02 Aug 2021

The Social Rat (7) - Factors that Impact Lifelong Sociability in the Rat

Before we leave the subject of the social rat, I would like to round off with an overview of how the social resilience of a rat develops, and factors that impact sociability – particularly by disrupting it. Some of these factors can have a lifelong effect, while other will disturb social wellbeing in the short-term.  

Some of these influences can be addressed and even reversed but occasionally we may find ourselves working with a rat to build social resilience over a lifetime. The rat-human relationship can be affected as well as how the individual relates to other rats.  

The drivers of sociability are emotional and physical body states such as fear of isolation, panic at the prospect of social loss, the need for warmth and comfort, and the pleasure of bonding experiences. Likewise, the social process is disrupted by altered emotional and physiological body states, so let’s take a closer look as how this can happen.  

The Prenatal and Postnatal Experience  

The development of rats in utero and over the postnatal period is subject to something called developmental plasticity. This refers to the capacity of a developing animals to respond adaptively to the conditions experienced in the present to increase their chances of survival in the future. The changes that result in the individual are thought to be epigenetic.  

If the conditions experienced during early development predict a future of stress and high challenge, this causes either a ramp up or a turn down effect on stress responses and can lead to rats who are prone to anxiety (ramp up) or depression (ramp down). In pet rats this early programming can turn out to be a poor fit for the realities of the animal’s life.  

This is doubtless one of the most vulnerable times in the social development of the rat and experiences during this period can have a lifelong impact. There are many specific influences that have been studied in laboratory rats, so, I’m just going to pick out a few to give you a flavour of cause and effect.  

Intrauterine position  

When a foetus of either sex is positioned between two male foetuses they are influenced by increased testosterone in utero. This leads to a lifetime 

effect of increased masculinisation, associated with changes in physical characteristics and an increase in both aggressive behaviours and hormonal disruption as the rat matures.  

When a foetus of either sex is positioned between two females, the effect is feminisation under the influence of increased oestrogen. This can result in smaller, more feminine males with smaller testicles and reduced testosterone levels.  

Clearly, these hormonal influences in utero can have an effect on the sociability of some rats, creating both: 

  • feisty individuals with increased aggression and therefore reduced sociability,  
  • docile individuals with lower levels of aggression and increased sociability.  

Prenatal stress  

The effects of prenatal stress have been widely studied in rats. Stressful episodes experienced during pregnancy (including social stress), can cause a lifetime epigenetic disruption of normal stress responses in the offspring.  This can make an individual rat more - or less - affected by a stressful event.  

Heightened stress responses often lead to anxiety states (including social anxiety), and fear driven aggression. Lowered stress responses can lead to depressive states, which can look like docility and detachment in the rat.  Reduced stress responses can decrease the perception of risk while heightened stress responses over-emphasise it.  

Mothering and separation  

The quality of mothering in rats is measured in terms of:  

  • time spent in the nest,  
  • time spent feeding,  
  • time spent grooming the babies,  
  • desire to retrieve separated or scattered young.  

The stronger the mothering response is, the more time she will spend in these activities and the healthier the attachment bonds will be between mother and offspring – and vice versa. 

Separation during the first 2-3 weeks of life – either from maternal neglect or removal of the babies from the mother – can have a deleterious effect on the attachment bonds, reducing mothering behaviour over time (that is, a greater rate of decline than the natural fall off of attentiveness that occurs with time). Repeated removals of 1-2 minutes or one longer removal are sufficient to impact attachment.  

Removal of very young babies for handling induces a stress response in both the mother and the neonates that has been shown to negatively impact both attachment and mothering. However, in an attentive mother a period of intensive grooming of the babies following separation helps to mitigate the effects and can positively affect resilience to future stress.  

Any period of prolonged separation between mother and neonate has the potential to increase lifetime anxiety responses. The younger the baby and the longer the separation the greater, the effect. This extends to sibling (or substitute sibling) company, right through the adolescent period into young adulthood.  

Housing a baby rat alone for any reason is an ethical concern because of the lifelong impact on the wellbeing of the individual and their ongoing ability to form healthy social relationships. Other than maternal loss, this is the single most deleterious experience a young rat can endure, and it always results in increased levels of anxiety and stress in the adult rat.  

Because the effect is chronic it can sometimes cause depression and “opt out” rather than obvious anxiety. Either way, future social relationships can prove difficult and the ability to read and respond appropriately to social signalling from other rats can be severely diminished. But in a welcoming and supportive group, such behaviours can be learned at any age, at least to a degree.  

