Spatial Genetic Structure Patterns of Phenotype-Limited and Boundary-Limited Expanding Populations: A Simulation Study

Xiangjiang Zhan,Dunwu Qi,Bin Lu,Qian Wang,Qiang Dai,Norman Johnson,Jinzhong Fu

doi:10.1371/journal.pone.0085778

Abstract

Range expansions may create a unique spatial genetic pattern characterized by alternate genetically homogeneous domains and allele frequency clines. Previous attempts to model range expansions have mainly focused on the loss of genetic diversity during expansions. Using individual-based models, we examined spatial genetic patterns under two expansion scenarios, boundary-limited range expansions (BLRE) and phenotype-limited range expansions (PhLRE). Our simulation revealed that the genetic diversity within populations lost quickly during the range expansion, while the genetic difference accumulated between populations. Consequently, accompanying the expansions, the overall diversity featured a slow decrease. Specifically, during BLREs, high speed of boundary motion facilitated the maintenance of total genetic diversity and sharpened genetic clines. Very slight constraints on boundary motion of BLREs drastically narrowed the homogeneous domains and increased the allele frequency fluctuations from those levels exhibited by PhLREs. Even stronger constraints, however, surprisingly brought the width of homogeneous domains and the allele frequency fluctuations back to the normal levels of PhLREs. Furthermore, high migration rates maintained a higher total genetic diversity than low ones did during PhLREs. Whereas, the total genetic diversities during BLREs showed a contrary pattern: higher when migration was low than those when migration was high. Besides, the increase of migration rates helped maintain a greater number of homogeneous domains during PhLREs, but their effects on the number of homogeneous domains during BLREs were not monotonous. Previous studies have showed that the homogenous domains can merge to form a few broad domains as the expansion went on, leading to fewer homogeneous domains. Our simulations, meanwhile, revealed that the range expansions could also rebuild homogeneous domains from the clines during the range expansion. It is possible that that the number of homogeneous domains was determined by the interaction of merging and newly emerging homogeneous domains.

Highlights

Species range expansion is an important biological process, which has shaped global biodiversity patterns
We aim to explore different spatial patterns of genetic variations, the number of genetically homogeneous domains and the fluctuations of allele frequencies, at the expansion front generated by the phenotype-limited range expansions (PhLRE) and boundary-limited range expansions (BLRE) with varied speeds of boundary motion
Discussion (a) The difference between PhLREs and BLREs Our simulations showed stripe-like genetic patterns in expanded populations, which were equivalent to the genetic sectoring patterns established by previous studies [20,21,23]

Summary

Introduction

Species range expansion is an important biological process, which has shaped global biodiversity patterns. A BLRE is typically a slow process, which happens when species expand their ranges along with the emergence of new, accessible, unoccupied, suitable habitat outside their current distribution areas. Several previous studies have investigated the spatial genetic consequences of PhLREs. In general, a species’ range expansion is often accompanied by loss of genetic diversity because of the founder effect [2,17,18,19]. We aim to explore different spatial patterns of genetic variations, the number of genetically homogeneous domains and the fluctuations of allele frequencies, at the expansion front generated by the PhLREs and BLREs with varied speeds of boundary motion. The impacts of migration and reproduction on the spatial genetic patterns were examined

Methods

Results

Discussion