Isolation by environmental distance in mobile marine species: molecular ecology of franciscana dolphins at their southern range

Abstract

The assessment of population structure is a valuable tool for studying the ecology of endangered species and drafting conservation strategies. As we enhance our understanding about the structuring of natural populations, it becomes important that we also understand the processes behind these patterns. However, there are few rigorous assessments of the influence of environmental factors on genetic patterns in mobile marine species. Given their dispersal capabilities and localized habitat preferences, coastal cetaceans are adequate study species for evaluating environmental effects on marine population structure. The franciscana dolphin, a rare coastal cetacean endemic to the Western South Atlantic, was studied to examine these issues. We analysed genetic data from the mitochondrial DNA and 12 microsatellite markers for 275 franciscana samples utilizing frequency-based, maximum-likelihood and Bayesian algorithms to assess population structure and migration patterns. This information was combined with 10 years of remote sensing environmental data (chlorophyll concentration, water turbidity and surface temperature). Our analyses show the occurrence of genetically isolated populations within Argentina, in areas that are environmentally distinct. Combined evidence of genetic and environmental structure suggests that isolation by distance and a process here termed isolation by environmental distance can explain the observed correlations. Our approach elucidated important ecological and conservation aspects of franciscana dolphins, and has the potential to increase our understanding of ecological processes influencing genetic patterns in other marine species.

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

“…(2010) reported that their BASW location, near RN, did not differ from their BAS location (named as NC and CL in this study). Based on the published information of that study, we were not able to compare our results with neither BASW nor BAS.…”

“…Overall, similar levels of genetic variation for both the microsatellite and mtDNA data were observed between localities in this study (Tables 1 and 4), and these were comparable with those previously found in the FMA IV (Méndez et al., 2008; Méndez, Rosenbaum, Subramaniam, et al., 2010). We found that MH and RN presented several private alleles, in comparison with NC and CL (Table 1), and that these were found in all, but one case, at the edges of the allele sizes (data not shown).…”

“…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).…”

“…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).…”