ABSTRACT Iphigenia brasiliensis is a bivalve mollusk exploited as a shellfish and subsistence resource on the Brazilian coast, mainly in the north and northeast regions. Genetic (allozyme electrophoresis revealed eight gene loci) and morphological variations (multivariate morphometry of valves used 13 linear measurements of traditional and 19 Fourier coefficients of geometric morphometry) were studied, considering the geographic (445 km of the southwest tropical Atlantic), environmental (mangroves and channels of communication with the sea of three estuaries in the state of Rio de Janeiro), and temporal dimensions (over two years). I. brasiliensis showed high levels of genetic variation (the average number of alleles per locus ranged from 2.8 to 3.4, and the average heterozygosity ranged from 0.441 to 0.675). Bayesian analysis of population partitioning showed that the highest LnP(D) value was achieved for K = 3. These results indicated mixed ancestry, possibly oscillations in the dispersion dynamics among the different sampling groups, and temporal oscillations in the population sizes due to the anthropogenic influence on the studied estuaries. The results of morphological variation, inferred by the PERMANOVA from the Fourier analysis, indicated that a similar influence might occur in valves (also, the discriminant analysis showed that different groups could be consistently identified). In this sense, the studied populations may be organized in a dynamic of metapopulations. Finally, these are the first data on morphological and genetic variation of the species in the latitudinal, environmental, and temporal dimensions studied simultaneously, thus providing relevant information for the exploration, management, and conservation of this commercially important species.

RESUMO Dois morfotipos de Coryphaena hippurus (dourado e palombeta) encontrados ao longo da costa brasileira são considerados espécies diferentes por pescadores e mercadores das regiões de desembarque do estado do Rio de Janeiro. Além disso, esses morfotipos são comercializados por valores diferentes e sofrem diferentes pressões de pesca. Desta forma, a definição do status taxonômico desses morfotipos é importante, tanto em termos econômicos quanto biológicos. A fim de investigar esse problema foi utilizado o método de eletroforese de aloenzimas com a amostragem de dezessete loci para 117 indivíduos dos dois morfotipos de C. hippurus obtidos em desembarques pesqueiros na região de Cabo Frio/RJ (Brasil). Os dados indicaram uma homogeneidade entre os conjuntos gênicos dos morfotipos. A despeito disso, diferenças entre os conjuntos gênicos de dourado e palombeta foram encontradas, devido, especialmente, ao locus álcool desidrogenase. A hipótese de seleção natural é discutida como possível explicação para esses resultados.

ABSTRACT Two Coryphaena hippurus morphotypes (dourado and palombeta) are found along the Brazilian coast and are considered by Rio de Janeiro’s fisherman and fishmongers as two different species. Furthermore, these morphotypes are commercialized under different values and suffer different fishing pressure. Therefore, a definition of their taxonomic status is an important economic and biological matter. In order to investigate this problem, allozyme electrophoresis method was undertaken for seventeen loci on 117 individuals of C. hippurus sampled at Cabo Frio/RJ (Brazil). The data indicate homogeneity between the morphotypes gene pools. Nevertheless, differences were found for genetic variation among dourado and palombeta, especially due to alcohol dehydrogenase locus. Natural selection hypothesis is discussed in explaining these findings.