Host Specificity of a Parasitic Fluke: IsPosthodiplostomum minimuma Centrarchid-Infecting Generalist or Specialist?

Abstract

Parasite host specificity has important implications for species diversity estimates, food web dynamics, and host shifts. "White grub" is the metacercaria stage of a fluke ( Posthodiplostomum minimum ) that occurs in many fish species, but no attempt has been made to quantify variation in host use by this worm. Here we used 2 approaches to evaluate host specificity within the strain that infects centrarchids ( P. minimum centrarchi). First, we measured parasite loads in 2 centrarchid hosts, bluegill ( Lepomis macrochirus ) and white crappie ( Pomoxis annularis ), from Spring Lake in McDonough County, Illinois. We found that infection levels differed significantly between these hosts. Prevalence in bluegill was 100% and the median intensity was 940 metacercariae, but only 57% of white crappie were infected (median intensity = 4). Site specificity of white grub also differed significantly between the 2 hosts. In bluegills, kidneys were most heavily infected, whereas in white crappies, livers harbored the most worms. We also performed a literature survey of P. minimum prevalence estimates from 14 centrarchid species from other localities. We calculated the mean white grub prevalence for each host species and used this to calculate STD*, a quantitative index of host specificity. STD* was 1.33, significantly closer to the value for a specialist (STD* = 1.00) than a generalist (STD* = 2.00). This reflects the fact that P. minimum prevalence is higher in Lepomis species than it is in centrarchids outside this genus. These data show that P. minimum centrarchi specializes on Lepomis species, but the causes of this specialization are unknown. This worm may be a single species that differs in host use due to ecological or physiological host differences, or it may be a complex of species that vary in host use for similar reasons. Genetic data are required to evaluate these possibilities.

Free-ranging avifauna as a source of generalist parasites for captive birds in zoological settings: An overview of parasite records and potential for cross-transmission

“…On the contrary, others can be found in many host species, which are considered as generalists [ 14 – 16 ]. Parasite-sharing usually depends on the similarity of physiological characteristics among host species, which is likely to be higher in hosts that are closely related phylogenetically and/or share similar feeding habits, ecological niches, or geographic locations [ 14 , 17 – 21 ]. According to Rohde [ 22 ], a method to estimate parasite host specificity consists of the evaluation of “the number of host species from which the parasite has been collected.” Other methods comprise the estimation of the variation in parasite infection levels among host species and the analysis of phylogenetic distinctiveness of hosts [ 13 , 14 , 22 ].…”

Infection patterns and molecular data reveal host and tissue specificity ofPosthodiplostomumspecies in centrarchid hosts

“…3 and 4) to infer host-specificity within Centrarchidae (Locke et al 2010). Based on infections in bluegill ( Lepomis macrochirus ) vs white crappie ( Pomoxis annularis ) and literature reviews, Lane et al (2015) suggested that P. minimum is more of a host specialist than previously recognized and that P. m. centrarchi is a Lepomis specialist lacking host preferences outside of the genus. Given the molecular evidence for multiple Posthodiplostomum ‘minimum’ species within centrarchids, we refer to metacercariae in this study as Posthodiplostomum and identify specific species when appropriate.…”

Life-history trade-offs in a generalist digenean from cetaceans: the role of host specificity and environmental factors

“…A fundamental question regarding host specificity is the extent to which a putative generalist parasite performs equally well in all exploited host species, namely, whether these hosts are all equally compatible for the parasite [ 4 ]. This question has important implications, not only for understanding the evolution of specificity, but also for population dynamics and epidemiology of generalist parasites [ 5 ].…”