The taxonomic status and the distribution of
Rosenvingea
species need attention because of the difficulties in morphological identification in the laboratory as well as in the field. We analyzed mitochondrial
cox
3 and plastid
psa
A gene sequences from
Rosenvingea
species from Vietnam, Mexico and Panama in combination with morphological examinations. Our results confirmed the occurrence of
R. intricata
and
R. orientalis
in Vietnam.
R. intricata
formed dense decumbent mats with many flat branches, often inter-adhesive, and was up to 5 cm in diameter.
R. orientalis
thalli were up to 18 cm long with narrow (less than 2 mm in width) tubular to compressed fronds. Both
cox
3 and
psa
A phylogenies revealed the non-monophyly of the genus
Rosenvingea
, as reported previously for other scytosiphonacean genera.
INTRODUCTION
The genus
Rosenvingea
Børgesen is a tropical to subtropical genus of scytosiphonacean brown algae that includes seven currently accepted species (
Guiry and Guiry 2014
).
Rosenvingea
is distinguished by its erect thalli with alternate or dichotomous branches, an apical to subapical meristem, a single plastid and prominent pyrenoid in vegetative cells, hollow medulla, and phaeophycean hairs and plurangial sori scattered on the thallus surface (
Børgesen 1914
,
Abbott and Huisman 2004
,
Norris 2010
,
West et al. 2010
).
Børgesen (1914)
established the genus with
R. sanctae-crucis
Børgesen as the type and included three other species in the genus
Asperococcus
J. V. Lamouroux as follows,
R. fastigiata
(Zanardini) Børgesen,
R. intricata
(J. Agardh) Børgesen, and
R. orientalis
(J. Agardh) Børgesen. Subsequently three more species were added:
R. antillarum
(P. Crouan & H. Crouan) M. J. Wynne,
R. floridana
(W. R. Taylor) W. R. Taylor, and
R. nhatrangensis
E. Y. Dawson (
Dawson 1954
,
Taylor 1955
,
Wynne 1997
). However, the species circumscription in
Rosenvingea
is very confused. For example,
R. sanctae-crucis
, the type of
Rosenvingea
, was suggested to be conspecific with
R. orientalis
(
Earle 1969
,
Littler and Littler 2000
,
Wynne 2005
,
Dawes and Mathieson 2008
,
Nelson and Wilcox 2010
).
Wynne (1997)
treated
R. floridana
as a synonym of
R. antillarum
, although
Norris (2010)
considered that both species are not conspecific. The cosmopolitan or endemic distribution patterns of
Rosenvingea
species are, accordingly, doubtful.
The first molecular analysis of
Rosenvingea
was based on sequences of
rbc
L and
rbc
S from Japanese specimen of
R. intricata
(
Kogame et al. 1999
) and was followed with
psa
A by
Cho et al. (2006)
. Subsequently,
R. intricata
was analyzed with additional seven genes, plastid
atp
B,
psa
A, and
psb
A, and mitochondrial
atp
9,
cox
1,
cox
3, and
nad
11 (
Silberfeld et al. 2010
). The second species included in molecular taxonomic study is
R. orientalis
that was sequenced for
psa
A and
cox
3 (
West et al. 2010
,
Lee et al. 2014
).
Dawson (1954)
described
R. nhatrangensis
as a new species and also reported
R. orientalis
in Nha Trang, Vietnam. Afterwards,
R. intricata
was reported in southern Vietnam (
Pham 1969
) and additional record from northern Vietnam (
Nguyen et al. 1993
). Another species,
R. fastigiata
was also reported to occur in northern Vietnam (
Nguyen et al. 1993
,
2013
). We collected two species of
Rosenvingea
in Nha Trang during March and April 2011. Together with morphological observations, we analyzed both
cox
3 and
psa
A gene from these specimens so as to provide a better understanding of species diversity and phylogenetic relationships in
Rosenvingea
.
MATERIALS AND METHODS
Representative
Rosenvingea
specimens were collected from mid intertidal zone in Cam Ranh Bay, Nha Trang, Vietnam, and specimens collected in Mexico and Panama were also included in analyses for comparison (
Table 1
). All specimens collected were mounted on herbarium sheets. Small parts of the specimens were cut for molecular analyses. Photographs were taken with a DP-71 camera (Olympus, Tokyo, Japan) attached to a BX-51 microscope (Olympus). Voucher specimens were deposited at the Department of Biology, Chungnam National University, Daejeon, Korea (CNUK).
