[Séb_59]

Hereditas
Volume 141 Issue 3 Page 252 - December 2004


Karyological evidence for interspecific hybridization between Cichla monoculus and C. temensis (Perciformes, Cichlidae) in the Amazon


MARINEIDE NEVES ALVES BRINN, JORGE IVAN REBELO PORTO and ELIANA FELDBERG,

Cichla monoculus, Cichla temensis (peacock bass or tucunaré), and its presumed hybrids, were cytogenetically analyzed. The fish were collected at three distinct sites in the central Amazon basin, namely in the Uatumã (C. monoculus, C. temensis and their natural hybrid), Jaú (C. temensis), and Solimões rivers (C. monoculus). The two species and the natural hybrid showed the same diploid number, 2n=48 acrocentric chromosomes. Single NORs were detected in the distal region of the long arm in all three species. However, in C. monoculus, the NOR was found on the second pair of the complement, in C. temensis, on the third pair and in the hybrid two NOR patterns were found, one on the second pair and the other on the third pair of chromosomes. The two species and the hybrid have their constitutive heterochromatin located in the pericentromeric region of all chromosomes and an interstitial C-band located on the largest chromosome pair. The great similarity in the chromosome number and morphology, chromosome size class differences, the NOR patterns and C-banding suggested chromosomal stasis during speciation and hybridization of Cichla.

[wildwolf]

salut
très intéressant!
ce qui irait dans le sens de la prise en compte de l'hybridation comme facteur de spéciation.
Lau.
Ps : séb, as tu eu le temps de regarder si tu avais l'article de Stiassny sur les tilapia?

[Hulk]

Une preuve de plus, si c'était nécessaire, que la spéciation n'est pas quelque chose de "propre et net", et que la présence d'individus intermédiaires ne signifie pas forcément qu'on a affaire à une même espèce (et réciproquement, d'ailleurs).

Ce Message a été édité par: Hulk le 09-02-2005 18:10

[Hulk]

C'est ton petit doigt qui t'a soufflé ça? Eh! bien, il ne s'est pas trompé. Tu vois qu'il est plus utile que lorsque tu le mets dans l'orifice des autres...

[xavier.longy]

Coquins les quinquagénaires....

[Hulk]

Coquins les quinquagénaires....

J'espère que -allitération mise à part-, tu ne m'inclus pas dans les quinquagénaires, ou alors, c'est que tu n'as pas été long à trouver la valve de mon occiput!

[Hulk]

je savais que ça te ferait plaisir d'être assimilé à un quinquagénaire.
ceci dit, je ne fais pas non plus partie de cette caste....

Ne me dis pas que tu fais déjà partie des sexy-génaires?

[wildwolf]

salut
hybridation, hybridation quand tu nous tiens!!
dans le lac Barombi Mbo :

Reticulate sympatric speciation in Cameroonian crater lake cichlids.

Schliewen UK, Klee B.

Department of Ichthyology, Bavarian State Collection of Zoology (ZSM), Munchhausenstr, 21, 81247 Munich, Germany. schliewen@zsm.mwn.de.

BACKGROUND: Traditionally the rapid origin of megadiverse species flocks of extremely closely related species is explained by the combinatory action of three factors: Disruptive natural selection, disruptive sexual selection and partial isolation by distance. However, recent empirical data and theoretical advances suggest that the diversity of complex species assemblages is based at least partially on the hybridization of numerous ancestral allopatric lineages that formed hybrids upon invasion of new environments. That reticulate speciation within species flocks may occur under sympatric conditions after the primary formation of species has been proposed but not been tested critically. RESULTS: We reconstructed the phylogeny of a complex cichlid species flock confined to the tiny Cameroonian crater lake Barombi Mbo using both mitochondrial and nuclear (AFLP) data. The nuclear phylogeny confirms previous findings which suggested the monophyly and sympatric origin of the flock. However, discordant intra-flock phylogenies reconstructed from mitochondrial and nuclear data suggest strongly that secondary hybridization among lineages that primarily diverged under sympatric conditions had occurred. Using canonical phylogenetic ordination and tree-based tests we infer that hybridization of two ancient lineages resulted in the formation of a new and ecologically highly distinct species, Pungu maclareni. CONCLUSIONS: Our findings show that sympatric hybrid speciation is able to contribute significantly to the evolution of complex species assemblages even without the prior formation of hybrids derived from allopatrically differentiated lineages.


voilà
Lau.
ps : et les quadra, quinqua et autre sexagénaire, ça s'hybride aussi??niark, niark!