on the map display the haplotype frequencies found at each location. Populations codes are given in Table 1.