No abstract

Anthropogenic translocations are the main vectors of intercontinental invasions. Molecular tools have been important in the study of biological invasions, helping to identify the source of non‐native species mainly when these species are rapidly colonizing the new territories. The aims of this study were: (i) to characterize genetic sequences of the Daphnia lumholtzi population in Brazil (Upper Paraná River floodplain) for the first time; (ii) to compare these sequences with available sequences at GenBank; and (iii) to contribute new sequences of gene 12S from D. lumholtzi. Specimens were collected from a lake of the Paraná River for gene comparison (COI and 12S sequences). Genetic sequences from populations outside Brazil were obtained from GenBank. D. lumholtzi specimens sequenced in this study are genetically close to populations from the United States and Mexico and considerably distant from Australian populations. Our data confirm that populations present in the Paraná River floodplain probably came from the United States, where they arrived through introduction of African fish. The genetic similarity between our specimens and populations from Mexico and the morphological discrepancy between them reinforces the importance of molecular analysis for accurate identification of a species and its origin.

Biological invasions are one of the major threats to the integrity of aquatic ecosystems worldwide. We examined the influence of reservoirs, availability of food resources, abiotic resistance, and biotic resistance on the distribution of Daphnia lumholtzi, a non‐native cladoceran that is spreading through habitats in the upper Paraná River basin, Brazil. We sampled 48 sites distributed in four habitat types: reservoirs, lakes, tributaries, and the main river. D. lumholtzi densities were higher in reservoirs than in other habitat types (lentic and lotic). We found a significant correlation between a higher density of D. lumholtzi and the distance from reservoirs to the other sampling points. Additionally, a relationship between D. lumholtzi and types of environments was noted. It is known that cladocerans, including D. lumholtzi, have a reduced swimming ability, which makes it difficult for them to overcome currents and consequently establish or maintain large populations in lotic environments. Further research is needed to identify other factors responsible for the species' occurrence in this system and to determine the possible effects this species may have on the native community.