Parasitic life and environment of monogenean: geometric morphometric study of haptoral anchors in seven Diplorchis species (Monogenea: Polystomatidae).

Abstract

Background: The development of larger monogeneans and their survival on more active hosts is thought to have led to the emergence of haptoral suckers and, in some instances, anchors, enabling a more stable anchorage. Because of their strict host specificity, the morphological variation of anchors in genus Diplorchis (Monogenea: Polystomatidae) may be determined to a large degree by adaptation to the host species, its habitat and ecological environment to ensure stable attachment.

Methods: In this study, we estimated the interspecific and intraspecific differences of haptoral anchors and other morphological characteristics in six recorded species of Diplorchis and one unidentified species parasitizing Sylvirana maosonensis (Bourret, 1937) in China using geometric morphometrics.

Results: Geomorphometric analyses revealed significant differences in the shape and size of the anchors among the seven species, indicating that the morphological differences in anchors can be used as a basis for species identification within the genus Diplorchis. In addition, we found that the same Diplorchis species collected from different localities not only differed significantly in anchor form, but also in body size and haptor size, as well as haptoral sucker size. This may reflect the effect of different habitat environments on biological/behavioral activities of the same host, thus further affecting the stable attachment of flatworms within species. Interestingly, in two species collected from the same localities, we found no significant differences in anchor or sucker size, while body size and haptor size all differed significantly. Meanwhile, the significant differences in anchor shape may suggest that the attachment mechanism of the different Diplorchis species is related to the variation in anchor shape.

Conclusions: From the perspective of morphological adaptation to the environment, the study not only indicated that the morphological variation of Diplorchis anchors can be used as an auxiliary tool to distinguish species, but also found that the morphological differences in the anchors were influenced by factors such as host species, habitat and ecological environment. This may provide a basis for a better understanding of host-parasite interaction.