Abstract
Quaternary climate fluctuations have profoundly affected the current distribution patterns and genetic structures of many plant and animal species in the Qinghai-Tibetan Plateau (QTP) and adjacent mountain ranges, e.g. Tianshan (TSR), Altay, etc. In this greater area disjunct distributions are prominent but have nevertheless received little attention with respect to the historical processes involved. Here, we focus on Pedicularis kansuensis to test whether the current QTP and TSR disjunction is the result of a recent Holocene range expansion involving dispersal across arid land bridge(s) or a Pleistocene range fragmentation involving persistence in refugia. Two chloroplast DNA spacers were sequenced for 319 individuals from 34 populations covering the entire distribution range of this species in China. We found a total of 17 haplotypes of which all occurred in the QTP, and only five in the TSR. Overall genetic diversity was high (HT = 0.882, HS = 0.559) and higher in the QTP than in the TSR. Genetic differentiation among regions and populations was relatively low (GST = 0.366) and little evidence for a phylogeographic pattern emerged. The divergence times for the four main lineages could be dated to the early Pleistocene. Surprisingly, the two ubiquitous haplotypes diverged just before or around the Last Glacial Maximum (LGM) and were found in different phylogenetic lineages. The Species Distribution Model suggested a disappearance of P. kansuensis from the TSR during the LGM in contrast to a relatively constant potential distribution in the QTP. We conclude that P. kansuensis colonized the TSR after the LGM. The improbable long-distance dispersal by wind or water across arid land seed flow may well have had birds or men as vector.
Highlights
Tectonic events and climate fluctuations have profoundly shaped the current distribution patterns and genetic structures of many plant and animal species in temperate zones of the Northern Hemisphere [1,2,3,4]
The level and spatial distribution of genetic diversity within a species is dependent on the combination of life-history traits, e.g. longevity, breeding system [26,27], which can mask the genetic imprint of historical processes
Leaf tissue of P. kansuensis was collected from 34 populations across the Qinghai-Tibetan Plateau (QTP) and the Tianshan region (TSR) in western China (Table 1)
Summary
Tectonic events and climate fluctuations have profoundly shaped the current distribution patterns and genetic structures of many plant and animal species in temperate zones of the Northern Hemisphere [1,2,3,4]. The present day distribution of plant and animal species is strongly influenced by these historical processes which potentially and iteratively led to range shifts, range expansion, range contraction and/or range fragmentation. In this context, a disjunct distribution could either be the result of long-distance dispersal from a source area into a suitable new area [15,16,17,18] or the consequence of disruption of the previously continuous distribution range [19,20]. The level and spatial distribution of genetic diversity within a species is dependent on the combination of life-history traits, e.g. longevity, breeding system [26,27], which can mask the genetic imprint of historical processes
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