Genetic structure of Mugil cephalus L. populations from the northern coast of Egypt

Abstract

Aim: The gray mullet, Mugil cephalus, has been farmed in semi-intensive ponds with tilapia and carps in Egypt for years. The current study used the fluorescent amplified fragment length polymorphism (F-AFLP) technique to search for genetic differences between the populations of M. cephalus in the northern region of Egypt and to detect the gene flow between sampled locations and the homogeneity within M. cephalus genetic pool in Egypt. Materials and Methods: To fulfill the study objectives 60 (15/location) samples were collected from four northern coast governorates of Egypt (Alexandria “sea,” Kafr El-Sheikh “farm,” Damietta “farm” and Port Said “sea”). Three replicates of bulked DNA (5 samples/replicate) for each location were successfully amplified using the standard AFLP protocol using fluorescent primers. DNA polymorphism, genetic diversity, and population structure were assessed while positive outlier loci were successfully detected among the sampled locations. Based on the geographical distribution of sampling sites, the gene flow, the genetic differentiation, and correlations to sampling locations were estimated. Results: A total of 1890 polymorphic bands were scored for all locations, where 765, 1054, 673, and 751 polymorphic bands were scored between samples from Alexandria, Kafr El-Sheikh, Damietta and Port Said, respectively. The effective number of alleles (ne) for all bulked samples combined together was 1.42. The expected heterozygosity under Hardy–Weinberg assumption (He) for all bulked samples combined together was 0.28. Bulked samples from Damietta yielded the lowest ne (1.35) and the lowest He (0.23) when inbreeding coefficient (FIS) = 1. Bulked samples from Kafr El-Sheikh scored the highest ne (1.55) and the highest He (0.37). Bulked samples from Alexandria scored 1.40 for ne and 0.26 for He, while bulked samples from Port Said scored 1.39 for ne and 0.26 for He. The observed bulked samples formed three sub-population groups, where none is limited to a certain sampling location. A high differentiation among locations was detected, however, is not fully isolating the locations. Gene flow was 0.58. Positive outliers loci (117) were detected among the four sampled locations while weak significant correlation (r=0.15, p=0.03) was found for the distance between them. Conclusion: Even though this species is cultivated in Egypt, the wild population is still present and by the current study a flow of its genes is still exchanged through the northern coast of Egypt. Which contribute to the cultivated populations leading to heterogeneity in its genetic pool and consequently affects the production consistency of M. cephalus in Egypt.

Keywords

• fluorescent amplified fragment length polymorphism
• isolation by distance
• Mantel test
• marine fish
• Mugil cephalus
• natural selection pressure
• population structure