Aedes aegypti is the principal vector of the yellow fever virus and the four dengue serotypes and its hemorrhagic fever viruses. The genetic variability and differentiation of four Aedes aegypti populations from São Luis Island in the Brazilian state of Maranhão was analyzed based on the sequences of a fragment of the mitochondrial ND4 gene. A total of 58 sequences of 337 bps were analyzed, revealing the existence of 10 haplotypes, of which five were considered to be unique. Haplotype diversity for the total population was 0.6273 and nucleotide diversity 0.00748. The haplotype tree produced from the data indicated the presence of two mitochondrial lineages of the dengue vector, one of which was characterized by the H6 haplotype, found only in the population from one site (Raposa), and may represent the recent introduction of this lineage to the island. The results of the AMOVA indicated that the majority of the genetic variation (74.38%) was found within populations. However, the significant Fst value of 0.2572 indicates a certain inter-population differentiation which may result in differences in the vectorial capacity of the insect, its susceptibility to the virus or even resistance to insecticides or other ecological adaptations, all of which may limit the effectiveness of programs for the control of Ae. aegypti.

Leporinus is one of the most speciose genera of the order Characiformes, with 81 valid species distributed throughout much of Central and South America. The considerable diversity of this genus has generated extensive debate on its classification and internal arrangement. In the present study, we investigated the species diversity of the genus Leporinus in central northern Brazil, and conclude that six valid species—Leporinus maculatus, Leporinus unitaeniatus, Leporinus affinis, Leporinus venerei, Leporinus cf. friderici, and Leporinus piau—are found in the hydrographic basins of the Brazilian states of Maranhão, Piauí, and Tocantins. We analyzed 182 sequences of the Cytochrome Oxidase subunit I gene, of which, 157 were obtained from Leporinus specimens collected from the basins of the Itapecuru, Mearim, Turiaçu, Pericumã, Periá, Preguiças, Parnaíba, and Tocantins rivers. The species delimitation analyses, based on the ABGD, ASAP, mPTP, bPTP, and GMYC methods, revealed the presence of four distinct molecular operational taxonomic units (MOTUs), identified as L. maculatus, L. unitaeniatus, L. affinis, and L. piau (from the Parnaíba River). The bPTP method restricted L. venerei to a single MOTU, and confirmed the occurrence of this species in the rivers of Maranhão for the first time. The separation of L. cf. friderici into two clades and the subsequent formation of different operational taxonomic units was consistent with polyphyly in this species, which indicates the existence of cryptic diversity. The arrangement of L. cf. friderici and L. piau in two different clades supports the conclusion that the L. piau specimens from Maranhão were misidentified, based on their morphological traits, reflecting the taxonomic inconsistencies that exist among morphologically similar species. Overall, then, the species delimitation methods employed in the present study indicated the presence of six MOTUs—L. maculatus, L. unitaenitus, L. affinis, L. cf. friderici, L. venerei, and L. piau. In the case of two other MOTUs identified in the present study, one (L. venerei) is a new record for the state of Maranhão, and we believe that the other represents a population of L. piau from the basin of the Parnaíba River.