Out‐of‐India dispersal of Paliurus (Rhamnaceae) indicated by combined molecular phylogenetic and fossil evidence

Abstract

Paliurus (Rhamnaceae) is a small genus with a narrow and disjunct distribution in East Asia and the Mediterranean. Fossil evidence from the Late Cretaceous to the present suggests it once had a broad geographic distribution, encompassing parts of India, North America, Asia, and Europe. To reconstruct the evolutionary history of Paliurus and understand the origin of the disjunction observed today in the Northern Hemisphere, phylogenetic and biogeographical reconstructions were performed based on ITS, trnL-F, and rbcL sequences. Paliurus is shown to be a monophyletic genus, which could be divided into two clades as suggested by previous studies. Biogeographical inference integrated with fossil information indicates that the origin and dispersal pattern of the genus coincide with the "Out-of-India" hypothesis. The genus may have originated in India or other parts of Gondwana and then dispersed to East Asia after the collision of the Indian subcontinent with Eurasia, and to North America via the Bering land bridge. Paliurus appears to have reached the Mediterranean region in the late Oligocene following closure of the Turgai Strait. The uplift of the Qinghai-Tibet Plateau and the advent of drying and cooling climates during the Miocene may have fragmented the distribution of the genus, shaping the biogeographical patterns observed today. Paliurus populations in different regions either became extinct or adapted to changes in local ecological conditions following global climatic shifts through geological time.

The influence of the Gondwanan breakup on the biogeographic history of the ziziphoids (Rhamnaceae)

“…However, Chen et al. () proposed an ‘out of India’ hypothesis for Paliurus , claiming that Paliurus (and potentially the whole tribe) migrated with the Indian plate from Gondwana to Asia. This is additionally supported by the presence of a fossil closely related to extant Paliurus from the Palaeogene/Cretaceous boundary in India.…”

“…and Ziziphus sp. from India, and † Archeopaliurus from South America (Chen et al., ; Correa et al., ; Singh, Prasad, Kumar, Rana, & Singh, ). Younger fossils of the ziziphoids are, however, also distributed in the Northern Hemisphere, such as multiple Eocene (and younger) taxa of Ziziphus and Paliurus (Burge & Manchester, ; Li et al., ), and the Late Miocene fossils of Ceanothus and Distigouania (Axelrod, , ; Chambers & Poinar, ).…”

“…Furthermore, we coded India separately, as this Gondwanan fragment drifted northward in absolute isolation, and might have acted as a raft, as previously hypothesised by Chen et al. (). We allowed a maximum combination of six ancestral areas (as this is the minimum given by the pantropical distribution of Colubrina asiatica (L.) Brongn).…”

“…The family was recently revised, and many DNA sequences were produced (Hauenschild, Matuszak, Muellner‐Riehl, & Favre, ; Hauenschild, Salazar, Muellner‐Riehl, & Favre, ,b; Kellermann & Udovicic, ; Richardson, Fay, Cronk, Bowman, & Chase, ; Richardson, Fay, Cronk, & Chase, ). More than 25 fossil taxa are described within the family, rather evenly distributed through time and across main lineages, e.g., in Paliureae and Rhamneae (Chen et al., ; Correa, Jaramillo, Manchester, & Gutierrez, ). The family consists of three major clades, the large rhamnoid (300+ species) and ziziphoid (600+ species) clades, as well as the species‐poor ampeloziziphoid (10+ species) clade (Richardson, Fay, Cronk, & Chase, ).…”

Role of the Qinghai-Tibetan Plateau uplift in the Northern Hemisphere disjunction: evidence from two herbaceous genera of Rubiaceae

“…Climate cooling began in the Middle Eocene (but see Prothero, 1994 14 for an exception) and subsequent aridification in the Miocene–Pliocene are commonly accepted as the main causes of disjunctions between floristic elements of eastern Asia and western Eurasia from the once widespread Cenozoic flora 1 , 2 , 4 , 15 – 18 . The important contribution of the uplift of the QTP and downstream influences to these processes has been recognized 19 – 22 . By changing the regional climate and creating a physical barrier to flora exchange, the uplift had various impacts on the biodiversity of the QTP and adjacent areas including extinctions, floristic reorganizations and adaptive radiation 23 – 25 .…”