Bryozoans are returning home: recolonization of freshwater ecosystems inferred from phylogenetic relationships

Abstract

Bryozoans are aquatic invertebrates that inhabit all types of aquatic ecosystems. They are small animals that form large colonies by asexual budding. Colonies can reach the size of several tens of centimeters, while individual units within a colony are the size of a few millimeters. Each individual within a colony works as a separate zooid and is genetically identical to each other individual within the same colony. Most freshwater species of bryozoans belong to the Phylactolaemata class, while several species that tolerate brackish water belong to the Gymnolaemata class. Tissue samples for this study were collected in the rivers of Adriatic and Danube basin and in the wetland areas in the continental part of Croatia (Europe). Freshwater and brackish taxons of bryozoans were genetically analyzed for the purpose of creating phylogenetic relationships between freshwater and brackish taxons of the Phylactolaemata and Gymnolaemata classes and determining the role of brackish species in colonizing freshwater and marine ecosystems. Phylogenetic relationships inferred on the genes for 18S rRNA, 28S rRNA, COI, and ITS2 region confirmed Phylactolaemata bryozoans as radix bryozoan group. Phylogenetic analysis proved Phylactolaemata bryozoan's close relations with taxons from Phoronida phylum as well as the separation of the Lophopodidae family from other families within the Plumatellida genus. Comparative analysis of existing knowledge about the phylogeny of bryozoans and the expansion of known evolutionary hypotheses is proposed with the model of settlement of marine and freshwater ecosystems by the bryozoans group during their evolutionary past. In this case study, brackish bryozoan taxons represent a link for this ecological phylogenetic hypothesis. Comparison of brackish bryozoan species Lophopus crystallinus and Conopeum seurati confirmed a dual colonization of freshwater ecosystems throughout evolution of this group of animals.

The joint evolution of the Myxozoa and their alternate hosts: A cnidarian recipe for success and vast biodiversity

“…This, together with the fact that P. hydriforme occurs in freshwater fish, prompted some authors to suggest a freshwater origin of the Myxozoa. However, the last common ancestor of today's Phylactolaemata first evolved in marine environments and only secondarily occupied freshwaters habitats (Koletic, Novosel, Rajevic, & Franjevic, ). The oldest known annelid hosts (polychaetes) and the oldest known vertebrate hosts (Chondrichthyes) of myxozoans are predominantly or even exclusively marine, with myxozoan species from cartilaginous fishes clustering in basal positions (Figure ; Gleeson & Adlard, ; Kodádková et al., ).…”

“…This, together with the fact that P. hydriforme occurs in freshwater fish, prompted some authors to suggest a freshwater origin of the Myxozoa. However, the last common ancestor of today's Phylactolaemata first evolved in marine environments and only secondarily occupied freshwaters habitats (Koletic, Novosel, Rajevic, & Franjevic, 2015). The oldest known annelid hosts (polychaetes) and the oldest known vertebrate hosts ( (Tedersoo, Bahram, & Dickie, 2014) explain myxozoan hyperspeciation in some clades, and for a better understanding of the ecological and evolutionary principles than impact on diversity in this parasite group much research is still required.…”

The life of the freshwater bryozoan Stephanella hina (Bryozoa, Phylactolaemata)—a crucial key to elucidating bryozoan evolution

“…With its typical features, such as the colony structure, the jelly-like ectocyst and the mostly missing connection between endo- and ectocyst, it is clear that this species cannot be assigned to the Plumatellidae as it has been in previous studies (e.g. [17, 58]), but merits a separate family Stephanellidae as originally proposed by Lacourt [15]. Besides the clear distinguishing features presented above, Stephanellidae is, together with the Plumatellidae, the only phylactolaemate family to produce sessoblasts (sessile dormant stages/statoblasts).…”

A new cheilostome bryozoan from a dinosaur site in the Upper Cretaceous (Campanian) Judith River Formation of Montana

“…seurati may be the best ecological analogue for the Campanian species. Conopeum seurati is generally characterized as a brackish-water species (e.g., Koletic et al, 2014). According to Ryland (1970), European populations of C .…”