In this study, we present the first molecular records of the freshwater jellyfish Craspedacusta sowerbii (Cnidaria, Hydrozoa) for Argentina and Brazil, obtained from specimens collected at Dique Berta Vidal de Battini (San Luis Province), Ariranha do Ivaí (Paraná State), and Videira (Santa Catarina State), respectively. These results are highly relevant, as previous reports in both countries are scarce and lack genetic confirmation.
The phylogenetic analysis, based on the mitochondrial COI marker, showed that the Argentine sequences form a well-supported clade together with Brazilian samples from Paraná, suggesting a biogeographic connection and genetic cohesion among these groups. These samples also integrate into a broader lineage that includes records from Chile, Japan, Italy, and Canada, reaffirming the cosmopolitan nature and invasive potential of C. sowerbii.
The differences observed between the Santa Catarina and Paraná populations could be attributed to several factors: geographic barriers and distinct hydrographic basins that limited direct genetic exchange. The genetic proximity among Argentina, Paraná, and Chile may reflect both historical dispersal and human-mediated colonization. In contrast, the genetic divergence observed in the Santa Catarina population could be explained not only by its isolation due to naturals barriers but also by following a dispersal route different from Paraná and Argentina, which has kept it more genetically separated.
These preliminary results should be interpreted with caution, as they are based on a single marker and a limited number of samples. However, given the ecological impact of the species, monitoring its presence is crucial to understanding potential alterations in local communities. This context highlights the importance of expanding molecular and ecological studies, integrating hydrological and anthropogenic information, which will guide management strategies that respect regional conservation practices.
This study represents an essential starting point for understanding the genetic structure, dispersal pathways, and potential ecological impact of C. sowerbii in local freshwater ecosystems.
