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Genetic differentiation and phylogeography of partially sympatric species complex Rhizophora mucronata Lam. and R. stylosa Griff. using SSR markers.

Wee AK, Takayama K, Chua JL, Asakawa T, Meenakshisundaram SH - BMC Evol. Biol. (2015)

Bottom Line: Our results demonstrated the general genetic distinctiveness of R. mucronata and R. stylosa, and potential hybridization or introgression between them.Our findings have important implications on the conservation of mangroves, especially relating to replanting efforts and the definition of evolutionary significant units in Rhizophora species.These results serve as the foundation for the conservation genetics of R. mucronata and R. stylosa and highlighted the need to recognize the genetic distinctiveness of closely-related species, determine their respective genetic structure, and avoid artificially promoting hybridization in mangrove restoration programmes.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, Graduate School of Science, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba, 263-8522, Japan. alisonwks@xtbg.ac.cn.

ABSTRACT

Background: Mangrove forests are ecologically important but globally threatened intertidal plant communities. Effective mangrove conservation requires the determination of species identity, management units, and genetic structure. Here, we investigate the genetic distinctiveness and genetic structure of an iconic but yet taxonomically confusing species complex Rhizophora mucronata and R. stylosa across their distributional range, by employing a suite of 20 informative nuclear SSR markers.

Results: Our results demonstrated the general genetic distinctiveness of R. mucronata and R. stylosa, and potential hybridization or introgression between them. We investigated the population genetics of each species without the putative hybrids, and found strong genetic structure between oceanic regions in both R. mucronata and R. stylosa. In R. mucronata, a strong divergence was detected between populations from the Indian Ocean region (Indian Ocean and Andaman Sea) and the Pacific Ocean region (Malacca Strait, South China Sea and Northwest Pacific Ocean). In R. stylosa, the genetic break was located more eastward, between populations from South and East China Sea and populations from the Southwest Pacific Ocean. The location of these genetic breaks coincided with the boundaries of oceanic currents, thus suggesting that oceanic circulation patterns might have acted as a cryptic barrier to gene flow.

Conclusions: Our findings have important implications on the conservation of mangroves, especially relating to replanting efforts and the definition of evolutionary significant units in Rhizophora species. We outlined the genetic structure and identified geographical areas that require further investigations for both R. mucronata and R. stylosa. These results serve as the foundation for the conservation genetics of R. mucronata and R. stylosa and highlighted the need to recognize the genetic distinctiveness of closely-related species, determine their respective genetic structure, and avoid artificially promoting hybridization in mangrove restoration programmes.

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PCoA scatter plot showing the genetic distance among individuals according to oceanic region. The percentage of total variation attributed to each axis is as indicated. Rhizophora mucronata individuals are indicated with yellow markers; Rhizophora stylosa individuals are indicated with red markers.
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Fig2: PCoA scatter plot showing the genetic distance among individuals according to oceanic region. The percentage of total variation attributed to each axis is as indicated. Rhizophora mucronata individuals are indicated with yellow markers; Rhizophora stylosa individuals are indicated with red markers.

Mentions: We detected an overall strong genetic structure across all populations, with significant genetic differentiation (FST) estimated at 0.737 averaging all loci and populations (p < 0.001). All pairwise population genetic differentiation was significant at the p < 0.001 level, except between adjacent R. mucronata populations MA1 and MA2 (pairwise FST = 0.013, p > 0.05), and R. stylosa populations VA1 and VA2 (pairwise FST = 0.044, p > 0.05). Pairwise FST estimates are listed in Additional file 1: Table S4. The PCoA results demonstrated a clear genetic differentiation between R. mucronata and R. stylosa, as well as among oceanic region in each species (Figure 2). There was no overlap between species, except for (1) several R. mucronata individuals from the South China Sea region observed in the R. stylosa clusters, and (2) an overlap of R. mucronata individuals from Bali Sea (IN4) with R. stylosa individuals from northwest Pacific Ocean (MIC). Model-based individual assignment via STRUCTURE was in agreement with the PCoA results. We found strong support for two genetic clusters among our samples that generally corresponded to the respective species (Figure 3). All R. mucronata individuals had > 90% of inferred ancestry from the same genetic cluster except for several individuals in populations SEY, IN2, PH1 and IN4. R. mucronata individuals from PA1 had more than 50% inferred ancestry from the R. stylosa genetic cluster, hence may represent putative hybrids between the two species. Similarly, mixed inferred ancestry was also found in R. stylosa individuals from MIC.Figure 2


Genetic differentiation and phylogeography of partially sympatric species complex Rhizophora mucronata Lam. and R. stylosa Griff. using SSR markers.

