Disease Ecology and Evolutionary Genetics
We are studying the interaction between animal and pathogen and the consequences that an infection has on the survival and reproduction of the animal. Why do some animals become ill and others do not? How are their migrations affected? What role do collective interactions within a flock play in a response to disease? Why and how does, for example, a mallard die? And what constitutes the immuno-genetic basis of all this?
Living in an aquatic habitat, mallards are exposed to a diverse and rich fauna of microorganisms (bacteria, viruses, fungi, and parasites). Most of these microorganisms are harmless for the birds. There are, however, several pathogens, such as the influenza virus, to which the birds are also exposed. During evolution, most pathogens have reached a certain balance with their hosts, the birds: the host does not become ill despite optimal propagation of the virus. If the pathogen mutates, for example in the case of the highly pathogenic influenza (avian bird flu), or if the host's immune system is not able to control the infection, there is no longer any equilibrium and the host experiences disadvantages. Migratory lifestyle challenges the immune system even more because migration is an intense form of exercise and therefore impacts the energy budget of the whole organism – incl. energetic costs of immune defense. Additionally, encountering diverse locations during migration brings the organism into contact with a sundry of more pathogens. Dense aggregations of individuals on stopover sites and inter-individual interactions and the collective behaviour of whole groups are characteristic for shaping emergence of infectious diseases in a small-world network.
It is the immune system of a host that determines how the defense against pathogens is carried out. Vertebrates have evolved a complex immune system that comprises, besides physical barriers (e.g., skin), an innate component with which these animals were born and that does not change throughout their lives, and an adaptive component which continuously accommodates for changes in the pathogen community. The genetic basis of the immune system carries the signature of millions of years of evolution. Comparative analyses of immune genes between individuals within a species as well as comparisons between closely and distantly related duck species are key in understanding immune pathways.
Among (migratory) waterfowl, the mallard is most familiar to researchers and a preferred model for immuno-ecological studies. The mallards at the Max Planck Institute for Ornithology in Radolfzell are held in our new aviaries for short experiments or for breeding. They are tested for pathogens and different parameters of their immune systems are studied. Then, they are fitted with a GPS and acceleration logger, in addition to heart-rate and body-temperature loggers before they are released and observed by this telemetry while roaming in their natural surroundings. Other species of ducks can also be housed and bred for comparative studies of the genetic basis of their immune system, or for deciphering their evolution into distinct species with immunological traits of which some can be distinct, and others shared.