The evolutionary history of shearwaters: genomic analyses to resolve a radiation of pelagic seabrids
[eng] How populations differentiate and become new species is a foundational question to the field of evolutionary biology and has important implications for the generation of both local and global patterns of species-level biodiversity. Ernst Mayr emphasised the importance of geographical isolation...
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| Format: | doctoral thesis |
| Status: | Published version |
| Publication Date: | 2021 |
| Country: | España |
| Institution: | Universidad de Barcelona |
| Repository: | Dipòsit Digital de la UB |
| OAI Identifier: | oai:diposit.ub.edu:2445/183003 |
| Online Access: | https://hdl.handle.net/2445/183003 http://hdl.handle.net/10803/673437 |
| Access Level: | Open access |
| Keyword: | Filogènia Genètica de poblacions Biogeografia Genòmica Ocells marins Phylogeny Population Genetics Biogeography Genomics Sea birds |
| Summary: | [eng] How populations differentiate and become new species is a foundational question to the field of evolutionary biology and has important implications for the generation of both local and global patterns of species-level biodiversity. Ernst Mayr emphasised the importance of geographical isolation as a driver of speciation: “populations in separate locations begin a process of differentiation, and once differentiation is sufficient the populations have become two species”. In marine environments, the lack of obvious physical barriers would suggest that panmixia, especially in highly mobile species, or isolation-by-distance, in other cases, will prevail. However, there is some counterintuitive evidence of fine-scale differentiation among populations and species in a number of mobile marine organisms, a phenomenon that has been described as the “marine species paradox”. Seabirds of the order Procellariiformes present some of the most extreme examples of this paradox. On the one hand, Procellariiformes are highly mobile pelagic seabirds with a high dispersal ability and perform some of the longest animal migrations on Earth. On the other hand, they show high philopatry to their breeding grounds, which is expected to limit gene flow and therefore reinforce genetic differentiation. This thesis aims to gain insights into the patterns and processes that contribute to genetic and phenotypic diversification, speciation and dispersal across multiple evolutionary timescales. To this end, I focus on shearwaters (Calonectris, Puffinus and Ardenna), a globally distributed and threatened group of Procellariiformes. Through an integrative approach combining two types of phylogenomic markers, which evolve at different nucleotide substitution rates, and state-of-the-art phylogenetic and introgression analyses, I inferred a robust phylogeny. This approach allowed to discover that the majority of the phylogenetic conflict in shearwaters is generated by high levels of incomplete lineage sorting (ILS) due to rapid speciation events. Divergence time estimation analyses highlighted a severe impact of the Pliocene marine megafauna extinction on shearwaters, probably caused by a sudden reduction in the availability of coastal habitat. Subsequently, the late Pliocene-early Pleistocene was inferred as a period of high and rapid speciation and dispersal, probably promoted by Pleistocene climatic shifts. Biogeographic analyses showed that surface ocean currents promote species dispersal and founder events are a main mode of speciation in shearwaters. Our analysis, combining genomic data with morphological and ecological evidence, did not support any of the current taxonomic classifications for the North Atlantic and Mediterranean Puffinus shearwaters, and so I propose a more accurate taxonomy for the group. Moreover, the detection of fine-scale genetic structure within Puffinus shearwater species, highlights the need for management of evolutionary significant units below the species level. Population genomics analyses identified genetic drift as the major process shaping the genomic landscapes of divergence. In conclusion, the marriage of these various investigations identifies a prevalence of ILS across different timescales, highlights the important role of paleoceanographic events in promoting diversification, and demonstrates the importance of neutral evolution at driving population differentiation in pelagic seabirds. Overall, this thesis showcases the use of multiple genomic approaches, leveraging phylogenetic and population genetic analyses across multiple timescales, to shed light on the evolutionary history of shearwaters. |
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