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

The franciscana, Pontoporia blainvillei, is a dolphin that experiences exte nsive incidental mortality in fisheries throughout its restricted distribut ion and is perhaps the most exploited species along the Atlantic coast of S outh America. However, the basic information required fur effective conserv ation 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 franci scana that were captured incidentally by gillnet fisheries of Rio Grande do Sul and Rio de Janeiro, Brazil. Of 11 haplotypes found, 5 were exclusive t o franciscana from Rio Grande do Sul and 6 were found only in franciscana f rom Rio de Janeiro and no haplotypes were shared between locations. Reconst ruction of the phylogenetic relationships among the haplotypes through a ma ximum-likelihood analysis of sequences revealed two distinct lineages that were consistent with the geographic sampling locations. Analysis of molecul ar variance also showed the population structure (phi(ST) = 0.403, p < 0.00 01). Furthermore, the estimate of nucleotide diversity for the northern pop ulation (0.38 +/- 0.13%) was significantly lower than for the southern popu lation (1.01 +/- 0.30%). The genetic evidence indicated that at least two p opulations of franciscana exist.