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The first records of the tapeworm genus Pedibothrium from nurse sharks ( Ginglymostoma cirratum ) in the eastern Pacific and eastern Atlantic Oceans provide 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. brevispine . Tapeworm specimens discovered in the collection of J. Cadenet, taken from G. cirratum off Goree near Dakar, Senegal in 1947, were of P. globicephalum and P. manteri . These tapeworm faunas are consistent with those found previously in small and large nurse sharks, respectively, in the western Atlantic 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 G. cirratum may have resulted from vicariant events associated with the formation of the Atlantic Ocean. However, fossils of at least two extinct species of Ginglymostoma are also known from both sides of the Atlantic Ocean. Short of parallel evolution of three different species of Ginglymostoma on either side of the Atlantic Ocean, these data seem more consistent with dispersal as an explanation for this disjunction and are thus of limited utility for extending the age of this host–parasite association at this time. Analysis 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. |
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