From 1845 to 1935, the Hudson's Bay Company recorded the annual numbers of skins of lynxes and snowshoe hares delivered by hunters from what is now Canada. The numbers fluctuated at a rhythm of about 10 years. The ups and downs of the lynx population followed those of the snowshoe rabbits with a certain delay. Although the hunters also affected the population numbers, the periodic fluctuations became the textbook example of the so-called Lotka-Volterra model of population dynamics in predator-prey relationships.
Researchers of the Museum für Naturkunde Berlin have investigated whether this model applies to population sizes and the frequency of genetic variants in populations of hosts and parasites.
Number and diversity
"We want to check whether we can find traces of the oscillation of population sizes in the genome, in the genetic diversity of the populations," says project leader Wolfgang Stephan. Together with colleagues at the Technical University of Munich, he developed a mathematical method for studying the genetic variability of populations that undergo such fluctuations.
There is a simple correlation between population size and genetic diversity: a larger population has more genetic variants than a smaller one. However, if a population recovers from a low number, it is still detectable in the genome. Diversity is limited. Population growth then leaves its mark again: as an increase in singletons. These are genetic variants that occur only once in a sample. The number of singletons increases and decreases with population size.
The researchers compare minor fluctuations in host and parasite with a trench war. The opponents face each other without anyone gaining the upper hand and shifting the balance of the populations. The other extreme, in the comparison an arms race, are strong fluctuations. In this case, a particularly successful variant establishes itself in almost the entire population of one side. The population grows until the other side finds an answer and the ratio begins to reverse.
The researchers now want to investigate native tomato plants that can be infected by a fungus. The goal is to find out which genes are important for the interaction between host and parasite. From this, conclusions could be drawn for the breeding of resistant varieties.
Project-title
Recurrent selective sweeps versus trench warfare in host-parasite coevolution: the influence of population size changes
Duration
01.12.2015 - 30.11.2018
Partners
Technical University of Munich
Funding
Deutsche Forschungsgemeinschaft - DFG