The Effect of Social Environment Behavior Development

Blotched Gray

Arizona

Eastern

Barred Tiger Salamander

US Canada Distribution by Species

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.

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

•These are called typical type larvae.

•Typical type Larvae eat 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

Environmentally induced cannibalism.

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

Example: Territoriality in cichlid fish

Two morphs of adult cichlid:1. Reproductively active males2. 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

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

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.

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+)

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

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:1. Juvenile hormone levels are manipulated? 2. 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.

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

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.

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

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.

Environmental factors mediate behavior via changes in the nervous system.

Some changes appear to be independent of experience