Background: House mice are commensal animals with a nearly global distribution, structured into well-differentiated local populations. Besides genetic differences between the populations, they have also diverged behaviorally over time, whereby it remains open how fast general behavioral characteristics can change. Here we study the competitive potential of two very recently separated populations of the Western house mouse (Mus musculus domesticus) by using two different approaches – one under controlled cage conditions, the other under more natural conditions in enclosures mimicking a secondary encounter condition.

Results: We observe a clear bias in the competitive ability towards one of the populations for both tests. The measured behavioral bias is also reflected in the number of hybrid offspring produced in the enclosures.

Conclusion: Our data suggest that key behavioral characteristics with a direct influence on relative fitness can quickly change during the evolution of populations. It seems possible that the colonization situation in Western Europe, with a rapid spread of the mice after their arrival, would have favored more competitive populations on the expansion front. The study shows the possible impact of behavioral changes on the evolution of populations.

1. Data from Dyad experiments. This excel sheet contains two spreadsheets. The first contains information about all behaviors to be observed during the Dyad Experiments. The second spreadsheet contains the metadata (age, weight, population origin, Dyad Number) of all mice used in in the Dyad Experiment, as well as the number of occurrences of each behavior.

2. Data from the Enclosure Experiment. This excel sheet contains three spreadsheets. "legend" contains all information about all columns in the other two spreadsheets. Spreadsheet "room113" and "room114" contains all information about all mice in the enclosure experiment in the respective room.