Panbiogeographical analysis of the shark genus Rhizoprionodon (Chondrichthyes, Carcharhiniformes, Carcharhinidae)

Abstract

The distributional patterns of the seven species of Rhizoprionodon were analysed using the panbiogeographical method of track analysis. The individual tracks of Rhizoprionodon suggest that the genus is mainly an Indian-Atlantic Ocean group. Five generalized tracks were found: (1) Caribbean, defined by R. porosus and R. terraenovae; (2) eastern coast of South America, defined by R. porosus and R. lalandei; (3) Indian Ocean, defined by R. acutus and R. oligolinx; (4) north-western Australia, defined by R. acutus, R. oligolinx and R. taylori; (5) north-north-eastern Australia, defined by R. acutus and R. taylori. Only R. longurio was not included in any generalized track, and its distribution is restricted to the eastern Pacific Ocean. Two biogeographical nodes were found at the intersection of the generalized tracks 1 and 2 (Caribbean Sea) and generalized tracks 4 and 5 (north Australia). The generalized tracks overlap with those found in several unrelated marine taxa. Overall, the generalized tracks are associated with warm currents. The biogeographical nodes found (Caribbean and Australian) are coincident with the global distribution of mangroves.

Negligible evidence for regional genetic population structure for two shark species Rhizoprionodon acutus (Rüppell, 1837) and Sphyrna lewini (Griffith & Smith, 1834) with contrasting biology

“…This is counter-intuitive to the process of allopatric speciation, driven by vicariant events, that is thought to have shaped the evolutionary history of the majority of marine organisms. In reality, it is the imprint of marine vicariant events, such as the collision of the African and Asian continents in the Miocene (23 to five million years ago) that shaped the evolution of species within the genus Rhizoprionodon (Gallo et al 2010), as well as marine dispersal processes that drive marine species diversity (Barber and Bellwood 2005;Bourjea et al 2007;Schluessel et al 2010).…”

“…Sphyrna lewini is a coastal and semi-oceanic shark found worldwide in the Atlantic, Pacific and Indian Oceans (Baum et al 2007). Rhizoprionodon acutus is a continental shelf species with a more restricted distribution on the western and eastern African coasts, in the Arabian Sea, the Indo-West Pacific Ocean and the northern Australian coastline (Gallo et al 2010). There is a considerable size difference between the species: S. lewini is large with a maximum size of around 340 cm (TL) and R. acutus is much smaller (100 cm, Australia; 178 cm, Africa) (Last and Stevens 2009).…”

Diversity and renewal of tropical elasmobranchs around the Middle Eocene Climatic Optimum (MECO) in North Africa: New data from the lagoonal deposits of Djebel el Kébar, Central Tunisia

“…First recorded in the Early Eocene of Morocco (Arambourg, 1952), Cenozoic evidence of the genus Rhizoprionodon is relatively common in tropical deposits of the Tethys seaway during the Late Eocene, from the Caribbean sea to the Jordanian coast (e.g., Case, 1981;Mustafa and Zalmout, 2002), leading some authors to propose that the current distribution of the seven recent species, today unknown in Mediterranean sea, is most likely a result of a former widespread distribution along Tethyan mangroves in the mid-Cenozoic, affected by successive vicariance events (Briggs, 1995;Musik et al, 2004;Gallo et al, 2010). It is noteworthy that certain extant species of Rhizoprionodon are possibly known since Late Eocene deposits but distinctive specific characters on teeth suffer from a conservative dental morphology among genera, as observable in the literature devoted to those taxa (Springer, 1964;Compagno, 1988;Herman et al, 1991).…”

Track analysis beyond panbiogeography

“…It is interesting to note that the problem of finding generalized tracks where only parts of individual tracks overlap has been found also in some manual analyses (e.g. Nihei & de Carvalho, 2005;Gallo et al, 2007Gallo et al, , 2010, where the number of generalized tracks found is larger than that expected (≤ n/2, where n is the number of individual tracks).…”