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Uplift-driven diversification in the Hengduan Mountains, a temperate biodiversity hotspot - PubMed

  • ️Sun Jan 01 2017

Uplift-driven diversification in the Hengduan Mountains, a temperate biodiversity hotspot

Yaowu Xing et al. Proc Natl Acad Sci U S A. 2017.

Abstract

A common hypothesis for the rich biodiversity found in mountains is uplift-driven diversification-that orogeny creates conditions favoring rapid in situ speciation of resident lineages. We tested this hypothesis in the context of the Qinghai-Tibetan Plateau (QTP) and adjoining mountain ranges, using the phylogenetic and geographic histories of multiple groups of plants to infer the tempo (rate) and mode (colonization versus in situ diversification) of biotic assembly through time and across regions. We focused on the Hengduan Mountains region, which in comparison with the QTP and Himalayas was uplifted more recently (since the late Miocene) and is smaller in area and richer in species. Time-calibrated phylogenetic analyses show that about 8 million y ago the rate of in situ diversification increased in the Hengduan Mountains, significantly exceeding that in the geologically older QTP and Himalayas. By contrast, in the QTP and Himalayas during the same period the rate of in situ diversification remained relatively flat, with colonization dominating lineage accumulation. The Hengduan Mountains flora was thus assembled disproportionately by recent in situ diversification, temporally congruent with independent estimates of orogeny. This study shows quantitative evidence for uplift-driven diversification in this region, and more generally, tests the hypothesis by comparing the rate and mode of biotic assembly jointly across time and space. It thus complements the more prevalent method of examining endemic radiations individually and could be used as a template to augment such studies in other biodiversity hotspots.

Keywords: biogeography; dispersal; molecular clocks; speciation; vascular plants.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.
Fig. 1.

Map of the Hengduan Mountains region in relation to the QTP and Himalayas.

Fig. 2.
Fig. 2.

Assembly of regional floras by colonization and in situ speciation events in 19 plant clades, inferred from ancestral-range reconstructions on time-calibrated molecular phylogenies. Shaded regions indicate the 5 to 95% quantile intervals for the cumulative number of events through time from 500 pseudoreplicated joint biogeographic histories designed to account for phylogenetic uncertainty (discussed in the text). Panels on the right focus on the last 20 Ma, in which differences in regional assembly are most apparent. In the Hengduan Mountains region, cumulative in situ speciation overtakes colonization about 8 Ma, whereas for the Himalayas–QTP colonization remains the dominant process. In situ speciation thus seems to have played a disproportionately large role in assembling the Hengduan Mountains flora since the late Miocene compared with the Himalayas–QTP, consistent with the theory of uplift-driven diversification in the Hengduan Mountains region.

Fig. 3.
Fig. 3.

Rolling estimates of in situ speciation rates through time for the Hengduan Mountains and Himalayas–QTP regions from inferred biogeographic histories of 19 plant clades. Lines indicate medians and shaded areas indicate 5 to 95% quantile intervals from 500 pseudoreplicated joint histories designed to account for phylogenetic uncertainty (discussed in the text). Regional rates begin to diverge about 8 Ma, with the Hengduan Mountains showing a striking increase in in situ speciation relative to the Himalayas–QTP.

Fig. 4.
Fig. 4.

Rolling estimates of colonization rates through time for the Hengduan Mountains, Himalayas–QTP, and temperate/boreal East Asia regions from inferred biogeographic histories of 19 plant clades. Lines indicate medians and shaded areas indicate 5 to 95% quantile intervals from 500 pseudoreplicated joint histories designed to account for phylogenetic uncertainty (discussed in the text). Dispersal between the Hengduan Mountains and Himalayas–QTP increases in the last 2 Ma relative to dispersal between either region and temperate/boreal East Asia.

Fig. 5.
Fig. 5.

Reconstructions of ancestral geographic range (Left) and net diversification rate (Right) on the maximum clade credibility tree, with branch lengths set to posterior means, for Rhododendron. Ancestral ranges are maximum-likelihood estimates at the start and end of each branch. Net diversification values are branch-segment means of the posterior distribution estimated by BAMM. Filled circles on the right indicate branches that appear in the 95% credible set of distinct shift configurations, with the size and label of a circle indicating the cumulative probability of the branch over all configurations in the credible set. On the left, the marginal odds ratio for a shift in diversification regime along a branch is drawn for branches where the ratio exceeds 20. Geographic regions are coded as follows: AUS, Australasia; CWA, central/western Asia; EAS, temperate-boreal East Asia; EUR, Europe; HEN, Hengduan Mountains; HIM, Himalayas–QTP; NAM, North America; and SEA, Southeast Asia. Hengduan species cluster primarily in two clades, both of which show evidence of ancestral shifts to higher diversification rate in the mid-to-late Miocene.

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