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Conspecificity of two morphologically distinct calcified red algae from the northwest Pacific Ocean: Galaxaura pacifica and G. filamentosa (Galaxauraceae, Rhodophyta)

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ABSTRACT

Background: Members of the calcified red algal genus, Galaxaura, are distributed predominantly in warm temperate, subtropical, and tropical regions worldwide. The capacity of these algae to form calcified thalli could play a critical role in the carbon cycle of these ecosystems. Previous studies have suggested that the reported species diversity of Galaxaura may be exaggerated due to a lack of knowledge regarding external morphological differences between gametophytic and tetrasporophytic plants (or among different life stages) of a single species.

Results: To examine this issue, this study collected specimens of two morphologically distinct Galaxaura from Taiwan and the Philippines. These specimens were initially identified as two species (G. pacifica Tanaka and G. filamentosa Chou ex Taylor) based on their morphological features. Our molecular analyses, however, unexpectedly showed that these two specimens shared 100% identical rbc L sequences, indicating that they represented a single species comprising two distinct external morphologies. Furthermore, our extensive observations and molecular analyses on several specimens from different locations in southern Taiwan has revealed that these morphological differences could be due to seasonal variation.

Conclusions: This study proposes that G. “filamentosa” from the Philippines could represent the remnants of the lower villous part of older gametophytic plants of G. pacifica after senescence of the upper smooth part of the thallus. As such we propose that these two previously distinct algal species from the northwest Pacific Ocean as a single species, G. pacifica. This study shows that the biodiversity of the calcified red algae Galaxaura could be overestimated without the assistance of molecular tools. Additionally, this study provides insights into the biodiversity and unique biology of the calcified red algae Galaxaura.

Electronic supplementary material: The online version of this article (doi:10.1186/1999-3110-54-1) contains supplementary material, which is available to authorized users.

No MeSH data available.


Related in: MedlinePlus

Variations of the external morphologies of gametophyticG. pacificafor the specimens collected from three different locations in southern Taiwan.(A-C) Specimens from Xiao-Liu-Qiu Island, southern Taiwan in summer showing different size of the villous basal portion (arrows) and different density of the glabrous upper portion. One specimen (C) even showed the decay of glabrous upper portion (arrowheads); (D-E) Specimens from Small Port, Kenting National Park (KNP), southern Taiwan in winter showing smaller villous basal portion (arrows) and highly branched glabrous upper portion of material from Wukeuitung, Xiao-Liu-Qiu Island, southern Taiwan in summer; (F) Specimen from Sail Rock, KNP, southern Taiwan in winter showing tiny villous basal portion (arrows) and highly branched glabrous upper portion. (G-I) Magnification of the villous basal portion (arrows) for the specimens from Wukeuitung, Xiao-Liu-Qiu Island, southern Taiwan in summer. Arrowheads in C indicate that the glabrous upper portion eventually decays or dies off in the senescing plant; (J-K) Magnification of the villous basal portion (arrows) in specimen from Small Port, KNP, southern Taiwan in winter; (L) Magnification of the villous basal portion (arrows) in specimen from Sail Rock, KNP, southern Taiwan in winter.
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Fig2: Variations of the external morphologies of gametophyticG. pacificafor the specimens collected from three different locations in southern Taiwan.(A-C) Specimens from Xiao-Liu-Qiu Island, southern Taiwan in summer showing different size of the villous basal portion (arrows) and different density of the glabrous upper portion. One specimen (C) even showed the decay of glabrous upper portion (arrowheads); (D-E) Specimens from Small Port, Kenting National Park (KNP), southern Taiwan in winter showing smaller villous basal portion (arrows) and highly branched glabrous upper portion of material from Wukeuitung, Xiao-Liu-Qiu Island, southern Taiwan in summer; (F) Specimen from Sail Rock, KNP, southern Taiwan in winter showing tiny villous basal portion (arrows) and highly branched glabrous upper portion. (G-I) Magnification of the villous basal portion (arrows) for the specimens from Wukeuitung, Xiao-Liu-Qiu Island, southern Taiwan in summer. Arrowheads in C indicate that the glabrous upper portion eventually decays or dies off in the senescing plant; (J-K) Magnification of the villous basal portion (arrows) in specimen from Small Port, KNP, southern Taiwan in winter; (L) Magnification of the villous basal portion (arrows) in specimen from Sail Rock, KNP, southern Taiwan in winter.

