~ 1075 ~  Journal of Entomology and Zoology Studies 2018; 6(1): 1075-1080 E-ISSN: 2320-7078 P-ISSN: 2349-6800 JEZS 2018; 6(1): 1075-1080 © 2018 JEZS Received: 12-12-2017 Accepted: 15-01-2018 Chaitra Ganapati Bhat Division of Nematology, ICAR-Indian Agricultural Research Institute, New Delhi, India Jyoti Kushwah Division of Nematology, ICAR-Indian Agricultural Research Institute, New Delhi, India Vishal S Somvanshi Division of Nematology, ICAR-Indian Agricultural Research Institute, New Delhi, India Pankaj Division of Nematology, ICAR-Indian Agricultural Research Institute, New Delhi, India Correspondence Chaitra Ganapati Bhat Division of Nematology, ICAR-Indian Agricultural Research Institute, New Delhi, India Dauers, sexual plasticity and variant mouth forms: lessons on phenotypic plasticity from phylum nematoda Chaitra Ganapati Bhat, Jyoti Kushwah, Vishal S Somvanshi and Pankaj Abstract Organisms develop and evolve in diverse environment. This environment modulates the translation of genotype into phenotype. Phenotypic plasticity or polyphenism is defined as a phenomenon where an organism adopts different phenotypes depending on the environment. Alternatively, a phenotype may be insensitive to a given set of environmental conditions - a phenomenon called as ‘environmental robustness’. Nematodes are one of the best models in Kingdom Animalia to study the environment- specific responses of organisms because of specific characteristics, viz., species richness, omnipresence, numerical abundance etc. Formation of dauer larvae under unfavorable conditions, alternate life cycles of certain parasitic nematodes, different mouth morphology and environment induced sexual flexibility are classic examples of phenotypic plasticity in nematodes. However, the knowledge of molecular mechanisms underlying phenotypic plasticity is still scant, and a lot more research is required to understand it better and propose a unified theory for phenotypic plasticity in organisms. Keywords: Phenotypic plasticity, Environmental robustness, Nematodes, Dauer, Sexual plasticity Introduction Organisms develop and evolve in a diverse environment by responding to the environmental changes. This environmental heterogeneity modulates the translation of genotype into phenotype, ultimately affecting the biological organization and phenotypic outcome of the organisms. The phenotype of the organism refers to the actual observed properties, such as morphology, development or behaviour of an organism or it is the physical expression or characteristics of the trait. Phenotypic expression is encoded by the genotype i.e., the genetic makeup of a specific organism or set of genes in DNA which are responsible for a particular trait. Organisms with the same genotype should produce similar phenotypes. But variations are there in phenotypes encoded by the same genotype which results from genotype and environmental interactions. It is very important to know the interaction between organism, genotype and phenotype to understand the plasticity induced in phenotypic characters. Phenotypic plasticity is defined as an ability of a genotype to produce phenotypic variation under varying environmental conditions [1] . If the phenotypic plasticity is induced at the developmental level, it is also referred to as developmental plasticity. Phenotypic plasticity is important in evolutionary biology and ecology and is crucial to the life traits of higher organisms, such as order and duration of critical life happenings such as the development of juveniles, dormant stage formation, and sexual maturity [1] . The dormant stage formation is seen in all domains of life as a survival strategy. For example, the formation of spores in fungi and bacteria, plant seed dormancy, and alternative life cycles in animal kingdoms. These alternative survival tactics are illustrations of phenotypic plasticity. In the insects, the butterfly wing morphs, different hymenopteran castes, the sexually dimorphic beetle horns, and alternating aphid generations exhibiting various physiological and morphological characters are some other examples for phenotypic [2] (Figure 1).