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.
Highlights
Spatial genetic studies have increased in the last decades in many taxa while temporal genetic studies, despite being essential to understand biodiversity distribution, are still scarce
Previous studies in the portunid crab Liocarcinus depurator showed that the Almeria-Oran front did not represent a significant barrier to gene flow, whereas Ibiza Channel acted as the main genetic barrier[14]
In order to characterize the stability of marine genetic barriers through time we have explored spatial and temporal differentiation in L. depurator across the three main oceanographic discontinuities along the Atlantic-Mediterranean transition
Summary
Spatial genetic studies have increased in the last decades in many taxa while temporal genetic studies, despite being essential to understand biodiversity distribution, are still scarce. Studies sampling the same areas during multiple time periods should be carried out to identify whether the observed genetic variation is due to historical and/or contemporary processes, and demonstrate whether mitochondrial DNA markers are suitable or not to describe present day connectivity patterns. Three oceanographic discontinuities along the Atlantic-Mediterranean transition in the south and eastern Iberian Peninsula (Gibraltar Strait, Almeria-Oran Front and Ibiza Channel) have been shown to restrict gene flow in several marine species. Previous studies in the portunid crab Liocarcinus depurator showed that the Almeria-Oran front did not represent a significant barrier to gene flow, whereas Ibiza Channel acted as the main genetic barrier[14] Such unexpected result was attributed to historical and/or contemporary processes. Genetic diversity was found to vary across years, which indicates that both historical and contemporary processes affecting population genetic structure can be unveiled using mitochondrial DNA markers when temporal samples are used
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