A new species of coelacanth

Une nouvelle espèce de coelacanthe. Preuves génétiques et morphologiques

A new species of coelacanth

Laurent Pouyaud ^a*^{, b}, Soetikno Wirjoatmodjo^c, Ike Rachmatika^c, Agus Tjakrawidjaja^c, Renny Hadiaty^c, Wartono Hadie^d

^a Institut de recherche pour le développement (IRD-Orstom), Wisma Anugraha, Jalan Taman Kemang 32B, Jakarta 12730, Indonésie

^b Laboratoire génome et population (CNRS), UPR 9060, 34000 Montpellier, France

^c Division of Zoology, Research and Development Center for Biology, Indonesian Institute of Sciences (LIPI), Cibinong, Indonésie

^d Research Institute of Freshwater Fisheries (RIFF), Jakarta, Indonésie

(Reçu le 24 février 1999, accepté le 8 mars 1999)

Comptes rendus de l'Académie des sciences - Série III - Sciences de la vie / Life Sciences - 1999, 322, 261-267.

Abstract — To test the assumption of the existence of a possible new population of coelacanth in Indonesia, we sequenced the mitochondrial DNA from cytochrome b and 12S rDNA genes, and described the morphological features of the specimen discovered on July 1998. Significant differences in base sequences revealed that the Comorean and the Indonesian coelacanth belong to distinct populations. Estimation of divergence time, high transition—transversion ratios, preponderance of third position silent substitution, strong morphological differentiation and geographical isolation led us to consider that the Indonesian coelacanth is a new species, Latimeria menadoensis n. sp., closely related to L. chalumnae. (© Académie des sciences / Elsevier, Paris.)

Abridged version

On July 1998, the arrival of a lost relative was registered for the celebration of the Diamond Jubilee of the coelacanth Latimeria chalumnae Smith. This discovery of an Indonesian population of coelacanth, almost 10 000 km from the known population in the Comoros immediately raised new taxonomic, biogeographic and conservation implications.

To test the assumption of the existence of a possible new population, we sequenced the mitochondrial DNA from cytochrome b and 12S rDNA genes, and described morphological features of the Indonesian specimen. Our data were then compared with those available from specimens of the Comorean population.

Percentage differences in base sequences are 4.85 % for the 845 base pairs of the partial cytochrome b gene (transition— transversion 13 :1) and 2.85 % for the 984 base pairs of the total 12S rDNA gene (transition—transversion 2.4 :1).

Previous molecular analysis conducted both from the most evolving part of the control region and multilocus DNA fingerprints of 16 individuals of the Comoros and one of Mozambique revealed a low genetic variability comparable to that observed on consanguine stocks of laboratory fish. It enforced ecological observations arguing that the breeding stock at Grand Comoro has a very narrow habitat range with a small relict population. These results strongly suggest that the Comorean and the Indonesian coelacanths belong to distinct populations. Nevertheless, the high transition—transversion ratios and the preponderance of third position silent substitutions (76 %) observed is typical for comparisons between closely related species or between populations within species.

Morphometrical comparison carried out between both populations showed strong differentiation. Sixty-three per cent of the measurements assessed on the Indonesian specimen are excluded from the range of corresponding values described on five individuals of L. chalumnae. The Indonesian specimen is characterised by a shorter head length (23 % SL versus 24—26 % SL); shorter predorsal length (38 % SL versus 40 % SL for PD₁ ; 60 % SL versus 63—65 % SL for PD₂); a slender body depth (20 % SL versus 27 % SL); a caudal peduncle longer (31 % SL versus 26—28 % SL); a longer caudal fin (16 % SL versus 15 % SL). Concerning meristic counts, the Indonesian coelacanth is characterised by a greater number of rays on the second dorsal fin (27 versus 29-31), on the ventral caudal lobe (24 versus 21—22) and on the supplementary caudal lobe (30 versus 25—26).

Many parameters, such as the genetic and morphological differentiation, the evidence of geographical isolation from the vast distance between cryptic populations, the dynamics of the current distribution coupled with the discontinuity of the habitat and the existence of a distinct coloration pattern, lead us to consider that the Indonesian coelacanth is a new species. We propose to name this species Latimeria menadoensis, referring to its sampling location. Nevertheless, we must keep in mind that this species is closely related to L. chalumnae. Referring to an abundant literature concerning approximate molecular clock/evolutionary time calibrations, we are able to give an estimation of the time divergence between the two populations of coelacanth. Two different rates of sequence divergence were used for the 12S rDNA (1 % of nucleotidic substitution per million years) and for the cytochrome b (2 % of nucleotidic substitution per million years). According to these rates, we estimate a divergence time from their common ancestor around 1 220 000 years with cytochrome b and around 1 420 000 years with 12S rDNA. With regards the long history of coelacanth this range of divergence time makes it a recent event, and there is no doubt that this fascinating fish will continue to give us new surprising information.

Remerciements : Les auteurs tiennent à remercier C. Combes, A. Pariselle, D. Aurelle, M. Legendre, J.-F. Renno, J. Slembrouck, C. Tsigenopoulos et P. Levang représentant de l’IRD (ex-Orstom) en Indonésie pour son soutien financier.

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