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

Abstract

BackgroundRecently, population genetic studies of Mediterranean marine species highlighted patterns of genetic divergence and phylogeographic breaks, due to the interplay between impacts of Pleistocene climate shifts and contemporary hydrographical barriers. These factors markedly shaped the distribution of marine organisms and their genetic makeup. The present study is part of an ongoing effort to understand the phylogeography and evolutionary history of the highly dispersive Mediterranean green crab, Carcinus aestuarii (Nardo, 1847), across the Mediterranean Sea. Recently, marked divergence between two highly separated haplogroups (genetic types I and II) of C. aestuarii was discerned across the Siculo-Tunisian Strait, suggesting an Early Pleistocene vicariant event. In order to better identify phylogeographic patterns in this species, a total of 263 individuals from 22 Mediterranean locations were analysed by comparing a 587 basepair region of the mitochondrial gene Cox1 (cytochrome oxidase subunit 1). The examined dataset is composed of both newly generated sequences (76) and previously investigated ones (187).ResultsOur results unveiled the occurrence of a highly divergent haplogroup (genetic type III) in the most north-eastern part of the Mediterranean Sea. Divergence between the most distinct type III and the common ancestor of both types I and II corresponds to the Early Pleistocene and coincides with the historical episode of separation between types I and II. Our results also revealed strong genetic divergence among adjacent regions (separating the Aegean and Marmara seas from the remaining distribution zone) and confirmed a sharp phylogeographic break across the Eastern Mediterranean. The recorded parapatric genetic divergence, with the potential existence of a contact zone between both groups in the Ionian Sea and notable differences in the demographic history, suggest the likely impact of paleoclimatic events, as well as past and contemporary oceanographic processes, in shaping genetic variability of this species.ConclusionsOur findings not only provide further evidence for the complex evolutionary history of the green crab in the Mediterranean Sea, but also stress the importance of investigating peripheral areas in the species’ distribution zone in order to fully understand the distribution of genetic diversity and unravel hidden genetic units and local patterns of endemism.Electronic supplementary materialThe online version of this article (10.1186/s12862-018-1167-4) contains supplementary material, which is available to authorized users.

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

“…One of the main aims of evolutionary genetics is to discern the evolutionary processes responsible for driving and shaping geographic distribution of genetic variation of populations, as well as disentangling the origin of their genetic structure [1–4]. Integrative evidences from palaeogeographic, palaeoclimatic and phylogeographical investigations have brought in-depth knowledge to this issue, pointing out to the significant impact of Pleistocene climatic shifts on forging contemporary genetic polymorphisms [5–8].…”

“…Phylogeographic investigations across different parts of the globe have documented such patterns and allowed retrieving cryptic refugia in many marine species, such as in the seaweed Palmaria palmata across the English Channel [12] and the brown alga Sargassum polycystum across the southern Chinese coast [13]. The occurrence of phylogeographic breaks along with genetic imprints of glacial refugia have been also invoked in population genetic studies of East Atlantic and Mediterranean marine species such as in the gastropod Nassarius nitidus [14] and the green crab Carcinus aestuarii [8]. In contrast, range expansion primed by a rising sea level, following environmental warming during interglacials, could result in rapid population growth and consequent genetic homogeneity as a result of secondary contact between previously isolated evolutionary lineages [11].…”

“…In contrast, range expansion primed by a rising sea level, following environmental warming during interglacials, could result in rapid population growth and consequent genetic homogeneity as a result of secondary contact between previously isolated evolutionary lineages [11]. The impact of these historical factors, intensified by the effects of contemporary environmental and oceanographic gradients, could have been potentially involved in shaping present day genetic variation and population structure in marine species [8, 15].…”

“…The Mediterranean Sea and the contiguous northEast Atlantic Ocean represent a suitable area to study biogeographical processes and investigate evolutionary patterns of diversification in marine species [2, 8, 16]. 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].…”

“…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].…”