Wee AK, Takayama K, Chua JL, Asakawa T, Meenakshisundaram SH - BMC Evol. Biol. (2015)

PCoA scatter plot showing the genetic distance among individuals according to oceanic region. The percentage of total variation attributed to each axis is as indicated. Rhizophora mucronata individuals are indicated with yellow markers; Rhizophora stylosa individuals are indicated with red markers.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4389924&req=5

Fig2: PCoA scatter plot showing the genetic distance among individuals according to oceanic region. The percentage of total variation attributed to each axis is as indicated. Rhizophora mucronata individuals are indicated with yellow markers; Rhizophora stylosa individuals are indicated with red markers.
Mentions: We detected an overall strong genetic structure across all populations, with significant genetic differentiation (FST) estimated at 0.737 averaging all loci and populations (p < 0.001). All pairwise population genetic differentiation was significant at the p < 0.001 level, except between adjacent R. mucronata populations MA1 and MA2 (pairwise FST = 0.013, p > 0.05), and R. stylosa populations VA1 and VA2 (pairwise FST = 0.044, p > 0.05). Pairwise FST estimates are listed in Additional file 1: Table S4. The PCoA results demonstrated a clear genetic differentiation between R. mucronata and R. stylosa, as well as among oceanic region in each species (Figure 2). There was no overlap between species, except for (1) several R. mucronata individuals from the South China Sea region observed in the R. stylosa clusters, and (2) an overlap of R. mucronata individuals from Bali Sea (IN4) with R. stylosa individuals from northwest Pacific Ocean (MIC). Model-based individual assignment via STRUCTURE was in agreement with the PCoA results. We found strong support for two genetic clusters among our samples that generally corresponded to the respective species (Figure 3). All R. mucronata individuals had > 90% of inferred ancestry from the same genetic cluster except for several individuals in populations SEY, IN2, PH1 and IN4. R. mucronata individuals from PA1 had more than 50% inferred ancestry from the R. stylosa genetic cluster, hence may represent putative hybrids between the two species. Similarly, mixed inferred ancestry was also found in R. stylosa individuals from MIC.Figure 2

Bottom Line: Our results demonstrated the general genetic distinctiveness of R. mucronata and R. stylosa, and potential hybridization or introgression between them.Our findings have important implications on the conservation of mangroves, especially relating to replanting efforts and the definition of evolutionary significant units in Rhizophora species.These results serve as the foundation for the conservation genetics of R. mucronata and R. stylosa and highlighted the need to recognize the genetic distinctiveness of closely-related species, determine their respective genetic structure, and avoid artificially promoting hybridization in mangrove restoration programmes.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, Graduate School of Science, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba, 263-8522, Japan. alisonwks@xtbg.ac.cn.

ABSTRACT

Background: Mangrove forests are ecologically important but globally threatened intertidal plant communities. Effective mangrove conservation requires the determination of species identity, management units, and genetic structure. Here, we investigate the genetic distinctiveness and genetic structure of an iconic but yet taxonomically confusing species complex Rhizophora mucronata and R. stylosa across their distributional range, by employing a suite of 20 informative nuclear SSR markers.

Results: Our results demonstrated the general genetic distinctiveness of R. mucronata and R. stylosa, and potential hybridization or introgression between them. We investigated the population genetics of each species without the putative hybrids, and found strong genetic structure between oceanic regions in both R. mucronata and R. stylosa. In R. mucronata, a strong divergence was detected between populations from the Indian Ocean region (Indian Ocean and Andaman Sea) and the Pacific Ocean region (Malacca Strait, South China Sea and Northwest Pacific Ocean). In R. stylosa, the genetic break was located more eastward, between populations from South and East China Sea and populations from the Southwest Pacific Ocean. The location of these genetic breaks coincided with the boundaries of oceanic currents, thus suggesting that oceanic circulation patterns might have acted as a cryptic barrier to gene flow.

Conclusions: Our findings have important implications on the conservation of mangroves, especially relating to replanting efforts and the definition of evolutionary significant units in Rhizophora species. We outlined the genetic structure and identified geographical areas that require further investigations for both R. mucronata and R. stylosa. These results serve as the foundation for the conservation genetics of R. mucronata and R. stylosa and highlighted the need to recognize the genetic distinctiveness of closely-related species, determine their respective genetic structure, and avoid artificially promoting hybridization in mangrove restoration programmes.

Show MeSH