A system for automatic recording of social behavior in a free-living wild house mouse population König et al. König et al. Anim Biotelemetry (2015) AbstractBackground: Our research focuses on mechanisms that promote and stabilize social behavior, fitness consequences of cooperation, and how interactions with conspecifics structure groups and populations. To this end, we studied wild house mice (Mus musculus domesticus) in the laboratory, in semi-natural enclosures and in the field. In 2002, we initiated a project on a free-living population of house mice in a barn near Zurich, Switzerland, where mice were equipped with RFID transponders and were provided with 40 nest boxes for resting and breeding. The population typically comprised between 250 and 400 mice. Methods:To analyze social group membership, social interactions and social preferences of the mice in our study population over their lifespan, we installed a continuous transponder reading system (AniLoc, FBI Science GmbH, Germany). Mice accessed nest boxes through tunnels equipped with two antennas each. When a mouse implanted with an RFID transponder passed the electromagnetic field of an antenna, its identity was transmitted and registered in real time with AniLoc. Additionally, body weights of mice were automatically registered at eight drinking facilities (Intelliscale, FBI Science GmbH, Germany). Here, a mouse sits on a freely movable platform that connects to a scale registering body weight when drinking, and an antenna around the head of the water bottle registers the drinking individual's RFID transponder. Results:The system enabled continuous remote monitoring of the behavior of a free-living, open population of house mice, when using nest boxes and when drinking. Since such safe places are an important resource for survival and reproduction, time of day, duration and frequency of meetings with conspecifics reveal information about the function of their interactions. Trigger efficiency of antennas was 98.2 %. Mice entered and left the nest boxes with an average speed of 0.03 m/s, which is within the antennas' detection capacity (detection speed of 1 m/s or 3.6 km/h). The antenna devices documented not only social structuring of our study population but also spatial genetic structuring. The observation that mice lived in rather closed social groups and tended to share nest boxes with relatives highlights the importance of kin selection for the evolution and maintenance of social behavior. Conclusions:We suggest that such automatic recording of activity, spatial distribution and social interactions is helpful not only in field studies, for a variety of species, but also in captivity or laboratory studies, to answer basic questions in behavioral ecology, population ecology, population genetics, conservation biology, disease ecology, or animal welfare.

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Polyandry is widespread across animal taxa, and subjects males to intense post-copulatory sexual selection which favors adaptations that enhance a male's paternity success, either by decreasing the risk of sperm competition and/or by increasing the competitiveness of the ejaculate. Copulatory plugs deposited by males are thought to have evolved in the context of sperm competition. However, experimental studies that assess the function of copulatory plugs remain scarce. Moreover, most studies have used unnatural manipulations, such as ablating plug-producing male glands or interrupting copulations. Here, we investigated whether repeated ejaculation affects plug size in a mammalian model species, the house mouse. When males experience short periods of sexual rest we found that plug size decreased over repeated ejaculations so that time since last ejaculation can be applied as an approximation for plug size. We induced natural variation in plug size arising from variation in male sexual restedness, and investigated the behavior and paternity success of rival males. Male behavior in the offensive mating role (second) was influenced, albeit not significantly, by the sexual restedness of the first male-to-mate, and therefore the size of his plug. However, second males sired a significantly greater proportion of embryos when competing against a male that had recently mated compared to a male that had not. This supports a potential role of the plug in promoting a male's competitive fertilization success when remating occurs, which could be mediated both by delaying female remating and by ensuring efficient sperm transport through the female reproductive tract.

A selective sweep is the result of strong positive selection driving newly occurring or standing genetic variants to fixation, and can dramatically alter the pattern and distribution of allelic diversity in a population. Population-level sequencing data have enabled discoveries of selective sweeps associated with genes involved in recent adaptations in many species. In contrast, much debate but little evidence addresses whether "selfish" genes are capable of fixation-thereby leaving signatures identical to classical selective sweeps-despite being neutral or deleterious to organismal fitness. We previously described R2d2, a large copy-number variant that causes nonrandom segregation of mouse Chromosome 2 in females due to meiotic drive. Here we show population-genetic data consistent with a selfish sweep driven by alleles of R2d2 with high copy number (R2d2 HC ) in natural populations. We replicate this finding in multiple closed breeding populations from six outbred backgrounds segregating for R2d2 alleles. We find that R2d2 HC rapidly increases in frequency, and in most cases becomes fixed in significantly fewer generations than can be explained by genetic drift. R2d2HC is also associated with significantly reduced litter sizes in heterozygous mothers, making it a true selfish allele. Our data provide direct evidence of populations actively undergoing selfish sweeps, and demonstrate that meiotic drive can rapidly alter the genomic landscape in favor of mutations with neutral or even negative effects on overall Darwinian fitness. Further study will reveal the incidence of selfish sweeps, and will elucidate the relative contributions of selfish genes, adaptation and genetic drift to evolution.