Patterns of population structure at microsatellite and mitochondrial DNA markers in the franciscana dolphin (Pontoporia blainvillei).

The franciscana dolphin, Pontorporia blainvillei, is an endemic cetacean of the Atlantic coast of South America. Its coastal distribution and restricted movement patterns make this species vulnerable to anthropogenic factors, particularly to incidental bycatch. We used mitochondrial DNA control region sequences, 10 microsatellites, and sex data to investigate the population structure of the franciscana dolphin from a previously established management area, which includes the southern edge of its geographic range. F-statistics and Bayesian cluster analyses revealed the existence of three genetically distinct populations. Based on the microsatellite loci, similar levels of genetic variability were found in the area; 13 private alleles were found in Monte Hermoso, but none in Claromecó. When considering the mitochondrial DNA control region sequences, lower levels of genetic diversity were found in Monte Hermoso, when compared to the other localities. Low levels of gene flow were found between most localities. Additionally, no evidence of isolation by distance nor sex-biased dispersal was detected in the study area. In view of these results showing that populations from Necochea/Claromecó, Monte Hermoso, and Río Negro were found to be genetically distinct and the available genetic information for the species previously published, Argentina would comprise five distinct populations: Samborombón West/Samborombón South, Cabo San Antonio/Buenos Aires East, Necochea/Claromecó/Buenos Aires Southwest, Monte Hermoso, and Río Negro. In order to ensure the long-term survival of the franciscana dolphin, management and conservation strategies should be developed considering each of these populations as different management units.

Morphological analysis of the flippers in the Franciscana dolphin, Pontoporia blainvillei, applying X-ray technique.

Pectoral flippers of cetaceans function to provide stability and maneuverability during locomotion. Directional asymmetry (DA) is a common feature among odontocete cetaceans, as well as sexual dimorphism (SD). For the first time DA, allometry, physical maturity, and SD of the flipper skeleton--by X-ray technique--of Pontoporia blainvillei were analyzed. The number of carpals, metacarpals, phalanges, and morphometric characters from the humerus, radius, ulna, and digit two were studied in franciscana dolphins from Buenos Aires, Argentina. The number of visible epiphyses and their degree of fusion at the proximal and distal ends of the humerus, radius, and ulna were also analyzed. The flipper skeleton was symmetrical, showing a negative allometric trend, with similar growth patterns in both sexes with the exception of the width of the radius (P ≤ 0.01). SD was found on the number of phalanges of digit two (P ≤ 0.01), ulna and digit two lengths. Females showed a higher relative ulna length and shorter relative digit two length, and the opposite occurred in males (P ≤ 0.01). Epiphyseal fusion pattern proved to be a tool to determine dolphin's age; franciscana dolphins with a mature flipper were, at least, four years old. This study indicates that the flippers of franciscana dolphins are symmetrical; both sexes show a negative allometric trend; SD is observed in radius, ulna, and digit two; and flipper skeleton allows determine the age class of the dolphins.

Reproductive aspects of male franciscana dolphins (Pontoporia blainvillei) off Argentina.

As the first study to investigate reproductive aspects of male franciscana dolphin -Pontoporia blainvillei - in Argentine waters, the aim of this paper was to assess sexual maturity by using histological and morphometric methods. P. blainvillei was labeled as "Vulnerable" by the IUCN in 2008. The specimens analyzed were either incidentally caught in artisanal fishing nets (n=47) or found stranded on the beach (n=3). Testis weight and testicular index of maturity were reliable indicators of sexual maturity, being their values: MTW: 1.14 ± 0.60-4.49 ± 1.94; IM: 0.03 ± 0.01-0.09 ± 0.03, for immature and mature specimens' respectively. It was found that the hierarchical cluster analysis (HCA) might be appropriate for establishing sexual maturity stage, based on both the body morphometric measurements and age. The values for age, standard length and total weight at attainment sexual maturity were 2.92-3.54 years, 126.19-126.27 cm and 23.47-23.75 kg. Considering the extremely low relative testis weight, the reversed sexual length dimorphism, the absence of secondary sexual characteristics, and the lack of scars from intrasexual combats in males, the hypothesis that sperm competition does not occur in the species, and male combats for accessing female reproductive may be rare for P. blainvillei is reinforced. All these features fit the species within a serial monogamous mating system.