Limits...
Exploring species limits in two closely related Chinese oaks.

Zeng YF, Liao WJ, Petit RJ, Zhang DY - PLoS ONE (2010)

Bottom Line: Using SSR (simple sequence repeat) and AFLP (amplified fragment length polymorphism) markers, we found that interspecific genetic differentiation is significant and higher than the differentiation among populations within taxa.One SSR locus and five AFLPs are significant outliers against neutral expectations in the interspecific FST simulation analysis, suggesting a role for divergent selection in differentiating species.All results based on SSRS and AFLPS reached the same conclusion: Q. liaotungensis and Q. mongolica maintain distinct gene pools in most areas of sympatry.

View Article: PubMed Central - PubMed

Affiliation: Key Laboratory of Silviculture of the State Forestry Administration, Research Institute of Forestry, Chinese Academy of Forestry, Beijing, China.

ABSTRACT

Background: The species status of two closely related Chinese oaks, Quercus liaotungensis and Q. mongolica, has been called into question. The objective of this study was to investigate the species status and to estimate the degree of introgression between the two taxa using different approaches.

Methodology/principal findings: Using SSR (simple sequence repeat) and AFLP (amplified fragment length polymorphism) markers, we found that interspecific genetic differentiation is significant and higher than the differentiation among populations within taxa. Bayesian clusters, principal coordinate analysis and population genetic distance trees all classified the oaks into two main groups consistent with the morphological differentiation of the two taxa rather than with geographic locations using both types of markers. Nevertheless, a few individuals in Northeast China and many individuals in North China have hybrid ancestry according to Bayesian assignment. One SSR locus and five AFLPs are significant outliers against neutral expectations in the interspecific FST simulation analysis, suggesting a role for divergent selection in differentiating species.

Main conclusions/significance: All results based on SSRS and AFLPS reached the same conclusion: Q. liaotungensis and Q. mongolica maintain distinct gene pools in most areas of sympatry. They should therefore be considered as discrete taxonomic units. Yet, the degree of introgression varies between the two species in different contact zones, which might be caused by different population history or by local environmental factors.

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Related in: MedlinePlus

Geographic distribution of Quercus liaotungensis and Q. mongolica in China and location of populations sampled.Shadows show the distribution of Q. liaotungensis and Q. mongolica, respectively, according to Zhang [38]. Filled circles: Q. liaotungensis; open circles: Q. mongolica; half filled circles: intermediate populations.
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pone-0015529-g001: Geographic distribution of Quercus liaotungensis and Q. mongolica in China and location of populations sampled.Shadows show the distribution of Q. liaotungensis and Q. mongolica, respectively, according to Zhang [38]. Filled circles: Q. liaotungensis; open circles: Q. mongolica; half filled circles: intermediate populations.

Mentions: Leaf samples were collected from 419 individuals from a total of 15 oak populations across their distribution range in China (Table 1 and Fig. 1). Individuals were identified in the field as Q. liaotungensis (smooth acorn cupule), or Q. mongolica (rough acorn cupule), following Higher Plants of China [38]. Our observations suggest that Q. mongolica has smoother trunk bark than Q. liaotungensis. Therefore, the character of trunk bark was also considered where acorn cupule morphology alone was not sufficient to differentiate oak individuals (population THl and THm from Tonghua, and population SPl and SPm from Siping). According to above rules, four ‘pure’ Q. liaotungensis populations were sampled. Populations ZW and WA are located in areas where Q. mongolica is completely absent (allopatric range); CF2 and FS are located in areas from the sympatric range where Q. mongolica is locally absent. Three pure Q. mongolica populations were also collected. Populations HH and MR are located in areas where Q. liatungensis is completely absent (allopatric range); Dan is within the sympatric range in an area where Q. mongolica is locally absent. At three locations both species were found within mixed forests. Individuals were randomly sampled and then categorized into different species as far as possible, thus resulting in three pairs of populations: SPl and SPm, THl and THm, and NAl and NAm, where the lower-case letter ‘l’ represents Q. liaotungensis and ‘m’ Q. mongolica. In addition, one Q. liaotungensis-type population (Dmy) and one morphologically intermediate population (Dtt) were sampled from the Dongling Mountain region where controversy has arisen among Chinese taxonomists because of the existence of a broad array of morphologically intermediate trees [43]. These last two populations were excluded from the diversity and differentiation analyses due to the dominance of intermediates in Dtt and too small population sizes for Dmy. Leaf tissues (1–3 leaves per tree) were collected from each sampled tree, dried with silica gel and taken back to the laboratory.


