A evolução é um processo muito mais rápido do que Darwin imaginou

segunda-feira, maio 17, 2010

Fat lips evolve at record speed

18:18 14 May 2010 by Andy Coghlan

Fish in a remote crater lake in Nicaragua are splitting into separate species at breakneck speed.

It has taken the lake cichlids just 100 generations and as many years to evolve an entirely new physical feature: very fat lips. Most estimates of how fast species evolve new features are based on models, which generally indicate that it could take up to 10,000 generations. Some models suggest just tens of generations are enough, but such rapid change has never been documented before.

Cichlids evolved their fat lips in 100 generations (Image: Axel Meyer)

Axel Meyer at the University of Konstanz in Germany and his team say the fat-lipped fish occupy a different ecological niche from their thin-lipped cousins, despite living in the same lake, which fills a volcanic crater formed 1800 years ago. They don't eat the same diet and observations of captive fish in a tank suggest they avoid mating with each other – though lab experiments show they can still interbreed. Meyer says the fact that if they avoid mating with each other in the wild, as seems likely, they are well on the way to becoming separate species.
Read more here/Leia mais aqui: New Scientist


Rapid sympatric ecological differentiation of crater lake cichlid fishes within historic times

Kathryn R Elmer , Topi K Lehtonen , Andreas F Kautt , Chris Harrod and Axel Meyer

BMC Biology 2010, 8:60doi:10.1186/1741-7007-8-60

Published: 12 May 2010

Abstract (provisional)


After a volcano erupts, a lake may form in the cooled crater and become an isolated aquatic ecosystem. This makes fishes in crater lakes informative for understanding sympatric evolution and ecological diversification in barren environments. From a geological and limnological perspective, such research offers insight about the process of crater lake ecosystem establishment and speciation. In the present study we use genetic and coalescence approaches to infer the colonization history of Midas cichlid fishes (Amphilophus cf. citrinellus) that inhabit a very young crater lake in Nicaragua--the ca. 1800 year-old Lake Apoyeque. This lake holds two sympatric, endemic morphs of Midas cichlid: one with large, hypertrophied lips (~20% of the total population) and another with thin lips. Here we test the associated ecological, morphological and genetic diversification of these two morphs and their potential to represent incipient speciation.


Gene coalescence analyses [11 microsatellite loci and mitochondrial DNA (mtDNA) sequences] suggest that crater lake Apoyeque was colonized in a single event from the large neighbouring great lake Managua only about 100 years ago. This founding in historic times is also reflected in the extremely low nuclear and mitochondrial genetic diversity in Apoyeque. We found that sympatric adult thin- and thick-lipped fishes occupy distinct ecological trophic niches. Diet, body shape, head width, pharyngeal jaw size and shape and stable isotope values all differ significantly between the two lip-morphs. The eco-morphological features pharyngeal jaw shape, body shape, stomach contents and stable isotopes (delta15N) all show a bimodal distribution of traits, which is compatible with the expectations of an initial stage of ecological speciation under disruptive selection. Genetic differentiation between the thin- and thick-lipped population is weak at mtDNA sequence (FST = 0.018) and absent at nuclear microsatellite loci (FST < 0.001).


This study provides empirical evidence of eco-morphological differentiation occurring very quickly after the colonization of a new and vacant habitat. Exceptionally low levels of neutral genetic diversity and inference from coalescence indicates that the Midas cichlid population in Apoyeque is much younger (ca. 100 years or generations old) than the crater itself (ca. 1 800 years old). This suggests either that the crater remained empty for many hundreds of years after its formation or that remnant volcanic activity prevented the establishment of a stable fish population during the early life of the crater lake. Based on our findings of eco-morphological variation in the Apoyeque Midas cichlids, and known patterns of adaptation in Midas cichlids in general, we suggest that this population may be in a very early stage of speciation (incipient species), promoted by disruptive selection and ecological diversification.