User:Fishratthings/Predictive adaptive response

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A predictive adaptive response (PAR) is a developmental trajectory taken by an organism during a period of developmental plasticity in response to perceived environment al cues. This PAR does not confer an immediate advantage to the developing organism; however, if the PAR correctly anticipates the postnatal environment it will be advantageous in later life, if the environment the organism is born into differs from that anticipated by the PAR it will result in a mismatch. PAR mechanisms were first recognized in research done on human fetuses that investigated whether poor nutrition results in the inevitable diagnosis of Type 2 diabetes in later life. PARs are thought to occur through epigenetic mechanisms that alter gene expression, such as DNA methylation and histone modification, and do not involve changes to the DNA sequence of the developing organism. Examples of PARs include greater helmet development in Daphnia cucullata in response to maternal exposure to predator pheromones, rats exposed to glucocorticoid during late gestation led to an intolerance to glucose as adults, production of winged morphotypes in aphids triggered by tactile stimulation in overcrowded environments, and coat thickness determination in vole pups by the photoperiod length experienced by the mother. Two hypotheses to explain PAR are the "thrifty phenotype" hypothesis and the developmental plasticity hypothesis.