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Genetic diversity in three invasive clonal aquatic species in New Zealand.

Lambertini C, Riis T, Olesen B, Clayton JS, Sorrell BK, Brix H - BMC Genet. (2010)

Bottom Line: The successful growth and establishment of invasive clonal species may be explained not by adaptability but by pre-existing ecological traits that prove advantageous in the new environment.Low levels of genetic diversity were found in all three species and appeared to be due to highly homogeneous founding gene pools.Direct evidence of such evolutionary events is, however, still insufficient.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biological Sciences, Aarhus University, Arhus C, Denmark. carla.lambertini@biology.au.dk

ABSTRACT

Background: Elodea canadensis, Egeria densa and Lagarosiphon major are dioecious clonal species which are invasive in New Zealand and other regions. Unlike many other invasive species, the genetic variation in New Zealand is very limited. Clonal reproduction is often considered an evolutionary dead end, even though a certain amount of genetic divergence may arise due to somatic mutations. The successful growth and establishment of invasive clonal species may be explained not by adaptability but by pre-existing ecological traits that prove advantageous in the new environment. We studied the genetic diversity and population structure in the North Island of New Zealand using AFLPs and related the findings to the number of introductions and the evolution that has occurred in the introduced area.

Results: Low levels of genetic diversity were found in all three species and appeared to be due to highly homogeneous founding gene pools. Elodea canadensis was introduced in 1868, and its populations showed more genetic structure than those of the more recently introduced of E. densa (1946) and L. major (1950). Elodea canadensis and L. major, however, had similar phylogeographic patterns, in spite of the difference in time since introduction.

Conclusions: The presence of a certain level of geographically correlated genetic structure in the absence of sexual reproduction, and in spite of random human dispersal of vegetative propagules, can be reasonably attributed to post-dispersal somatic mutations. Direct evidence of such evolutionary events is, however, still insufficient.

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AMOVA within and among NZ populations of 2a) L. major, 2b) E. densa, 2c) E. canadensis. 2d) AMOVA within and among NZ samples, considered as one single population, and one Danish genotype of E. canadensis. Population specific FST indices indicate how much each population contributes and deviates from the weighted average FST.
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Figure 2: AMOVA within and among NZ populations of 2a) L. major, 2b) E. densa, 2c) E. canadensis. 2d) AMOVA within and among NZ samples, considered as one single population, and one Danish genotype of E. canadensis. Population specific FST indices indicate how much each population contributes and deviates from the weighted average FST.

Mentions: The analysis of molecular variance showed higher percentages of genetic variation within populations than among populations in all species. Similar levels of population differentiation were found in E. densa (average Fst = 0.27; p-value = < 0.001) and in L. major (average Fst = 0.23; p-value = 0.02), whereas E. canadensis populations showed higher genetic structure (average Fst = 0.32; p-value < 0.001). The population specific Fst indices (Figure 2) show how much the Fst of each population contributes and deviates from the weighted average Fst. Monoclonal populations showed the highest specific Fst, but these values are affected by the clonal nature of the populations. Heterozygosity, calculated as covariance component of the total variance, is "zero" in monoclonal populations and Fst corresponds to the total heterozygosity of the sample set, or is very close to it, depending on the algorithm used. Even though Fst values cannot be interpreted in terms of gene flow among populations, the different average Fst values in the three species give an idea of differences in genetic structure at the population level. The population comparison test and the exact test of population differentiation showed no population differentiation in E. canadensis. In L. major the Tikitapu and Otamangakau populations had a significant pairwise Fst of 0.35 (p-value = 0.03). In E. densa the McLaren and Swan populations had a significant pairwise Fst of 0.82 (p-value = 0.04 ). Population differentiation was not confirmed by the exact test of population differentiation in both species. Genetic differentiation between the NZ E. canadensis populations and the Danish genotype was 0.75 (p-value = 0.05), indicating that the NZ genotypes were more similar to each other than they were to the Danish clone. Nei's unbiased minimum genetic distances ranged between 0 and 0.01 between all pairs of populations in L. major. In E. densa they ranged between 0 and 0.06; however, only one population (McLaren) had genetic distances over 0.02 with all the other populations. By excluding McLaren, the range decreased to 0 - 0.02. Pairwise genetic distances among E. canadensis populations ranged between 0.01 and 0.08. Nei'unbiased minimum genetic distance was 0.17 between the NZ E. canadensis clones and the Danish genotype. The genetic distance values appeared to better reflect the genetic similarities among the populations than the Fst values and confirmed differences in genetic structure in the populations of the three species.


