Polygenic adaptation as an effective molecular basis of adaptation in fish species

Rapid adaptation of organisms happens opposed to the natural and unnatural factors usually caused by human activities. Of the most recent examples, the color change in guppies and the body depth variation in response to the global warming can be counted. The phenotypic adaptability of fish to various types of new environmental parameters has been widely studied recently. While the macroscopic changes of phenotypic traits are usually visible, understanding the genetic and genomic basis of these changes are more complicated. Two distinct research approaches, including population genetics and quantitative genetics, have led to the introduction of two different views regarding the molecular basis of the adaptation process: adaptation by "selective sweeps" or by small changes in allelic frequency (shifts). In fact, the effective genetic basis in creating these changes can be caused by a small number of genes with large effect or a large number of genes with smaller effects. Recently, subtle frequency changes for selective sweeps have also been observed. On the other hand, it was reported that the polygenic adaptation can also occur through large allelic frequency changes (Sweep-like selection signature). GWAS as a powerful analytical approach links the polygenic traits with their underlying genetic architecture; however, the SNPs identified by GWAS are a small fraction of the genetic variation of complex traits. Hence, polygenic multilocus approaches (analysis of covariation among markers) surpass the traditional GWAS in these types of studies. Sturgeons are the most ancient fish species which are endemic to the Caspian Sea. It seems that the polygenic adaptation is one of the main molecular processes which enables these species to survive against the odd environmentally variations in each habitat.

Keywords:

Genomic variations , GWAS , Polygenic adaptation , Selective sweep , SNP