The Effect of Social Environment Behavior Development
Barred Tiger Salamander
Arizona
Gray
Blotched
US Canada Distribution by Species
Eastern
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.
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 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.
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
Socio-environmental factors mediate behavior in many cases via
hormonal control.
Example: Territoriality in cichlid fish
Two morphs of adult cichlid:
1. Reproductively active males
2. 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.
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.
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+)
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
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.
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.
Some changes appear to be independent of experience