Population Genetic Structure and Social Kin Associations of Franciscana Dolphin, Pontoporia blainvillei

Abstract

We investigated population and social structure of the franciscana dolphin, Pontoporia blainvillei, an endemic and the most endangered cetacean of the southwestern Atlantic Ocean. We analyzed samples from the Rio de la Plata estuary obtained in Uruguayan waters and from the Atlantic Ocean obtained in both Uruguayan and Brazilian waters. Mitochondrial and microsatellite DNA markers were used to study differentiation between the estuary and the ocean and the association between kinship and social group structure. Although multilocus analyses suggested that franciscanas are structured into 2 subpopulations (K = 2, divergence among clusters: F(ST) = 0.06, P = 0.002; R(ST) = 0.3, P = 0.001), mitochondrial markers did not support such divergence (F(ST) = 0.02, P = 0.12; Ф(ST) = 0.06, P =0.06). However, these units are not entirely segregated geographically. Regarding social structure, some groups are composed by first-order related individuals (R ≥ 0.5, P < 0.5). Overall, the data suggest that matrilines could be the social unit in this species. We argue that the divergence found could be associated to local adaptation and social structure, resulting from either feature leading to a recent divergence or reflecting equilibrium between local differentiation and gene flow. This evidence supports considering franciscanas from the Rio de la Plata estuary a discrete management unit.

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

“…Although this result should be regarded with caution since the ability of the tests performed to detect the bias in dispersal is limited mainly due to the lack of extreme bias in dispersal, the low to moderate dispersal estimates, and the number of loci and samples analyzed (Goudet et al., 2002), previous franciscana dolphin studies also found a lack of sex‐biased dispersal (Costa Urrutia et al., 2012; Méndez et al., 2008), supporting our findings.…”

“…In accordance with a previous mtDNA control region analysis (Gariboldi et al., 2015), high rates of gene flow (Table 3 and mtDNA results) and a lack of genetic differentiation between CL and NC were observed based on the microsatellite loci and mtDNA analyses (Table 2), suggesting that individuals from both localities form a panmictic population. This may be due to close geographic proximity between localities which may entail similar resource use, as it was previously suggested for this species (Costa Urrutia et al., 2012; Gariboldi et al., 2015; Méndez et al., 2008; Méndez, Rosenbaum, Subramaniam, et al., 2010) and other cetaceans (Fullard et al., 2000; Hoelzel et al., 2007; Natoli et al., 2005). In fact, individuals from NC and CL were found to fed primary on Loligo sanpaulensis (Paso Viola, 2014; Paso Viola et al., 2014).…”

“…Sampling permits were issued by Dirección de Fauna Silvestre (Río Negro Province) and Dirección Provincial de Fiscalización y Uso Agropecuario de los Recursos Naturales (Buenos Aires Province), Argentina. Since three individuals were by‐caught simultaneously in this study, and considering that franciscana dolphins would travel in groups comprised in part of close relatives (Costa Urrutia et al., 2012; Méndez, Rosenbaum, Wells, Stamper, & Bordino, 2010; Valsecchi & Zanelatto, 2003), we analyzed only one of those individuals to reduce a potential bias in our analyses. Furthermore, all incidentally entangled or stranded franciscana dolphins used in this study were collected within each locality in sampling events that took place with at least one month of separation between each other.…”

“…Ten microsatellite loci developed for other cetacean species (Table S2) and already utilized for franciscana dolphins (Costa Urrutia et al., 2012; Méndez, Rosenbaum, Subramaniam, et al., 2010) were amplified. All forward primers were modified with a fluorescent dye.…”

“…Subsequent studies confirmed Secchi et al. 's subdivision and further suggested the existence of genetically differentiated populations within the FMAs (Costa Urrutia et al., 2012; Cunha et al., 2014; Gariboldi et al., 2015; Méndez, Rosenbaum, & Bordino, 2008; Méndez, Rosenbaum, Subramaniam, et al., 2010; Negri, 2011; Valsecchi & Zanelatto, 2003). Particularly, based on mtDNA and microsatellite data, the FMA IV would comprise four populations: (1) Samborombón West (SW)/Samborombón South (SS), (2) Cabo San Antonio (CSA)/Buenos Aires East (BAE), (3) Monte Hermoso (MH), and (4) Necochea (NC)/Claromecó (CL)/Buenos Aires Southwest (BASW)/Río Negro (RN) (Gariboldi et al., 2015; Lázaro et al., 2004; Méndez et al., 2008; Méndez, Rosenbaum, Subramaniam, et al., 2010) (Figure 1).…”