Nature vs Nurture

The development of an organism is an interactive process between genes and the environment

As an organism develops….

  • Genetic information interacts with changing internal and external environemnts
  • Genes become turned on and off by signals (expressed/repressed)
    • Signals are internal/cellular/chemical or external environmental stimuli (neurochemical/hormonal)
  • These interactions alter the assembly of the organism- its neural networks as well as other aspects of its physiological/anatomical systems
  • Central Dogma: DNA  → Transcription →  RNA  → translation → protein →  gene expressed

“Honey Bee (Apis mellifera linnaeus)” by Jim (CC BY 2.0)

Development of worker behavior in honey bees:

  • Variation in tasks is age dependent (cleaning, feeding, packing pollen, foraging). Younger bees work within the nest as nurses and then transition with age to become foragers.
  • Gene activity varies in the brains of “nurse” bees and “foragers”. Opposite gene activation patterns were observed in the analysis of their gene expression.
  • The Juvenile Hormone (JH): low concentrations are found in nurse bees, there are increased levels in the forager bee. A nurse bee treated with JH will begin to forage. Remove the JH glands of a forager and it will revert to nursing behaviors.
    • Hormonal influence on gene expression.
  • JH gene boosts at about 3 weeks. This is activated by the social behavior of their environment.
    • In the presence of foragers, the nurses had lower levels of JH
    • In the absence of foragers, the nurses had higher levels of JH
    • When older bees are added the colony, the young bees remain nurses. The presence of many foragers inhibits JH expression.
    • When many young bees are added to the colony, the resident young bees will transition to forager bees and the JH gene is expressed.
  • Older bees inhibit the transition to forager in others by manufacturing a compound called ethyl oleate. Secreted by glands within the crop.
    • An Ultimate Explanation: to ensure that there are enough nurses and foragers within the colony to sustain the hive. An adaptive adjustment to the ratio of nurses and foragers.

Environmental Influences: 

  • Environmental Factors are critical for every element of gene expression within organisms.
  • The environment supplies the molecular building blocks (RNA bases, amino acids, etc.) that are essential for DNA translation.  Sources include food and the atmosphere.
  • Gene Expression → environmental factor → gene expression → environmental factor
  • The combination of a constantly changing internal and external environments of the organism that influence the expression of genes.

“DNA is both inherited and environmentally responsive” -Gene Robinson

“Tea for Cockatoos” by Rob and Stephanie Levy (CC BY 2.0)

Begging Calls and Contact Calls in Galah and Cockatoo:

  • Reciprocal swap test for hatchlings: the babies that were placed in opposite nests will continue to do the begging call of its species but will make the contact call of the species that raised it.
  • Genes constructing the learning system may be responsible for these differences-the environmental influence of the types of calls that these birds can make.
  • Most traits are an interactive relationship between several different genes: polygenic
    • Learning is a polygenic trait
    • Genes are responsive to important sensory stimuli

“Galahs” by Ed Dunens (CC BY 2.0)

Learning:

  • The result of gene-environment interactions
  • Imprinting of baby geese on the first thing they see after hatching
  • Genes construct learning systems and genes are responsive to important sensory stimuli
  • Cross-fostering has different imprinting effects in two related species of songbirds.
    • Female Blue Tit fostered Great Tit hatchlings and vice versa.
      • GT fostered by BT pair with BT
      • BT fostered by GT pair with GT
    • Environmental differences: a Polistes wasps learn to recognize nestmates from odors and facial markings

“Eastern Garter Snake” by Fyn Kynd (CC BY 2.0)

  • Genetic Differences: cause behavioral differences among individuals.
    • A coastal Californian garter snake (Thamnophis elegans) has differences in their diets in different populations.
      • Inland populations eat fish and frogs
      • Coastal populations eat banana slugs – genetic adaptations to handle the slime of the slug?
      • Take hatchlings (naïve individuals) raised in the lab fed with generic food. Then give them slugs to determine if the baby snakes will consume slugs.
      • Data showed that inland baby snakes did not eat slugs regardless of lack of experience with other food. The coastal snakes did eat the slugs when they were introduced. -suggests genetic differences
      • Inland snakes tongue flicked at tadpole extract but not slug extract. Coastal snake tongue flicked at both extracts. ~ an evolutionary hypothesis: Inland ancestral non-slug eating population migrated towards the coast and alleles for slug eating become more abundant in the coastal regions because of the abundance of slugs as a prey source.

“Mouse” by Jason Bolonski (CC BY 2.0)

  • Sometimes a single gene can have a large influence on a behavior that is expressed. This is due to cascading events on the cellular level to activate/deactivate other genes.
    • For mice, a single gene affects maternal behavior. The gene fosB is responsible for maternal behavior. Those without this gene will be neglectful.
      • The environment still affects maternal behavior
      • Cascading effects on other genes into the phenotypic behavior that is observed.
      • Environmental cue causes this gene to be expressed. The olfactory stimulation from her pups activates the gene.

 

 

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