Abstract
Understanding the underlying mechanisms of species origin, divergence, and distribution patterns of the intercontinental disjunct taxa has long fascinated botanists. Based on 4,894 genome-wide single-nucleotide polymorphism dataset, we present a molecular phylogenetic reconstruction of genus Corylus (Betulaceae), which have a disjunct distribution between Eurasia and North America (NA). The aim is to explore the speciation patterns and evolutionary relationships of Corylus species by establishing a general phylogenetic framework with extensive sampling. Both the molecular phylogeny inferred from recombination-free dataset and structure analysis support the division of Corylus into four major clades (A–D). Recombination tests and hybridization detection reveal extensive recombination and hybridization events among different clades, which have potentially influenced the speciation process of Corylus. Divergence time estimation indicates that recent common ancestor (MRCA) of Corylus occurred in late Eocene (∼36.38 Ma) and subsequent rapid diversification began during Miocene. Ancestral area reconstruction shows that Corylus originated from southwest China. The arrival of two clades (Clades B and C) to NA was well supported by the long distance dispersal crossing the Bering land bridge. The Himalayas, European-Mediterranean area, and other distribution regions are primarily the recipients of dispersal taxa. Vicariance after dispersal plays an important role in speciation.
Highlights
In the Northern Hemisphere, intercontinental disjunction of related plant species among eastern Asia (EA), Europe, and North America (NA) has long fascinated botanists and biogeographers (Tiffney and Manchester, 2001; Xiang and Soltis, 2001; Donoghue and Smith, 2004; Wen and Ickert-bond, 2009; Xiang et al, 2015)
Despite various interpretations for the disjunction based on different taxa, it has been generally recognized that climatic fluctuations over the Cenozoic and two intercontinental land bridges, i.e., the North Atlantic Land Bridge (NALB) and the Bering land bridge (BLB), have played important roles in shaping current disjunctions of the Northern Hemisphere flora
Mutation and gene recombination provide the original impetus for biological evolution, which is the intrinsic factor of speciation, while selection will externally retain dominant species that can be well suitable for certain ecological conditions
Summary
In the Northern Hemisphere, intercontinental disjunction of related plant species among eastern Asia (EA), Europe, and North America (NA) has long fascinated botanists and biogeographers (Tiffney and Manchester, 2001; Xiang and Soltis, 2001; Donoghue and Smith, 2004; Wen and Ickert-bond, 2009; Xiang et al, 2015). Multiple origins and complex evolutionary patterns of this intercontinental disjunction have been discussed based on fossils, molecular, and geologic evidence. Due to the complex biotic responses to diverse abiotic factors in the Northern Hemisphere, there still remains much to explore about the evolutionary history of the disjunction patterns and the underlying mechanisms of species diversification. The speciation mechanisms may be associated with various factors such as probable gene mutations, potential recombination, and hybridization phenomena, and a series of dispersal and vicariance events. Comprehensive analyses including all these aspects are very few
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