Mentions: After we determining that G. pacifica and G. “filamentosa” are the same species, this study observed that specimens from different locations in southern Taiwan showed a range of external morphological variation in different seasons. Figure 2 shows that the specimens from Xiao-Liu-Qiu Island collected in the summer often possess a tuft of larger and distinctly villous branches in the lower part of the thallus (Figure 2A-2C, 2G-2I). The overall size of the lower villous part of the thallus and the density of upper glabrous branches vary among different individuals within the population. Some individuals had few clusters of loosely dichotomous glabrous branches in the upper part of the thallus (Figure 2A) and a tuft of wider and larger villous branches in the lower part of the thallus (Figure 2G). Some individuals had few clusters of densely dichotomous glabrous branches in the upper part of the thallus (Figure 2B) and a tuft of narrower and smaller villous branches in the lower part of the thallus (Figure 2H). Interestingly, one of the specimens consisted solely of very few glabrous branches in the upper part of the thallus (Figure 2C) and some residuals of glabrous branches can still be seen attaching on the lower villous branches (arrowheads in Figure 2C, 2I). A careful examination of the glabrous branches on this particular specimen showed that most of them were old and showed numerous lesions (image not shown). This observation suggests that the glabrous branches might eventually decay or die off in summer and the villous branches might be retained for some time after the decay/die-off of the glabrous branches, often leading to its misidentification as G. filamentosa (imagine the scenario that the last cluster of glabrous branches and those residuals decay in Figure 2C). In contrast, the specimens from Small Port (Figure 2D-2E, 2J-2K) and Sail Rock (Figure 2F, 2L) collected in the winter showed a tuft of small villous branches in the lower part of the thallus. The size of the villous branches in the lower part of the thallus and the density of the glabrous branches in the upper part vary across different individuals within the overall local population. In some cases, involving presumably more mature individuals, plants show several clusters of densely glabrous branches in the upper part of the thallus (Figure 2D) and a tuft of small villous branches in the lower part (Figure 2J). In other cases, representing presumably younger individuals, plants possess few clusters of densely dichotomous glabrous branches in the upper part of the thallus (Figure 2E-2F) and a tuft of tiny (occasionally unnoticeable) villous branches (Figure 2K-2L). To better quantify the external morphological difference among the specimens from different locations, we estimated the ratio between the height of the glabrous branch (G) and the villous branch (V). The G/V ratio of the specimens from Xiao-Liu-Qiu Island in summer is significantly smaller than those from Small Port and Sail Rock collected in the winter based on our comparison (Figure 3; p < 0.05). This result supports our previous observations that the specimens in the summer have larger villous branches than those in the winter. To rule out the possibility that our observed external variation results from the comparison of two different species, we additionally obtained rbc L sequences of the specimens from Small Port and Sail Rock and then compared these with that from Xiao-Liu-Qiu Island, as well as that from Sorsogon, Philippines. Results revealed that they share 100% identical rbc L sequences, indicative of conspecificity. Phylogenetic analysis also supports the same conclusion as they are grouped together (Figure 4). However, the inter-specific relationship differs from previous results. The lack of statistical support suggests that a difference might be caused by insufficient informative sites from the smaller set of characters (669 vs. 1407) used in this analysis (Figure 4). Because the glabrous branches of G. pacifica contain considerable mucilage, it is often difficult to obtain pure DNA for further PCR reactions. The traditional CTAB method (Doyle and Dickson, 1987) with at least three rounds of chloroform: isoamyl alcohol (24:1) treatments works more effectively than the commercial DNA extraction kit. Morphological observations and molecular analyses revealed that the villous branches are small in the winter and grow larger in the summer. Considering that one of the specimens from Xiao-Liu-Qiu Island showed extremely scarce glabrous branches (Figure 2F), it is tempting to speculate that the material identified as G. filamentosa might be the remaining villous part of senescing G. pacifica. Similar gross morphology and G/V ratio among specimens obtained during similar seasons over different years (e.g., Figure 2D-2E from March in 2003 and Figure 2F from February in 2012) (Figure 3) suggests that environmental cues such as temperature might serve as the most significant factor affecting external morphological development in G. pacifica.Figure 2


