Developmental Plasticity and Symbiosis

• Developmental plasticity


  The ability of one genotype to produce more than one phenotype when exposed to different environments
• Phenotypic plasticity


  The ability of an organism to react to an environmental input with a change in form, state, movement, or rate of activity
• Polyphenism


  Density-dependent, diet-induced, or other environmentally-induced changes in an organism's phenotype
• Density-dependent polyphenisms


  • Desert ("plague") locust Schistocerca gregaria - low density morph has green pigmentation and miniature wings, high density morph has deep pigmentation and wings/legs for migration
• Diet-induced polyphenisms


  • Honeybee Apis mellifera - royalactin induces functional ovaries and increased body weight in queens
• Diet-induced polyphenisms


  • Dung beetle - whether a male has horns or not depends on the amount and quality of dung he eats as a larva, not his genes
• Dietary alterations


  Can produce changes in DNA methylation which affect the phenotype
• Predator-induced polyphenisms


  The ability of a developing organism to respond to the presence of a predator by changing its morphology and behavior to be less susceptible to predation
• Kairomones


  Chemicals secreted by predators to trigger defenses in their prey
• Environmental factors can lead to phenotypic alterations beyond physical structures, including the timing of developmental processes
• Several behaviors, including learning and the inclination for stress, can be generated by the environment via developmental pathways
• Seasonal polyphenism


  The development of distinct phenotypes in different seasons, an important adaptive response for multivoltine organisms
• Temperature-dependent sex determination (TSD) is a widespread non-genetic process of sex determination among vertebrates, including reptiles
• Aromatase

  An enzyme that helps convert sex steroids which determine the sex of the organism
• The morphological phenotype is often accompanied by a behavioral phenotype
• Developmental plasticity/neuroplasticity


  Changes in neural connections during development as a result of environmental interactions and learning
• Neuroplasticity is the brain's ability to change and adapt due to experience
• Functional plasticity


  The brain's ability to move functions from a damaged area to other undamaged areas
• Structural plasticity


  The brain's ability to change its physical structure as a result of learning
• Polyphenic life cycles


  Changes in an organism's life cycle or metamorphosis that are influenced by environmental cues
• Larval settlement


  The ability of marine larvae to suspend development until they experience a particular environmental cue
• Diapause


  A suspension of development that can occur at the embryonic, larval, pupal, or adult stage, induced by stimuli that presage a change in the environment
• Polyphenism in tadpoles of the spadefoot toad Scaphiopus couchii

  • Typical morph is an omnivore feeding on arthropods and algae
• Polyphenic life cycles


  • Changes in an organism's life cycle or metamorphosis that are influenced by environmental cues
  • The ability of marine larvae to suspend development until they experience a particular environmental cue is called larval settlement
  • Diapause is a suspension of development that can occur at the embryonic, larval, pupal, or adult stage and is induced by stimuli that presage a change in the environment
• Polyphenic life cycles


  • Spadefoot toad tadpoles developing a wider mouth and stronger jaws when ponds are drying out quickly
• This increase in brain corticotropin-releasing hormone is thought to be responsible for the subsequent elevation of the thyroid hormones that initiate metamorphosis