Abstract Potimirim is one of the 40 genera of Atyidae restricted to America, which occurs in coastal freshwater habitats and questions about population status and variability have been emerging. Potimirim brasiliana occurs in Brazil from the northeastern to southeastern region. In order to evaluate the hypothesis of genetic structure among populations, we performed molecular analyses with specimens from all known limit of distribution of the species. The molecular markers used were COI and 28S. Phylogenetic trees were obtained by maximum likelihood and Bayesian analyses, and a haplotype network was obtained based only on COI. We found clear separation between P. brasiliana, P. potimirim, P. glabra and Potimirim sp 2. No pattern of structuration was found among P. brasiliana, but the haplotype network showed geographic pattern of structuration for the congener P. potimirim. The lack of genetic structuration among P. brasiliana can be explained by its life cycle that requires brackish water to complete their larval development. The larvae and juvenile in contact with these habitats can spread through oceanic currents, especially in higher rainfall seasons, maintaining the gene flow. The explanation for the geographical pattern found among P. potimirim is still missing and aspects about its lifecycle and larval development should be investigated.

A recent taxonomic revision indicated that Macrobrachiumpotiuna, an endemic prawn in Brazilian freshwater drainages, exhibits wide morphological variability along its limited geographical distribution. However, in some cases, taxonomic doubts at the species level have no clear morphological resolution. Considering that no molecular data of M. potiuna along its distribution were available to provide a complete and integrated overview, we analyzed 21 partial sequences (531 bp) from the mitochondrial 16S rRNA gene of M. potiuna and 9 sequences from outgroup species, by maximum likelihood and parsimony, in order to investigate the possibility of the existence of cryptic species, within the morphologically based M. potiuna. The topologies obtained revealed that M. potiuna represents a monophyletic clade. Nevertheless, two clades supported by both analyses were formed within the M. potiuna taxon. The mean genetic divergence between these two groups was 0.044 ± 0.007, and within each group (i.e., M. potiuna "sensu stricto" andM. potiuna "Affinis-Clade") the divergences were 0.010 ± 0.003 and 0.028 ± 0.005, respectively. As far as we know, this is the first report to show a genetic separation between populations of prawns with abbreviated larval development in South American drainages. Pending additional analysis, to propose a conclusive inference, the existence of these distinct genetic groups must be considered in future studies with the morphologically based M. potiuna. In addition, we extended the known northern distribution with a record from the state of Bahia.

Una revisión taxonómica reciente reveló que el camarón endémico, Macrobrachium potiuna, distribuido en riachuelos brasileños, presenta una alta variabilidad morfológica a lo largo de su limitada distribución geográfica. Sin embargo, los problemas taxonómicos a nivel de especie no parecen tener clara resolución en algunos casos. Considerando que no hay datos moleculares disponibles de M. potiuna a lo largo de su distribución, que puedan proveer una visión general completa e integrada, se analizaron 21 secuencias parciales (531pb) del gen mitocondrial 16S, de M. potiuna y 9 secuencias del grupo externo, usando máxima verosimilitud y máxima parsimonia, para investigar la posibilidad de que exista una especie críptica dentro de M. potiuna. Las topologías obtenidas mostraron que M. potiuna es un grupo monofilético. Sin embargo, se formaron dos clados internos, bien soportados por ambos análisis. La divergencia genética promedio entre estos dos grupos fue de 0,044 ± 0,007; dentro de los clados (i.e., M. potiuna "sensu stricto" y M. potiuna "Affinis-Clade") las divergencias fueron de 0,010 ± 0,003 y 0,028 ± 0,005, respectivamente. Hasta donde se sabe, este es el primer estudio que muestra una separación entre las poblaciones de camarones de agua dulce de Sudamérica con desarrollo larval abreviado. En espera de un análisis más exhaustivo, que proponga una conclusión definitiva, la existencia de estos dos grupos genéticos distintos debe ser considerada en estudios futuros de M. potiuna, basados únicamente en morfología. De manera adicional, este trabajo incluye una extensión en la distribución norte de M. potiuna hasta el estado de Bahía.

Freshwater prawns are distributed in rivers and streams of inland and brackish waters throughout America. In Brazilian waters are registered 35 species into 4 families (Atyidae, Euryrhynchidae, Palaemonidae, and Sergestidae). Information about the geographic distribution of this fauna is scattered in the literature and frequently not founded on documented data in scientific collections. Here we examined a series of specimens and detected several new records and extension of the known distribution of some freshwater shrimps in Brazil.

Los langostinos de agua dulce se distribuyen en los ríos y arroyos de aguas continentales y salobres en toda América. En aguas brasileñas se registran 35 especies pertenecientes a 4 familias (Atyidae, Euryrhynchidae, Palaemonidae y Sergestidae). La información bibliográfica sobre la distribución geográfica de esta fauna es dispersa y con frecuencia obtenida de las colecciones científicas. En este estudio se examinaron una serie de muestras en las cuales se presentan varios registros nuevos de la distribución reconocida para algunos camarones de agua dulce de Brasil.

Os camarões de água doce do gênero Macrobrachium Spence Bate, 1868 encontram-se amplamente distribuídos em rios de regiões tropicais e subtropicais e representam um grupo com taxonomia controversa. Os caracteres morfológicos comumente utilizados para separação de espécies apresentam uma grande variação intraespecífica. Dúvidas sobre o status taxonômico de M. birai Lobão, Melo & Fernandes, 1986, M. holthuisi Genofre & Lobão, 1978 e M. petronioi Melo, Lobão & Fernandes, 1986 foram levantadas devido à alta similaridade morfológica das primeiras com relação à M. olfersi (Wiegmann, 1836) e da última com relação à M. potiuna (Müller, 1880). Assim, foi realizada uma análise morfológica detalhada de tais espécies, incluindo novos caracteres comumente não utilizados na identificação dos táxons. A partir dos resultados obtidos, juntamente com dados moleculares, concluímos que M. birai e M. holthuisi são sinônimos-júnior de M. olfersi, e M. petronioi é sinônimo-júnior de M. potiuna. Portanto, considerando-se tais sinonímias, são reportadas 17 espécies válidas para o território brasileiro.

The freshwater prawns of the genus Macrobrachium Spence Bate, 1868 are widely distributed in rivers of tropical and subtropical regions and represent an interesting group with controversial taxonomy. The morphological characters traditionally used to separate species have shown a high intraspecific variation. Doubts about the status of M. birai Lobão, Melo & Fernandes, 1986, M. holthuisi Genofre & Lobão, 1978 and M. petronioi Melo, Lobão & Fernandes, 1986 have been arisen due to the high resemblance of the former two species with M. olfersi (Wiegmann, 1836), and the latter one with M. potiuna (Müller, 1880). Therefore, we performed a detailed morphological analysis of these species, including new characters not usually used in the species recognition. The present results here with molecular data lead us to conclude that M. birai and M. holthuisi are junior synonyms of M. olfersi, and M. petronioi is a junior synonym of M. potiuna. Considering these synonymies, 17 valid species are now reported for the Brazilian territory.