Advances in biogeography in the age of a new modern synthesis

Abstract

Biogeography is a highly interdisciplinary field that integrates evidence from systematics, paleontology, geology, and ecology to study the patterns and processes shaping the distributions of life over a wide range of spatial and temporal scales (Lomolino et al., 2004; Wen et al., 2013). The last two decades have been an exciting period for the development of biogeography, with major advances in biogeographic methods, phylogenomics, phylogeography, big data, biodiversity science, ecology, paleontology, and geology (Ree & Smith, 2008; Ronquist & Sanmartín, 2011; Wen et al., 2013, 2017; Matzke, 2014). Recently, there have been calls for the integration of various approaches, for example, historical‐versus‐ecological‐oriented (Wiens & Donoghue, 2004) and pattern‐versus‐process‐oriented (Ebach & Tangney, 2007), promoting statistical phylogeography (Knowles & Maddison, 2002), and linking plant and ecosystem functional biogeography (Reichstein et al., 2014). Parametric or model‐based statistical approaches have been developed in biogeography that incorporate biogeographic processes such as dispersal, range expansion, or extinction for the inference of range evolution (Ree & Sanmartín, 2009). Recent developments in phylogenomic tools (Zimmer & Wen, 2015) are breathing new life into integrative biogeography, providing a more robust phylogenetic framework (Wen et al., 2013). Today, biogeography is at the era of a new modern synthesis that incorporates data from phylogenetics/phylogenomics, ecology, paleobiology, population biology, and geology, with new analytical tools. We herein present the special issue “Advances in biogeography in the age of a new modern synthesis,” which features 12 papers. Four papers focus on the classical Asian–New World biogeographic disjunctions (Wen, 1999; Wen et al., 2010, 2016). Valcárcel & Wen (2019) employ the chloroplast genome sequences and integrate fossil evidence to tackle the deep continental Asian radiation of the core Araliaceae clade and discuss the multiple biogeographic disjunctions between eastern Asia and the New World. Liu et al. (2019) employ the complete chloroplast genome and ribosomal DNA repeat sequences through the genome skimming approach to explore the evolutionary diversification of the Photinia complex of Rosaceae, which was considered to be disjunctly distributed in subtropical to tropical Asia and the Neotropics. The new phylogenomic framework shows that the Neotropical “Photinia” diverged early from a large New World clade, while the Asian Photinia is more closely related to other Asian taxa. The tribe Maleae of Rosaceae had an early New World diversification and subsequently diversified in Asia. Zhang et al. (2019b) conduct plastome phylogenomic analyses of Torreya and infer the divergence between the eastern North American T. taxifolia with its eastern Asian relatives in the late Miocene, but a much younger disjunction is inferred between the western North American T. californica and the eastern Asian T. grandis. The authors argue for the climatic oscillations and environmental changes during and after the late Tertiary in shaping up the intercontinental biogeography of Torreya. Lee et al. (2019) explore the eastern Asian‐North American biogeographic disjunctions in the small subfamily Orontioideae of Araceae using an extensive taxon sampling. The disjunction in the eastern Asian‐eastern North American Symplocarpus was dated to be 4.5–1.4 Ma during the Pliocene to the Pleistocene, while that between eastern Asia and western North America in Lysichiton was estimated to be 1.9–0.5 Ma during the Pleistocene, supporting the Bering land bridge biogeographic connection (Wen et al., 2016; Graham, 2018). The phylogenetic results with the dense taxon sampling also reveal that the taxonomy of eastern Asian Symplocarpus needs to be reassessed. The two papers by Li et al. (2019) and Tang et al. (2019) shed insights into the broader biogeographic disjunctions of the Northern Hemisphere (Donoghue & Moore, 2003; Harris et al., 2017). Li et al. (2019) report a well‐resolved phylogeny of the maple genus Acer, a well‐known tree lineage of the Northern Hemisphere, using over 500 nuclear genes from the next‐gen anchored hybrid enrichment approach. Eastern Asia is the current center of diversity of Acer, and it was also inferred to be the ancestral area. Acer subsequently spread to North America and Europe/western Asia since the early Eocene. The two disjunctions between eastern Asia and eastern North America were dated to be in the Miocene. Tang et al. (2019) report on fruit macrofossils of the extinct genus Lagokarpos from Tibet, the first record of the genus in Asia. Lagocarpos was previously only known from western North America and Germany from the latest Paleogene to the early middle Eocene. This new record in Tibet supports the biogeographic link between the Qinghai‐Tibet Plateau (QTP) and other floras of the Northern Hemisphere as well as the tropical or subtropical climate in central QTP during the Paleogene (also see Wen et al., 2014). Two studies report the remarkable worldwide geographic success of plant diversifications. Otero et al. (2019) explore the long‐distance dispersals as mechanisms for several major biogeographic disjunctions (Madrean‐Tethyan, amphitropical, and trans‐Pacific) in the diversification of Omphalodeae of Boraginaceae, as facilitated by epizoochorous traits. Martín‐ Bravo et al. (2019) reconstruct the worldwide biogeographic