School of Biosciences

RESEARCH

Linking host stress responses and personality to parasite dynamics

Behaviours that are consistent across time and context are equivalent to personality in humans. Behaviours, including those relating to personality, are often linked to stress physiology. For example, animals that show a larger hormonal response to a stressor (release more stress hormone) will frequently also show a larger behavioural response, and will generally be shyer, more risk averse, and less active. The link between behavior and stress physiology is likely to be complex, and may be at least partially due to correlated selection, or the pleiotropic effects of one set of genes on both behavior and stress physiology, or behaviour may itself be partially determined by underlying stress physiology. Ultimately, consistent differences in behaviour and/or physiology will have fitness consequences for individuals.

I am currently using a fish host – gyrodactylid parasite system (the guppy, Poecilia reticulata, and Gyrodactylus turnbulli) to test the consequences of variation in personality and stress responsiveness on disease dynamics: How do they affect susceptibility to infection, and the transmission of infections between individuals? In many studies of host-parasite interactions, and especially in models of host-parasite dynamics, hosts are assumed to all be similar. However, in reality, this is never the case: As well as personality and stress responsiveness, individuals vary in their sex, age, reproductive status and in many other ways. Using information about the causes of variability in susceptibility and transmission increases our understanding of how parasite populations spread within and between host populations.

A gyrodactylid parasite. © T.A.Bakke.

These monogenean worms show exponential growth on their hosts. They are ubiquitous ectoparasites of teleost fish, and have a huge economic impact on species used in fisheries, aquaculture and the aquarium trade. This specimen is Gyrodactylus salaris, a species that has devastated the Norwegian salmon fishery.

The effects of predation pressure on behaviour and physiology

Fieldwork in a typical habitat for Brachyrhaphis episcopi , in the Panamanian rainforest  © G.Archard (2008

How do ecological variables shape the behaviour and stress responses of animals? I am particularly interested in the role of predation pressure, a strong natural selection pressure in the wild. Prey animals in different populations coexist with different species and numbers of predators. These differences in predation pressure result in predictable differences in a whole range of life history traits, including behaviour and physiology.

The effects of predation pressure are particularly evident in some prey species, where populations differ greatly in the number of predators that they co-exist with. Classic examples of this include some freshwater livebearing fish. I have worked with the guppy (Poecilia reticulata) from Trinidad and Tobago, and the Panamanian bishop (Brachyrhaphis episcopi). Experiments have included both lab and field work, and have involved the measurement of natural variation both between and within populations, as well as experimental manipulations.

Female Brachyrhaphis episcopi in a tank in the laboratory © G.Archard (2011)

Aequidens coeruleopunctatus, a common B. episcopi predator in Panamanian streams and rivers © G.Archard (2010)

Behaviour, stress hormones and animal welfare

I am interested in using measures of stress hormones and behavior to improve the welfare of captive animals. I have done this using RIA of blood samples from Xenopus laevis, the most common amphibian found in laboratories. I am now using a remote technique where water samples that have held individual fish are collected. Fish pass hormones over their gills, and these are then extracted from the holding water and analysed with EIA.

Examples of glucocortiocoid steroid hormones. © R.Palme (2008)
Cortisol is the primary stress hormone in fish and many mammal species. Corticosterone is the primary stress hormone in rodents, birds, amphibians and reptiles

Joanne Cable, Cock van Oosterhout and Ryan Mohammed catching guppies in  Trinidad
© G.Archard (2006)

Collaborators:

Joanne Cable, Ecological adaptations of host-parasite systems. Dr Cable is my host as a Marie Curie Fellow at Cardiff

Prof. Ryan Earley, Alabama University, USA: Remote measurement of fish hormones, links between stress physiology and behaviour

Ryan S. Mohammed, University of the West Indies, Trinidad and Tobago: Ecology and natural infections of wild guppies in Trinidad

Prof. Julian Partridge, University of Bristol, UK: Ecology of fish vision

Dr. Cock van Oosterhout, University of East Anglia, UK: Guppy MHC and parasite resistance; modeling of parasite dynamics