Evidence of cryptic speciation in the invasive hydroid Cordylophora caspia (Pallas, 1771) (Cnidaria, Hydrozoa) supported by new records

The invasion of non-native species has been a chronic problem in reservoirs of hydroelectric plants. Among the species recorded in Brazil, the cnidarian Cordylophora caspia is often misidentified as macrophytes or completely overlooked, although reports state that the colonies obstruct structures and pipes in industrial plants, generating high maintenance costs. In addition to modifying the ecological balance of invaded ecosystems, studies indicated that C. caspia can influence the occurrence of other invasive species, such as Limnoperna fortunei. In this study, we reported two new records for C. caspia in Brazil, the first occurrence in Minas Gerais and Goiás. We described the colonies in detail and reviewed the known geographic distribution of the species in Brazilian waters. We provided the first Brazilian genetic sequences of the species, which were phylogenetically placed into a broad evolutionary inference using C. caspia COI sequences available from different regions of the world. Our results indicate that there is no clear pattern of ecophysiological specialization of main clades regarding salinity that would justify the validation of the nominal C. lacustris for freshwater specimens. High levels of genetic differentiation in the lineages support the existence of multiple cryptic species within the genus Cordylophora. Finally, our ancestral state reconstruction analysis suggested a presumed freshwater origin for C. caspia and independent shifts between fresh and brackish waters. Advances in the study of populations from different regions of the world will be important for further understanding species delimitation, possible routes of invasion, economic impacts, and ecological interactions, including with other invasive species.