Population differentiation in the franciscana (Pontoporia blainvillei) from two geographic locations in Brazil as determined from mitochondrial DNA control region sequences

Abstract

The franciscana, Pontoporia blainvillei, is a dolphin that experiences extensive incidental mortality in fisheries throughout its restricted distribution and is perhaps the most exploited species along the Atlantic coast of South America. However, the basic information required for effective conservation of this species is lacking. To understand the population structure of this platanistoid dolphin, we sequenced 418 base pairs (bp) of the control region and 68 bp of the adjacent pro-tRNA gene of the mtDNA from 20 franciscana that were captured incidentally by gill-net fisheries of Rio Grande do Sul and Rio de Janeiro, Brazil. Of 11 haplotypes found, 5 were exclusive to franciscana from Rio Grande do Sul and 6 were found only in franciscana from Rio de Janeiro and no haplotypes were shared between locations. Reconstruction of the phylogenetic relationships among the haplotypes through a maximum-likelihood analysis of sequences revealed two distinct lineages that were consistent with the geographic sampling locations. Analysis of molecular variance also showed the population structure (phiST = 0.403, p < 0.0001). Furthermore, the estimate of nucleotide diversity for the northern population (0.38 ± 0.13%) was significantly lower than for the southern population (1.01 ± 0.30%). The genetic evidence indicated that at least two populations of franciscana exist.