Developing spider embryos.
Lt: expressing the original dachshund gene. Rt: expressing the duplicate gene.
Photo credit: Nikola-Michael Prpic,
Göttingen Center for Molecular Biosciences,
University of Göttingen, Germany
If you're an arthropod and unable to fly you need to be good at scuttling, so you need legs that scuttle efficiently. Spiders and scorpions have good scuttling legs because they have kneecaps or patellae. In the arachnid limbs, the patella forms a unique limb segment that gives their legs greater scuttleability.
The way they evolved these patellae has just been worked out and published in Molecular Biology and Evolution. It is acutely embarrassing to the creationist frauds who tell their dupes that no new information can arise by mutation and that mutations are invariably harmful so will be rapidly eliminated. It is an example of a common method by which new information can arise in the genome and an example of how redundant or 'junk' genes can be exapted for an entirely new function. There is even a scientific term for this - 'neofunctionalisation'. Add that to your dictionary.
A team from Georg-August-University, Göttingen, Germany, led by Natascha Turetzek, who were looking for reasons why some spider species have longer legs than others, studied the so-called 'dachshund' (dac) gene, which plays a major role in arthropod limb development. Although this gene didn't account for the differences between species that they were looking for, they discovered a copy of the dachshund gene never before described in the arachnids.
By observing when and where this duplicate gene is expressed in the developing embryo they discovered that it becomes active in the patella region of the developing arachnid limb. Deactivating the gene resulted in spiders with their patella fused to the tibia and effectively, a single limb segment where there should be two.
The acquisition of a novel function, or neofunctionalisation, protects duplicated genes from redundancy and subsequent loss, and is a major force that drives adaptive evolution. Neofunctionalisation has been inferred for many duplicated genes based on differences in regulation between the parental gene and its duplicate. However, only few studies actually link the new function of a duplicated gene to a novel morphological or physiological character of the organism. Here we show that the duplication of dachshund (dac) in arachnids (spiders and allies) is linked with the evolution of a novel leg segment, the patella. We have studied dac genes in two distantly related spider species, the entelegyne spider Parasteatoda tepidariorum and the haplogyne spider Pholcus phalangioides. Both species possess two paralogous dac genes that duplicated before the split between entelegyne and haplogyne spiders. In contrast to the evolutionarily highly conserved dac1, its duplicate dac2 is strongly expressed in the patella leg segment during embryogenesis in both species. Using parental RNA interference in P. tepidariorum we show that dac2 is required for the development of the patella segment. If dac2 function is impaired, then the patella is fused with the tibia into a single leg segment. Thus, removing the function of dac2 experimentally reverts P. tepidariorum leg morphology into a stage before the duplication of dac and the evolution of the patella segment. Our results indicate that the origin of the patella is the result of the duplication and subsequent neofunctionalisation of dac in the arachnid lineage.
Neofunctionalisation of a duplicate dachshund gene underlies the evolution of a novel leg segment in arachnids
Natascha Turetzek, Matthias Pechmann, Christoph Schomburg, Julia Schneider and Nikola-Michael Prpic
Molecular Biology and Evolution (2015) doi: 10.1093/molbev/msv200
So, would any creationist like to offer an explanation of this? How does this example of a duplicated gene being used for a new purpose fit with the claim that no new information can arise in a genome and that mutations are invariably harmful?
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