Molecular analysis of the social and population structure of the franciscana (Pontoporia blainvillei): conservation implications

Résumé

Fifteen franciscanas, including four members of a putative social group, were genetically typed in order to: (1) obtain insights into the social organisation of this poorly known dolphin species; and (2) clarify its population sub-structure across the species range. Samples were screened for 10 nuclear markers (microsatellites) and sequenced for 269bp of the mitochondrial DNA control region. The results indicate that franciscana dolphins may travel in kin groups which might include, besides mothers with their calves or juvenile offspring, the fathers of the youngest group members. All four individuals from the presumed social group shared the same mitochondrial haplotype, suggesting that the social unit might be matrilineally structured. Comparative analyses of mitochondrial data available from a previous study of two adjacent populations (19 additional haplotypes) suggest the existence of at least three distinct populations. This population fragmentation, together with the relatively low genetic variability, suggests that the franciscana dolphin is a potentially vulnerable species, which may require some management effort to ensure its preservation. Consistent with a previous study, the population occupying the northernmost extremity of the species distribution range was found to be the least variable, most isolated, and therefore potentially the most vulnerable.