Leverhulme Early Career Fellow
Disease and infection are a constant hazard for all organisms, but variation in immunity among individuals, populations and species, is widespread. My research investigates the causes and consequences of variation in immune defences. Using methods that allow me to study the immune function of animals –– particularly birds –– in their natural, free-living settings, I try to relate these measures of immunity to aspects of physiology, life history and the habitats that individuals live in. In particular I am interested in trying to relate variation in immunity to differences in disease pressures between environments.
Honeyguides, Afrotropical brood parasites, lark species, avian eggs.
My current research addresses a key concept in the field of ecological immunology: that trade-offs involving the immune system underlie much of the immunological variation observed within and among animal populations and species. Developing and maintaining an immune system is energetically costly, requiring resources that are often limited. If increased disease and antigen exposure requires greater investment in immunity, this could have detrimental effects on other resource-demanding processes such as growth. Especially for young, immunologically-naïve animals this poses a problem, since investment in growth andin immunity are both vital for proper development.
To investigate how young birds allocate limited energetic resources between immunity and growth, I use an exciting brood parasite system in Zambia. Brood parasites are ideal subjects for studying the evolution of immune defences, because they exploit the parental care of other host species. This leaves brood parasite offspring exposed to diverse immunological challenges, including host-specific microbes and parasites against which they may have no specific defences. Thus, there are good ecological reasons to expect consistent differences in the strength of the selection pressures exerted on the immune defences of brood parasites vs. their hosts.
Working in collaboration with Dr Claire Spottiswoode, I study brood-parasitic Honeyguides and their hosts. Shortly after hatching, Honeyguide chicks kill their host nest-mates, which are left in the nest chamber to rot. This gruesome behaviour (see here for videos) means that, compared to host chicks, Honeyguides likely face greater immune challenges as chicks. This might select for more rapidly developed and stronger immune defences, creating an extraordinary 'natural experiment' in evolution. Crucially, high growth rates typical of brood parasites suggest that trade-offs between immune defence and growth will be especially apparent.
By using experimental manipulations of nest contamination and monitoring immune responses and growth rates throughout the nestling period I aim to test:
1. Whether exposing chicks to greater contamination promotes stronger immune responses but lower growth rates due to resource allocation trade-offs between immunity and growth.
2. Whether distinct evolutionary histories of immune challenge exposure in the nest cause Honeyguides and hosts to trade-off immunity and growth differently.
This work will provide valuable information on how animals adapt to cope with changing disease threats while simultaneously improving our knowledge of how resource trade-offs drive immunological variation.2. Whether distinct evolutionary histories of immune challenge exposure in the nest cause Honeyguides and hosts to trade-off immunity and growth differently.
Also available on my Google Scholar profile.
- Schroeder, J., Dugdale H.L., Radersma R., et al. & Horrocks, N.P.C. (2013) Fewer invited talks by women in evolutionary biology symposia. J. Evol. Biol. (This paper was widely discussed online, including by Science, The Telegraph, The Times, and Athene Donald’s blog).
- Horrocks N.P.C., Vollrath, F., & Dicko C. (2013) The silkmoth cocoon as humidity trap and waterproof barrier. Comp. Biochem. Physiol. A 164: 645-652.
- Matson K.D., Horrocks N.P.C., Tieleman B.I., & Haase E. (2012) Intense flight and endotoxin injection elicit similar effects on leukocyte distributions but dissimilar effects on plasma-based immunological indices in pigeons. J. Exp. Biol. 215: 3734-3741.
- Horrocks N.P.C., Hegemann A., Matson K.D., Hine K., Jaquier S., Tinbergen, J.M., Shobrak M., Williams J.B., & Tieleman B.I. (2012) Immune indexes of larks from desert and temperate regions show weak associations with life history, but stronger links to environmental variation in microbial abundance. Physiol. Biochem. Zool. 85: 504-515.
- Matson K.D., Horrocks N.P.C., Versteegh M.A., & Tieleman B.I. (2012) Baseline haptoglobin concentrations are repeatable and predictive of certain aspects of a subsequent experimentally-induced inflammatory response. Comp. Biochem. Physiol. A 162: 7-15.
- Horrocks N.P.C., Matson K.D., Shobrak M., & Tieleman B.I. (2012) Seasonal patterns in immune indices reflect microbial loads on birds but not microbes in the wider environment. Ecosphere 3: art. 19.
- Horrocks N.P.C., Matson K.D., & Tieleman B.I. (2011) Pathogen pressure puts immune defense into perspective. Integr. Comp. Biol. 51: 563-576.
- Horrocks N.P.C., Tieleman B.I., & Matson K.D. (2011) A simple assay for measurement of ovotransferrin – a marker of inflammation and infection in birds. Methods Ecol. Evol. 2: 518-523.
- van de Crommenacker J., Horrocks N.P.C., Versteegh M.A., Komdeur J., Tieleman B.I., & Matson K.D. (2010) Effects of immune supplementation and immune challenge on oxidative status and physiology in a model bird: Implications for ecologists. J. Exp. Biol. 213: 3527-3535.
- Horrocks N., Perrins C., & Charmantier A. (2009) Seasonal changes in male and female bill knob size in the Mute swan Cygnus olor. J. Avian Biol. 40: 511-519.
- Horrocks N., Pounder R. (2006) Who’s for five nine-hour shifts a week? Clin. Med. 6: 440-442.
- Horrocks N., Pounder R., RCP Working Group. (2006) Working the night shift: preparation, survival and recovery – a guide for junior doctors. Clin. Med. 6: 61-67.