Specimens andcox3 andpsaA sequences of the taxa included in this study
Specimens and cox3 and psaA sequences of the taxa included in this study
Information on specimens used for the molecular study is given in
Table 1
. DNA extraction, PCR amplification, and sequencing followed
Boo et al. (2011)
. Primer pairs for the amplification and sequencing of each gene were F49–R20 for
cox
3 (
Boo et al. 2010
,
2011
) and psaA130F-psaA940R and psaA870F-psaA1760R for
psa
A (
Yoon et al. 2002
).
Phylogenies of
cox
3 and
psa
A datasets were reconstructed using maximum likelihood (ML), including
Ectocarpus siliculosus
(Dillwyn) Lyngbye and
Pylaiella littoralis
(Linnaeus) Kjellman as outgroups. ML analyses were performed with RAxML v.7.2.8 (
Stamatakis 2006
) using the GTR + GAMMA + I model. We used 200 independent tree inferences, applying options of automatically optimized subtree pruning regrafting rearrangement and 25 distinct rate categories in the program to identify the best tree. Statistical support for each branch was obtained from 1,000 bootstrap replications with the same substitution model.
Bayesian inference was performed for individual datasets with MrBayes v.3.2.1 (
Ronquist et al. 2012
) using the Metropolis-coupled Markov Chain Monte Carlo (MC3) with the GTR + GAMMA + I model. For each matrix, two million generations of two independent runs were performed with four chains and sampling trees every 100 generations. The burn-in period was identified graphically by tracking the likelihoods at each generation to determine whether they reached a plateau. The 40,002 trees sampled at the stationary state were used to infer Bayesian posterior probabilities (BPP).
RESULTS
- Phylogeny ofcox3 andpsaA
A 627-nucleotide portion of
cox
3 was aligned for 40 sequences including 12
Rosenvingea
and one previously published sequence of
R. intricata
from New Caledonia. Variable sites occurred at 284 positions (45.3%), of which 222 positions (35.4%) were parsimoniously informative.
R. intricata
differed by 32-39 bp (5.5-6.7%) from
Rosenvingea
sp. collected in Hawaii and Mexico and by 40-45 bp (6.9-7.7%) from
R. orientalis
from Vietnam. There was a difference of 42 bp (7.2%) between
Rosenvingea
sp. and
R. orientalis
. One sequence from New Caledonia (GQ368280) was highly divergent from other sequences of
R. intricata
(28 bp, 4.8%). Pairwise divergence within
R. intricata
(except the New Caledonia specimen) ranged up to 8 bp (1.4%). The phylogenetic relationships of
Rosenvingea
, using
cox
3 sequences, showed a well-supported Scytosiphonaceae consisting of eight genera (
Fig. 1
). There was no resolution of the phylogenetic relationships among sequences of
R. intricata
sequences.
Maximum likelihood tree of Rosenvingea inferred from the phylogenetic analysis of cox3 sequences. Values shown near branches are bootstrap values (1,000 iterations) and Bayesian posterior probabilities. Only bootstrap values >50% and Bayesian posterior probabilities >0.90 are shown.
A 1,488-nucleotide portion of the
psa
A gene was compared across 28 sequences including six
Rosenvingea
and three previously published sequences collected from New Caledonia, Mexico and Japan. Variable sites occurred at 392 positions (26.3%), of which 256 positions (17.2%) were parsimoniously informative.
R. intricata
differed by 88-98 bp (6.3-7.0%) from
R. orientalis
. The
psa
A sequence of
R. intricata
from the Vietnamese specimen differed by 11 bp (0.8%) from the specimen from Panama, 54 bp (3.9%) from the New Caledonian specimen, and 92 bp (6.6%) from the Japanese specimen. In the
psa
A tree (
Fig. 2
),
R. intricata
from Vietnam and Panama together with
R. intricata
from New Caledonia formed a monophyletic group with moderate support values (68% for ML and 0.94 for BPP). This group was closely related to
Hydroclathrus
with maximum support values. One published sequence of
R. intricata
collected from Japan did not belong to the group of samples from Vietnam and Panama, but rather sister to
Colpomenia sinuosa
(Mertens ex Roth) Derbès & Solier.