Conspecificity of two morphologically distinct calcified red algae from the northwest Pacific Ocean: Galaxaura pacifica and G. filamentosa (Galaxauraceae, Rhodophyta)
Variations of the external morphologies of gametophyticG. pacificafor the specimens collected from three different locations in southern Taiwan.(A-C) Specimens from Xiao-Liu-Qiu Island, southern Taiwan in summer showing different size of the villous basal portion (arrows) and different density of the glabrous upper portion. One specimen (C) even showed the decay of glabrous upper portion (arrowheads); (D-E) Specimens from Small Port, Kenting National Park (KNP), southern Taiwan in winter showing smaller villous basal portion (arrows) and highly branched glabrous upper portion of material from Wukeuitung, Xiao-Liu-Qiu Island, southern Taiwan in summer; (F) Specimen from Sail Rock, KNP, southern Taiwan in winter showing tiny villous basal portion (arrows) and highly branched glabrous upper portion. (G-I) Magnification of the villous basal portion (arrows) for the specimens from Wukeuitung, Xiao-Liu-Qiu Island, southern Taiwan in summer. Arrowheads in C indicate that the glabrous upper portion eventually decays or dies off in the senescing plant; (J-K) Magnification of the villous basal portion (arrows) in specimen from Small Port, KNP, southern Taiwan in winter; (L) Magnification of the villous basal portion (arrows) in specimen from Sail Rock, KNP, southern Taiwan in winter.
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Fig2: Variations of the external morphologies of gametophyticG. pacificafor the specimens collected from three different locations in southern Taiwan.(A-C) Specimens from Xiao-Liu-Qiu Island, southern Taiwan in summer showing different size of the villous basal portion (arrows) and different density of the glabrous upper portion. One specimen (C) even showed the decay of glabrous upper portion (arrowheads); (D-E) Specimens from Small Port, Kenting National Park (KNP), southern Taiwan in winter showing smaller villous basal portion (arrows) and highly branched glabrous upper portion of material from Wukeuitung, Xiao-Liu-Qiu Island, southern Taiwan in summer; (F) Specimen from Sail Rock, KNP, southern Taiwan in winter showing tiny villous basal portion (arrows) and highly branched glabrous upper portion. (G-I) Magnification of the villous basal portion (arrows) for the specimens from Wukeuitung, Xiao-Liu-Qiu Island, southern Taiwan in summer. Arrowheads in C indicate that the glabrous upper portion eventually decays or dies off in the senescing plant; (J-K) Magnification of the villous basal portion (arrows) in specimen from Small Port, KNP, southern Taiwan in winter; (L) Magnification of the villous basal portion (arrows) in specimen from Sail Rock, KNP, southern Taiwan in winter.
Mentions: After we determining that G. pacifica and G. “filamentosa” are the same species, this study observed that specimens from different locations in southern Taiwan showed a range of external morphological variation in different seasons. Figure 2 shows that the specimens from Xiao-Liu-Qiu Island collected in the summer often possess a tuft of larger and distinctly villous branches in the lower part of the thallus (Figure 2A-2C, 2G-2I). The overall size of the lower villous part of the thallus and the density of upper glabrous branches vary among different individuals within the population. Some individuals had few clusters of loosely dichotomous glabrous branches in the upper part of the thallus (Figure 2A) and a tuft of wider and larger villous branches in the lower part of the thallus (Figure 2G). Some individuals had few clusters of densely dichotomous glabrous branches in the upper part of the thallus (Figure 2B) and a tuft of narrower and smaller villous branches in the lower part of the thallus (Figure 2H). Interestingly, one of the specimens consisted solely of very few glabrous branches in the upper part of the thallus (Figure 2C) and some residuals of glabrous branches can still be seen attaching on the lower villous branches (arrowheads in Figure 2C, 2I). A careful examination of the glabrous branches on this particular specimen showed that most of them were old and showed numerous lesions (image not shown). This observation suggests that the glabrous branches might eventually decay or die off in summer and the villous branches might be retained for some time after the decay/die-off of the glabrous branches, often leading to its misidentification as G. filamentosa (imagine the scenario that the last cluster of glabrous branches and those residuals decay in Figure 2C). In contrast, the specimens from Small Port (Figure 2D-2E, 2J-2K) and Sail Rock (Figure 2F, 2L) collected in the winter showed a tuft of small villous branches in the lower part of the thallus. The size of the villous branches in the lower part of the thallus and the density of the glabrous branches in the upper part vary across different individuals within the overall local population. In some cases, involving presumably more mature individuals, plants show several clusters of densely glabrous branches in the upper part of the thallus (Figure 2D) and a tuft of small villous branches in the lower part (Figure 2J). In other cases, representing presumably younger individuals, plants possess few clusters of densely dichotomous glabrous branches in the upper part of the thallus (Figure 2E-2F) and a tuft of tiny (occasionally unnoticeable) villous branches (Figure 2K-2L). To better quantify the external morphological difference among the specimens from different locations, we estimated the ratio between the height of the glabrous branch (G) and the villous branch (V). The G/V ratio of the specimens from Xiao-Liu-Qiu Island in summer is significantly smaller than those from Small Port and Sail Rock collected in the winter based on our comparison (Figure 3; p < 0.05). This result supports our previous observations that the specimens in the summer have larger villous branches than those in the winter. To rule out the possibility that our observed external variation results from the comparison of two different species, we additionally obtained rbc L sequences of the specimens from Small Port and Sail Rock and then compared these with that from Xiao-Liu-Qiu Island, as well as that from Sorsogon, Philippines. Results revealed that they share 100% identical rbc L sequences, indicative of conspecificity. Phylogenetic analysis also supports the same conclusion as they are grouped together (Figure 4). However, the inter-specific relationship differs from previous results. The lack of statistical support suggests that a difference might be caused by insufficient informative sites from the smaller set of characters (669 vs. 1407) used in this analysis (Figure 4). Because the glabrous branches of G. pacifica contain considerable mucilage, it is often difficult to obtain pure DNA for further PCR reactions. The traditional CTAB method (Doyle and Dickson, 1987) with at least three rounds of chloroform: isoamyl alcohol (24:1) treatments works more effectively than the commercial DNA extraction kit. Morphological observations and molecular analyses revealed that the villous branches are small in the winter and grow larger in the summer. Considering that one of the specimens from Xiao-Liu-Qiu Island showed extremely scarce glabrous branches (Figure 2F), it is tempting to speculate that the material identified as G. filamentosa might be the remaining villous part of senescing G. pacifica. Similar gross morphology and G/V ratio among specimens obtained during similar seasons over different years (e.g., Figure 2D-2E from March in 2003 and Figure 2F from February in 2012) (Figure 3) suggests that environmental cues such as temperature might serve as the most significant factor affecting external morphological development in G. pacifica.Figure 2

