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Mate choice and reproductive strategies in recently diverged populations of the house mouse (Mus musculus domesticus)


Montero,  Inka
Department Evolutionary Genetics, Max Planck Institute for Evolutionary Biology, Max Planck Society;

Tautz,  Diethard
Department Evolutionary Genetics, Max Planck Institute for Evolutionary Biology, Max Planck Society;

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Montero, I. (2010). Mate choice and reproductive strategies in recently diverged populations of the house mouse (Mus musculus domesticus). PhD Thesis, Christian-Albrechts Universität, Kiel.

Population divergence is an important process in the evolution of lineages and can occur rapidly through the interaction of random genetic drift with natural and sexual selection. While natural selection operates on differences in fitness with respect to the local environment, sexual selection acts on the reproductive success of individuals through pre- and postcopulatory mate choice. Recently separated populations of the Western European house mouse Mus musculus domesticus were investigated for mating preferences. The study system consisted of two populations, one sampled in the Cologne/Bonn region, referred to as the “German population” and one from the Massif Central, termed here the “French population”. These populations have been separated for at most 3,000 years. Although this time span is short in evolutionary terms, they already show genetic differentiation. To test whether population divergence is reflected in mate choice, I carried out four replicates of a long-term experiment, in which individually tagged mice of both populations were held for 6 month in a semi-natural enclosure. As controls, I conducted cage experiments, where females could choose between males of both populations during a 6 day period. Paternities in the enclosure populations were determined by microsatellite typing of all individuals and they were used as measures for mate choice and reproductive success. The frequent monitoring of the populations during which animals were examined individually allowed the assessment of their physical condition. Furthermore, I examined the influence of a selfish genetic element, the t haplotype, on pre- or postcopulatory mate choice for the different population backgrounds. Finally, I analyzed whether the population divergence is also reflected in relative frequencies of female strategies such as polyandry and communal breeding. Founder animals of the long-term experiment did not follow a consistent mate choice pattern, while individuals born in the enclosures showed a significant preference for partners who had a father from the same population as themselves. In the controlled cage experiment, there was no consistent preference pattern regarding population background. However, female littermates that grew up in the same cage chose males coming from one population, indicating an environmental influence. These findings are discussed in the context of behavioral and genomic imprinting. German and French founder animals differed slightly in reproductive success. Among the F1 individuals, the comparison of reproductive success between individuals with a mixed population background (i.e. with parents from different populations) versus animals with a pure background (i.e. with parents from the same population) revealed no significant differences. Nevertheless, when looking at the combination of measures for reproductive success, such as offspring number, number of mating events, and offspring per mating, in 5 out of 6 parameters “pure” individuals outperformed the “mixed” individuals, which might indicate a slight decrease in hybrid fitness. No different influences were detected between German, French and hybrid animals regarding the t haplotype or different frequencies of female multiple mating and communal breeding. Influences of the t haplotype were restricted to a slight decrease in offspring number in successful mating events between t/wt animals for all combinations of population backgrounds. Contrary to theoretical assumptions and other experiments, no evidence for an increased multiple mating frequency or avoidance of partners with t/wt was found. Polyandry and communal breeding seemed to be general strategies in females of pure as well as mixed population backgrounds, and both strategies increased in frequency with an increasing population density. Females displaying these strategies had a slightly higher reproductive success in semi-natural conditions: Mothers with litters sired by several males had a higher reproductive success than mothers with only single paternity litters. A higher reproductive success was also detected for females which grew up in communally reared litters. Summarizing the outcome of the study, the recently diverged populations do not vary in partner choice: no differences in mate choice or reproductive strategies were observed. However, females preferred mates that had fathers from the same population as themselves, a pattern which I will call the “father related assortative mating pattern”. This suggests the presence of cues which enable the differentiation between “one’s own population” and “the other population”. In addition, the results gave insights into the benefits of costly female reproductive strategies.