| Summary: | In this thesis we studied how the changes in the climate determine the distribution, diversity and conservation of a very representative group of the Arctic avifauna, the shorebirds. In the first chapter we explored the changes in the ranges of the Arctic shorebirds during the Pleistocene glacial cycles, and how that shaped the current diversity of subspecies. We combined species distribution models, fossil evidence and estimation on the distribution of the tundra to compare the distribution of the breeding and wintering ranges between the present (representing an interglacial period) and the last glacial maximum (LGM) ca. 21,000 years ago. We found that the species with described subspecies predominantly experienced fragmentation of their breeding ranges during glacial cycles, especially during the glacial periods. On the other hand, most of the monotypic species maintained continuous breeding ranges during glacial and interglacial periods. This supports that the Pleistocene glacial cycles provided a mechanism for allopatric speciation that originated the current pattern of intraspecific diversity in these species. Additionally, we recovered that, despite changes in the breeding ranges, there was an overall lack of overlap with the wintering ranges and the long-distance migration between them remain uninterrupted during glacial periods. This migration likely contributed to originate and maintain the diversity between populations over multiple glacial cycles. While the first chapter provided a spatial mechanism of diversification during the glacial cycles, this needs to be confirmed by genetic data to support that the timing of this diversification falls within the Pleistocene. To better estimate divergence time within species, we performed the most comprehensive calibration of the mitochondrial molecular clock in birds to date. We included full mitochondrial genomes from 621 bird species and 25 reliable fossil calibrations and estimated the substitution rates for each of the mitochondrial genes in every lineage ...
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