R. orientalis
was placed in the clade that includes
R. intricata, Hydroclathrus clathratus
(C. Agardh) Howe,
H. tenuis
C. K. Tseng & Lu,
Chnoospora implexa
J. Agardh, and
Colpomenia sinuosa
(95% for ML and 1.0 for BPP).
Maximum likelihood tree of Rosenvingea inferred from the phylogenetic analysis of psaA sequences. Values shown near branches are bootstrap values (1,000 iterations) and Bayesian posterior probabilities. Only bootstrap values >50% and Bayesian posterior probabilities >0.90 are shown.
- Morphology ofRosenvingea intricataandRosenvingea orientalis
Thalli of
R. intricata
were brown to dark brown in color, up to 5 cm in height and 5 mm in diameter (
Fig. 3A
-
D
). The thalli formed a dense decumbent mat with many branches that were often inter-adhesive. The axes were cylindrical to compressed, subdichotomously to irregularly lobed, 4-6 mm in diameter, becoming narrower distally. Apices of branches were mostly rounded.
Morphology of Rosenvingea intricata and R. orientalis from Vietnam. (A-D) morphology of R. intricata. (A & B) Herbarium specimens collected at Cam Ranh Bay, Nha Trang, Vietnam. (C & D) Subdichotomous to irregular branches. (E-H) Morphology of R. orientalis. (E & F) Herbarium specimens of R. orientalis collected at Cam Ranh Bay, Nha Trang, Vietnam. (G) Dichotomous branches in the upper thallus. (H) Holdfast. Scale bars represent: A, B, E & F, 1 cm; C & D, 500 µm; G & H, 200 µm.
Thalli of
R. orientalis
were up to 18 cm long with narrow (less than 2 mm in width), tubular to compressed fronds that are dichotomously branched in the upper thallus (
Fig. 3E
-
H
). The thalli were golden to light brown in color, with hollow axes, up to 2 mm in diameter. Branches were dichotomous to irregularly lobed, usually tapering at the base and apex, ends of branches nearly hair-like.
DISCUSSION
Our analyses of mitochondrial
cox
3 and plastid
psa
A sequences clearly showed the occurrence of two genetically and morphologically distinct species of
Rosenvingea
from Nha Trang, Vietnam. We collected both species in Cam Ranh Bay, Nha Trang, Vietnam, and have assigned these species to
R. intricata
and
R. orientalis
. Morphological comparison with other
Rosenvingea
species is given in
Table 2
.
Morphological comparison ofRosenvingea fastigiataandR. intricatawith similar species
Morphological comparison of Rosenvingea fastigiata and R. intricata with similar species
R. intricata
is the most common species in the genus reported in tropical to subtropical waters of the world (see
Guiry and Guiry 2014
). In
cox
3 and
psa
A trees (excluding the Japanese taxon in the
cox
3 tree due to the unavailability of the samples),
R. intricata
was separated into three different taxa. The first group was composed of specimens from Vietnam, Mexico, and Panama. The morphology of our plants is consistent with the description and illustration of
R. intricata
(
Børgesen 1914
,
Earle 1969
). We therefore recognized this taxon as
R. intricata
because the clade in our analyses included specimens collected from near the type locality in Veracruz, Mexico. Accordingly, our study confirmed the previous reports on the occurrence of
R. intricata
in Vietnam (
Pham 1969
,
Nguyen et al. 1993
) as well as Baja California in Mexico (
Norris 2010
) and Panama (
Wysor and De Clerck 2003
). The second taxon was the New Caledonia taxon (as GQ368280 in
cox
3, GQ368338 in
psa
A) that formed a sister to
R. intricata
. The pairwise divergence of
psa
A (54-55 bp, 3.9%) between the New Caledonian taxon and
R. intricata
is similar or higher than that between scytosiphonacean species (e.g., 2.2% between
Scytosiphon lomentaria
and
S. dotyi
) (
Cho et al. 2006
). The third taxon distinguished consisted of the Japanese specimens (DQ239784) and was distantly related to other taxa of
Rosenvingea
. These results reveal an urgent need for further molecular analysis of specimens currently assigned to
R. intricata
in various countries (see
Guiry and Guiry 2014
).