Altered Fear and Stress Responses  

Many early life experiences can affect fear learning and the stress response.  These are two emotional and physiological areas of a rat’s life that can significantly impact their social relationships, both in terms of establishing and maintaining bonds. We’ve looked at several ways that stress responses are affected, so now let’s investigate fear learning.  

Most fear is learned rather than instinctive, and most fear-learning takes place during adolescence under social and environmental influences. This period – when fear is readily learned and committed to long term memory – is often referred to as the sensitive or critical period. It occurs at different ages in different species – always coinciding with adolescence.  

Sensitivity is often at its height at the beginning and end of the adolescent period. Indeed, one source described adolescence as “an extreme form of general sensitivity”! Great description. During this period, sensory perception, emotional learning and fear learning are all at their peak.  

An example of this is the adaptive neuronal changes that occur in the brain of a rat in response to a life-threatening predation experience, which lead to long-term memory formation. Having just one such experience leads to fear learning and associated memories, which in turn protect the individual from future predation.  

Infant rats display rapid, spontaneous forgetting. When they experience a fearful event that is paired with a non-threatening ‘trigger’, such as something painful happening while in a certain cage, fear of the trigger – in this case, the cage - is lost within a week.  

The same unpleasant event, when experienced in adolescence can lead to a lifetime fear response to the ‘trigger’. By adulthood, fear learning generally only occurs in response to traumatic events, as adults are much less sensitive to this process than adolescents.  

We need to understand that although rats become sexually mature around 5 to 6 weeks, they are not socially mature until 5 to 6 months. This period (5 weeks to 6 months) is the period when social fear learning is at its most sensitive.  

Learned fear can include triggers that impact both rat/rat and rat/human relationships. Examples include:  

  • Fear of hands.  
  • Fear of a specific human.  
  • Fear of specific types of handling.  
  • Fear of a rat who has been overly aggressive – note that this fear can be generalised to other rats of the same variety if there are strong visual cues, such as markings.  
  • Fear of being confined in a small space with a particular rat who bullies or aggresses them. This can potentially initiate long-term fear towards both the rat and the tank or cage in which the incident happens. 

Fear is learned by outcome (the rat hurt me) and association (this is where I was when the rat hurt me) and is noticed by the brain because of the perception of threat that accompanies it. It is then committed to long term memory as the brain’s mechanism for protecting the individual from future harm. The result is often avoidance of ‘the rat’ and ‘the place’ where the incident took place.  

However, fear, stress and anxiety do not exist as isolated entities but work together to create the unique emotional experience of the individual rat.  This means that a fear inducing event that we perceive to be minor can actually have a significant effect on a rat who is already stressed, overstimulated by the environment, or suffering anxiety from a disturbance event – such as sibling separation, rehoming or the introduction of unknown rats.  

Stable Temperamental Traits  

Rats are a species known to have stable temperamental traits. These are the foundational characteristics of the temperament of the rat that will remain constant throughout life. While all traits will have a genetic influence, they are also impacted by prenatal and postnatal experiences, adolescent fear learning and social learning - all of which, we can influence.  

“Temperamental trait” refers to where a rat sits along several spectrums:  

  • Extreme neophobia through to neophiliac behaviour.  
  • High anxiety through to low anxiety.  
  • High explorative through to low explorative behaviour.
  • Introversion through to extroversion.  

Recognising stable temperamental traits can help us to identify the rats most likely to struggle in a variety of social situations. We are then able to adjust our approach to cater for our outlying rats. I used to have a rat who was moderate in all traits except for introversion. She was a well-rounded rat who just preferred her own company. She didn’t interfere negatively with the other rats, but often removed herself from group activities.  

Most of the time she lived peaceably on the fringes of the collective, but she really didn’t cope well when I took the rats with me to a house sit in a moderately sized cage (they normally live free in a small bedroom). If I’d been armed with this insight into temperamental traits back then, I could have predicted this and made alternative arrangements.

It’s easy to understand how a highly anxious, neophobic, introvert could be an extremely difficult rat to introduce to newcomers. Thankfully, most rats are moderate in their traits (average!) and are therefore better equipped to deal with the rigors of, rehoming, introductions and other disturbance events.  

Hormonal Influences  

We all know how significantly male and female reproductive hormones can influence social behaviour. Excess of hormones or hormonal imbalances add another layer of emotionality to the factors that we have already considered. Where social aggression (towards rats and/or humans) is an issue, neutering of both sexes can be helpful.  

In male rats, aggression is often related to high levels – or imbalance – of androgens (masculinising hormones), often exacerbated by working to maintain high status within a group of males. Castration reduces testosterone production significantly, and aggression almost always lessens post-neuter.  

