Quaternary phylogeography: the roots of hybrid zones |
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Authors: | Godfrey M Hewitt |
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Institution: | (1) Biological Sciences, UEA, Norwich, NR4 7TJ, UK |
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Abstract: | The older history of hybrid zones is explored through consideration of recent advances in climatology, paleontology and phylogeography
in the Late Cenozoic, particularly the Quaternary Period with its major climatic cycles. The fossil record shows that these
ice ages and their nested millennial oscillations caused substantial changes in species distributions and with genetic evidence
allows deduction of refugia and colonization routes in arctic, temperate, desert and tropical regions. The age of divergence
between hybridizing lineages varies from the Late Pleistocene to the Late Miocene, implying much range change and varying
selection on sister lineages. Hybridizing lineages in the Tropical and Temperate regions range in age from young to old, but
those studied in the Arctic are no more than a few ice ages old and their refugial roots are not clear. Mid to low latitude
regions often show parapatric patchworks of lineages and multiple refugia stable through many climatic oscillations. Particular
hybrid zones may have formed more than once; while some expansions were not the same, producing reticulation and introgression
in previous glacial cycles. Hybrid-zone roots are complex and deep, and considerations of their complexity can reveal evolutionary
pathways of species. They are indeed windows on evolution. |
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