Age of association between the nurse shark, Ginglymostoma cirratum, and tapeworms of the genus Pedibothrium (Tetraphyllidea : Onchobothriidae): implications from geography

The first records of the tapeworm genus Pedibothrium from nurse sharks (Gin glymostoma cirratum) in the eastern Pacific and eastern Atlantic Oceans pro vide new insights on the age of the association between these tapeworms and this host. Four individuals of G. cirratum examined from the southern tip of the Baja Peninsula, Mexico, were found to host P. manteri and P. brevisp ine. Tapeworm specimens discovered in the collection of J. Cadenet, taken f rom G. cirratum off Goree near Dakar, Senegal in 1947, were of P. globiceph alum and P. manteri. These tapeworm faunas are consistent with those found previously in small and large nurse sharks, respectively, in the western At lantic Ocean. The distributional data, combined with the non-vagile habits of the nurse shark, indicate this host-parasite association dates from the most recent completion of the Panamanian Isthmus, approximately 2 Mya. This suggests that P. manteri and P. brevispine have remained unchanged for at least 2 Myr. The data from the eastern Atlantic Ocean are less informative. The amphi-Atlantic distribution of P. manteri and P. globicephalum in P. c irratum may have resulted from vicariant events associated with the formati on of the Atlantic Ocean. However, fossils of at least two extinct species of Ginglymostoma are also known from both sides of the Atlantic Ocean. Shor t of parallel evolution of three different species of Ginglymostoma on eith er side of the Atlantic Ocean, these data seem more consistent with dispers al as an explanation for this disjunction and are thus of limited utility f or extending the age of this host-parasite association at this time. Analys is of the degree of genetic divergence among individuals of G. cirratum and among individuals of the broadly distributed species of Pedibothrium from all three localities would be extremely interesting. (C) 2001 The Linnean S ociety of London.