Health risks in living environment determine evolution of immune system

Evolution is all around us, even right in front of our eyes. Animal research into the differences between closely related species (and sub-species) living in very different surroundings is a good way to examine the details of how evolution ‘works’, in other words, how it causes diversity in life on earth.
Irene Tieleman is an evolution researcher. As a Tenure Track Professor at the Center for Ecological and Evolutionary Studies (CEES) of the University of Groningen she supervised Maaike Versteegh and Nicholas Horrocks, both of whom will be awarded a PhD at the University of Groningen on 24 February 2012 for research into the stonechat and a number of species of lark, respectively.

Irene Tieleman and her group focus on the relationship between birds’ physiological characteristics (such as energy consumption, immune system and stress hormones), their behaviour and life history (clutch size and lifespan) and the way these factors interact with their surroundings (e.g. risk of disease in certain areas). Field research is conducted in Arctic and temperate areas, as well as in the tropics and the desert. Tieleman acquired substantial funding for her research and is a Rosalind Franklin Fellow at the University of Groningen.

Stonechat

Maaike Versteegh explored the link between various physiological characteristics, and between these characteristics and the birds’ life history. Her research question was ‘What is the effect of genes and environment on these characteristics?’ She studied four sub-species of the stonechat, a small songbird. The sub-species originated from areas with a tropical, temperate or continental climate. The environmental factors in the areas differ in various ways. One of the ways is seasonal variation, which is much more extreme in areas with a continental climate than in tropical areas. The stonechats studied had spent their entire life in captivity, making it likely that mutual differences would be genetic.

No evidence to support theory

Versteegh was able to undermine the theory claiming that links between specific physiological characteristics have restricted life history evolution. She now suspects that environmental factors, such as food or germs, have a far greater impact on the evolution of physiology and life history. Versteegh spent a year monitoring the seasonal variations in the birds’ energy consumption and immune systems. She discovered huge differences in the annual patterns of the various sub-species. The seasonal variations in both energy consumption and immune system therefore have a genetic basis, and both have evolved under the influence of the seasonal variations in their differing living environments.

Immune system and evolution

In his research, Nicholas Horrocks concludes that the quality of the immune system is largely determined by evolution. He discovered that birds from areas with a high risk of disease (temperate and tropical climates), have better immune systems than birds from areas with a lower risk of disease (desert).He studied the huge variation in immunological function observed within and between species. He hopes that this will shed new light on how differences in immunity develop and how the variation in immune systems relates to other physiological characteristics of animals and their surroundings.

Larks

Horrocks studied a number of species of lark. Various species of this family of songbirds live in the desert (Saudi Arabia), in tropical (Kenya) and in temperate (the Netherlands) climates. The larks display different combinations of characteristics, such as the number of eggs they lay and how often they breed per year (known as ‘life history’). These factors could affect the amount of energy they have left to build up a strong immunological defence. However, these birds live in environments featuring different disease risks, and this could also be a factor in determining how strong their immune system needs to be to provide adequate protection from infection.

New technique

By developing new techniques for gauging the risk of disease, Horrocks discovered that the birds’ risk of disease has a greater impact on the strength of their immune system than their life history. This contradicts some previous studies, which seemed to show that a busy family life (many and/or large clutches) had a detrimental effect of the immune system of the parent birds.

More information

Maaike Versteegh (Groningen, 1976) studied biology at the University of Groningen. Her thesis is entitled Physiology in a life history perspective: Stonechats’ adaptations to different environment.
Nicholas Horrocks (London, 1979) studied biology at the University of Oxford, UK. His thesis is entitled The role of disease risk and life history in the immune function of larks in different environments.
Both studies were financed with a Veni grant, awarded to the candidates’ supervisor Professor B. Irene Tieleman by the Netherlands Organisation for Scientific Research (NWO). Professor Tieleman has now also been awarded a Vidi grant. Both candidates will be awarded a PhD in Mathematics and Natural Sciences at the University of Groningen on 24 February 2012.

Note for the press

- More information: Prof. B. Irene Tieleman, b.i.tieleman rug.nl, tel. +31 (0)50 363 8096/2040, website Physiological Ecology Group of Irene Tieleman.