Morphological disparity despite genetic similarity; new species of Lobosorchis Miller & Cribb, 2005 (Digenea: Cryptogonimidae) from the Great Barrier Reef and the Maldives

Abstract

Examination of the humpback red snapper, Lutjanus gibbus (Perciformes: Lutjanidae), from Lizard Island off the Great Barrier Reef and Rasdhoo Atoll, Maldives revealed the presence of a new species of Lobosorchis (Digenea: Cryptogonimidae), L. polygongylus n. sp. Lobosorchis polygongylus n. sp. is distinguished from the typeand only other species, L. tibaldiae by the combination of body size, oral spine number (60–81 in L. polygongylus, 47–56 in L. tibaldiae) and number of testes (13–25 in L. polygongylus, 9 in L. tibaldiae). Bayesian inference analysis using data from the internal transcribed spacers 1 and 2 (ITS1 and ITS2), 5.8S and the large subunit (LSU) nuclear ribosomal DNA of L. polygongylus, L. tibaldiae and species of Beluesca, Caulanus, Chelediadema, Neometadena, Latuterus, Retrovarium and Siphoderina was performed to explore phylogenetic relationships of species of Lobosorchis with other cryptogonimid taxa. Despite the significant morphological differences between Lobosorchis polygongylus and L. tibaldiae, these two species differed consistently by only 5 base pairs (bp) over the entire ITS region (3 bp in ITS1, 0 bp in 5.8S and 2 bp in ITS2) and 1 bp in the LSU rDNA regions examined. The ITS2 rDNA region was sequenced from metacercariae obtained from the fins, flesh or body cavities of a number of fishes belonging to the Blenniidae, Pomacentridae and Tetraodontidae and analysed using minimum evolution analysis with L. polygongylus and L. tibaldiae. This revealed the presence of two additional genotypes (putative Lobosorchis sp. A and B), which consistently differed from L. polygongylus by 1 and 4 bp, L. tibaldiae by 1 and 4 bp and from each other by 3 bp over the ITS2 dataset. Although these genetic differences are relatively small, when evaluated in light of the differences observed between L. polygongylus and L. tibaldiae (which are morphologically quite distinct) and differences seen in other congeneric cryptogonimid taxa, the ITS2 rDNA data alone suggest that at least two more species of Lobosorchis are present at Lizard Island. These data also suggest that the ITS2 rDNA region alone is suitable for resolving operational taxonomic units (OTUs) at the species level within the Cryptogonimidae based on what was observed in this and other cryptogonimid systems. A morphological description of metacercariae of L. tibaldiae obtained from two species of Pomacentridae at Heron Island, off the Great Barrier Reef is also provided.