ABSTRACT.A genetic study of the neotropical river otter Lontra longicaudis (Olfers, 1818), which has an unknown conservation status, was carried out at the Taim Ecological Station and the margins of the Vargas stream, Rio Grande do Sul, southern Brazil. Faecal samples were collected, and DNA was extracted using a silica-guanidine method. Five microsatellite loci were amplified using PCR with heterologous primers previously described for Lutra lutra (Linnaeus, 1758). Sixteen faecal samples out of 29 from Taim and 11 out of 14 from Vargas stream margins contained enough DNA for genetic analysis. A total of 49 different alleles were found at both localities, from which 18 were exclusively found in individuals from Taim and 17 were exclusives from Vargas individuals. The most common allele was the same at both locations for three loci (Lut715, Lut733, and Lut818). A high level of genetic diversity was found at both sites (Ne Taim =4.1, Ho Taim =0.299, He Taim =0.681; Ne Vargas =4.9, Ho Vargas =0.355, He Vargas =0.724), being higher at the Vargas stream site. A high and significant level of heterozygote deficiency was observed at most loci according to the χ 2 test. The homogeneity χ 2 test (P≤0.001) showed that there were significant differences in the allele frequencies between the two locations. Genotyping for more than one locus was possible in 81.5% of samples, from which only 37% were possible to genotype for more than three loci. A low degree of relatedness was found among individuals from Taim (R=0.055±0.310), but an even lower value of relatedness was found at the Vargas site (R= -0.285±0.440). The significant degree of differentiation (I=0.890; F ST =0.059) found between Taim and Vargas individuals suggests that there is more than one population of otters in the southern extreme of Brazil, which probably are associated with the water body systems found in this region, the Mirim and the Caiuvá/Flores/Mangueira Lagoons. The high genetic diversity and low relatedness found at the Vargas stream, lead us to believe that the Vargas stream may be acting as a corridor between these water bodies for otter dispersion. KEYWORDS.Neotropical river otter, genetic markers, Taim, non-invasive sampling, genetic diversity.RESUMO. Genotipagem através de microsatélites extraídos de amostras fecais em Lontra longicaudis do sul do Brasil. A lontra neotropical de rio Lontra longicaudis (Olfers, 1818), cujo estado de conservação é ainda desconhecido, foi estudada geneticamente na Estação Ecológica do Taim e nas margens do arroio Vargas, RS, sul do Brasil. Amostras de fezes foram coletadas e o DNA foi extraído por um método de sílica-guanidina. Cinco locos de microsatélites foram amplificados por PCR utilizando primers heterólogos previamente descritos para Lutra lutra (Linnaeus, 1758). Dezesseis amostras de fezes de um total de 29 coletadas no Taim e onze das 14 obtidas no arroio Vargas contiveram DNA suficiente para prosseguir com a analise genética. Um total de 49 alelos foram obtidos, dos quais 18 foram exclusivos de indivíduos...

The doubly uniparental mode of inheritance, characteristic of the Mytilidae, consists of an F-type mitochondrial lineage transmitted only through females and an M-type lineage present only in male gonads and therefore transmitted only through males. In this work, we search for evidence of two mitochondrial lineages in Perna perna by studying the same 16S rRNA region that allowed for the discovery of doubly uniparental inheritance in the Mytilus group and in one venerid clam. The region was screened for substitutions using eight restriction enzymes to analyze two kinds of tissues (somatic and gonadal) from 20 males and 20 females from the south of Brazil. A restriction map was constructed after confirming restriction sites with sequence analysis. After amplification with the same primers used in previous studies, a fragment of 517 bp was obtained, which was 10 bp shorter than the one from Mytilus species. No variation was found among individuals or between sexes or kinds of tissue (gonadal and somatic). The absence of variation in this region was confirmed by sequence analysis, and this result left us unable to reject the hypothesis of common maternal mitochondrial inheritance. The 16S rDNA sequence obtained for Perna perna was aligned with twenty-three representative sequences from fifteen mytilid species available in GenBank, and a neighborjoining tree was constructed. The phylogenetic analysis showed all Perna species clustered together in a single branch, which was supported 100% by bootstrap analysis and was more closely related to the branch of the Mytilus group than the other representative genera of the Mytilidae.