Diversidade genética das populações de Melampus coffeus (Linnaeus, 1758) ao longo da costa cearense

Abstract

Melampus coffeus is a pulmonate gastropod commonly found in estuaries along the west coast of the Atlantic. They are important nutrient recyclers because they are macro-detritivorous organisms. Considering the ecologic importance of M. coffeus, its pontencial as a bioindicator and its distribution in estuaries subjected to various level of anthropogenic pressure, this project aimed at characterizing the genetic diversity of M. coffeus populations along the coast of Ceará using the mitochondrial gene COI as a molecular tool. Samples were collected from six estuaries of Ceara's coast (Rivers Ceará, Cocó, Pacoti, Acaraú, Guriú and Barra Grande). During the experiment 138 sequences were analysed, each one containing 426bp. We found 81 haplotypes, 73 of these occurring uniquely Haplotype 1 was the most abundant, occurring 45 times across all the estuaries. The haplotype diversity showed middle value of 0.893 and the nucleotide diversity showed middle of 0.00526. The variations between the sequences occurred mostly within populations and the diversity rates showed a high degree of intra-population variation and little inter-population variation. A low level of genetic structuring was observed among the estuaries, with an overall fixation index (FST) of 0.0069 (P=0.02). The difference between populations, estimated through the number of substitutions, was 0.004 and 0.006, indicating a low degree of divergence between the estuaries. The neutrality tests showed statistically significant negative values, indicating that the population is likely to have suffered a recent expansion. This is in agreement the results obtained from the mismatch distribution analysis and the haplotype network. Comparing populations from Ceará with those from Florida and Puerto Rico it was observed a high degree of genetic structuring with the variations occurring mainly between the groups. In conclusion, M. coffeus from Ceara's coast showed high genetic variability with no detectable structuring among estuaries. The local populations seem to have suffered a recent expansion. The populations from Ceará are clearly isolated from those from Puerto Rico and Flórida sugesting a long and stable process of population structuring over time.