Molecular diversity and morphology of the genus Actinotrichia (Galaxauraceae, Rhodophyta) from the western Pacific, with a new record of A. robusta in the Andaman Sea

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  • ABSTRACT

    Actinotrichia is a calcified galaxauracean red algal genus with temperate and tropical distributions in the Indian and Pacific Oceans. Morphological characteristics, along with rbcL and cox1 sequences, were analyzed from specimens collected in the western Pacific and the Indian Oceans. Both rbcL and cox1 data confirmed the occurrence of A. fragilis, A. robusta, and Actinotrichia sp. in this region. The presence of A. fragilis was verified in tropical Indo-Pacific and temperate northeast Asian waters and was characterized by high genetic diversity. Although A. robusta commonly occurs in the East China Sea, we confirmed its presence on rocks and crustose algae in the subtidal zone of three islands in the Andaman Sea. Actinotrichia sp. was similar to A. calcea in morphology and distribution, but with sufficiently different sequences, thus, additional sampling over the range will enable a more realistic evaluation of its taxonomic status.


  • KEYWORD

    Actinotrichia fragilis , Actinotrichia robusta , cox1 , genetic diversity , rbcL , red algae , systematics

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  • [Table 1.] Species, collection or sequence source, and GenBank accession numbers of rbcL and cox1 sequences
    Species, collection or sequence source, and GenBank accession numbers of rbcL and cox1 sequences
  • [Table 2.] Pairwise divergence matrix of Actinotrichia using rbcL and cox1 sequence data
    Pairwise divergence matrix of Actinotrichia using rbcL and cox1 sequence data
  • [Fig. 1.] Maximum likelihood tree of Actinotrichia inferred from rbcL sequences. Values shown near branches are bootstrap values (1,000 iterations) and Bayesian posterior probabilities. Only bootstrap values >50% and Bayesian posterior probabilities >0.95 are shown. PH, Philippines; JP, Japan; TW, Taiwan; ID, Indonesia; TH, Thailand; OM, Oman; KR, Korea; GP, Guadeloupe.
    Maximum likelihood tree of Actinotrichia inferred from rbcL sequences. Values shown near branches are bootstrap values (1,000 iterations) and Bayesian posterior probabilities. Only bootstrap values >50% and Bayesian posterior probabilities >0.95 are shown. PH, Philippines; JP, Japan; TW, Taiwan; ID, Indonesia; TH, Thailand; OM, Oman; KR, Korea; GP, Guadeloupe.
  • [Fig. 2.] Maximum likelihood tree of Actinotrichia inferred from cox1 sequences. Values shown near branches are bootstrap values (1,000 iterations) and Bayesian posterior probabilities. Only bootstrap values >50% and Bayesian posterior probabilities >0.95 are shown. PH, Philippines; ID, Indonesia; TH, Thailand; KR, Korea; HW, Hawaii; JP, Japan.
    Maximum likelihood tree of Actinotrichia inferred from cox1 sequences. Values shown near branches are bootstrap values (1,000 iterations) and Bayesian posterior probabilities. Only bootstrap values >50% and Bayesian posterior probabilities >0.95 are shown. PH, Philippines; ID, Indonesia; TH, Thailand; KR, Korea; HW, Hawaii; JP, Japan.
  • [Fig. 3.] Actinotrichia fragilis (Forsskal) Børgesen. (A) Morphology of thallus in Cebu, Philippines. (B) Morphology of herbarium specimen collected in Ilocos Norte, Philippines. (C) Dichotomously branched thallus. (D) Section of gametophyte branch with assimilatory filaments arising from the outermost cortical cells (arrows). (E) Three to four cortical cell layers with assimilatory filament (arrow) and medullar portion. (F) Young spermatangial branch with primary spermatangial filament (arrowhead) and secondary spermatangial filaments (arrows). (G) Spermatangial conceptacle showing the numerous terminal spermatangia (arrowheads) and peripheral layer of conceptacle (arrows). (H) Early carpogonial branch showing carpogonium with trichogyne, hypogynous with 2-sterile branches (arrows) and basal cell. (I) Developed carpogonial branch showing carpogonium with trichogyne, hypogynous with enlarge sterile branch (arrowheads) and basal cell bearing numerous involucral filaments (arrows). (J) Mature cystocarp showing gonimoblast filament bearing carposporangia and paraphyses (arrowheads) arising from pericarp (arrows). (K) Tetrasporophyte branches with assimilatory filaments (arrows). (L) Terminal and lateral tetrasporangia on assimilatory filaments. (M) Cruciate tetrasporangia. b, basal cell; c, carpogonium; cp, carpospores; g, gonimoblast; h, hypogynous cell; spb, spermatangial branch; t, trichogyne. Scale bars represent: B, 1 cm; C & K, 1 mm; D, 100 μm; E, G, J, L & M, 50 μm; F, H & I, 20 μm.
