Wide geographic distribution of overlooked parasites: Rare Microsporidia in Gammarus balcanicus, a species complex with a high rate of endemism

Abstract

Parasites and other symbionts deeply influence host organisms, and no living organism can be considered to have evolved independent of its symbionts. The first step towards understanding symbiotic influences upon host organisms is a strong supporting knowledge of parasite/symbiont diversity. Parasites of freshwater amphipods are diverse, with Microsporidia being a major group. These intracellular parasites impact gammarid fitness in different ways, ranging from reduced fitness to increased fecundity. Many Microsporidia have been recorded using molecular data, with multiple taxa pending formal taxonomic description. While some parasites are common, others are known only through sporadic records of single infections. In this study, we focus on rare/sporadic microsporidian infections within Gammarus balcanicus, a host species complex with a high level of endemism. In addition to enriching our knowledge on Microsporidia parasite diversity in amphipod hosts, we test whether these symbionts are specific to G. balcanicus or if they are the same taxa infecting other gammarid species. Of 2231 hosts from 87 sites, we catalogued 29 sequences of "rare" Microsporidia clustering into 19 haplogroups. These haplogroups cluster into 11 lineages: four pre-described taxa (Cucumispora roeselum, C. ornata, C. dikerogammari and Enterocytospora artemiae) and seven 'Molecular Operational Taxonomic Units', which are known from previously published studies to infect other European amphipod species. Our study significantly widens the geographic range of these Microsporidia and expands the known spectrum of hosts infected. Our results suggest that these parasites are ancient infections of European gammarids. For some host-parasite systems, we hypothesize that the common parasite ancestors that infected the hosts' common ancestors, diversified alongside host diversification. For others, we observe Microsporidia taxa with wide host ranges that do not follow host phylogeny.

Keywords: Amphipoda; Geographic range; Host range; Host-parasite association; Parasite richness.

Graphical abstract

Fig. 1

Gammarus balcanicus sampling sites. Sites are identified by black dots with numbers as in Table S1 (87). See Additional Table S1 for details (e.g. sampling sizes, GPS coordinates). Countries identified with ISO code. Map created by authors using Qgis 2.18.4 (QGIS Development Team 2009).

Fig. 2

Bayesian phylogenetic reconstruction of Microsporidia based on partial small ribosomal subunit rDNA alignment (Supplementary data 1). Labels in bold and in blue frames are parasites of Gammarus balcanicus found in the present study. These labels show the name of the parasite (in case of described species) or in the case of undescribed taxa the name consist of: M. sp (= Microsporidium sp.) followed by clade number sensuVossbrinck and Debrunner-Vossbrinck (2005), MOTU, haplogroup number (e.g. b01, b02), then the country where it was found (two letter ISO code, see Table S1), the number of infected populations (=pop.), and the total number of infected individuals (=ind.). Labels with accession numbers are parasite sequences taken from GenBank. These labels show the accession number, the parasite name given in the associated publication, the order of the host (except for amphipod hosts where the family is provided). Microsporidia clade numbers are as in Vossbrinck and Debrunner-Vossbrinck (2005). Branches are collapsed for the two genera Nosema and Dictyocoela (triangle sizes not reflecting actual size). Abbreviation: PP, Bayesian posterior probability. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)

Fig. 3

Geographic distribution of the main rare Microsporidia infecting Gammarus balcanicus, showing their occurrence in other gammarid species over Europe. Each map (A–H) refers to the parasite taxa presented in the bottom-right inset. The host and geographic range of the Microsporidia based on this study and 1) literature data: Terry et al. (2004); Wattier et al. (2007); Krebes et al. (2010); Ovcharenko et al. (2010); Bacela-Spychalska et al. (2012); Rode et al. (2013); Grabner et al., 2014; ; ; Bojko et al. (2015); ; 2018; Weigand et al. (2016); Quiles et al. (2019); 2) Gen Bank sequences: MT645708 (Chen,Y. and Jiang, H. direct submission); KP699690 (Bacela-Spychalska, K. direct submission) and 3) Bacela and Ovcharenko, unpublished data.