Being Individual

Grey seal breeding colonies are stressful places. Hundreds or even thousands of females arrive on shore every autumn, jostling and moving about to find the perfect spot to give birth and nurse their pups. As the season progresses, pups begin to wander about, trying to avoid the hormonal males who are picking fights and waiting for females to transition from pup-provisioning to reproducing. And these are just the social stressors. There are also varying weather patterns, storms, tourism, and the occasional scientist sneaking through the colony to conduct research.

In a paper published recently in Scientific Reports, researchers from Durham University, the Sea Mammal Research Unit and the Alaska SeaLife Center explored if individual differences in female grey seal stress-coping styles provided any benefits in this natural, but at times chaotic, environment in terms of raising their pups. They found mothers with reactive coping styles tended to vary more in their reproductive expenditure, and consequently in their pup’s growth rates and fitness, compared to more proactive mothers.

What is a “coping style?”

When exploring how animals respond to environmental or anthropogenic stressors, one option is to conduct behavioral observations and look for changes associated with a stimuli. For example, we can observe that seals raise their heads and check on their pups when a novel stimulus goes by (in this case a remote-controlled car named “Rocky”), and from previous research, we know that there are consistent individual differences in these behaviors—aka they exhibit personalities.

One of our study females equipped with a heart rate monitor and accelerometer being approached by “Rocky”. The data transmitted from the heart rate monitor will tell us how, and when, her heart rate changes – and give us an insight into how ‘stressed’ she was by the presence of this novel stimulus.

However, behavioral data alone doesn’t always provide the whole picture. If a seal doesn’t raise its head, is it peacefully sleeping or is it ‘scared stiff with heart racing’?

Measuring how much the gap between successive heart beats varies while at rest can tell us a lot about an individual’s stress-coping style. (Image from: Shuert et al. 2018, Animal Biotelemetry)

A ‘coping style’ refers to a suite of individually consistent behavioral and physiological traits that shape how an individual responds to a stimuli. By recording both behavioral and physiological data concurrently, we can determine if individual female grey seals are more proactive (‘one-size fits all’) or reactive (flexible). In this study, the team focused on recording resting heart-rate variability as the physiological parameter since it has been linked to coping styles in other species.

Is one coping style better than another?

Researchers found that on average, proactive and reactive mums didn’t differ in their expenditures–that is, how much ‘milk energy’ they transferred to pups–and therefore their pups’ growth rates were also similar. However, they did find that reactive mothers varied more from the average daily expenditure, relative to proactive mums. This suggests that reactive mums try to ‘match’ their expenditure to the local environment; sometimes succeeding (above average) and sometimes failing (below average).

So if both coping styles on average result in the same fitness…..why is this a big deal?

We all are very aware that the natural environment is rapidly changing. One factor linked to climate change is the increasingly unpredictable local weather patterns. We know from previous work that grey seal breeding success is linked to weather—higher temperatures and lower rainfall can increase stress and change colony dynamics—but typically we have looked at these effects across all individuals equally.

Coping styles provide a link to assess an individual’s ability to respond to changes in their environment. While under current conditions, both coping styles on average had similar benefits in terms of pup growth, but changing environmental patterns will likely impact proactive and reactive individuals differently. Along with other research into this topic, these findings suggest we might need a new framework for considering vulnerability to change, one that focuses at the individual-level.

While there are no grey seals in Alaska, coping styles have been observed in many vertebrate animals. Therefore, assessing the extent of variation in coping styles within wild populations, and their responses to changing environmental conditions, is a vital step in understanding species’ resilience to rapid environmental change, particularly in places like the Arctic where changes are accelerating.

Twiss, S.D., Shuert, C.R., Brannan, N. et al. Reactive stress-coping styles show more variable reproductive expenditure and fitness outcomes. Sci Rep 10, 9550 (2020).

Check out more about this work at

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