Interests
Biological responses to stress are energetically costly. Stress can be either positive (eustress), if it makes individuals more resilient, or negative (distress), if it overwhelms organisms' natural defences, and produces detrimental conditions. By diverting resources into the stress response, organisms shift their priorities for energy allocation, which can impact on fitness and survival, such that stress provides a strong selective pressure.
Seals, stress and energy balance
Seals are interesting and informative model animals for the study of the stress, and its impact on energy balance. They routinely experience physiological stress as part of their daily and seasonal activities. Seals are air breathing mammals that make a living under water in the cold, deep dark ocean, but need to come to the surface to breathe, and to come ashore to rest, breed and moult.
On a dive by dive basis they are exposed to a barrage of potentially damaging conditions. Diving on a single breath hold means they need to conserve oxygen and they restrict blood flow largely to the heart and brain. Other tissues experience repeated ischaemia reperfusion, and the resulting sporadic and repeated hypoxia that can result in free radical damage. High levels of dissolved nitrogen in the blood stream, as a result of repeated diving, and their rapid rate of ascent at the end of a dive means they need to have mechanisms in place to avoid the bends and shallow water black out. All this is in the face of the high thermal conductivity of the water, which adds the risk of hypothermia if an animal has an insufficient amount of insulation. To avoid this problem seals have thick blubber, which then creates added energetic costs of overcoming buoyancy during diving. Along with colleagues at the Sea Mammal Research Unit, we've been working to understand how seals manage blood distribution and oxygenation using Near Infra Red Spectroscopy. We've also used the technique to better understand physiological responses to sensory stimulation and anaesthesia.
While they are on land seals face the possibility of overheating as a result of thick blubber. They are also away from their food source, and so they need to fast. While fasting they are often engaged in highly metabolically costly activities such as regenerating hair, lactating, defending pups or territory, or just undergoing rapid development. Particularly during the breeding season, tension runs high on close packed breeding colonies and animals experience considerable aggression with the risk of injury and infection. Even if they find a quiet corner, it is possible that they experience oxidative damage or dehydration leading to proteotoxic stress.
Seals are apex predators. Their individual and population level health can act as an indicator of the health of the ecosystem. However in addition to their ‘lifestyle stressors’, they face anthropogenic stress from direct or indirect competition from humans and other predators for access to fish; disturbance on haul out or displacement from foraging grounds as a result of human activity; and the accumulation of lipophilic contaminants in their blubber layer, which acts as a metabolic fuel source while they are fasting as well as insulation while at sea. Being fat is very important for seals: in their first year, the survival of seal pups depends on how fat they are. Clearly, if stress has a negative impact on energy balance in these animals, it will have a detrimental effect by reducing recruitment into the breeding population.
Seals, obesity and diabetes
Seals have a high fat diet, high body fat content and high levels of circulating glucose, all of which are reminiscent of the diabetic and obese condition in humans. Diabetes and obesity lead to complications that stem from local inflammation in humans, but there is no evidence that seals experience similar problems. The differences between seals and humans in regulation of fat stores and glucose could give considerable insight into the management of diabetes and obesity.
I am interested in how these animals regulate storage and use of metabolic fuel sources, and the similarities and differences between seals and the development of obesity and diabetes in humans. I am also interested in how they withstand the natural (fasting, pressure change, hypoxia etc) and man-made (pollutants, disturbance etc) stressors that they encounter on a dive –by dive, daily or seasonal basis, and the links between susceptibility/ resilience and body condition. Our recent NERC funded grant to explore the impact of pollutants on fat tissue function in seals showed that PCBs can alter blubber function in suckling pups, with potential consequenes for their survival.
This research involved scientists based at Abertay, and at the Sea Mammal Research Unit (http://www.smru.st-andrews.ac.uk/) in St Andrews, scientists in Belgium at the Universite de Liege and the Universite Catholique de Louvain. We use an approach that allows us to expose small pieces of blubber (explants) to man-made environmental pollutants in the lab and then find out whether they respond differently to hormones that are important in regulating fat tissue function. We have measured the metabolic responses of the explants and extent to which different genes and signalling pathways are switched on or off; the ability of the cells to accumulate or mobilise fat; the production of cellular stress markers; and the release of important chemical signals from the fat. This work helps us understand the whether exposure to anthropogenic chemicals alters energy balance amd has negative ecological consequences in seals, and predict the negative effects these chemicals may have on people in terms of obesity and weight management.
I supervised Holly Armstrong on her PhD investigating eustress and distress in grey seals. Her project aimsed to describe the changes in cellular defence genes with natural and anthropogenic stressors, and to explore trade off in their expression different key tissue types. She also has some experimental data from the explant work investigating effects of PCB exposure on fat tissue. She worked as a post doc in my lab analysing blood and tissue culture media samples to better understand the effects of hormones and POPs on fat cell function.
Laura Oller Lopez, joined us in 2017 for her PhD project on oxygenation, vascaulrity and inflammation in blubber tissue. Her work involves analysiing data from the whole animal (body fatness from photogrammetry), tissue level in vivo (using near infra red spectroscopy and oxygen probes to look at oxygen delivery in blubber), histology (fat tissue structure) and at the molecular level (gene expression of fat tissue during development and under experimental hypoxia). Her first first authorship showing the pO2 in blubber of grey seals and how it changes with fatness came out in summer 2021.
Seals as vectors and reservoirs of antimicrobial resistance genes
Myself and colleague, Scott Cameron, are working on a project together with Debbie Russell at SMRU, to better understand the prevalence of antimicrobial resistance in the seal population in the UK. PhD student Lauren Arkoosh is working with us to better characterise and map antimicrobial resistance genes in seal faeces from arond the UK. We are also working on samples provided by colleagues at CEH Edinburgh from the birds on the Isle of May to look at cross over between the seal and bird resistome profiles.
Other projects
Recently I worked with the marine vertebrate research group at Plymouth University, where I was previously based, on other projects too. We worked together on a project investigating the effects of shipping noise on seals in highly stratified waters, which meant collaborating with acousticians and oceanographers. I also work with scientists in Exeter and at Plymouth Marine Laboratory on the links between diet and microplastic exposure in seals.
I co-supervised Matt Carter, a PhD student with Clare Embling (https://www.plymouth.ac.uk/staff/clare-embling), Debbie Russell (http://www.smru.st-andrews.ac.uk/staffProfile.aspx?sunID=dr60) and Phil Hosegood (https://www.plymouth.ac.uk/staff/philip-hosegood). Matt's project uncovered details of the development of foraging behaviour in grey seal pups and is part funded by NERC and the School of Marine Science and Engieering at Plymouth. He has gone on to do postdoctoral work at the Sea Mammal Research Unit.
I am also working on a project with Sean Twiss at Durham University on metabolic rate, breathing and heart rate control in grey seal pups to better understand how they develop diving skills early in life.
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