Chow S et al. (2014), On the fourth Diadema species (Diadema-sp) from...

ECB-ART-43529

PLoS One 2014 Jul 01;97:e102376. doi: 10.1371/journal.pone.0102376.

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On the fourth Diadema species (Diadema-sp) from Japan.

Chow S , Kajigaya Y , Kurogi H , Niwa K , Shibuno T , Nanami A , Kiyomoto S .

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Four long-spined sea urchin species in the genus Diadema are known to occur around the Japanese Archipelago. Three species (D. savignyi, D. setosum, and D. paucispinum) are widely distributed in the Indo-Pacific Ocean. The fourth species was detected by DNA analysis among samples originally collected as D. savignyi or D. setosum in Japan and the Marshall Islands and tentatively designated as Diadema-sp, remaining an undescribed species. We analyzed nucleotide sequences of the cytochrome oxidase I (COI) gene in the "D. savignyi-like" samples, and found all 17 individuals collected in the mainland of Japan (Sagami Bay and Kyushu) to be Diadema-sp, but all nine in the Ryukyu Archipelago (Okinawa and Ishigaki Islands) to be D. savignyi, with large nucleotide sequence difference between them (11.0%±1.7 SE). Diadema-sp and D. savignyi shared Y-shaped blue lines of iridophores along the interambulacrals, but individuals of Diadema-sp typically exhibited a conspicuous white streak at the fork of the Y-shaped blue iridophore lines, while this feature was absent in D. savignyi. Also, the central axis of the Y-shaped blue lines of iridophores was approximately twice as long as the V-component in D. savignyi whereas it was of similar length in Diadema-sp. Two parallel lines were observed to constitute the central axis of the Y-shaped blue lines in both species, but these were considerably narrower in Diadema-sp. Despite marked morphological and genetic differences, it appears that Diadema-sp has been mis-identified as D. savignyi for more than half a century.

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Genes referenced: LOC100887844 LOC100893907 LOC115925415

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	Figure 1. Collection localities for Diadema samples in Japan.A, Arasaki, Sagami Bay; B, Waka, Iki Island; C, Sesoko, Okinawa Island; D, Fukai, Ishigaki Island.
	Figure 2. Neighbor-joining phylogenetic tree from COI sequence data.Bootstrap support (>50%) after 1,000 replications is shown at each node. See Table 1 for species designations.
	Figure 3. Underwater images of Diadema setosum.A to F correspond to DST1 to 6 (see Table 1). Note conspicuous white spots on the median naked interambulacral areas, and light colored periproctal cone with orange or red ring.
	Figure 4. Underwater images of Diadema savignyi.A to F correspond to DSV19, 21, 23 to 26 (see Table 1). Note the central axis of the Y-shaped blue lines of iridophores along the median naked interambulacral area was approximately twice as long as the V-component, and comprised of two parallel lines.
	Figure 5. Underwater images of Diadema-sp.A to F correspond to DSV1 to 3, and 12 to 14 (see Table 1). Note the central axis of the Y-shaped blue lines of iridophores along the median naked interambulacral area which was represented by a single line, and similar in length to the V-component. Projection of periproctal cone was observed in one individual (C), but brown in color and an orange ring was not observed. The Y-shaped blue lines of iridophore were usually accompanied by a conspicuous white streak at the fork region (A to C, F), while individuals exhibiting a Y-shaped blue broken line (E) and the absence of a white streak (D, E) were rarely observed.
	Figure 6. Primary tubercle arrangements on the interambulacral areas (bar = 5 mm).A, Diadema-sp.; B, Diadema savignyi; C, Diadema setosum. Outer and inner series of primary tubercles in Diadema-sp. were initiated on the 3rd (rarely 2nd or 4th) and 6th (rarely 5th) coronal plates, respectively (A). Those in D. savignyi began on the 3rd (rarely 2nd or 4th) and 6th (B); and in D. setosum, on the 3rd or 4th (rarely 5th) and 7th or 8th (rarely 6th) coronal plates (C).

References [+] :

Lessios, Population structure and speciation in tropical seas: global phylogeography of the sea urchin Diadema. 2001, Pubmed, Echinobase