Comparative phylogeography and demographic history of European shads (Alosa alosa and A. fallax) inferred from mitochondrial DNA

Abstract

BackgroundComparative broad-scale phylogeographic studies of aquatic organisms provide insights on biotic responses to the paleohydrological dynamics associated with climatic oscillations. These insights can be used to formulate a framework for understanding the evolutionary history of a species or closely related taxa as well as aid in predictive modeling of further responses to climate change. Anadromous fishes constitute interesting models for understanding the relative importance of environmental versus biological factors in shaping intraspecific genetic substructure on the interface between marine and freshwater realms. European shads, Alosa alosa and A. fallax are anadromous species that have persisted through historical large-scale environmental perturbations and now additionally face an array of anthropogenic challenges. A comprehensive phylogeographic investigation of these species is needed to provide insights on both the historical processes that have shaped their extant genetic structure and diversity, and the prospects for their future management and conservation.ResultsDespite introgressive hybridization, A. alosa and A. fallax are genetically divergent, congruent with previous studies. Three similarly divergent mtDNA clades were recognized within both A. fallax and A. alosa, most likely originating during common periods of isolation during the Pleistocene among the studied oceanographic regions. Periods of basin isolation apparently extended to the Black Sea as additional Alosa clades occur there. The present day geographic distribution of genetic diversity within European Alosa sp. suggests the existence of a strong but permeable barrier between the Atlantic and Mediterranean seas, as shown for a number of other aquatic species. Overall mtDNA diversity is considerably lower for A. alosa compared to A. fallax, suggesting that the former species is more sensitive to climatic as well as anthropogenic changes. For A. fallax, migration from the Mediterranean to the Atlantic was detected but not in the opposite direction, with colonization of the North Atlantic probably occurring after last glacial maximum.ConclusionThe similar haplotype network topologies between the two species support a common intraspecific history of isolation. Despite these similarities, A. alosa and A. fallax have clearly responded differently to the hydrological dynamics of the Pleistocene, as reflected in their distinct demographic histories. As the species additionally occupy different ecological niches it should not be surprising that they differ in resilience to natural or human-mediated climatic changes. For A. fallax, it is further clear that its demographic response to large-scale hydrological events is not synchronized between the Atlantic and Mediterranean basins. These regional and species-specific differences should be incorporated into future predictive modeling of biological response to climate change as well as current management concepts.

Introgressive hybridization between the Atlantic and Pacific herrings (Clupea harengus and C. pallasii) in the north of Europe

“…In marine fishes, comparable amounts of introgression are known from the Mediterranean soles and sturgeons (She et al 1987;Congiu et al 2001), Northwest Atlantic redfish (Roques et al 2001) and North Pacific rockfish (Seeb 1998;Muto et al 2013). In clupeids, the two anadromous shad species Alosa alosa and A. fallax also show widespread and regionally variable introgression in European rivers and coastal waters (Faria et al 2012).…”

A salt bath will keep you going? Euryhalinity tests and genetic structure of caridean shrimps from Iberian rivers

“…River-system changes related to glaciation events have shaped the current geographical distribution of freshwater environments, whereas life-history traits and dispersal capabilities affect population connectivity (Faria et al, 2012;Filipe et al, 2009). Freshwater ecosystems represent a small portion of the hydrosphere and they are particularly susceptible to anthropogenic stressors (Dudgeon et al, 2006;Vörösmarty et al, 2010).…”

Anisakis infection in allis shad, Alosa alosa (Linnaeus, 1758), and twaite shad, Alosa fallax (Lacépède, 1803), from Western Iberian Peninsula Rivers: zoonotic and ecological implications

“…This explanation seems fairly unlikely due to previously suggested homing behaviour (Alexandrino 1996;Sabatié et al 2000), the existence of three different haplogroups throughout the Atlantic basin and the geographic distribution of genetic diversity within both shad species, which suggests the existence of a strong but permeable barrier between Atlantic and Mediterranean populations (Jolly et al 2012;Faria et al 2012). Moreover, both Moroccan shad populations are considered almost extinct (Sabatié and Baglinière 2001).…”

“…Historically, their distributions along the eastern Atlantic coast extended from Iceland and Norway in the north to Morocco in the south ). In addition, A. fallax is found throughout the Mediterranean Sea although rare in the Marmara and Black sea, whilst A. alosa formerly occurred in the western Mediterranean (Ceyhan et al 2012;Faria et al 2012).…”