Abstract
Due to anthropogenic factors, the franciscana dolphin, Pontoporia blainvillei, is the most threatened small cetacean on the Atlantic coast of South America. Four Franciscana Management Areas have been proposed: Espiritu Santo to Rio de Janeiro (FMA I), São Paulo to Santa Catarina (FMA II), Rio Grande do Sul to Uruguay (FMA III), and Argentina (FMA IV). Further genetic studies distinguished additional populations within these FMAs. We analyzed the population structure, phylogeography, and demographic history in the southernmost portion of the species range. From the analysis of mitochondrial DNA control region sequences, 5 novel haplotypes were found, totalizing 60 haplotypes for the entire distribution range. The haplotype network did not show an apparent phylogeographical signal for the southern FMAs. Two populations were identified: Monte Hermoso (MH) and Necochea (NC)+Claromecó (CL)+Río Negro (RN). The low levels of genetic variability, the relative constant size over time, and the low levels of gene flow may indicate that MH has been colonized by a few maternal lineages and became isolated from geographically close populations. The apparent increase in NC+CL+RN size would be consistent with the higher genetic variability found, since genetic diversity is generally higher in older and expanding populations. Additionally, RN may have experienced a recent split from CL and NC; current high levels of gene flow may be occurring between the latter ones. FMA IV would comprise four franciscana dolphin populations: Samborombón West+Samborombón South, Cabo San Antonio+Buenos Aires East, NC+CL+Buenos Aires Southwest+RN and MH. Results achieved in this study need to be taken into account in order to ensure the long-term survival of the species.
Highlights
Knowledge of population structure and patterns of gene flow are key components of management efforts, as they contribute to a better understanding of the ecology and the adaptive potential of species [1,2,3,4]
From the analysis of the mitochondrial DNA (mtDNA) control region of the 72 samples collected in this study, we detected 22 haplotypes, including 5 novel ones (GenBank accession numbers: KP670446 to KP670450), totalizing 60 haplotypes for the entire distribution range of the species (S1 Table)
Several samples analyzed here were those used in Negri [31], we did not find haplotype N1 in our data set, and haplotype N3 was found in CL, not in NC as it was reported in that study (S1 Table)
Summary
Knowledge of population structure and patterns of gene flow are key components of management efforts, as they contribute to a better understanding of the ecology and the adaptive potential of species [1,2,3,4]. As a result of stochastic and/or anthropogenic factors, the species population sizes may decline. If these populations become isolated, random genetic drift and inbreeding processes may be crucial in making them more vulnerable than larger ones to local extinction and the loss of genetic variation, resulting in a decrease in fitness [10,11]. Its distribution makes franciscana vulnerable to anthropogenic activities, mainly to incidental by-catch [17,18,19]. Owing to its high incidental mortality in fishing gillnets [14,20,21,22,23], it is the most threatened small cetacean in the Southwestern Atlantic Ocean [24,25] and was classified as “Vulnerable” by the International Union for Conservation of Nature (IUCN) [26]. Annual mortality in franciscana dolphins reaches up to 2–5%, approximately (e.g. [14,15,22,28]), severely impacting on size and connectivity among populations, and may result in the loss of the species evolutionary potential [3,29]
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