Hallo!
Ich habe heute bei
Zeit.de einen kurzen Artikel über Artenbildung ohne geografische Trennung gefunden. Die beiden dort zitierten Artikel sind zwar nicht frei zugänglich, aber ich denke, die Abstracts kann ich trotzdem posten:
Hybrid origin of a swordtail species (Teleostei: Xiphophorus clemenciae) driven by sexual selection,
AXEL MEYER, WALTER SALZBURGER and MANFRED SCHARTL, Molecular Ecology online, 25.01.2006.
Abstract:
The swordlike exaggerated caudal fin extensions of male swordtails are conspicuous traits that are selected for through female choice. Swords are one of only few examples where the hypothesis of a pre-existing bias is believed to apply for the evolution of a male trait. Previous laboratory experiments demonstrated that females prefer males with longer swords and even females from some swordless species show an affiliation for males of sworded species. Earlier phylogenetic studies based on maternally inherited mitochondrial DNA placed the sworded southern swordtail Xiphophorus clemenciae with swordless platies, contradicting its morphology-based evolutionary affinities. The analyses of new nuclear DNA markers now recover its traditional phylogenetic placement with other southern swordtails, suggesting that this species was formed by an ancient hybridization event. We propose that sexual selection through female choice was the likely process of hybrid speciation, by mating of platy females with males of an ancestral swordtail lineage. In artificial crosses of descendent species from the two potential ancestral lineages of X. clemenciae the hybrid and backcross males have swords of intermediate lengths. Additionally, mate choice experiments demonstrate that hybrid females prefer sworded males. These experimental lines of evidence make hybridization through xeno-specific sexual selection by female choice the likely mechanism of speciation.
Sympatric speciation in Nicaraguan crater lake cichlid fish,
Marta Barluenga, Kai N. Stölting, Walter Salzburger, Moritz Muschick and Axel Meyer,
Nature, 439, 719.
Abstract:
Sympatric speciation, the formation of species in the absence of geographical barriers, remains one of the most contentious concepts in evolutionary biology. Although speciation under sympatric conditions seems theoretically possible1, 2, 3, 4, 5, empirical studies are scarce and only a few credible examples of sympatric speciation exist6. Here we present a convincing case of sympatric speciation in the Midas cichlid species complex (Amphilophus sp.) in a young and small volcanic crater lake in Nicaragua. Our study includes phylogeographic, population-genetic (based on mitochondrial DNA, microsatellites and amplified fragment length polymorphisms), morphometric and ecological analyses. We find, first, that crater Lake Apoyo was seeded only once by the ancestral high-bodied benthic species Amphilophus citrinellus, the most common cichlid species in the area; second, that a new elongated limnetic species (Amphilophus zaliosus) evolved in Lake Apoyo from the ancestral species (A. citrinellus) within less than 10,000 yr; third, that the two species in Lake Apoyo are reproductively isolated; and fourth, that the two species are eco-morphologically distinct.
Ist aber wohl nur was für Hardcore-Hobby-Biologen..
Grüße, Borbi