Salamander polyploid amazes with its genome (s)
Ambystoma mole salamander image; Credit: Robert D. Denton, Ohio State University
With axolotls among their relatives, its little wonder that the unisexual mole salamanders provide a wealth of interest as genomes become unravelled. Ambystoma species that are sexual (instead of parthenogenetic) include A. laterale, A. texanum and A. tigrinum. It has now been found that these 3 species have their genomes neatly included in the unisexual Ambystoma. The ancestors of this
lady have conveniently been breeding with the 3 sexual species, creating the triploid unisexual.
This kind of polyploidy has long been recognised in plants and animals as driving evolution. Kyle E. McElroy and his colleagues from the University of Iowa and Ohio State University, US, collected their animals from Ohio and composed
transcriptomes for all 4 of the species concerned. Other species already have genomes available. They published in Genome Biology and Evolution under the title
Genome Expression Balance in a Triploid Trihybrid Vertebrate.
Their starting point was to establish if any dominance of genes occurred between the competing genotypes. Polyploids need much more study to understand how significant their genes are in establishing the phenotypes of, for example, domestic wheat as well as many different animal species. The effects of polyploidy seem to be basically a higher level of gene expression and increased adaptive potential, but nutritional requirements may alter in polyploid species. This means the species gets bigger, grows quicker but may silence the effects of some genes. In the Ambystoma, 73% of the 3 sets of genes seemed able to express themselves. This denied any theory that dominance would be expressed in animal polyploids, though the Ambystoma texanum genome achieved the highest level of expression.
The authors assume there is a balance between all of the genomes, as the unisexual expresses its unique polyploid genes in just the same way as the sexual species. As far as other animals are concerned, the next steps are to increase the number of polyploid animal species studied. With genetics advancing rapidly, the evolution of the science itself is becoming remarkable, let alone the possibilities of polyploid discoveries in the future. As far as the North American salamanders, and many others, are concerned, the emphasis must be on their conservation, as with their famous Asian and American giants, such as this Ozark hellbender salamander, Cryptobranchus alleganiensis, here described in 2011.