MORPHOLOGICAL OBSERVATION AND DETAILED MOLECULAR CHARACTERIZATION OF FISCHOEDERIUS ELONGATUS (DIGENEA: GASTROTHYLACIDAE) FROM THE RUMEN OF DOMESTIC CATTLE IN CAMBODIA.

Abstract

Fischoederius elongatus (Poirier, 1883) is a common rumen fluke found in Asia and Africa. Nucleotide sequence data for F. elongatus have been reported but are limited to certain ribosomal and mitochondrial DNA regions. High diversity in the nucleotide sequences of the mitochondrial cytochrome c oxidase subunit 1 (COI) haplotypes has been reported in some Asian countries. Some researchers have advocated the possibility of cryptic species within F. elongatus based on the high genetic diversity within the species as well as the genetic distance within and between sister species. However, the number of examined parasites, hosts, and geographic regions was limited in these studies, and the intraspecific variation of the species remains unclear. Therefore, additional studies are required to provide more insight into the genetic variation of F. elongatus. This study characterized F. elongatus in the rumen of Cambodian cattle and documented its genetic information and intraspecific variation. The flukes were morphologically identified, and the molecular structure of the 28S and COI regions was analyzed. The partial sequences of 28S from the 45 specimens yielded 2 genotypes, and the 28S sequences of F. elongatus seem to be highly conserved in Cambodia. In contrast, partial sequences of COI from 44 specimens exhibited 29 distinct haplotypes, and the similarity among the haplotypes was 92.9-99.7%, indicating high diversity of the COI sequence in the Cambodian F. elongatus population. In both 28S and COI phylogenetic trees, the present sequences formed a single clade with Gastrothylacidae species; however, the 4 genera within the family did not form genus-specific clades. These results suggest that complete species identification of Gastrothylacidae is difficult to perform based solely on the 28S and COI sequences. The molecular population genetics of F. elongatus in Cambodia were found to be highly diverse in COI sequences, and a star-like haplogroup was also detected. In addition, some haplotypes were identical to those from neighboring countries, such as India and Thailand, and no distinct country-specific haplogroups were found. Therefore, ancient domestication, artificial migration, and the contemporary import of host cattle may have involved genetic populations in these countries. Highly diverse COI haplotypes were found with few or no differences in morphology, and the diverse haplotypes found in the current and previous studies were unlikely to originate from cryptic species.