FITNESS HERITABLITY · Selection and inheritance of quantitative traits in the wild: maternal effects in a long-lived species

Final Activity Report Summary - FITNESS HERITABLITY (Selection and inheritance of quantitative traits in the wild: maternal effects in a long-lived species)

The objective of this project was to further our understanding on evolutionary processes occurring in wild populations. Evolution depends on genetic variation: when there is little variation, the pace of evolution will be slower than when there is a lot. Some of our major results show that this genetic variation can vary according to the environment, or according to time. First, to compare genetic variation and heritability in different environment, we compiled numerous studies of amphibians, birds, molluscs, fish, mammals and insects that have measured genetic variation for the same character in different natural environments. Our analyses showed that when the environment is more favourable, more genetic variation is expressed. This means that evolution may proceed more rapidly in favourable conditions than in unfavourable conditions. This finding has important implications for our general understanding of how animals adapt to variable environments. Second, to understand how heritability varies over time, we studied the heritability of breeding date in mute swans by splitting a long-term dataset in classes of individuals of different ages. We showed, for the first time in a natural population, that heritability varies dramatically depending on which ages are considered. Breeding date was heritable for swans early and late in their lives, but not for the majority of the lifespan. These findings suggest that studies of old individuals in the wild can provide an important perspective on how ageing evolves in natural populations. The mute swan long-term monitoring also helped us to illustrate how animals in the wild behave when they are subject to natural selection. This seems a straightforward-enough question, but is one that we do not understand well. Even very well-studied characteristics - the clutch size (number of eggs laid by a female) of birds is a good example - do not always behave as we might expect. Clutch size is often under natural selection, and has plentiful genetic variation. Under such conditions, we expect to see clutch size evolving in the direction favoured by selection. Many long-term studies of bird populations have looked for, but not seen these changes. By using the long-term data on British mute swans in Abbotsbury, we showed that clutch size can indeed evolve in the direction predicted by evolutionary theory. Using measures of selection, and comparisons of parents, offspring, and other relatives to work out the genetic component of clutch size, we showed that the rate of evolution was just as predicted by theory. We hypothesised that a recent change in management, resulting in abundant food-supplies, may have enabled the swans to evolve towards a new, larger, clutch size. Finally, we have used the same dataset to study how and why ageing occurs in the wild. Ageing is the process by which individuals have reduced survival and reproduction when getting old. It has seldom been studied in the wild because of the difficulty to track down individuals over their lifetime. The long-term monitoring of Abbotsbury's mute swans over almost 40 years allowed us to describe how their reproductive performance decline with age, and it also allowed us to test some predictions explaining why ageing has evolved. In particular, we have shown that there is a genetic trade-off between the age at which birds start to reproduce and the age at which they last breed. Although both traits are heritable and they are both under selection, this genetic link between them can prevent them from evolving. This suggests that cessation of reproduction in old animals in the wild has evolved because of evolutionary trade-offs.

Data: CORDIS, © European Union