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Abstract Migratory divides, hybrid zones between populations that use different seasonal migration routes, are hypothesised to contribute to speciation. Specifically, relative to parental species, hybrids at divides are predicted to exhibit (1) intermediate migratory behaviour and (2) reduced fitness as a result. We provide the first direct test of the second prediction here with one of the largest existing avian tracking datasets, leveraging a divide between Swainson's thrushes where the first prediction is supported. Using detection rates as a proxy for survival, our results supported the migratory divide hypothesis with lower survival rates for hybrids than parental forms. This finding was juvenile‐specific (vs. adults), suggesting selection against hybrids is stronger earlier in life. Reduced hybrid survival was not explained by selection against intermediate phenotypes or negative interactions among phenotypes. Additional work connecting specific features of migration is needed, but these patterns provide strong support for migration as an ecological driver of speciation.
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Migratory divides coincide with reproductive barriers across replicated avian hybrid zones above the Tibetan Plateau
Abstract Migratory divides are proposed to be catalysts for speciation across a diversity of taxa. However, it is difficult to test the relative contributions of migratory behaviour vs. other divergent traits to reproductive isolation. Comparing hybrid zones with and without migratory divides offers a rare opportunity to directly examine the contribution of divergent migratory behaviour to reproductive barriers. We show that across replicate sampling transects of two pairs of barn swallow (Hirundo rustica) subspecies, strong reproductive isolation coincided with a migratory divide spanning 20 degrees of latitude. A third subspecies pair exhibited no evidence for a migratory divide and hybridised extensively. Within migratory divides, overwintering habitats were associated with assortative mating, implicating a central contribution of divergent migratory behaviour to reproductive barriers. The remarkable geographic coincidence between migratory divides and genetic breaks supports a long‐standing hypothesis that the Tibetan Plateau is a substantial barrier contributing to the diversity of Siberian avifauna.
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- PAR ID:
- 10457088
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Ecology Letters
- Volume:
- 23
- Issue:
- 2
- ISSN:
- 1461-023X
- Format(s):
- Medium: X Size: p. 231-241
- Size(s):
- p. 231-241
- Sponsoring Org:
- National Science Foundation
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