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Arizona. Barred Tiger Salamander. Gray. Blotched . US Canada Distribution by Species. Eastern. The Effect of Social Environment Behavior Development . Environmentally Induced Neoteny. Some populations of Tiger Salamanders express a “neotenic” phenotype

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The Effect of Social Environment Behavior Development

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Arizona

Barred Tiger Salamander

Gray

Blotched

US Canada Distribution by Species

Eastern

The Effect of Social Environment Behavior Development


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Environmentally Induced Neoteny.

  • Some populations of Tiger Salamanders express a “neotenic” phenotype

    • Common in western North America and especially at high altitudes

    • Population density is low food is abundant

    • These salamanders become sexually mature and can reproduce BUT they do not metamorphose

    • Develop essentially into adult tadpoles with enlarged breathing gills

  • Neotenic tiger salamanders can become larger than individuals that metamorphose, reaching total lengths of 15 inches.


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Environmentally induced cannibalism.

  • Under normal circumstances salamander larvae metamorphose from the tadpole-like larvae into the terrestrial dwelling adults

    • These are called typical type larvae.

    • Typical type Larvaeeat aquatic insects

  • However, under a specific set of environmental circumstances a cannibal type develops.

    • Specially adapted mouths

    • Physically larger than the typical type.

    • Cannibal type larvae develop and metamorphose faster


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Environmentally induced cannibalism.

  • Cannibals only appear when:

    • Population densely is high

    • Prey relatedness is low

    • Thus appears to be population desnity driven and mediated by relatedness of the population


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Socio-environmental factors mediate behavior in many cases via hormonal control.

Example: Territoriality in cichlid fish

  • Two morphs of adult cichlid:

    • Reproductively active males

    • Satalite males

  • Changes in social status of males causes a reversible change in the size of an identified group of gonadotropin-releasing hormone (GnRH) neurons in the hypothalamus.

  • When males changes socially from a satellite to dominant status (by acquiring a territory):

    •  Up to an 8 fold increase in size GnRH cells

    • Release of GnRH drives increases gonadal size and hormonal output

      • Increases territorial behavior to other fish.

        • Wards off other males

        • attracts females

      • Enhances coloration

    • Also occurs in females but is controlled by reproductive state not social status/interaction

    • Loosing territory reverses this effect


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    Socio-environmental factors mediate behavior in many cases via hormonal control.

    • Example: honeybee behavior development.

    • Honeybees are one of many species of social insect.

    • Division of labor is a key feature among  social insect societies.

      • It is this division of labor that is thought to be the key to the massive success of social insects in general.

    • One of the most impressive features of the division of labor is that the hive is able to modify its workforce based on need:

      • In this sense insect societies are PLASTIC.


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    Socio-environmental factors mediate behavior in many cases via hormonal control.

    • Three basic morphs in the hive:

    • Queen: reproductive element

    • Drone: serve only reproductive role 

    • Worker: (females) typically non reproductive and serve various roles associated with colony growth and maintenance

      • can be tens to hundreds of thousands per hive

      • normally move through a sequence of behavioral roles or casts through out the lifespan:

        • cell cleaning (~1-3 days old)

        • nursing (~4-10 days)

        • internal food distribution (feeding others; ~4-15days)

        • pollen packing (~11-18 days)

        • guarding (~15-17 days)

        • scouting & foraging (~15+)


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    Socio-environmental factors mediate behavior in many cases via hormonal control.

    • Associated with progression through behavioral roles is a shift in levels of juvenile hormone.

    • Gene Robinson and his colleagues asked what happens to behavior when:

      • Juvenile hormone levels are manipulated?

      • Colony conditions are changed?

    • If young bees are treated with juvenile hormone they will become "precocious foragers" exhibiting foraging related behaviors prior to normal onset of foraging behavior.

    • If you remove the corpora allata, the juvenile hormone gland bees do not develop into foragers.

      • This effect can be rescued by application of juvenile hormone.


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    Socio-environmental factors mediate behavior in many cases via hormonal control.

    • However, changing the social stratification of the hive also influences the rate of development to compensate for the manipulation:

    • If you remove all foragers precocious (~1 week old ) foragers will develop.

      • if you then replace the removed bees with young bees precocious foragers still emerge

      • If you replace removed bees with foragers from another hive precocious foragers do not emerge


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    Socio-environmental factors mediate behavior in many cases via hormonal control.

    This means that socio-hormonal interaction of older bees influences the hormonal expression and behavior of  younger bees.

    This is a mechanism by which the hive maintains a homeostatic balance of each worker cast.


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    Environmental factors mediate behavior via changes in the nervous system.

    • Not all changes in bee behavior are necessarily mediated by hormonal control

    • Foragers are adept learners.

    • Foraging experience changes brain activity and structure.

      • The mushroom bodies of the honeybee brain there is a correlated increase in synaptic complexity (cell fibers)

      • Antennal lobes also appear change their responses to odor stimuli once that odor has been learned.


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    Some changes appear to be independent of experience


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