Speciation inThaparocleidus(Monogenea: Dactylogyridae) Parasitizing Asian Pangasiid Catfishes

Abstract

The phylogeny of monogeneans of the genusThaparocleidusthat 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 ofThaparocleidusparasitizing Pangasiidae was confirmed. Low intraspecies molecular variability was observed in threeThaparocleidusspecies collected from geographically distant localities. However, a high intraspecies molecular variability was observed in twoThaparocleidusspecies 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 inThaparocleidus, 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 theThaparocleidus-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.