Having covered the general aspects of social behaviour in article one, and social learning in article two we are now going to begin to look in more detail at individual social behaviours. To do this we must first revisit the fundamental underpinning fact that all rats are individuals, whose behaviours are the product of their genetic predisposition, hormone balance, life experiences, and mental state.
Individuals are truly individual
I find it helpful to view all traits as having a bell curve distribution – so the majority of the rat population will fall within the central part of any continuum, with a big chunk being slightly more one trait than the other, but only a few being extreme.
Let’s take neophobia as an example. Neophobia (a suspicion or fear of new experiences, environments, rats, people, or things) decreases with domestication but is still a present and important trait in pet rats.
If the two ends of the continuum of neophobia are extremely neophobic and almost never neophobic, most rats will be in the somewhat neophobic group - often with a tendency towards one extreme or the other.
So, we could say that many rats have an average degree of neophobic – but within that average group, some will be more – or less – neophobic. Only a few will be almost always neophobic or almost never neophobic.
Of course, to fully see and measure a trait like neophobia we need to understand which behaviours are neophobic. We often think of neophobia in terms of refusal to eat new food or engage with a new toy, but neophobia drives many common behaviours. These would include behaviours such as showing caution when exploring a completely new, open environment, reluctance over a new activity like being weighed, or anxiety defecation during a new experience (like a journey to the vet).
The assessment of any single trait is further complicated by the interaction of the various stable (consistent throughout life) traits that all affect each other in producing the behaviour of the individual rat. These include:
These traits merge to create rats who are introverted, extroverted, stable, unstable, welcoming of newcomers, fearful of newcomers, aggressive towards newcomers, and so on. The higher the degree of anxiety experienced by an individual the less stable the other traits become.
Two successful survival strategies have been reported in rats based on the model of introversion and extroversion:
- A rat who tends towards neophobia and away from exploration and aggression has been termed introverted. Their survival strategy is to pull back, wait, and assess before acting.
- A rat who tends towards explorative behaviour and dominance or aggression has been termed extroverted. Their survival strategy is to move towards, experience, and fight if needed (as a last resort). When they are also sociable, they are often both high ranking and excellent leaders – some people call them “silent alphas”, but they can be just as accomplished in a supportive leadership role.
Both strategies have benefits and risks – so the whole group will be enhanced by having both. We also need to remember that a social introvert or extrovert can be a vastly different creature to an antisocial one, and a highly anxious, depressed, or traumatised individual can be volatile regardless of their underlying traits.
When the rats in group one are also sociable, they are often useful to have within groups. They can be skilled at managing relationships – some people call them “glue rats” as they have a cohesive effect on the group. Where they are less sociable or more anxious, they can be difficult rats to introduce to newcomers. They may be overly dramatic about the approaches of a more dominant or boisterous rat. They may also trigger aggressive responses in other rats.
When the rats in group two are also sociable, they are often both high ranking and excellent leaders – some can be “silent alphas”, but they can be just as accomplished in a supportive leadership role. When they are less sociable or more anxious, they can appear more volatile and can be difficult to introduce to newcomers as they can be quick to squabble.
However, the expression of emotions involving aggression and anxiety-related behaviours is essential for effective communication between individuals within any group. Rats are adapted to avoid injury by employing a whole raft of body language and vocalisation that leads to almost choreographed exchanges where these emotions can be diffused without bloodshed (or with minor injury).
In what ways are rats social?
In terms of the social exchanges that we would tend to view as positive, rats are capable of:
- Altruism (taking one for the team)
- Empathy (sharing and responding to the emotional distress of others)
- Nurturing (usually offspring or related youngsters, but can also – less commonly – be seen in caring for the sick and vulnerable).
- Co-operation (working together to benefit both oneself and others)
- Protectiveness (particularly when mothering)
- Social bonding (behaviours such as bedsharing, social grooming, playfulness, and shared endeavour)
- Social learning (learning from the behaviour of others).
In terms of the social behaviours that we would tend to view as negative, rats are capable of:
- Exclusion (isolating individuals from the group).
- Self-exclusion (isolating yourself from the group).
- Bullying (using status and physical power to deprive another rat of choice (eg. Food, water, shelter, company, freedom, etc.) that may also involve physical injury).
- Infanticide (killing the offspring of another rat).
- Aggression (hostile or violent behaviour as an expression of anger or rage).
- ‘Tidying up’ the dead (actually a socially protective behaviour that reduces the risk of predation).
In the next couple of articles in this series, we will be looking at each of these social behaviours in more detail. We’ll begin today with aggression, as it causes so much distress to human guardians.
Aggression in rats
Aggression is an adaptive strategy that drives behaviours that are important to the rat’s survival and fitness (in evolutionary terms). It is a heritable trait, and (from work with mice) several genes are known to be involved.
- influenced in the body by both inhibitory and excitatory neurotransmitters in the brain (including glutamate and dopamine),
- increased when serotonin is low,
- under the influence of the olfactory (smell) system,
- increased with increasing androgens (e.g. glucocorticoid and testosterone).
Aggression is also provoked by context – nursing females, males with mating rights (eg those housed with intact females), and females with breeding rights when faced with a female intruder, will all display aggression towards unknown rats.
Emotional context can also influence aggression. Anxiety is known to escalate aggression, and rats who have experienced isolation as youngsters show a higher tendency for aggressive behaviour. In fact, even for an older rat, a period of just four weeks living alone can increase the likelihood of aggression once a rat is re-introduced to company.
In wild rats, male aggression is necessary to ensure that a territory can be maintained in terms of access to food sources and mating partners. Female aggression is necessary to defend offspring. As a species, rats obey specific rules that allow for clear and “harmless” communication of aggression.
Most offensive aggression is a series of primarily harmless threat behaviours that allow the opponent to escape or to switch to submissive behaviours to avoid direct physical confrontation.
Defensive aggression is different. It is usually expressed in life-threatening (or perceived by the rat as life-threatening) situations and is linked to increased fear, rather than rage. There is often little – or no – signalling in advance to warn of defensive aggression, and the attack targets more vulnerable body parts (such as the head, belly, and genitals).
When managing groups of rats, we can work to educate ourselves as to what aggression ‘looks like’ between a pair of rats. Which movements and vocalisations are threat behaviours, and which are escape or submission behaviours? The main offensive-aggressive moves are piloerection (hair standing up) and side barging the opponent.
These are postures that show strength without the likelihood of injury. What happens next is usually determined by the response. If the opponent rat is standing their ground, they may stand nose to nose, whisker to whisker, or progress to a physical show of strength by pinning the opponent.
If the opponent rat retreats, the offensive rat will usually chase. If they submit, the offensive rat will hold in a pinned position until they are satisfied and certain of victory when then they will release the opponent unharmed.
Behavioural Brain Research Volume 75, Issues 1–2, February 1996, Pages 27-32
Social isolation increases aggressive behaviour and alters the effects of diazepam in the rat social interaction test
Frontiers in Behavioral Neuroscience 30 March 2010
Aggression and anxiety: social context and neurobiological links
Inga D. Neumann, Alexa H. Veenema and Daniela I. Beiderbeck
Neuroscience Letters. 2015 Jan 1; 584: 308–313.
High aggression in rats is associated with elevated stress, anxiety-like behavior, and altered catecholamine content in the brain
Gaurav Patki, Fatin Atrooz, Isam Alkadhi, Naimesh Solanki, and Samina Salim
Current Topics Behavioral Neuroscience - available in PMC 2015 Jan 1.
Neurogenetics of Aggressive Behavior – Studies in Rodents
Aki Takahashi1 and Klaus A. Miczek