Rapid Miocene–Pliocene dispersal and evolution of Mediterranean rajid fauna as inferred by mitochondrial gene variation

Abstract

Rajidae (colloquially known as skates and rays) experienced multiple and parallel adaptive radiations allowing high species diversity and great differences of species composition between regional faunas. Nevertheless, they show considerable conservation of bio‐ecological, morphological and reproductive traits. The evolutionary history and dispersal of North‐east Atlantic and Mediterranean rajid fauna were investigated throughout the sequence analysis of the control region and 16S rDNA mitochondrial genes. Molecular estimates of divergence times indicated recent origin and rapid dispersal of the present species. Compared with the ancient origin of the family (Late Cretaceous), the present species diversity arose in a relatively narrow time‐window (12 Myr) from Middle Miocene to Early Pleistocene, likely by speciation processes related to dramatic geological and climatic events in the Mediterranean. Nucleotide substitution rates and phylogenetic relationships indicated Mediterranean endemic skates derived from sister species with wider distribution during Late Pliocene–Pleistocene. Skate phylogeny and systematics obtained using mitochondrial gene variation were largely consistent with those based on morpho‐anatomical data.

Resolving taxonomic uncertainty in vulnerable elasmobranchs: are the Madeira skate (Raja maderensis) and the thornback ray (Raja clavata) distinct species?

“…Using the highly variable CR, we calculated a mean sequence divergence of 1.8 % between these two species, which equals that demonstrated by Pasolini et al (2011). Similarly, the sequence divergence we calculated between R. clavata and the endemic Mediterranean skate R. radula (2.3 %) compares well to previous estimates used to date the evolution of R. radula to less than 5 million years ago (2.9 %, estimated from data from Valsecchi et al 2005). This result supports the possibility that the independent demographic unit comprising specimens identified as R. maderensis and geographically proximate Azorean R. clavata represents an earlier stage of such a process of divergence.…”

“…Similarly, the rough ray (Raja radula), restricted to the Mediterranean (Morey et al 2009) is regarded as a sister species to R. clavata. This species is considered to have split from the main lineage (Valsecchi et al 2005), following re-colonisation of the western Mediterranean basin by R. clavata after the Late Miocene Messinian salinity crisis, around 5 Myr ago (Rogl 1998;Duggen et al 2003). The question of whether R. maderensis represents a distinct species, or merely another morphological variant of the polytypic thornback ray, therefore remains unanswered.…”

Node age estimations and the origin of angel sharks, Squatiniformes (Neoselachii, Squalomorphii)

“…Nevertheless, only a few analyses calculating divergence and origination dates have been performed so far (e.g. Valsecchi et al 2005;Stelbrink et al 2010;Straube et al 2010). Most of these studies used either small taxon samplings or were focused on a particular group.…”

Comparative phylogeography of two sister (congeneric) species of cardiid bivalve: Strong influence of habitat, life history and post-glacial history

“…This divergence was probably the result of the Messinian salinity crisis during which the Mediterranean was split into a number of isolated basins and lagoons with different salinity conditions (Hsü et al, 1977). These paleogeographic and paleoclimatic events have played an important role in the evolutionary history of several marine taxa (Hanel et al, 2002;Costagliola et al, 2004 and references therein; Valsecchi et al, 2005) including cardiids (Müller et al, 1999). According to the allopatric speciation scenario, which is the most likely for the two cockles, C. glaucum evolved in the area of the present Mediterranean Sea in basins with changing salinity and became adapted to a great salinity range.…”