Female aggression is more likely to be due to ovarian disease and hormonal imbalance, though for some female rats, higher testosterone levels can also add to the issue. To impact behavioural issues the ovaries must be removed during the operation, not just the uterus.  

When a rat experiences high levels of anxiety, neutering may not have the desired result, especially in males, where testosterone may be supporting the small amount of confidence an individual has. Time and energy given to confidence building and trust work with the rat may yield a better result over time.  

Sometimes a “stress holiday” – time away from the source of the fear to enable a rat to settle and calm after a period of high stress is enough to stop rats who causing drama within a group or biting humans. No animal can be expected to reduce these behaviours while kept in a high stress situation.  

Trauma – Disturbance Events  

I’m going to discuss these two influences of rat sociability as a single topic because there is a huge amount of overlap. Indeed, it could be argued that most rat trauma happens as a result of disturbance events. A disturbance  

event is anything that happens to a rat that significantly disrupts their normal routines, relationships and/or environment. 

Mild to moderate disturbance events include:  

  • · Removal of individual rats from the cage to give birth or because of illness, etc. – can vary from mild to serious for individuals within the cage group.  
  • Adding new items to the environment – only problematic for those rats who are strongly neophobic (thankfully uncommon amongst well-bred rats).  
  • Human caretaker illness or absence – can vary from mild to serious for some rats.  
  • Introduction of a stressor into the environment – e.g. a light bulb with a ultrasonic whine or a plug in air ‘freshener’.  
  • Travelling, shows and vet visits – events they can’t control and don’t understand. These often become less stressful with repetition, though vet visits may increase or vary in impact depending on the circumstances.  

Moderate to severe disturbance events include:  

  • Moving home. 
  • Separation from siblings.  
  • Introduction to other rats.  
  • Loss of a cage mate (often most traumatic in bonded pairs). 
  • Having surgery or severe illness.  
  • Living in or coming through a rescue environment.  
  • Injury.  
  • Being alone.  
  • Having no control over aversive circumstances.  

Reading through these lists it’s important to realise that several caveats apply. Firstly, rats are individuals with highly variable life experiences, stress responses and temperamental traits. An event that is not experienced as aversive or stressful by one can cause significant trauma to another.  

Some events, such as, moving home, having surgery, being alone and having no perception of control cause significant stress to almost all rats. Just because a rat looks ‘docile’ and calm, does not mean they are experiencing a positive internal state. 

When a rat is finding something overwhelmingly stressful, they will often stop resisting it and appear to calm. This is called learned helplessness – a “shut down” response that is seen in animals who feel they no longer have any control over what is happening to them. Such experiences are often traumatising.  

Where loss of control over things that are experienced as aversive lasts for several days or weeks, rats often enter a depressive state. Rats can be variably prone to this depending on their early life experiences, and some rats are more likely to respond with anxiety, which tends to be easier for humans to spot because it is more disrupting.  

Stress is cumulative. This means that mild to moderate aversive events can be traumatic to animals who are already experiencing significant stress.  The perception and effect of an aversive situation (how traumatic it feels) is also affected by physical factors, such as, disrupted sleep, pain, illness, hormone levels and so on.  

So, what does any of this have to do with a rat’s capacity to maintain positive social relationships? Acute stress, chronic stress and trauma can all reduce an animal’s capacity to engage meaningfully in social relationships.  This can show up as several behaviours in rats, including:  

  • Aggression.
  • Hyper dominance.
  • Bullying.
  • Fear.
  • Anxiety.
  • Hypersensitivity to the proximity of one or more cage mates. 
  • Provocative anxiety driven engagement – tends to provoke other rats into aggressive behaviour.  
  • Defensive guarding of a small “safe” place in the cage. 
  • Opt-out: living peaceably alongside – but not engaged with – other rats.  
  • Inappropriate hierarchical behaviours, like constant mounting. 
  • Reduced pro-social behaviours like grooming and bed sharing. 
  • Reduction in behaviours that rely on healthy social connection, such as, empathy, cooperation, nurturing and helping.  

As we draw to the close of the social rat series, I want to make it clear that we have doubtless only skimmed off the top of the iceberg in terms of the intricacies and complexities of the social life of the rat. There is much that is not studied or, as yet, understood, as well as many aspects that we only see in a generalised way – missing the details. The only expert in the social life of the rat is – the rat. The best we can hope for is to be aware and watchful for the information they will share with us. Even if that can only ever tell us a small part of the story…  


https://www.researchgate.net/post/At_what_age_can_a_rat_be_considered _on_puberty_stage2 



https://www.sciencedirect.com/science/article/pii/S2352289516300121 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4021821/ https://www.sciencedirect.com/science/article/pii/S2352289514000125 Alison Campbell © April 2021