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The Effect of Social Environment Behavior Development

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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  1. Arizona Barred Tiger Salamander Gray Blotched US Canada Distribution by Species Eastern The Effect of Social Environment Behavior Development

  2. 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.

  3. 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

  4. 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

  5. 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

  6. 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.

  7. 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+)

  8. 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.

  9. 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

  10. 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.

  11. 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.

  12. Some changes appear to be independent of experience

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