Europe-wide reassessment of Dictyocoela (Microsporidia) infecting native and invasive amphipods (Crustacea): molecular versus ultrastructural traits.

Microsporidia are common parasites infecting animals and protists. They are specifically common pathogens of amphipods (Crustacea, Malacostraca), with Dictyocoela spp. being particularly frequent and highly prevalent, exhibiting a range of phenotypic and ecological effects. Until now, seven species of Dictyocoela were defined, predominantly based on the genetic distance. However, neither the taxonomic status of this provisionally erected genus (based on eight novel sequences and one micrograph of the spore), nor its internal phylogenetic relationships have been clearly revealed. The formal description of the genus and of most of the putative species are still lacking. Here we aimed to fill this gap and performed both ultrastructural and molecular studies (based on SSU, ITS and partial LSU) using different species delimitation methods. As a consensus of these results and following conservative data interpretation, we propose to distinguish five species infecting gammarid hosts, and to keep the names introduced by the authors of the type sequences: Dictyocoela duebenum, D. muelleri, D. berillonum and D. roeselum. We provide full descriptions of these species. Moreover, thanks to our extensive sampling, we extend the known host and geographic range of these Microsporidia.

Gregarines (Apicomplexa) and microsporidians (Microsporidia) of native and invasive gammarids (Amphipoda, Gammaroidea), occurring in Poland.

The goal of our study was to recognize microparasites of alien gammarids inhabiting Polish inland and coastal waters versus those infecting local species. Twenty two localities including the Vistula, Oder and Bug Rivers, Vistula Lagoon, Goslawskie Lake, littoral of the Baltic Sea, as well as small rivers draining directly to the sea were investigated. In total, over 5000 individuals of 14 species of gammarids were collected and analyzed using light and electron microscopy. The studies have revealed five named and seven unnamed species of gregarines (Apicomplexa, Gregarinidae) as well as three named and seven unnamed species of microsporidians (Microsporidia, Nosematidae, Thelohaniidae) infecting six native and four invasive gammarid host species. All the above microparasites were new to Poland. Four species of gregarines (Uradiophora ramosa, U. longissima, Cephaloidophora similis, C. mucronata) and four microsporidians (Nosema dikerogammari, N. pontogammari, Thelohania sp. 2, Thelohania sp. 5) were associated with hosts of Ponto-Caspian origins. Evidently, these microparasites were transported to the area through the range expansion of their invasive hosts. Gregarines Cephaloidophora sp. 1 and Uradiophora sp. 1 were registered only in North American Gammarus tigrinus. Uradiophoera ramosa infects Ponto-Caspian (P. robustoides, D. villosus) and North-Americah hosts (G. tigrinus).