Abstract

Spatial scale partly explains the differentiated effects of habitat fragmentation on plant biodiversity, but the mechanisms remain unclear. To investigate the effects of habitat fragmentation on genetic diversity at different scales, we sampled Actinidia chinensis Planch. at broad and fine scales, China. The broad-scale sampling included five mountain populations and one oceanic island population (Zhoushan Archipelago), and the fine-scale sampling covered 11 lake islands and three neighboring land populations in Thousand-Island Lake (TIL). These populations were genotyped at 30 microsatellite loci, and genetic diversity, gene flow, and genetic differentiation were evaluated. Genetic differentiation was positively related to geographical distance at the broad scale, indicating an isolation-by-distance effect of habitat fragmentation on genetic diversity. The oceanic population differed from the mainland populations and experienced recent bottleneck events, but it showed high gene flow with low genetic differentiation from a mountain population connected by the Yangtze River. At the fine scale, no negative genetic effects of habitat fragmentation were found because seed dispersal with water facilitates gene flow between islands. The population size of A. chinensis was positively correlated with the area of TIL islands, supporting island biogeography theory, but no correlation was found between genetic diversity and island area. Our results highlight the scale-dependent effects of habitat fragmentation on genetic diversity and the importance of connectivity between island-like isolated habitats at both the broad and fine scales.

Highlights

  • Habitat fragmentation caused by anthropogenic activities is considered a key factor threatening biodiversity[1,2]

  • For the Thousand-Island Lake (TIL) fine-scale analysis, to test island biogeography theory, we investigated the abundance of A. chinensis on all TIL islands, except for the largest (JSI and MGI) islands, where population size was estimated by multiplying the average number of plants in three randomly sampled bays by the number of bays (Supplementary Table S1 and Fig. 1)

  • The genetic diversity of A. chinensis in TPZ, XHZ, and TIL-M was significantly greater than that in YAC, SYH, and Zhoushan Archipelago (ZSA), and the ZSA population significantly differed from the TPZ, XHZ, and TIL-M populations but not from YAC and SYH (Table 1)

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Summary

Introduction

Habitat fragmentation caused by anthropogenic activities is considered a key factor threatening biodiversity[1,2]. Habitat fragmentation affects biodiversity by increasing isolation between populations and decreasing effective population size, which alters inbreeding and genetic drift within populations, as well as gene-flow frequency between populations[3,4,5]. This mechanism can be explained by island biogeography theory[6,7]. Longdistance dispersal of seeds can promote gene flow and reduce the genetic distance between populations on a broad scale[32]. Spatial scale and species characteristics, such as dioecy, a long lifespan, and long-distance dispersal ability, should be considered when studying the effects of habitat fragmentation on genetic diversity

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