Genetic data on endangered twaite shad (Clupeidae) assessed in landlocked and anadromous populations: one or more species?

Abstract

Seven Italian populations of twaite shad Alosa fallax from Northern and Central Italy were investigated to assess genetic diversity by Cytochrome b (Cytb) gene sequencing. The two ecotypes histori- cally referred to landlocked and anadromous popula- tions were investigated for the first time from a genetic point of view, to clarify their phylogenetic relation- ships. Moreover, results obtained from populations coming from separated Adriatic and Tyrrhenian basins were compared with data assessed in samples of allis shad Alosa alosa from the Atlantic basin. All the Italian samples were recognized at species level as A. fallax, differing for five mutations from A. alosa. The analyses confirmed the occurrence of a single phylo- genetic lineage and of a single species within Italian waters, in both landlocked and migratory populations. The minimum spanning network identified six haplo- types for A. fallax and two haplotypes for A. alosa. The neighbour-joining tree and the maximum likelihood on the Cytb gene sequences confirmed two distinct lineages for A. alosa and A. fallax, without evidence of a separation at specific level within the A. fallax group. A weak separation due to incipient population differ- entiation was detected between anadromous and landlocked Italian populations, supporting the idea of a recent separation. The molecular data herein collected do not support the existence of the already controversial incipient species Alosa agone. Despite this, the two ecotypes could be considered as different management units from a conservation viewpoint.