Phylogeography on the rocks: The contribution of current and historical factors in shaping the genetic structure of Chthamalus montagui (Crustacea, Cirripedia)

Abstract

The model marine broadcast-spawner barnacle Chthamalus montagui was investigated to understand its genetic structure and quantify levels of population divergence, and to make inference on historical demography in terms of time of divergence and changes in population size. We collected specimens from rocky shores of the north-east Atlantic Ocean (4 locations), Mediterranean Sea (8) and Black Sea (1). The 312 sequences 537 bp) of the mitochondrial cytochrome c oxidase I allowed to detect 130 haplotypes. High within-location genetic variability was recorded, with haplotype diversity ranging between h = 0.750 and 0.967. Parameters of genetic divergence, haplotype network and Bayesian assignment analysis were consistent in rejecting the hypothesis of panmixia. C. montagui is genetically structured in three geographically discrete populations, which corresponded to north-eastern Atlantic Ocean, western-central Mediterranean Sea, and Aegean Sea-Black Sea. These populations are separated by two main effective barriers to gene flow located at the Almeria-Oran Front and in correspondence of the Cyclades Islands. According to the ‘isolation with migration’ model, adjacent population pairs diverged during the early to middle Pleistocene transition, a period in which geological events provoked significant changes in the structure and composition of palaeocommunities. Mismatch distributions, neutrality tests and Bayesian skyline plots showed past population expansions, which started approximately in the Mindel-Riss interglacial, in which ecological conditions were favourable for temperate species and calcium-uptaking marine organisms.

Genetic diversity and population structure of the rockpool shrimp Palaemon elegans based on microsatellites: evidence for a cryptic species and differentiation across the Atlantic–Mediterranean transition

“…Indeed, it was confirmed that the Almería-Orán Front acts on the population structure of several species as in P. elegans, e.g. the cuttlefish Sepia officinalis 40 , some fish species 41 , the barnacle Chthamalus montagui 42 or the wedge clam Donax trunculus 43 among others (see review in Patarnello et al 11 ). Notwithstanding, it is known that population connectivity across the Atlantic-Mediterranean transition is reduced in other species by different oceanographic discontinuities, namely the Strait of Gibraltar 24,44 , the Balearic Front and the Ibiza Channel 45,46 .…”

Parapatric genetic divergence among deep evolutionary lineages in the Mediterranean green crab, Carcinus aestuarii (Brachyura, Portunoidea, Carcinidae), accounts for a sharp phylogeographic break in the Eastern Mediterranean

“…This remarkable pattern of genetic break, within the Eastern Mediterranean, has also been recorded in crustaceans. Notably, Shemesh et al [ 108 ] and later Pannacciulli et al [ 18 ] revealed marked genetic isolation in the barnacle species Chthamalus montagui between the western-central Mediterranean Sea and Aegean-Black seas. Gene flow restriction between western and eastern Mediterranean populations was shown to be mainly linked to the hydrographic isolation of the Aegean Sea, and found to be more marked than that associated with the Siculo-Tunisian Strait [ 45 ].…”

“…In this context, the phylogeography of Mediterranean species underwent a common set of processes resulting from fragmentation within glacial refugia, range expansions via postglacial colonisation, and secondary contact zones among historically divergent lineages [ 4 , 12 , 15 – 18 ].…”

Phylogeographic and evolutionary history analyses of the warty crab Eriphia verrucosa (Decapoda, Brachyura, Eriphiidae) unveil genetic imprints of a late Pleistocene vicariant event across the Gibraltar Strait, erased by postglacial expansion and admixture among refugial lineages

“…Indeed, the severe palaeogeographic and palaeoclimatic shifts that this region has undergone throughout its history, resulting in the onset of specific oceanographic features across its coastline, have set the stage for the impact of evolutionary and demographic processes on forging genetic variation of marine species [14, 17]. Recent phylogeographic investigations have provided evidence for the occurrence of pronounced genetic boundaries between the East Atlantic and the western Mediterranean, and between the Western and Eastern Mediterranean basins [2, 8, 15, 18–22]. Further pronounced genetic breaks have also been documented in the eastern Mediterranean, notably between the Adriatic-Ionian seas and the Aegean-Marmara-Black seas [1, 8, 22–26].…”

“…Recent phylogeographic investigations have provided evidence for the occurrence of pronounced genetic boundaries between the East Atlantic and the western Mediterranean, and between the Western and Eastern Mediterranean basins [2, 8, 15, 18–22]. Further pronounced genetic breaks have also been documented in the eastern Mediterranean, notably between the Adriatic-Ionian seas and the Aegean-Marmara-Black seas [1, 8, 22–26].…”