Genetic diversity in three invasive clonal aquatic species in New Zealand.

Lambertini C, Riis T, Olesen B, Clayton JS, Sorrell BK, Brix H - BMC Genet. (2010)

AMOVA within and among NZ populations of 2a) L. major, 2b) E. densa, 2c) E. canadensis. 2d) AMOVA within and among NZ samples, considered as one single population, and one Danish genotype of E. canadensis. Population specific FST indices indicate how much each population contributes and deviates from the weighted average FST.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2902404&req=5

Figure 2: AMOVA within and among NZ populations of 2a) L. major, 2b) E. densa, 2c) E. canadensis. 2d) AMOVA within and among NZ samples, considered as one single population, and one Danish genotype of E. canadensis. Population specific FST indices indicate how much each population contributes and deviates from the weighted average FST.
Mentions: The analysis of molecular variance showed higher percentages of genetic variation within populations than among populations in all species. Similar levels of population differentiation were found in E. densa (average Fst = 0.27; p-value = < 0.001) and in L. major (average Fst = 0.23; p-value = 0.02), whereas E. canadensis populations showed higher genetic structure (average Fst = 0.32; p-value < 0.001). The population specific Fst indices (Figure 2) show how much the Fst of each population contributes and deviates from the weighted average Fst. Monoclonal populations showed the highest specific Fst, but these values are affected by the clonal nature of the populations. Heterozygosity, calculated as covariance component of the total variance, is "zero" in monoclonal populations and Fst corresponds to the total heterozygosity of the sample set, or is very close to it, depending on the algorithm used. Even though Fst values cannot be interpreted in terms of gene flow among populations, the different average Fst values in the three species give an idea of differences in genetic structure at the population level. The population comparison test and the exact test of population differentiation showed no population differentiation in E. canadensis. In L. major the Tikitapu and Otamangakau populations had a significant pairwise Fst of 0.35 (p-value = 0.03). In E. densa the McLaren and Swan populations had a significant pairwise Fst of 0.82 (p-value = 0.04 ). Population differentiation was not confirmed by the exact test of population differentiation in both species. Genetic differentiation between the NZ E. canadensis populations and the Danish genotype was 0.75 (p-value = 0.05), indicating that the NZ genotypes were more similar to each other than they were to the Danish clone. Nei's unbiased minimum genetic distances ranged between 0 and 0.01 between all pairs of populations in L. major. In E. densa they ranged between 0 and 0.06; however, only one population (McLaren) had genetic distances over 0.02 with all the other populations. By excluding McLaren, the range decreased to 0 - 0.02. Pairwise genetic distances among E. canadensis populations ranged between 0.01 and 0.08. Nei'unbiased minimum genetic distance was 0.17 between the NZ E. canadensis clones and the Danish genotype. The genetic distance values appeared to better reflect the genetic similarities among the populations than the Fst values and confirmed differences in genetic structure in the populations of the three species.

Bottom Line: The successful growth and establishment of invasive clonal species may be explained not by adaptability but by pre-existing ecological traits that prove advantageous in the new environment.Low levels of genetic diversity were found in all three species and appeared to be due to highly homogeneous founding gene pools.Direct evidence of such evolutionary events is, however, still insufficient.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biological Sciences, Aarhus University, Arhus C, Denmark. carla.lambertini@biology.au.dk

ABSTRACT

Background: Elodea canadensis, Egeria densa and Lagarosiphon major are dioecious clonal species which are invasive in New Zealand and other regions. Unlike many other invasive species, the genetic variation in New Zealand is very limited. Clonal reproduction is often considered an evolutionary dead end, even though a certain amount of genetic divergence may arise due to somatic mutations. The successful growth and establishment of invasive clonal species may be explained not by adaptability but by pre-existing ecological traits that prove advantageous in the new environment. We studied the genetic diversity and population structure in the North Island of New Zealand using AFLPs and related the findings to the number of introductions and the evolution that has occurred in the introduced area.

Results: Low levels of genetic diversity were found in all three species and appeared to be due to highly homogeneous founding gene pools. Elodea canadensis was introduced in 1868, and its populations showed more genetic structure than those of the more recently introduced of E. densa (1946) and L. major (1950). Elodea canadensis and L. major, however, had similar phylogeographic patterns, in spite of the difference in time since introduction.

Conclusions: The presence of a certain level of geographically correlated genetic structure in the absence of sexual reproduction, and in spite of random human dispersal of vegetative propagules, can be reasonably attributed to post-dispersal somatic mutations. Direct evidence of such evolutionary events is, however, still insufficient.

Show MeSH
Related in: MedlinePlus