Did genetic lineage divergence or spatial environmental variance lead to global subspecies differentiation of northern goshawk (Accipiter gentilis)?
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When a widely distributed species undergoes ecological or geological isolation, it tends to divide into subspecies. In general, subspecies differentiation is affected by environmental variance and genetic divergence. But the extent to which these two factors influence subspecies differentiation in species with different distribution ranges and modes of living, might be different. Despite having high breeding habitat fidelity, northern goshawk is a forest raptor that is widely dispersed. We investigated morphological traits in combination with the genetic background of northern goshawk individuals at a large global scale. We also collected genetic, palynological and climatic data to reveal what caused global subspecies differentiation in northern goshawk. Eurasian and North American subspecies populations are thought to have diverged approximately 660,000 years ago to undergo different evolutionary routes, which remarkably facilitated intercontinental subspecies differentiation through genetic lineage divergence. During the last glacial period (18,000 years ago) the different isolation levels of northern goshawk refugia on the continents caused genetic lineage divergences, which, however, are unlikely to have led to subspecies differentiation directly. Spatial environmental variance due to the wide distribution of northern goshawks made an important contribution to subspecies differentiation throughout continents.