From Settlers to Subspecies: Genetic Differentiation in Commerson’s Dolphins Between South America and the Kerguelen Islands

Sebastián Kraft,Sebastián Kraft,Paul Tixier,Paul Tixier,Paul Tixier,Paul Tixier,Paul Tixier,Paul Tixier,Amelia Viricel,C Scott Baker,Cristian Durante,Rodrigo Moraga,Mjosé Pérez-Alvarez,Paul Brickle,Christophe Guinet,Christophe Guinet,Marina Costa,Carlos Olavarría,Elie Poulin,Elie Poulin,Elie Poulin,Rocio Loizaga,Debbie Steel,Enrique Crespo

doi:10.3389/fmars.2021.782512

Abstract

Commerson’s dolphins (Cephalorhynchus commersonii) are separated into the subspecies C. c. commersonii, found along southern South America (SA) and the Falkland Islands/Islas Malvinas (FI/IM), and C. c. kerguelenensis, restricted to the subantarctic Kerguelen Islands (KI). Following the dispersal model proposed for the genus, the latter is thought to have originated from SA after a long-distance dispersal event. To evaluate this biogeographic scenario, a distribution-wide, balanced sampling of mitochondrial DNA (mtDNA) control region sequences was designed. New tissue samples from southern Chile, Argentina, FI/IM, and KI were added to published sequences from SA and KI, for a total of 256 samples. Genetic diversity indices, genetic and phylogeographic structure, and migration rates were calculated. One haplotype was shared between subspecies, with which all haplotypes of C. c. kerguelenensis formed a distinct group in the haplotype network. A new haplotype for C. c. kerguelenensis is reported. Differentiation in haplotype frequencies was found among localities within the distribution of C. c. commersonii, yet the phylogeographic signal was only statistically significant between subspecies. Coalescent-based historical gene flow estimations indicated migration between the northern and southern portions of the species’ range in SA as well as between SA and the FI/IM, but not between these and the KI. The net nucleotide divergence between dolphins from SA and the FI/IM was lower than the recommended threshold value suggested for delimiting subspecies, unlike that found between C. c. commersonii and C. c. kerguelenensis. The results are consistent with the model of post-glacial colonization of KI by South American C. commersonii, followed by an ongoing divergence process and subspecies status. Thus, C. c. kerguelenensis may represent the most recent diversification step of Cephalorhynchus, where isolation from their source population is driving a process of incipient speciation.

Highlights

Past climate fluctuations are known to have influenced the distribution of many species (Hewitt, 2000), as well as their population genetic structure (Collin and de Maintenon, 2002; Taylor and Hellberg, 2006)
Mitochondrial DNA control region haplotypes were successfully amplified and sequenced from skin samples collected in Fitzroy, Chile (n = 7); Bahía Camarones (n = 37), Puerto Deseado (n = 41), Punta Quilla (n = 25), and Monte León (n = 11) along the Argentine coastline; Falkland Islands/Islas Malvinas (FI/IM) (n = 52) and Kerguelen Islands (KI) (n = 24)
The genetic diversity indices we obtained for continental South America (SA) are similar to results from previous work conducted in this area

Summary

Introduction

Past climate fluctuations are known to have influenced the distribution of many species (Hewitt, 2000), as well as their population genetic structure (Collin and de Maintenon, 2002; Taylor and Hellberg, 2006). Changes in the geographic range of southern elephant seals (Mirounga leonina) during the Holocene are thought to have been driven by similar processes (de Bruyn et al, 2009). Such climatic and oceanographic variations have influenced the current distribution patterns of cetacean species. It has been shown that the population expansion of beluga whales (Delphinapterus leucas) into the western Nearctic and their dispersal routes from glacial refuges relates to the retreat of the Pleistocene ice cover (O’Corry-Crowe et al, 1997)

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Results

Conclusion