How can geographic isolation change

It effectively isolate the mating of individuals of population related to that species. The geographic isolation of species occurs, when the geographical barriers work as demarcating agent. The barriers of mating allow the isolated species to start to mate in different ways compared to the previous. This event is a proponent tool for allopatric speciation , It has been hypothesized that the adaptive genetic changes that has accumulated between allopatric populations result a new species.

How can geographic isolation change a population's gene pool? Dr Birendra Kumar Mishra. Imagine a situation in which a population extends over a broad geographic range, and mating throughout the population is not random. Individuals in the far west would have zero chance of mating with individuals in the far eastern end of the range. So we have reduced gene flow, but not total isolation. This may or may not be sufficient to cause speciation. Speciation would probably also require different selective pressures at opposite ends of the range, which would alter gene frequencies in groups at different ends of the range so much that they would not be able to mate if they were reunited.

Read about how speciation factored into the history of evolutionary thought. Or explore different modes of speciation , including:. Find additional lessons, activities, videos, and articles that focus on speciation. It can also deepen our understanding of how landscape variables affect dispersal and gene flow and shape patterns of genetic variation in nature 5 , 7. For aquatic plants, given that they live in fragmented islands in terrestrial landscapes, severe genetic differentiation by geographic isolation may be common 8 , 9 , representing an increasing genetic differentiation among populations with increasing geographic distance, as a result of reduced gene flow isolation by distance, IBD When ecological characteristics of habitats are dissimilar among natural populations, the probability of successful establishment of immigrants or their offspring may reduce.

However, relative studies on aquatic plants with incorporating environmental variations in the analysis of population divergence are limited 13 but see Zhao et al. Eurasian watermilfoil Myriophyllum spicatum L. This species occurs in various types of inland water bodies as it is tolerant to a wide range of water and climatic conditions 17 , which may be partly responsible for its cosmopolitan occurrences.

Eurasian watermilfoil is widely distributed in China and previously, we found that both geographic barriers and climate significantly affected population genetic differentiation across the entire country Wu et al. The large range in elevation and the complex landscape of this region offer an ideal place for us to explore the spatial genetic patterns of M. In this study, thirteen Eurasian watermilfoil populations were collected in the QTP and adjacent highlands Yunnan-Guizhou Plateau, YGP for genetic analysis using microsatellite markers.

The Bioclim layers climate and elevation were recruited as environmental variables along with the hydrological properties, which are important for aquatic plants 19 , 20 , for landscape analyses. Our aims were to 1 reveal population genetic structure and gene flow pattern; 2 assess the relative role of geographic isolation and environment heterogeneity in population genetic structure; and 3 find the main force driving genetic divergence of M. A total of genets were identified and all of the obtained genotypes were population specific.

The pairwise Bruvo distance ranged from 0. When the studied M. One of these was comprised five western populations and the other two subclusters comprised three eastern populations Fig. Two western populations were assigned to one subcluser and three eastern populations were assigned to another subcluster Fig. Population codes are shown on the side. The elevation range and main rivers are visualized.

A single vertical bar displays the membership coefficient of each individual, with sample site labeled. The IBD slope is 0. With PCA, we kept the first axis as an environmental variable because it explained The relative contributions of environmental variables to the axes are presented in Table S2.

In the YGP cluster, no significant correlation between genetic distance and geographic distance or environmental distance was found when the influence of the other factor was controlled, but the regression coefficients of genetic-geographical association were about three times higher than those of genetic-environmental association Tables 3 and 4. In the present study, a genetic structure was revealed where the QTP and YGP populations were assigned to independent genetic clusters Fig.

Further analyses revealed obviously internal phylogeographic structure in both regions Fig. A strong association between geographic and genetic distances at different spatial scales Fig. The IBD pattern was further confirmed by landscape analyses at the overall and finer spatial scales when the influence of environmental factors was considered Tables 3 and 4. It suggested that the geographic isolation was the main factor influencing gene flow among populations of M. The IBD pattern was highly associated with limited dispersal among populations in alpine environments.

Given few connections by water systems, the inter-population gene flow of M. Waterfowl play important roles in the seed dispersal of many aquatic plants 9 , 23 and the fact that some waterbirds e. High genetic differentiation and limited gene flow were also detected in some species of aquatic plants in the same region 28 , Therefore, the single means of dispersal and lack of mediators might aggravate the isolation of M.