Exploring species limits in two closely related Chinese oaks.

Zeng YF, Liao WJ, Petit RJ, Zhang DY - PLoS ONE (2010)

Geographic distribution of Quercus liaotungensis and Q. mongolica in China and location of populations sampled.Shadows show the distribution of Q. liaotungensis and Q. mongolica, respectively, according to Zhang [38]. Filled circles: Q. liaotungensis; open circles: Q. mongolica; half filled circles: intermediate populations.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2994836&req=5

pone-0015529-g001: Geographic distribution of Quercus liaotungensis and Q. mongolica in China and location of populations sampled.Shadows show the distribution of Q. liaotungensis and Q. mongolica, respectively, according to Zhang [38]. Filled circles: Q. liaotungensis; open circles: Q. mongolica; half filled circles: intermediate populations.
Mentions: Leaf samples were collected from 419 individuals from a total of 15 oak populations across their distribution range in China (Table 1 and Fig. 1). Individuals were identified in the field as Q. liaotungensis (smooth acorn cupule), or Q. mongolica (rough acorn cupule), following Higher Plants of China [38]. Our observations suggest that Q. mongolica has smoother trunk bark than Q. liaotungensis. Therefore, the character of trunk bark was also considered where acorn cupule morphology alone was not sufficient to differentiate oak individuals (population THl and THm from Tonghua, and population SPl and SPm from Siping). According to above rules, four ‘pure’ Q. liaotungensis populations were sampled. Populations ZW and WA are located in areas where Q. mongolica is completely absent (allopatric range); CF2 and FS are located in areas from the sympatric range where Q. mongolica is locally absent. Three pure Q. mongolica populations were also collected. Populations HH and MR are located in areas where Q. liatungensis is completely absent (allopatric range); Dan is within the sympatric range in an area where Q. mongolica is locally absent. At three locations both species were found within mixed forests. Individuals were randomly sampled and then categorized into different species as far as possible, thus resulting in three pairs of populations: SPl and SPm, THl and THm, and NAl and NAm, where the lower-case letter ‘l’ represents Q. liaotungensis and ‘m’ Q. mongolica. In addition, one Q. liaotungensis-type population (Dmy) and one morphologically intermediate population (Dtt) were sampled from the Dongling Mountain region where controversy has arisen among Chinese taxonomists because of the existence of a broad array of morphologically intermediate trees [43]. These last two populations were excluded from the diversity and differentiation analyses due to the dominance of intermediates in Dtt and too small population sizes for Dmy. Leaf tissues (1–3 leaves per tree) were collected from each sampled tree, dried with silica gel and taken back to the laboratory.

Bottom Line: Using SSR (simple sequence repeat) and AFLP (amplified fragment length polymorphism) markers, we found that interspecific genetic differentiation is significant and higher than the differentiation among populations within taxa.One SSR locus and five AFLPs are significant outliers against neutral expectations in the interspecific FST simulation analysis, suggesting a role for divergent selection in differentiating species.All results based on SSRS and AFLPS reached the same conclusion: Q. liaotungensis and Q. mongolica maintain distinct gene pools in most areas of sympatry.

View Article: PubMed Central - PubMed

Affiliation: Key Laboratory of Silviculture of the State Forestry Administration, Research Institute of Forestry, Chinese Academy of Forestry, Beijing, China.

ABSTRACT

Background: The species status of two closely related Chinese oaks, Quercus liaotungensis and Q. mongolica, has been called into question. The objective of this study was to investigate the species status and to estimate the degree of introgression between the two taxa using different approaches.

Methodology/principal findings: Using SSR (simple sequence repeat) and AFLP (amplified fragment length polymorphism) markers, we found that interspecific genetic differentiation is significant and higher than the differentiation among populations within taxa. Bayesian clusters, principal coordinate analysis and population genetic distance trees all classified the oaks into two main groups consistent with the morphological differentiation of the two taxa rather than with geographic locations using both types of markers. Nevertheless, a few individuals in Northeast China and many individuals in North China have hybrid ancestry according to Bayesian assignment. One SSR locus and five AFLPs are significant outliers against neutral expectations in the interspecific FST simulation analysis, suggesting a role for divergent selection in differentiating species.

Main conclusions/significance: All results based on SSRS and AFLPS reached the same conclusion: Q. liaotungensis and Q. mongolica maintain distinct gene pools in most areas of sympatry. They should therefore be considered as discrete taxonomic units. Yet, the degree of introgression varies between the two species in different contact zones, which might be caused by different population history or by local environmental factors.

Show MeSH
Related in: MedlinePlus