Differential gene expression turns on salamander attack mode

Hokkaido salamander larva in center with tadpole prey above (Image credit)

The transcriptomics field is boomin’. Approaches like RNA-seq have opened the flood gates to hundreds and hundreds of investigations that compare gene expression between biologically-interesting phenotypes, variants, species, etc.
Plastic phenotypes have been a fascinating area of study for decades in ecology, but the molecular mechanisms behind these phenotypes have only recently become more tractable. A good example of this type of  investigation by Matsunami et al. appears soon in Molecular Ecology:

The main aim of this study was to compare transcriptomic patterns in the brain and peripheral tissues between predator-exposed and prey- exposed larvae of the Hokkaido salamander by using RNA-seq technologies.

Phenotypic plasticity is well documented from both a predator and prey perspectives, and the Hokkaido Salamander is an example of a taxon that displays both types: a super-sized mouth (“attack morph”) when in habitats with large tadpole prey and a suite of traits (large gills, large tail fin; “defense morph”) when in habitats with potential invertebrate predators.

Matsunami et al. show that there were six times more differentially expressed genes among those salamanders that took on the phenotype induced by an invertebrate predator when compared to those that took on the phenotype induced by the presence of tadpole prey (103 vs 605 differentially expressed genes, respectively).
Because the increase in tail height induced by predation pressure is documented in other amphibian lineages, the authors hypothesize that the evolution of a new (plastic) phenotypes probably involves the co-option of pre-existing molecular mechanisms in combination with novel regulation:

In a species already capable of a certain plastic phenotypic response, some molecular mechanisms involved in the expression of pre-existing phenotype may be recruited for the production of the new plastic phenotype. For example, we found that some genes showed similar expression changes in both evolutionarily old predator-induced phenotypes and in evolutionarily newer prey-induced plastic phenotypes. Thus, the co-option and modification of gene networks already used for the expression of evolutionarily old plasticity may occur during the evolution of a novel plastic phenotypic response.

Matsunami M., Kitano J., Kishida O., Michimae H., Miura T. & Nishimura K. (2015). Transcriptome analysis of predator- and prey-induced phenotypic plasticity in the Hokkaido salamander (Hynobius retardatus), Molecular Ecology, n/a-n/a. DOI: http://dx.doi.org/10.1111/mec.13228

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