    Actinotrichia fragilis (Forsskal) Børgesen. (A) Morphology of thallus in Cebu, Philippines. (B) Morphology of herbarium specimen collected in Ilocos Norte, Philippines. (C) Dichotomously branched thallus. (D) Section of gametophyte branch with assimilatory filaments arising from the outermost cortical cells (arrows). (E) Three to four cortical cell layers with assimilatory filament (arrow) and medullar portion. (F) Young spermatangial branch with primary spermatangial filament (arrowhead) and secondary spermatangial filaments (arrows). (G) Spermatangial conceptacle showing the numerous terminal spermatangia (arrowheads) and peripheral layer of conceptacle (arrows). (H) Early carpogonial branch showing carpogonium with trichogyne, hypogynous with 2-sterile branches (arrows) and basal cell. (I) Developed carpogonial branch showing carpogonium with trichogyne, hypogynous with enlarge sterile branch (arrowheads) and basal cell bearing numerous involucral filaments (arrows). (J) Mature cystocarp showing gonimoblast filament bearing carposporangia and paraphyses (arrowheads) arising from pericarp (arrows). (K) Tetrasporophyte branches with assimilatory filaments (arrows). (L) Terminal and lateral tetrasporangia on assimilatory filaments. (M) Cruciate tetrasporangia. b, basal cell; c, carpogonium; cp, carpospores; g, gonimoblast; h, hypogynous cell; spb, spermatangial branch; t, trichogyne. Scale bars represent: B, 1 cm; C & K, 1 mm; D, 100 μm; E, G, J, L & M, 50 μm; F, H & I, 20 μm.
  • [Fig. 4.] Actinotrichia robusta Itono. (A) Morphology of thallus in Similan Islands, Thailand. (B) Morphology of herbarium specimen collected in Surin Islands, Thailand. (C) Branches appearing alternate. (D) Section of gametophyte branch with assimilatory filaments arising from the outermost cortical cells (arrows). (E) Three to four cortical cell layers with assimilatory filaments (arrows) and medullar portion. (F) Young spermatangial branch with several secondary spermatangial filaments (arrows). (G) Spermatangial conceptacle showing numerous terminal spermatangia (arrowheads) enclosed within peripheral layer of conceptacle (arrows). (H) Carpogonial branch initial showing carpogonium with trichogyne, hypogynous, and basal cell. (I) Young carpogonial branch showing carpogonium, hypogynous bearing lateral sterile branches (arrows), and basal cell with involucral filament initial (arrowhead). (J) Mature cystocarp with carposporangia arising along inner surface of pericarp (arrows) and paraphyses (arrowheads) intermixing with the gonimoblast filaments. (K) Tetrasporophyte branches with assimilatory filaments (arrows). (L) Terminally and laterally tetrasporangia on assimilatory filaments. (M) Well developed tetrasporangia. b, basal cell; c, carpogonium; co, cortex; cp, carpospores; h, hypogynous cell; spb, spermatangial branch; t, trichogyne. Scale bars represent: B, 1 cm; C & K, 1 mm; D & E, 100 μm; F, G, J, L & M, 50 μm; H & I, 20 μm.
    Actinotrichia robusta Itono. (A) Morphology of thallus in Similan Islands, Thailand. (B) Morphology of herbarium specimen collected in Surin Islands, Thailand. (C) Branches appearing alternate. (D) Section of gametophyte branch with assimilatory filaments arising from the outermost cortical cells (arrows). (E) Three to four cortical cell layers with assimilatory filaments (arrows) and medullar portion. (F) Young spermatangial branch with several secondary spermatangial filaments (arrows). (G) Spermatangial conceptacle showing numerous terminal spermatangia (arrowheads) enclosed within peripheral layer of conceptacle (arrows). (H) Carpogonial branch initial showing carpogonium with trichogyne, hypogynous, and basal cell. (I) Young carpogonial branch showing carpogonium, hypogynous bearing lateral sterile branches (arrows), and basal cell with involucral filament initial (arrowhead). (J) Mature cystocarp with carposporangia arising along inner surface of pericarp (arrows) and paraphyses (arrowheads) intermixing with the gonimoblast filaments. (K) Tetrasporophyte branches with assimilatory filaments (arrows). (L) Terminally and laterally tetrasporangia on assimilatory filaments. (M) Well developed tetrasporangia. b, basal cell; c, carpogonium; co, cortex; cp, carpospores; h, hypogynous cell; spb, spermatangial branch; t, trichogyne. Scale bars represent: B, 1 cm; C & K, 1 mm; D & E, 100 μm; F, G, J, L & M, 50 μm; H & I, 20 μm.
  • [Fig. 5.] Actinotrichia sp. (A) Morphology of herbarium specimen collected in Surin Islands, Thailand. (B) Dichotomous branches. (C) Three cortical cell layers with assimilatory filaments and medullar portion. Scale bars represent: A, 1 cm; B, 1 mm; C, 50 μm.
    Actinotrichia sp. (A) Morphology of herbarium specimen collected in Surin Islands, Thailand. (B) Dichotomous branches. (C) Three cortical cell layers with assimilatory filaments and medullar portion. Scale bars represent: A, 1 cm; B, 1 mm; C, 50 μm.