GEOGRAPHIC GENETIC STRUCTURE IN THE FRANCISCANA DOLPHIN (PONTOPORIA BLAINVILLEI)

Abstract

The franciscana, Pontoporia blainvillei, is endemic to the South Atlantic coast of South America. The species is of conservation concern because it suffers elevated mortality rates due to incidental captures in fishing nets, and perhaps it is one of the most threatened small cetaceans in this region. Previous morphological and genetic studies have suggested the existence of at least two distinct stocks to the north and south of Santa Catarina Island in Brazil. Fixed differences were found between a sample from Rio de Janeiro and one from Rio Grande do Sul, in southern Brazil. Using 94 sequences of the control region of mitochondrial DNA, we examined the genetic structure of the species. We found no shared haplotypes between Rio de Janeiro and samples from the southern range of the species distribution. However, a phylogenetic analysis suggests that the former population is diphyletic with respect to the southern samples. This suggests that the populations have not been isolated long enough to reach reciprocal monophyly. Furthermore, genetic differentiation is broadly consistent with a simple model of isolation by distance, that therefore appears as an alternative to a model of strict isolation of two stocks. The estimated levels of gene flow are higher among neighboring populations, and decrease as more distant localities are compared. Finally, the molecular data suggest that franciscanas have expanded in Rio de Janeiro.

Morphometric relationships of franciscana dolphin, Pontoporia blainvillei (Cetacea), off Rio Grande do Sul coast, southern Brazil

“…This suggested a model based upon a single sample of both sexes, with its increased precision due to larger sample size, may be preferable. Several morphometric and genetic studies (Pinedo, 1991(Pinedo, , 1995Secchi et al, 1998Secchi et al, , 2003aOtt et al, 2002;Ramos et al, 2002;Lázaro et al, 2004;Barreto and Rosas, 2006) have established the existence of three franciscana morphotypes/genotypes: one found in FMA I (Rio de Janeiro and Espírito Santo states, Brazil); a second one in FMA II (from São Paulo to Santa Catarina states, Brazil) and the third in FMA III and IV (from Rio Grande do Sul state, Brazil down to Buenos Aires Province, Argentina). Animals inhabiting FMA I are smaller than animals from FMA III and IV but larger than those from FMA II.…”

Conservation genetics of the franciscana dolphin in Northern Argentina: population structure, by-catch impacts, and management implications

“…Secchi and colleagues (Secchi et al 1998) performed a genetic analysis based on control region mtDNA data from 10 individuals from Rio de Janeiro and 10 individuals from Rio Grande do Sul, and suggested that these were two genetically distinct populations, supporting Pinedo (1991). Subsequently, Lazaro and colleagues (Lazaro et al 2004) used control region mtDNA data from 94 individuals sampled in Uruguay, in Buenos Aires, and from those previously studied by Secchi et al (1998) in Brazil. This recent study agreed with Secchi et al (1998) findings and further suggested the presence of two additional populations, one in what they called Rio de la Plata (Uruguay and northern Buenos Aires combined) and the other in Claromeco, Argentina.…”

Incidental mortality of franciscana dolphin (Pontoporia blainvillei) in Argentina

“…Franciscana shows a continuous presence along the coastal area of Buenos Aires Province (Corcuera, 1994). Recent studies conducted by Lázaro et al (2004) and Ott et al (2005) 8 described a substantial geographic heterogeneity in its distribution, particularly in the southern Buenos Aires Province, suggesting this area should be considered separately. Moreover, Mendez et al (2007) suggest that the franciscana population in The International Whaling Commission Scientific Committee (Donovan and Bjørge, 1995) has noted that incidental mortality estimates of 1% per year of an estimated population size are sufficient to concern over the status of small cetacean population and the catches of 2% per year may not be sustainable.…”