Abstract
Tadpoles of the anuran species Rana pirica can undergo predator-specific morphological responses. Exposure to a predation threat by larvae of the salamander Hynobius retardatus results in formation of a bulgy body (bulgy morph) with a higher tail. The tadpoles revert to a normal phenotype upon removal of the larval salamander threat. Although predator-induced phenotypic plasticity is of major interest to evolutionary ecologists, the molecular and physiological mechanisms that control this response have yet to be elucidated. In a previous study, we identified various genes that are expressed in the skin of the bulgy morph. However, it proved difficult to determine which of these were key genes in the control of gene expression associated with the bulgy phenotype. Here, we show that a novel gene plays an important role in the phenotypic plasticity producing the bulgy morph. A functional microarray analysis using facial tissue samples of control and bulgy morph tadpoles identified candidate functional genes for predator-specific morphological responses. A larger functional microarray was prepared than in the previous study and used to analyze mRNAs extracted from facial and brain tissues of tadpoles from induction-reversion experiments. We found that a novel uromodulin-like gene, which we name here pirica, was up-regulated and that keratin genes were down-regulated as the period of exposure to larval salamanders increased. Pirica consists of a 1296 bp open reading frame, which is putatively translated into a protein of 432 amino acids. The protein contains a zona pellucida domain similar to that of proteins that function to control water permeability. We found that the gene was expressed in the superficial epidermis of the tadpole skin.
Highlights
Phenotypic plasticity refers to the ability of a given genotype to produce different phenotypes in distinct environments
To identify candidate genes governing the inducible bulgy morph phenotype (Fig. 1), we prepared a functional microarray using 1020 genes selected by subtractive hybridization from 3469 cDNAs
Bulgy morph and candidate genes In a previous study, we used subtractive hybridization and microarray analysis to search for genes expressed in the skin of bulgy morph tadpoles induced by predatory larval salamanders [18]
Summary
Phenotypic plasticity refers to the ability of a given genotype to produce different phenotypes in distinct environments. The genetic basis of phenotypic plasticity continues to be a focal issue for evolutionary ecologists because this knowledge is crucial to understanding its evolution [5,6,7]. Inducible defenses are phenotypic changes induced directly by cues associated with biotic agents and are an example of phenotypic plasticity [8]. Anuran tadpoles have proved to be a useful model organism for studying inducible defenses as they commonly exhibit inducible morphological changes, such as increased tail depth, in the presence of a threat from predators [9,10]. Previous studies demonstrated that the inducible phenotypic changes in anuran tadpoles have a genetic basis [11,12], we still do not understand how these genetic mechanisms control the morphogenetic changes of inducible defense traits
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