Chapter 1: pg 5-19

Highlights Plasticity is a Normal Part of Development  Examples of phenotypic plasticity: Nemoria arizonaria larvae will resemble white oak flowers in the spring, but the caterpillars will look more like the twigs of the summer. Some species of turtles and alligators have the sex of the eggs determined by temperature, humans have very large an extensive network of immune cells that “learn” from the environment  1894- Oscar Hertwig summarized studies about phenotypic plasticity  1909- Wilhelm Johannsen distinguished the difference between phenotype and genotype, and how the phenotype is not solely and expression of the genotype, but also how it was affected by its environment (rejecting ’s 1839 proposal that all embryos’ development was compressed into the nucleus of the egg)  1909- Richard Woltereck- published paper on his research on how the genetically identical lines of Dalphnia (water flea) could produce different phenotypes during different times of the year o Created the idea of Reaktions-norm  It is currently a hotly debated subject area over whether or not this plays a huge role in the genetics of passing it on to young “ Eco-Devo” and Developmental Plasticity  Standard focused on internal dynamics where the genes produced the phenotypes, but now have discovered cell to cell communication that determines phenotype  Paracrine factors affect the adjacent cells, and then those cells make their paracrine factors to affect other cells, and the cooperative signaling between cells forms organs  Paul Weiss (1970), Oscar Hertwig (1894) and Curt Herbst (1901) catalogued environmental agents and discussed them as normal components in determining the phenotype of the embryo  Developmental plasticity is usually adaptive, but can also be maladaptive in certain circumstances  The turtle eggs displays the polyphenism viewpoint more  It is important to distinguish between polyphenism and polymorphism, where the actual genotype itself is different and it isn’t based on environmental cues  focuses more on the genetic makeup than the other two ideas, although the phenotypes itself are not caused by the genome, but the changes or markings on the genome Temperature-Dependent Phenotypes  Nearly all enzymatic activity is temperature-dependent o Example: tyrosinase enzyme in Siamese cats and Himalayan rabbits produces melanin, and the mutation of the phenotype is temperature dependent, so it works in colder areas but not warmer ones, thus allowing for darker color on the extremities and lighter color on the rest of the body Key Terms  Phenotypic plasticity- the ability of a single individual phenotype to develop into more than one phenotype; (or more recently) the ability of an organism to react to an environment input with a change in form, state, movement, or rate of activity  Ecological - an approach to embryonic development that studies the interactions between a developing organism and its environment  Paracrine factors- molecular signals released by one set of cells to induce gene expressions changes in adjacent cells