Monogeneans from Pangasiidae (Siluriformes) in Southeast Asia: V. Five new species of Thaparocleidus Jain, 1952 (Ancylodiscoididae) from Pangasius Nasutus

Speciation in Thaparocleidus (Monogenea: Dactylogyridae) parasitizing Asian Pangasiid catfishes

The phylogeny of monogeneans of the genus Thaparocleidus that parasitize the gills of Pangasiidae in Borneo and Sumatra was inferred from molecular data to investigate parasite speciation. The phylogeny of the Pangasiidae was also reconstructed in order to investigate host-parasite coevolutionary history. The monophyly of Thaparocleidus parasitizing Pangasiidae was confirmed. Low intraspecies molecular variability was observed in three Thaparocleidus species collected from geographically distant localities. However, a high intraspecies molecular variability was observed in two Thaparocleidus species suggesting that these species represent a complex of species highly similar in morphology. Distance-based and tree-based methods revealed a significant global fit between parasite and host phylogenies. Parasite duplication (i.e., intrahost speciation) was recognized as the most common event in Thaparocleidus, while the numbers of cospeciation and host switches were lower and similar to each other. When collapsing nodes correspond to duplication cases, our results suggest host switches in the Thaparocleidus-Pangasiidae system precluding congruence between host and parasite trees. We found that the morphometric variability of the parasite attachment organ is not linked to phylogeny, suggesting that the attachment organ is under adaptive constraint. We showed that haptor morphometry is linked to host specificity, whereby nonspecific parasites display higher morphometric variability than specialists.

A description of two new species of Ligophorus Euzet & Suriano, (Monogenea: Ancyrocephalidae) from Malaysian mugilid fish using principal component analysis and numerical taxonomy

Ligophorus belanaki n. sp. and Ligophorus kederai n. sp. are described from Liza subviridis Valenciennes, 1836 and Valamugil buchanani Bleeker, 1854, respectively. Ligophorus kederai n. sp. has fenestrated ventral anchors, while in L. belanaki n. sp. the ventral anchor is not fenestrated. Ligophorus belanaki n. sp. is similar to L. careyensis, one of its coexisting congeners, in the overall shape and size of hard parts, but differs in having a flat median piece in the structure of the AMP (antero-median protuberance of the ventral bar), copulatory organ with non-ornamented initial part and longer vaginal tube, compared to raised median piece in the AMP, ornamented initial part and comparatively shorter vaginal tube in L. careyensis. Ligophorus kederai n. sp. is similar to L. fenestrum, a coexisting congener, in having fenestrated ventral anchors, but differs in having longer points and narrower base. Ligophorus fenestrum, unlike L. kederai n. sp., also possesses fenestrated dorsal anchors. The principal component analysis (PCA) scatterplots indicate that the two new and eight known Ligophorus species from Malaysian mugilids can be differentiated based on the morphometries of their anchors, ventral bars and copulatory organ separately and when combined together. Numerical taxonomy (NT) analyses based on Jaccard's Index of Similarity and neighbour-joining clustering, is used to facilitate comparison of these two new species with the 50 known Ligophorus based on morphological and metric characters. The two new species are different from each other and the other 50 species in the overall shapes and sizes of hard parts, as indicated by the NT analyses.