Study shows anabantoid evolution

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Scientists have produced the first evolutionary family tree for the anabantoids based on molecular data to determine how the fishes are interrelated.

Ralf Britz of The Natural History Museum and Lukas Ruber and Rafael Zardoya of the Museo Nacional de Ciencias Naturales in Madrid used both mitochondrial and nuclear nucleotide sequence data to produce a phylogeny to study how the anabantoids evolved and are related to each other.

The study covered all 19 anabantoid genera and spanned 57 species, ranging from more unusual species such as the Pike-head, Luciocephalus pulcher, to Betta and Trichopterus species.

The enigmatic Pike-headThe study, which has just been published in the journal Systematic Biology, provides evidence to support the theory that the odd-looking Luciocephalus is a member of the so-called "spiral egg clade".

This is a group of osphronemid fishes whose eggs all have a distinctive spiraling ridges and intermittent grooves on the egg surface leading to a structure called the micropyle, which are believed to be a sperm-guiding system to aid fertilisation.

Luciocephalus shares the spiral-egg characters with Parasphaerichthys, Ctenops and Sphaerichthys, but until now nobody has been entirely sure how it is related to other anabantoids.

Berg, Greenwood and Liem all thought that Luciocephalus wasn't closely related to anabantoids, Bleeker, Gosline, Jordan, Weber and De Beaufort believed it was a close relative of anabantoides, while Britz hit the nail on the head in his studies between 1994 and 2001 in suggesting that the fish was a sister group to the chocolate gouramies of the Sphaerichthys genus.

Britz's view is strongly supported here, and the phylogeny shows that the spiral egg clade is monophyletic with Luciocephalus a sister group to Sphaerichthys.

OsphronemidsThe study also shed new light on the relationships of the four subfamiles of the Osphronemidae family - Osphroneminae, Belontiinae, Macropodusinae and Luciocephalinae.

The phylogeny suggests that Belontia is a sister group to Osphronemus, and that Colisa and Trichogaster are a sister group of the Macropodusinae.

For the in-depth details on the relationships of other anabantoids see the paper: Ruber L, Britz R and R Zardoya (2006) - Molecular phylogenetics and evolutionary diversification of labyrinth fishes (Perciformes: Anabantoidei). Systematic Biology, 55(3): 374-397, 2006.