Morphological variation in Echinorhynchus truttae Schrank, 1788 and the E. bothniensis Zdzitowiecki & Valtonen, 1987 species complex from freshwater fishes of northern Europe

Abstract

Echinorhynchus truttae and the E. bothniensis species complex are common parasites of salmoniform and other fishes in northern Europe. E. bothniensis and its sibling species E. 'bothniensis' are thought to be closely related to the Nearctic E. leidyi Van Cleave, 1924 based on morphological similarity and common usage of a mysid intermediate host. This study provides the first analysis of morphological and meristic variation in E. truttae and expands our knowledge of anatomical variability in the E. bothniensis group. Morphological variability in E. truttae was found to be far greater than previously reported, with part of the variance attributable to sexual dimorphism. E. truttae, the two species of the E. bothniensis group and E. leidyi displayed considerable interspecific overlap in the ranges of all conventional morphological characters. However, Proboscis profiler, a tool for detecting acanthocephalan morphotypes using multivariate analysis of hook morphometrics, successfully separated E. truttae from the other taxa. The E. bothniensis species group could not be reliably distinguished from E. leidyi (or each other), providing further evidence of the affinity of these taxa. Observations on the distribution of E. truttae in its definitive host population are also reported.