Population genetics under the Massenerhebung effect: The influence of topography on the demography of Acer morrisonense

Abstract

Aim The Massenerhebung effect (Mass elevation effect) refers to heat‐ or wind‐driven altitudinal distribution patterns of temperature‐dependent parameters among massifs with narrower range and lower elevation around peripheral and isolated mountains compared to core and continuous ones. Although common in ecology, this effect is rarely discussed in population genetics. Here, we use genetic markers to reveal population genetic patterns and also test the mountain‐ and sky‐barrier hypotheses relevant to the Massenerhebung distribution pattern of Acer morrisonense in Taiwan's rugged topography and varied local climates. Location The alpine and cloud forest of Taiwan. Taxon Acer morrisonense Hayata. Methods Two chloroplast DNA (cpDNA) fragments and 17 expressed sequence tag‐simple sequence repeat (EST‐SSR) loci, respectively, from 200 to 286 individuals were used to elucidate the phylogeographic pattern of pollen and seed dispersal of A. morrisonense. These data were combined with ecological niche modeling (ENM) to infer distribution range shifts and refugia. We also correlated the genetic‐divergence indices with spatial factors to clarify latitudinal and altitudinal effects on genetic diversity. Results The incongruent phylogeographic patterns of genetic distributions between nuclear and cpDNA markers indicate unhindered pollen flow but spatially constrained seed dispersal. Taken together with ENM, the genetic pattern further reflects historical colonization from central‐mountain refugia to edges since the Holocene. The Massenerhebung reduces the gene flow by the surrounding mountains and also causes lower genetic diversity compared to central alpine populations. Main conclusions This study is the first to reveal the influence of Massenerhebung effect on cpDNA genetic structure of montane trees and reflect the spatial trends of seed dispersal. This population genetic pattern can also be attributed to the demography‐related range shifts with paleoclimate fluctuations under complex mountain topography, supporting the mountain‐barrier hypothesis. The results have important implications for conserving the genetic diversity of species with a wide altitudinal distribution range.

Environmental Heterogeneity Leads to Spatial Differences in Genetic Diversity and Demographic Structure of Acer caudatifolium

“…According to PNC, the distribution range of the most suitable habitat varies temporally with climate change. ENM in this study indicated that A. caudatifolium upward shifted to mountain ranges after the LGM ( Figure 2 ), in contrast to the downward expansion of A. morrisonense from high mountains (Figure 5 of [ 7 ]). Among all maples in Taiwan, these two species have the closest phylogenetic relationship but are not sister species [ 12 , 13 , 14 ].…”

“…Like A. morrisonense , the chlorotypes of A. caudatifolium are differentiated from north to south (Figure 2b of [ 7 ]). However, the north-south differentiation of A. caudatifolium resulted from the collection of different ancient populations ( Figure 2 ), whereas divergent alpine refugia were responsible for the differentiation of A. morrisonense (Figure 5 of [ 7 ]).…”

“…Gene flow and demographic dynamics may be subject to spatial and environmental influences [ 5 , 6 ]. Given the rugged terrain distribution and steep environmental differences in mountain regions, the seed dispersal and pollen flow of mountain plants and their temporal range dynamics may jointly reflect topography and climate [ 7 ]. According to the center-periphery hypothesis [ 8 , 9 ], range change (e.g., spatial expansion) may be more adaptively constrained at range margins [ 10 ].…”

“…According to the center-periphery hypothesis [ 8 , 9 ], range change (e.g., spatial expansion) may be more adaptively constrained at range margins [ 10 ]. The core-to-edge decline of an adaptive genetic variation supports seed-based dispersal of mountainous maples in Taiwan rather than pollen flow [ 7 ]. However, whether the seed dispersal of maples in the same area but at lower elevations is also spatially and climate-related under climate change remains unknown.…”

“…Due to high seed dispersibility, the population genetic differentiation of A. caudatifolium is expected to be low. However, according to the mountain barrier hypothesis, mountains may hinder long-distance seed dispersal of low-elevation plants [ 7 ], resulting in population differentiation among mountain islands. In addition, the varied mountainous environment could affect population structure, interrupting gene flow.…”