Phylogeography of Aphanius fasciatus (Osteichthyes: Aphaniidae) in the Mediterranean Sea, with a focus on its conservation in Cyprus

Aphanius fasciatus is a small fish occurring in Mediterranean brackish environments. In Cyprus it is known from three localities separated by long stretches of coast. The genetic diversity of these populations was evaluated using fragments of two mitochondrial genes. A comparison with the other available data showed that Cyprus populations represent a distinct lineage. The other lineages are concentrated in a relatively small area between the Strait of Sicily and the Western Ionian Sea, while all other areas include a subset of these lineages, suggesting that the aforementioned area might have acted as a glacial refugium. Landlocked North-African populations diverge from all other populations, suggesting that they might have originated in the Late Pleistocene, during transgression events of the Mediterranean Sea in North-African inland water bodies. The genetic diversity of A. fasciatus varied across different Cyprus populations, with a pattern mirroring the degree of environmental degradation, which likely affected population genetic variability through demographic reductions. The three Cyprus populations showed genetic uniqueness, suggesting the need of population-based management practices; the low genetic diversity of two populations, and the number of threats affecting them, suggest that the species should be considered endangered at national level and deserves protection measures.

Within-shoal phenotypic homogeneity affects shoaling preference in a killifish

Anti-predator benefits associated with living in groups are multiple and taxonomically widespread. In fish shoals, individuals can exploit the confusion effect, whereby predators struggle to target a single individual among several individuals. Theory predicts that the confusion effect could be aided by homogeneity in appearance; thus, individuals should group by phenotypic characteristics, contributing to generating high within-shoal phenotypic homogeneity. While assortments by body size have been extensively documented, almost nothing is known about whether within-shoal homogeneity in body pigmentation affects shoaling preference. To investigate this issue, we used the Mediterranean killifish, Aphanius fasciatus , a shoaling species characterized by conspicuous vertical bars on body sides. Individual females were given a choice between two novel shoals characterized by either a high or low degree of homogeneity in the number of bars. As predicted, individual females preferentially associated with the shoal showing the higher phenotypic homogeneity. Our data demonstrated that fish might associate with the shoal that maximizes phenotypic homogeneity in body pigmentation, irrespective of their own phenotype.