Temporal and spatial genetic differentiation in the crab Liocarcinus depurator across the Atlantic-Mediterranean transition

Abstract

Spatial genetic studies often require sampling broadly separated areas, difficult to access simultaneously. Although comparing localities surveyed at different time periods might result in spurious genetic differentiation, there is a general believe on the stability of genetic structure through time, particularly if sampled localities are isolated or very distant. By analysing spatial and temporal genetic differentiation of the portunid crab Liocarcinus depurator we assessed the contribution of historical and contemporary processes on population connectivity patterns across three main oceanographic discontinuities along the Atlantic-Mediterranean transition: Gibraltar Strait, Almeria-Oran Front and Ibiza Channel. A partial fragment of the cytochrome oxidase I gene was sequenced in 366 individuals collected from localities at both sides of each discontinuity during three time periods. Although localities showed genetic fluctuations through time, a significant gradient was detected along the coast for all sampling periods. Significant inter-annual differences identified within the Alicante area, north of the Almeria-Oran Front, were associated with shifts in the relative contribution of Atlantic and Mediterranean water masses. The persistence of a clinal pattern in the Atlantic-Mediterranean transition area together with local fluctuations suggests a complex balance of dispersal and selection.

East is East and West is West: Population genomics and hierarchical analyses reveal genetic structure and adaptation footprints in the keystone species Paracentrotus lividus (Echinoidea)

“…The break between the Atlantic and the Mediterranean is not a clear‐cut one. Rather, there is a transitional zone across the Gibraltar Strait through the Alboran Sea, as observed in other species (Pascual et al, ; Schunter et al, ). The Alboran Sea has a complex hydrology, with a system of gyres (Millot, ; Sánchez‐Garrido, Lafuente, Fanjul, Sotillo, & De Los Santos, ) whose intensity and relative position can vary with time (Oguz, Macias, Garcia‐Lafuente, Pascual, & Tintore, ).…”

“…Accordingly, the genetic diversity is higher in this transition zone because those localities are a mixture of the genetic pools found at both sides of the barrier. Furthermore, the Almería‐Oran front is not a permanent barrier; rather, it is sensitive to fluctuations in circulation patterns that influence connectivity across oceans as found for the crab Liocarcinus depurator (Pascual et al, ). There is also evidence that temporal fluctuations in oceanographic currents may affect the genetic structure of the Mediterranean populations of P. lividus in the southern Iberian Peninsula (Calderón et al, ).…”

“…Even at small geographic scales, salinity values can change from c . 36.2‰ at the Atlantic side of the Gibraltar Strait to over 37.5‰ at the east of the Almería‐Oran front (Brankart & Brasseur, ; Hidalgo et al, ; Pascual et al, ). These gradients effectively pose selective pressures on a group known to have limited abilities to regulate their osmosis and ion concentrations (Binyon, ).…”

A population genomics insight by 2b‐RAD reveals populations' uniqueness along the Italian coastline in Leptopsammia pruvoti (Scleractinia, Dendrophylliidae)

“…Indeed, for marine fish, F ST values rarely exceed 0.1–0.15 within the Mediterranean Sea, even when considering species with a limited PLD, fragmented habitat and endemism level (Astolfi et al, ; Carreras et al, ; Carreras‐Carbonell, Macpherson, & Pascual, ; Congiu et al, ), and only raise to high values when considering sharks (Ashe et al, ), reptiles (Sethuraman et al, ) and some marine mammals (Fruet et al, ). Similar pictures of low differentiation are common in several benthic invertebrates, such as sponges ( Scopalina lophyropoda , Blanquer & Uriz, ), sea urchins ( Paracentrotus lividus , Maltagliati, Di Giuseppe, Barbieri, Castelli, & Dini, , Penant, Aurelle, Feral, & Chenuil, ), sea cucumbers ( Holothuria mammata , Borrero‐Pérez, Gonzàlez‐Wanguemert, Marcos, & Pérez‐Ruzafa, ), bivalves ( Pinna nobilis , Sanna et al, ) and crustaceans ( Liocarcinus depurator , Pascual et al, ; Carcinus aestuarii , Schiavina, Marino, Zane, & Melìa, ; Pachygrapsus marmoratus , Fratini et al, ).…”

“…For instance, when considering fish with a Mediterranean-Atlantic distribution, a weak differentiation is often found when comparing populations sampled at thousands of kilometres of distance (i.e., Milano et al, 2014;Souche et al, 2015), and extreme differences are found at most across major biogeographic/oceanographic transitions (Patarnello, Volckaert, & Castilho, 2007 and references therein). Indeed, for marine fish, F ST values rarely exceed 0.1-0.15 within the Mediterranean Sea, even when considering species with a limited PLD, fragmented habitat and endemism level (Astolfi et al, 2005;Carreras et al, 2017;Carreras-Carbonell, Macpherson, & Pascual, 2006;Congiu et al, 2002), and only raise to high values when considering sharks (Ashe et al, 2015), reptiles (Sethuraman et al, 2013) and some marine mammals (Fruet et al, 2014 Sanna et al, 2013) and crustaceans (Liocarcinus depurator, Pascual et al, 2016;Carcinus aestuarii, Schiavina, Marino, Zane, & Melìa, 2014;Pachygrapsus marmoratus, Fratini et al, 2016).…”