Abstract
BackgroundThe broad continuum between tropical and temperate floras in Eastern Asia (EAS) are thought to be one of the main factors responsible for a prominent species diversity anomaly of temperate plants between EAS and eastern North America (ENS). However, how the broad continuum and niche evolution between tropical and temperate floras in EAS contributes to lineage divergence and species diversity remains largely unknown.ResultsPopulation genetic structure, demography, and determinants of genetic structure [i.e., isolation-by-distance (IBD), isolation-by-resistance (IBR), and isolation-by-environment (IBE)] of Machilus thunbergii Sieb. et Zucc. (Lauraceae) were evaluated by examining sequence variation of ten low-copy nuclear genes across 43 populations in southeast China. Climatic niche difference and potential distributions across four periods (Current, mid-Holocene, the last glacial maximum, the last interglacial) of two genetic clusters were determined by niche modelling. North and south clusters of populations in M. thunbergii were revealed and their demarcation line corresponds well with the northern boundary of tropical zone in China of Zhu & Wan. The divergence time between the clusters and demographic expansion of M. thunbergii occurred after the mid-Pleistocene climate transition (MPT, 0.8–1.2 Ma). Migration rates between clusters were asymmetrical, being much greater from north to south than the reverse. Significant effects of IBE, but non-significant effects of IBD and IBR on population genetic divergence were detected. The two clusters have different ecological niches and require different temperature regimes.ConclusionsThe north-south genetic differentiation may be common across the temperate-tropical boundary in southeast China. Divergent selection under different temperature regimes (possibly above and below freezing temperature in winter) could account for this divergence pattern. The broad continuum between tropical and temperate floras in EAS may have provided ample opportunities for tropical plant lineages to acquire freezing tolerance and to colonize the temperate regions during the late-Cenozoic global cooling. Our findings shed deeper insights into the high temperate plant species diversity in EAS.
Highlights
The broad continuum between tropical and temperate floras in Eastern Asia (EAS) are thought to be one of the main factors responsible for a prominent species diversity anomaly of temperate plants between EAS and eastern North America (ENS)
The anomaly in species diversity has been associated with a few factors in EAS, such as high climatic and topographic heterogeneity, a stronger monsoon climate, and the broad continuum between tropical and temperate floras [3, 4, 7], which have stimulated many hypothesis-based phylogenetic and phylogeographic studies to elucidate the mechanisms underlying this prominent pattern [10,11,12,13]
Negative and mostly non-significant Tajima’s D values and Fu and Li’s D* and F* values were detected at the majority of 10 nuclear loci (Table S2)
Summary
The broad continuum between tropical and temperate floras in Eastern Asia (EAS) are thought to be one of the main factors responsible for a prominent species diversity anomaly of temperate plants between EAS and eastern North America (ENS). Owing to the general similarities in climate, vegetation types, and floristic composition between Eastern Asia (EAS) and eastern North America (ENA), a prominent species diversity anomaly of temperate plants between them has been bewildering generations of evolutionary biologists and ecologists [1,2,3,4,5,6,7] This phenomenon is even more intricate in view of the fact that the contemporary floras of the two regions are largely derived from a single paleoflora, the “Boreotropical flora”, that was broadly distributed across the Northern Hemisphere during the early Cenozoic [8, 9]. How the broad continuum between tropical and temperate floras contributes to the anomaly between EAS and ENA has received much less attention and seldom been tested explicitly
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
