to edit fish S. alburnoides

S. alburnoides       SIMILARY TO THE FANTASY WHY FISH


In fact, S. alburnoides forms a complex, consisting of hybrid and pure forms which are all labeled S. alburnoides. Whereas the hybrid forms include males and females, the nonhybrid forms are all males. These males "essentially represent a stable all-male lineage nested within an almost all-female lineage" (Alves et al., 2002).

 


The diploid all-male minnows reproduce with triploid, hybrid females, which make haploid eggs whose single chromosome set is identical to that of the males. With such matings producing only males, the male line is maintained, while the hybrid females produce more hybrids by reproducing with hybrid males.

The evolutionary origins of this complex remain unclear, but the adjacent diagram (taken from Alves et al., 2002) shows a speculated route. Diploid hybrids originate from a cross between the related Squalius pyrenaicus and an ancestor genetically identical to the male lineage of S. alburnoides. Another mating with a pure male gives a triploid hybrid, and that hybrid gives nonhybrid male S. alburnoides upon mating with nonhybrid males. Hybrid matings produce more hybrids. In this way, "the all-male lineage allowed preservation of the ancestral paternal nuclear genome" (Alves et al., 2002).

Given the unusual mechanisms at work in this complex, a reasonable number of papers have been produced on its subject. For instance, Cunha et al. (2004) calculated that the hybridization events started in the late Pliocene, and discussed the evolution of the complex. Robal et al. (2006), based on molecular evidence, posited an intergeneric origin for S. alburnoides, placing it closer to Anaecypris hispanica as a hybrid of A. hispanica and S. pyrenaicus.

Whatever the origin of the all-male line of S. alburnoides, its existence is yet another blow to the idea of "species" as a fixed, sacrosanct entity.


References

Alves, M. J.; Collares-Pereira, M. J.; Dowling, T. E.; and Coelho, M. M. (2002) The genetics of maintenance of an all-male lineage in the Squalius albuvnoides complex. Journal of Fish Biology 60 (3) , 649–662

Cunha, C.; Coelho, M. M.; Carmona, J. A.; and Doadrio, I. (2004) Phylogeographical insights into the origins of the Squalius alburnoides complex via multiple hybridization events. Molecular Ecology 13 (9) , 2807–2817

Robalo, J. I.; Sousa Santos, C.; Levy, A.; and Almada, V. C. (2006) Molecular insights on the taxonomic position of the paternal ancestor of the Squalius alburnoides hybridogenetic complex. Molecular Phylogenetics and Evolution, Volume 39, Issue 1, April 2006, Pages 276-281