A European melting pot of harbour porpoise in the French Atlantic coasts inferred from mitochondrial and nuclear data.

Eric Alfonsi,Olivier Van Canneyt,Jean-Yves Le Clec'H,Michael C Fontaine,Sami Hassani,Willy Dabin,François-Gilles Carpentier,Jean-Luc Jung,Sharyn Jane Goldstien

doi:10.1371/journal.pone.0044425

Abstract

Field surveys have reported a global shift in harbour porpoise distribution in European waters during the last 15 years, including a return to the Atlantic coasts of France. In this study, we analyzed genetic polymorphisms at a fragment of the mitochondrial control region (mtDNA CR) and 7 nuclear microsatellite loci, for 52 animals stranded and by-caught between 2000 and 2010 along the Atlantic coasts of France. The analysis of nuclear and mitochondrial loci provided contrasting results. The mtDNA revealed two genetically distinct groups, one closely related to the Iberian and African harbour porpoises, and the second related to individuals from the more northern waters of Europe. In contrast, nuclear polymorphisms did not display such a distinction. Nuclear markers suggested that harbour porpoises behaved as a randomly mating population along the Atlantic coasts of France. The difference between the two kinds of markers can be explained by differences in their mode of inheritance, the mtDNA being maternally inherited in contrast to nuclear loci that are bi-parentally inherited. Our results provide evidence that a major proportion of the animals we sampled are admixed individuals from the two genetically distinct populations previously identified along the Iberian coasts and in the North East Atlantic. The French Atlantic coasts are clearly the place where these two previously separated populations of harbour porpoises are now admixing. The present shifts in distribution of harbour porpoises along this coast is likely caused by habitat changes that will need to be further studied.

Highlights

The harbour porpoise (Phocoena phocoena), one of the smallest cetaceans, is widely distributed in the cold to temperate coastal waters of the northern hemisphere
Tissue samples were collected from 52 harbour porpoises, stranded or by-caught along the French coasts between 2000 and 2010 (Figure 1)
Allelic frequencies displayed no significant departure from Hardy-Weinberg expectations in the global sample (FIS = 0.01 (95CI:[20.08–0.12]), p = 0.314), nor for each sub-grouping we considered based on mitochondrial haplogroup (haplogroup a, fixation indexes (FIS) = 0.08 (95CI:[20.05–0.21]), p = 0.061 and b, FIS = 20.02 (95CI:[20.11–0.08]), p = 0.743), nor for sub-grouping based on geography (BEC, FIS = 0.02 (95CI:[20.10–0.17]), p = 0.304 and BOB, FIS = 20.01 (95CI:[20.07–0.07]),p = 0.596)

Summary

Introduction

The harbour porpoise (Phocoena phocoena), one of the smallest cetaceans, is widely distributed in the cold to temperate coastal waters of the northern hemisphere. The species occurs in three major areas, the North Pacific, the North Atlantic and the Black Sea [1,2]. In the North Atlantic Ocean, it is the most common cetacean species [3]. The North Atlantic population of harbour porpoise has recently been the subject of several studies, that focused mainly on its spatial and temporal distribution [3,4,5,6,7,8]. From the 1940s onwards, field observations (based on strandings, by-catch and sightings) reported that harbour porpoises, commonly encountered in the southern North Sea and off the coasts of the European mainland from Spain to Denmark, declined abruptly [9,10].

Methods

Results

Conclusion