View Article: PubMed Central

ABSTRACT

Background: Members of the calcified red algal genus, Galaxaura, are distributed predominantly in warm temperate, subtropical, and tropical regions worldwide. The capacity of these algae to form calcified thalli could play a critical role in the carbon cycle of these ecosystems. Previous studies have suggested that the reported species diversity of Galaxaura may be exaggerated due to a lack of knowledge regarding external morphological differences between gametophytic and tetrasporophytic plants (or among different life stages) of a single species.

Results: To examine this issue, this study collected specimens of two morphologically distinct Galaxaura from Taiwan and the Philippines. These specimens were initially identified as two species (G. pacifica Tanaka and G. filamentosa Chou ex Taylor) based on their morphological features. Our molecular analyses, however, unexpectedly showed that these two specimens shared 100% identical rbc L sequences, indicating that they represented a single species comprising two distinct external morphologies. Furthermore, our extensive observations and molecular analyses on several specimens from different locations in southern Taiwan has revealed that these morphological differences could be due to seasonal variation.

Conclusions: This study proposes that G. &ldquo;filamentosa&rdquo; from the Philippines could represent the remnants of the lower villous part of older gametophytic plants of G. pacifica after senescence of the upper smooth part of the thallus. As such we propose that these two previously distinct algal species from the northwest Pacific Ocean as a single species, G. pacifica. This study shows that the biodiversity of the calcified red algae Galaxaura could be overestimated without the assistance of molecular tools. Additionally, this study provides insights into the biodiversity and unique biology of the calcified red algae Galaxaura.

Electronic supplementary material: The online version of this article (doi:10.1186/1999-3110-54-1) contains supplementary material, which is available to authorized users.

No MeSH data available.


Related in: MedlinePlus