Divergence between Antarctic and South American marine invertebrates: what molecular biology tells us about Scotia Arc geodynamics and the intensification of the Antarctic Circumpolar Current

• Published in: Global and Planetary Change
• Main Authors: Poulin, Elie, González Wevar, Claudio, Díaz Lorca, Angie, Gérard, Karin, Hüne, Mathias
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier 2014
• Subjects: ACC onset and intensification; Central Scotia Sea; COI; Middle Miocene climatic transition; Molecular clock hypothesis (MCH); MtDNA divergence; Antarctic; Antarctic Peninsula; Nacella; Scotia Sea; Southern Ocean; The Antarctic; Antarc*; Antarctica
• Online Access: https://doi.org/10.1016/j.gloplacha.2014.07.017; https://repositorio.uchile.cl/handle/2250/153950

Continental drift processes such as major gateway openings have been historically advocated to explain the distribution of marine benthic taxa in the Southern Ocean (SO). The separation between Antarctic Peninsula and the southern tip of South America together with the onset of the Antarctic Circumpolar Current (ACC) represent the final step for the complete isolation of the Antarctic region. However, there is still controversy concerning the timing and mode of this process, and especially about the role of the Scotia Arc geodynamics in the development of a fully deep and intensified ACC circulation. Based on mitochondrial Cytochrome c Oxidase Subunit I (COI) sequences obtained from different taxa, we performed molecular comparisons between Antarctic and South American relatives to provide independent time estimations of Antarctica's isolation. We include in the analyses congeneric Antarctic and Patagonian near-shore marine benthic invertebrates including indirect developers (Nacella, Yoldia, Sterechinus, and Parbolasia) and brooders (Xymenopsis and Trophonella). Considering the levels of genetic differentiation between relatives from both regions and assuming the molecular clock hypothesis, we estimated the onset of their respective divergence. On one hand, similar levels of genetic distance in broadcast–spawners (7%–8.3%) support the hypothesis that the development of an effective barrier between Antarctica and South America occurred almost simultaneously for these groups. Divergence time estimations based on specific substitution rates indicate that the separation occurred near the Mio-Pliocene transition, long after the physical separation of both continents. Genetic distance and divergence time estimation in direct developers indicate an older separation time, close to the mid-Miocene. Even when the analyzed groups included both broadcast–spawners and brooder organisms, the divergence between Antarctic and South America lineages rather than being related to processes of continental drift, seems to be ...