R. orientalis
is distributed in subtropical to tropical waters of Kenya, Florida in USA, Southeast Asia, and Australasia (see
Guiry and Guiry 2014
). Its type locality is Manilla, the Philippines, and its diagnostic characters are the tubular to compressed thalli, the tall size (up to 30 cm), narrow diameter of branches (less than 2 mm), and dichotomous branches (
Børgesen 1914
,
Earle 1969
,
West et al. 2010
). Following previous phycologists’ opinions (
Earle 1969
,
Littler and Littler 2000
,
Abbott and Huisman 2004
,
Wynne 2005
),
Nelson and Wilcox (2010)
reported that
R. orientalis
may be conspecific with
R. santae-crucis
and the former has priority. Molecular analysis of type specimens or fresh collections of
R. santae-crucis
near the type locality are needed to resolve about the conspecificity of these taxa.
The absence of
R. nhatrangensis
in our collections despite our repeated samplings in the type locality, Nha Trang, Vietnam, suggests that there is an urgent need for an analysis of the type specimens of this and related taxa.
R. nhatrangensis
is distinguished by much inflated, lobed and short thalli with its wide diameter of branches (2.5-3.0 cm in lower part of erect thallus and 1.0-1.5 cm in the branches) (
Dawson 1954
).
R. fastigiata
var.
major
Reinbold reaches a branch diameter of 5 mm, and bears sori in rings around the hair groups. However, based on figures and description by
Dawson (1954)
,
Egerod (1974)
suggested that
R. nhatrangensis
may be conspecific with
R. fastigiata
var.
major
. Kochang Archipelago, Thailand, the type locality of this variety is close to Nha Trang, Vietnam, the type locality of
R. nhatrangensis
(
Reinbold 1901
,
Dawson 1954
). Fresh collection of
R. fastigiata
var.
major
in the type locality is necessary to confirm their conspecificity.
This is the first study using mitochondrial
cox
3 sequences to reveal the non-monophyly of the genus
Rosenvingea
. Our analyses showed that
Rosenvingea
that clustered with
Hydroclathrus
ssp., and
Chnoospora implexa
. This topology was also reflected in the
psa
A tree with the inclusion of
Colpomenia sinuosa
. The nonmonophyly of
Rosenvingea
revealed in the present study indicates the need for a reconsideration of the generic concept. However, based on the
cox
3 and
psa
A trees, it is to date impossible to combine or rearrange these genera based on molecular data as none of the genera are monophyletic in the analyses.
Chnoospora
,
Colpomenia
,
Petalonia
, and
Scytosiphon
in the family Scytosiphonaceae have been confirmed to be non-monophyletic in
rbc
L and / or
psa
A, and
cox
3 phylogenies (
Kogame et al. 1999
,
Cho et al. 2006
,
Lee et al. 2014
). As discussed by
Kogame et al. (1999)
and
Cho et al. (2006)
, further investigations based on taxon-wide sampling, and employing other supplementary gene sequences, life histories, and ultrastructure of gametes, are urgently needed to clarify the relationships of all these currently non-monophyletic genera of the Scytosiphonaceae.
In conclusion, we confirmed the occurrence of
R. intricata
and
R. orientalis
from Nha Trang, Vietnam. Our study therefore reveals that both species are distributed from Vietnam to Mexico and / or Panama. Further collection and careful examination of specimens will probably extend the known distributions of both species to surrounding Vietnamese waters. Additional investigations are needed to confirm the relationships of
R. nhatrangensis
with
R. intricata
and
R. fastigiata
var.
major
. The finding of cryptic species within
R. intricata
highlights the fact that the number of
Rosenvingea
species in the world inventory will increase with additional collections.
Acknowledgements
We thank Rafael Riosmena-Rodriguez for help in collection trip in Mexico, and Alison Sherwood and Cindy Fernandez for providing specimens from Hawaii and Panama, respectively. This work was supported by Research Fund of Chungnam National University, Daejeon, Korea to SMB and Research Fund of Vietnam Ministry of Science and technology (Program of East Sea and Islands) to DDH.
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