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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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Reduced median network of Elodea canadensis. The size of terminal nodes is proportional to genotype frequencies. Samples are labeled with population abbreviation (see Abbreviations) and sample number (1-3).
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Figure 7: Reduced median network of Elodea canadensis. The size of terminal nodes is proportional to genotype frequencies. Samples are labeled with population abbreviation (see Abbreviations) and sample number (1-3).

Mentions: The relationships among the clones of the three species are shown in the networks and Neighbour Joining (NJ) trees of Figures 3, 4, 5, 6, 7 and 8. The size of the terminal nodes in the network are proportional to the frequency of the genotypes and comparable in the three species. Although the samples of E. canadensis and E. densa showed similar levels of polymorphism (respectively 21.6% and 22.8% of the number of DNA fragments analysed) and higher than those of L. major (9.8%), the genetic pattern was different in the three species. In L. major the samples from the geographically close populations of Otamangakau and Taupo South appeared as a monophyletic group differentiated from a dominant genotype spread in every location (Figure 3). The interrelationships of Otamangakau and Taupo South clones, involving all samples from these populations, were supported by jack-knife values in the NJ tree (Figure 4). The other supported relationship in the NJ tree between two apparently very different and geographically distant clones collected at Rotoaira and Tikitapu lakes was also detected by the network, which introduced two common ancestral genotypes to explain their genetic affinities. The network of E. densa (Figure 5) showed a complex pattern of relationships and introduced a number of ancestral genotypes to connect the most different samples to the most spread clone, indicating a higher extent of differentiation than in L. major, as also evident by the larger number of polymorphic fragments. Apart from two clones collected at McLaren lake, whose relationship was confirmed also by jack-knife and bootstrap support in the NJ tree (Figure 6), E. densa populations did not appear to be genetically distinct. The network of E. canadensis showed a better defined structure than in E. densa and a number of monophyletic relationships among clones, including in many cases pairs of samples from the same populations or groups of genotypes from geographically close locations (Figure 7). As in L. major, the populations of Otamangakau and Taupo South appeared as a monophyletic group evolved from an ancestral genotype. The NJ tree provided jack-knife and/or bootstrap support for some of the relationships and showed a continuum of genetic differences among the samples and the populations of Otamangakau, Taupo South and Pongakawa (Figure 8).


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)

Reduced median network of Elodea canadensis. The size of terminal nodes is proportional to genotype frequencies. Samples are labeled with population abbreviation (see Abbreviations) and sample number (1-3).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 7: Reduced median network of Elodea canadensis. The size of terminal nodes is proportional to genotype frequencies. Samples are labeled with population abbreviation (see Abbreviations) and sample number (1-3).
Mentions: The relationships among the clones of the three species are shown in the networks and Neighbour Joining (NJ) trees of Figures 3, 4, 5, 6, 7 and 8. The size of the terminal nodes in the network are proportional to the frequency of the genotypes and comparable in the three species. Although the samples of E. canadensis and E. densa showed similar levels of polymorphism (respectively 21.6% and 22.8% of the number of DNA fragments analysed) and higher than those of L. major (9.8%), the genetic pattern was different in the three species. In L. major the samples from the geographically close populations of Otamangakau and Taupo South appeared as a monophyletic group differentiated from a dominant genotype spread in every location (Figure 3). The interrelationships of Otamangakau and Taupo South clones, involving all samples from these populations, were supported by jack-knife values in the NJ tree (Figure 4). The other supported relationship in the NJ tree between two apparently very different and geographically distant clones collected at Rotoaira and Tikitapu lakes was also detected by the network, which introduced two common ancestral genotypes to explain their genetic affinities. The network of E. densa (Figure 5) showed a complex pattern of relationships and introduced a number of ancestral genotypes to connect the most different samples to the most spread clone, indicating a higher extent of differentiation than in L. major, as also evident by the larger number of polymorphic fragments. Apart from two clones collected at McLaren lake, whose relationship was confirmed also by jack-knife and bootstrap support in the NJ tree (Figure 6), E. densa populations did not appear to be genetically distinct. The network of E. canadensis showed a better defined structure than in E. densa and a number of monophyletic relationships among clones, including in many cases pairs of samples from the same populations or groups of genotypes from geographically close locations (Figure 7). As in L. major, the populations of Otamangakau and Taupo South appeared as a monophyletic group evolved from an ancestral genotype. The NJ tree provided jack-knife and/or bootstrap support for some of the relationships and showed a continuum of genetic differences among the samples and the populations of Otamangakau, Taupo South and Pongakawa (Figure 8).

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