Two Key Studies of Hormones & Pheromones: Animals (DP IB Psychology)

Key Study One: Shivley et al. (2005)

Key Study: Hormones (animals): Shively et al. (2005)

Note: You learned about hormones in the SL Biological Approach (see the RNs on this site which cover the topic) using research by Zak et al. (2009) and Morhenn et al. (2008) which both investigate hormones in humans. This key study looks at the stress hormone cortisol in macaque monkeys so make sure that you DON’T use it when answering a question on hormones in relation to human behaviour - i.e. only use the research on this RN for a HL Extension question on Paper 1 Section B

Aim: To consider the extent to which stress (seen via heightened secretions of the stress hormone, cortisol) is linked to obesity and illness in macaque monkeys. Stress may contribute to the over-production of glucose which, if not burnt off by the body, is stored as fat cells, becoming visceral fat. Visceral fat may lead to obesity in particular body regions such as the abdomen and is particularly harmful to health (for both humans and monkeys) as it tends to bind around internal organs which in turn creates a range of health issues e.g. coronary health problems

Procedure:

A review article based on the findings of several pieces of research on the topic

Results: 

• The article found that female monkeys are used widely in research of this topic as they have shown themselves to be particularly vulnerable to social stress: they are highly sensitive to social hierarchies: e.g., who is the most dominant monkey, who is the next dominant, and so on down the hierarchy with decreasing dominance and increasing subordination

• Subordinate monkeys in typical monkey packs tend to have higher levels of cortisol, the stress hormone, in their system; they tend to be the victims of higher-status monkey’s aggressive acts; they are groomed less by other monkeys; they spend more time in isolation than other monkeys

• Thus the lower-status subordinate female monkeys experience long-term and intense levels of social stress on a daily basis

• Several studies reviewed by Shively et al. showed that there appears to be a link between social stress and visceral obesity: the subordinate female monkeys had higher levels of cortisol which can itself lead to an ‘emergency’ storing of energy in fat cells; they had a higher number of fat cells than other monkeys; higher cholesterol; a higher risk of heart disease and ovarian dysfunction

• The affected females also showed a higher sympathetic nervous system functioning (e.g. raised heart rate) which could in turn damage their artery walls 

Conclusion: Female macaque monkeys who have elevated levels of cortisol may be vulnerable to obesity which in turn could impact their health. 

Key terms: Cortisol  Visceral Fat  Social Hierarchies

Evaluation of Shiveley et al. (2009)

Strengths

• Macaque monkeys and humans share 93% of their DNA so these findings have some useful generalisability and may help to inform future interventions for treating obesity in humans

•  A review article allows the researchers to consider a wide range of studies which increases both reliability (large sample size and statistical power) and validity (large sample size and more likely to be representative) of the findings

Limitations

• The studies reviewed in the article are all correlational so cause-effect cannot be established

• Due to the fact that monkeys were used in the research there is still no way of determining full generalisability: stress may operate differently in monkeys than it does in humans

Key Study Two: Martin et al. (2005): The Role of Pheromones in Red-backed Salamanders & Territoriality

Key study: Pheromones (animals): Martin et al. (2005)

Note: You learned about pheromones in the SL Biological Approach (see the RNs on this site which cover the topic) using research by Zhou et al. (2014) and Hare et al. (2017) which both investigate pheromones in humans. This key study looks at pheromones in red-backed salamanders so make sure that you DON’T use it when answering a question on pheromones in relation to human behaviour - i.e. only use the research on this RN for a HL Extension question on Paper 1 Section B

Aim: To investigate the extent to which pheromones are linked to territorial behaviour in male red-backed salamanders  

Subjects: 30 male red-backed salamanders, collected from a forest near to the University of Virginia. The salamanders were kept in lab conditions for 4 months before the experiment and then afterwards they were returned to the forest

Procedure:

The procedure was instigated to determine the territorial behaviour of the salamanders as it is thought that they are able to detect the pheromones of conspecifics (members of the same species). Territorial behaviour is any behaviour which involves the animal defending its environment from possible intruders (which is more likely to happen if the intruder is also male) 

Each salamander was placed in an experimental chamber for 5 days so that it could establish territoriality over the space. On the sixth day, the salamander was exposed to the following conditions:

1. the salamander was exposed to male pheromones on filter paper inside a petri dish

2. the salamander was exposed to no pheromones at all (control condition)

3. the salamander was exposed to female pheromones on filter paper inside a petri dish

The salamander was placed within the experimental environment with the petri dish within reach. The researchers observed each salamander for the following territorial behaviours: number of nose taps to the petri dish and/or the filter paper; threat behaviours such as extended limbs, an arched back, a raised tail

Results:

The male salamanders were able to distinguish both male and female pheromones outside the petri dish from the control condition, and they responded more threateningly toward male pheromones than from those of the female salamanders

Conclusion: Red-backed male salamanders may use pheromones to detect territorial threats, particularly from other male salamanders

Evaluation of Martin et al. (2005)

Strengths

• By keeping all the salamanders in lab conditions for 4 months the animals began the experimental phase with the same baseline level of time in captivity which increases the reliability of the findings

• The findings support the hypothesis that red-backed salamanders use pheromones to protect their territory which has some generalisability to other animal species e.g. cats, bulls, horses

Limitations

• The behaviours observed by the researchers may not have been the result of territoriality: other factors may have produced the aggressive behaviour e.g. anxiety, over-excitability, the effect of incarceration after living in captivity after a lifetime in the wild

• The study only used male salamanders so the findings are not fully generalisable to female salamanders and have little generalisability for humans

Key terms: Territoriality  Conspecifics  Petri dish

Keep out! A red-back salamander defends its territory