Cytogenetic and sequence comparison of adultPhyllodistomum(Digenea: Gorgoderidae) from the three-spined stickleback with larvae from two bivalves

Abstract

Due to the low informative value of available morphological characters, cytogenetic and molecular methods, based on rDNA sequencing, were used to characterize adult and larval stages ofPhyllodistomumspp. Species studied have 18 chromosomes with comparable absolute and relative lengths. Conventional Giemsa staining and karyometric analysis revealed clear differences in chromosome morphology of larvalPhyllodistomumspp. infecting two bivalve host species,Sphaerium corneumandPisidium amnicum. However, karyotypes of adultP. foliumfrom three-spined sticklebacks and larval stages fromS. corneumappear almost identical both with respect to the relative lengths and centromeric indices of the corresponding chromosome pairs. The entire internal transcribed spacer (ITS) region (ITS-1, 5.8S and ITS-2) and the D1-D3 region of 28S gene were sequenced and compared. Again, sufficient differences were observed between larvalPhyllodistomumspp., while adultP. foliumand larvae fromS. corneumshowed a high level of similarity. So, both cytogenetic and molecular data support the suggestion that they represent developmental stages of the same species. The results were compared with published data obtained by cytogenetic and molecular studies on the otherPhyllodistomumspecies. Differences revealed in karyotype and rDNA sequences leads to the conclusion that the cercariaeum ofP. foliumsensu Sinitsin, 1905 could not be regarded as the larva of adultP. foliumfrom three-spined stickleback.