Morphological variability in Echinorhynchus gadi, E. leidyi, and E. salmonis (Acanthocephala: Echinorhynchidae) from fishes in northern Canadian waters

Abstract

Morphological variability of Echinorhynchus gadi, E. leidyi, and E. salmonis was evaluated from 30 collection sites in northern Canada. Nine new hosts were recorded. Mixed infections with the three species, in addition to their high morphological variability, made the identification of Echinorhynchus spp. from northern waters unreliable in the absence of information on morphological variability from local and geographically distant populations. Worm age, host species, and geographic location contributed to the variability of several taxonomically important characters: proboscis size and shape, hook size and number, body shape, and egg size. These characters had considerably greater variability and interspecific overlap in ranges than previously reported. Identifications were most reliable when based on gravid females. Individual males and immature females could generally be identified, with about 90% or greater reliability, using a multivariate comparison of proboscis measurements to a data set based on gravid females from the entire study area. Meristogram analysis revealed some intraspecific similarities and interspecific differences in proboscis hook shape but patterns varied geographically. While meristograms corroborated specimen identifications based on more comprehensive analyses, they were unreliable, when used alone, on Arctic and north temperate populations of echinorhynchids. Morphological variability between populations of Echinorhynchus spp. in different lakes was greater than could be accounted for by host species and the environment. It is hypothesized that this geographic variability may be a consequence of restricted gene flow between isolated populations causing geographic isolation of morphological variants.