Hormones and Social Behavior pt 2

V1aR Overexpression (Vasopressin)

Facilitates social bonding especially in ventral pallidum

When looking at meadow voles, they injected viral vectors. A control (LacZ gene), V1aR-CP (missed target) and V1aR-VP (correct region ventral pallidum)

This increases the time that males spent with pups, it also facilitated pair bonding, investigation of pups and, time spent with partners

Effects of Vasopressin

Vasopressin receptors are directly correlated with social bonding.

Expression of receptors facilitates social bonding

Knock down of receptors inhibits social bonding

Types of Aggression

Maternal: Following parturition (oxytocin and prolactin)

Paternal: For monogamous species

Territorial

Intermale aggression (defensive and offensive)

Predatory: food aquisition

Most aggression

Is associated with males

Increase at puberty

Changes with seasons

Castration and replacement effects are predictable

Male Aggression

Fight to increase reproductive success

Gain and maintain territory and other resources

Defend females

Increase status within a group

Male Red Deer and Rutting Areas

Males red deer breed in short days (autumn)

Usually docile except during breeding

Females are fertile for only about three weeks

Aggression and Testosterone (deer)

Elevated testosterone cause antlers to grow and be maintained

Antlers grow seasonally so testosterone is seasonal

Antlers act as a weapon for aggression

Seasonal Changes in Stags

Circulating testosterone starts to increase in July and reaches highest peak in September

Aggressive behavior follows peaking during the mating season (amputation of antlers drops rank but does not drop T)

Antler growth follows testosterone and peaks in November (exogenous T can lead to maintenance of antlers)

Cost of Testosterone

Decreased immune function, parental care, deplete energy reserves

In mountain spiny lizard T implants make them more aggressive and active, patrol territory more, do more pushups, and deplete energy, less time foraging

Life at the Top (Social Rank)

Being second in the hierarchy may come with more benefits than being at the top

You do not have to watch your back all the time, top rank would be very stressed (high stress level)

Female Syrian Hamster Aggression

Model organism for female aggression

Females live in burrows and fend off intruders

Due to aggression, it is difficult to house females with conspecifics in the lab

Estrogen and progesterone (estrus) inhibit aggression which allows males to mate without injury

Effects of Hormones on Hamster Aggression

Female Siberian Hamsters are more aggressive during non-breeding periods (short days, autumn) than during breeding periods (long days), they breed in the summer

During short days there are non-genomic mechanisms of estrogen and changes from estrogen occur rapidly

During long days changes are modulated by genomic mechanisms

It is likely that estrogen and progesterone inhibit aggression during breeding seasons

Nongenomic vs Genomic Mechanisms

Genomic mechanisms are changes in transcription or changes in genes (these take longer)

Non-genomic mechanisms are modulated by membrane bound receptors that act like g-coupled proteins and second messenger pathways that are faster in producing effects

This can be controlled by adding and removing receptors from the brain

Short days vs Long days

During the winter months, (non-breeding season) females have lower circulating estrogen, higher aggression

During the summer, females have higher estrogen and this likely inhibits aggression

Melatonin

Influences androgen concentrations

Acts as seasonal switch

Shifts from gonadal to adrenal regulation of aggression

Effects of Estradiol on Aggression

Facilitates higher aggression during nonbreeding conditions and lower aggression during breeding conditions.

Fast increases in aggression due to non—genomic factors

No treatment effect on aggression during the breeding season

Behaviors Influencing Hormones

Male Syrian Hamsters that lose fights have reduced androgen levels for many days

Rhesus monkeys that are defeated by high-ranking males have reduced testosterone for weeks while champions have increased levels

The Challenge Hypothesis and Testosterone

There are three levels of testosterone, constitutive (non-breeding levels), regulated periodic (a bit higher levels), and regulated facultative (where animals increase their T to respond to environment)

If levels were constantly high, it would be hard for animals to assess what is actually necessary aggressive behavior

Challenge Hypothesis and Monogamy

Usually in monogamous species

Essentially challenges are met with temporary increases in T otherwise T is maintained at constant intermediate

In monogamous species testosterone levels rise with simulated intrusions

Usually have lower T levels but also exhibit sharp changes in T

Challenge Hypothesis and Polygamous Species

There are no increases in testosterone when there is territorial intrusion but they will respond behaviorally

This is because they always have high levels of testosterone

Effects of an Intruder

Facilitates a sustained rise in plasma T requires increases in plasma LH

After an intruder, testosterone and LH will stay high to keep bird prepared

Seasonal LH and T Concentrations

Over entire populations and months, rise in LH is first then rise in T, showing general increases in breeding seasons

Individually, these match more closely. Before breeding, both rise and as broods develop there will be peaks and troughs, after breeding it drops significantly

What is the cause of T increases in birds

T concentrations may reflect competition

In some species, peaks in males T levels are due to territory acquisition and defense of fertile mates or colony nesting

Essentially there are individual variation, species variation, and seasonal variation

Neural Components of Aggression

Animals are using senses to make decisions about environment

Sensory systems will always be involved (olfaction, hypothalamus, PVN, MeA)

There is also a stress component using a stress response and hippocampus and PVN

PAG determines what is positive and what is negative in regard to stress and aggression

Stress can also inhibit aggression via inhibitory inputs from olfaction, hippocampus, and PVN