Phylogenetic status of four new species of Acanthobothrium (Cestoda:Tetraphyllidea) parasitic on the wedgefish Rhynchobatus laevis (Elasmobranchii:Rhynchobatidae): implications for interpreting host associations

Abstract

A recent major revision of the elasmobranchs of Australia, which expanded the described fauna from 190 to 307 species, has serious implications for our understanding of the host associations of parasites of Australian elasmobranchs. Most importantly, it questions the identities of the host records for many parasite species. This study focuses on cestodes of the tetraphyllidean genus Acanthobothrium parasitising Rhynchobatus, a batoid genus, the Australian elements of which have recently been revised. Four new cestode species are described from Rhynchobatus laevis (Bloch & Schneider, 1801) from the Northern Territory, Australia. These species differ from their ~160 congeners in several morphological respects. They differ conspicuously from their four Australian congeners also hosted by a Rhynchobatus species, all four of which (i.e. Acanthobothrium bartonae Campbell & Beveridge, 2002, Acanthobothrium gibsoni Campbell & Beveridge, 2002, Acanthobothrium lasti Campbell & Beveridge, 2002 and Acanthobothrium rhynchobatidis Subhapradha, 1955) were reported from Rhynchobatus djiddensis (Forsskål, 1775), a batoid species no longer considered to occur in Australian waters. This suggests that one or both of the other Australian members of Rhynchobatus (i.e. R. australiae Whitley, 1939 and R. palpebratus Compagno & Last, 2008) are likely candidates as hosts for one or more of the latter four species. With respect to the relationships among congeners parasitising the same host species, phylogenetic analyses of sequence data of the D1–D3 region of 28S rDNA for three of the four new cestode species support previous work suggesting that congeners parasitising the same host species are not each other’s closest relatives. This study also serves to emphasise the importance of careful scrutiny of host identities, particularly in systems such as this, in which host taxonomy is under active revision.

Four new species of Acanthobothrium van Benden, 1850(Cestoda: Onchoproteocephalidea) from the guitarfish, Rhynchobatus cf. djiddensis (Elasmobranchii: Rhynchobatidae), from the Persian Gulf and Gulf of Oman

“…As a consequence, R. djiddensis has been the specific identity assigned to hosts of this genus in most instances in the past. Fyler and Caira (2010) addressed this problem and discussed the true identity of species of Rhynchobatus that host of Acanthobothrium. They questioned the host identifications of Campbell and Beveridge (2002) in Australia and Yang and Lin (1994) in China, based on observations of Last and Stevens (2009) who argued that R. djiddensis is restricted in distribution to the Western Indian Ocean.…”

“…Rhynchobatus djiddensis is so far restricted to the Western Indian Ocean (Last and Stevens 2009) and occurs in Indian offshore waters (Raje et al 2007). Therefore, according to Fyler and Caira (2010), it is most likely that R. djiddensis and R. laevis are candidate hosts of A. rhynchobatidis Subhapradha, 1955, originally described from Indian waters. Our host specimens do not entirely correspond to the original description of R. djiddensis, resulting in our tentative host identification as Rhynchobatus cf.…”

“…Most recently, Fyler and Caira (2010) added A. bobconniorum Fyler et Caira, 2010, A. hypermekkolpos Fyler et Caira, 2010, A. jeanneae Fyler et Caira, 2010and A. matttaylori Fyler et Caira, 2010 from Rhynchobatus laevis (Bloch et Schneider) from Australia.…”

A DNA Sequence–Based Approach To the Identification of Shark and Ray Species and Its Implications for Global Elasmobranch Diversity and Parasitology

“…We note, for example, that the transformation in the taxonomy of Australian elasmobranchs that occurred between the first edition of Sharks and Rays of Australia (Last and Stevens, 1994) and the second edition (Last and Stevens, 2009) was, unfortunately, not reflected in the host identifications of work on Australian elasmobranch parasites over the intervening time (see Fyler and Caira, 2010). In collaborations between parasitologists and host taxonomists, it is, however, important to recognize that while their interests are mutually compatible, the methods employed in field situations may differ.…”

“…The accurate identification of hosts is of paramount importance in studies of any parasitological system if the results are to be meaningful. However, as our understanding of elasmobranch diversity has grown, so too has the number of instances in which longstanding concepts of host associations have been challenged (e.g., Caira et al, 2007;Jensen and Caira, 2008;Fyler and Caira, 2010;Desjardins and Caira, 2011;Koch et al, 2012;Cielocha and Jensen, 2011;White et al, 2010c). The current project grew out of a global survey of elasmobranch (38) tapeworms that was initiated in the mid-1980s by J.N.C.…”