A series of environmental factors varied along the elevation gradient and among them, climate was a fundamental factor that could cause genetic divergence in the population 30 , Higher-altitude environments contained severe constraints e.

In the present study, no significant correlation existed between genetic differentiation and the environmental dissimilarity that mainly arose from elevational differences when the effects of geographic isolation were considered, suggesting that the genetic adaptation of M. Wang et al. In addition, phenological shifts e. However, this mechanism should not greatly contribute to genetic divergence in M. In conclusion, we highlighted the influence of geographic isolation on the pattern of the gene flow and genetic differentiation of M.

However, physical barriers and climate rather than geographic distance significantly affected the population genetic differentiation of M. Different results confirmed that the main factor driving genetic divergence might vary in different regions or at different scales A variety of studies are needed to help us obtain a deeper understanding of how abiotic factors influence the evolutionary processes of freshwater plants. A total of individuals of M.

We sampled between 6 and 20 plants from each population according to the population size. Hybridization between M. In our previous study, we confirmed that hybridization between these two species also occurred in the QTP of China Hybrid populations identified by morphological traits and genetic data were not included in the present study. We previously isolated 20 microsatellite loci from M.

Fourteen of these loci Myrsp1—7, Myrsp9, Myrsp12—16 and Myrsp18 were used in the present study because of their successful amplification in all populations. Genotyping was performed using GeneMapper 4. Only the genotypes of the genets were kept for subsequent analysis Table 1. Because the allelic copies of microsatellites were ambiguous in polyploid species, we could not determine the exact genotypes of heterozygotes in M. Additionally, the statistics of microsatellite markers were developed for diploid organisms and were not suitable for polyploid organisms Therefore, we converted the microsatellite data to a binary format as dominant data 43 , 44 for genetic structure analysis.

The values were calculated in R software version 3. This index has been proven to be an adequate estimator for polyploids when full genotypes are not required Because individuals from the same site cannot be considered as independent samples, we randomly picked one individual per sampling site to calculate pairwise Bruvo distances.

We repeated the process times and averaged the values of the genetic distance obtained across all of the random sub-samples of individuals for each pair of populations The geographical distribution of different clusters identified was mapped using ArcGIS 9.

In order to assess potential hierarchical structure, each identified cluster was also analyzed separately. DAPC is an adequate analysis of genetic clustering for polyploidy organisms and does not require the populations to be in Hardy-Weinberg equilibrium The method required a priori clustering algorithms determined by k-means and the best number of clusters was assessed using the Bayesian information criterion BIC Mantel tests with 10, permutations were used to detect IBD pattern based on matrices of pairwise Bruvo distance and geographic distance among all populations, as implemented in GenAlEx 6.

Because two genetic clusters corresponding to the QTP and YGP were identified see results , we also performed Mantel tests in each region separately. The properties of the water were also considered. Prior to analysis, all Bioclim variables and elevation values were standardized.

The environmental distance between populations was the Euclidean distance calculated with the values of PCA axes. Multiple matrix regression with randomization MMRR is a novel and robust approach for estimating the independent effects of potential factors, especially in situations of low-to-moderate gene flow How to cite this article : Wu, Z. Great influence of geographic isolation on the genetic differentiation of Myriophyllum spicatum under a steep environmental gradient.

Sork, V. Landscape approaches to historical and contemporary gene flow in plants. Trends Ecol. Slatkin, M. Gene flow in natural populations. Article Google Scholar. Bohonak, A. Dispersal, gene flow and population structure.

Orsini, L. Drivers of population genetic differentiation in the wild: isolation by dispersal limitation, isolation by adaptation and isolation by colonization. Wang, I. Isolation by environment.

Shafer, A. Widespread evidence for incipient ecological speciation: a meta-analysis of isolation-by-ecology. Lee, C. Quantifying effects of environmental and geographical factors on patterns of genetic differentiation. Barrett, S. Evolutionary processes in aquatic plant populations. Why are most aquatic plants widely distributed? Dispersal, clonal growth and small-scale heterogeneity in a stressful environment.

Acta Oecol. Wright, S. Isolation by distance. Genetics 28, — Genetic structure is correlated with phenotypic divergence rather than geographic isolation in the highly polymorphic strawberry poison-dart frog. De Meester, L. The monopolization hypothesis and the dispersal—gene flow paradox in aquatic organisms. Storfer, A.