We investigated the application of a recently developed genetic test for sex bias in dispersal. This test determines an animal's 'assignment index' or the expected frequency of its genotype in the population in which it is captured. Low assignment indices indicate a low probability of being born locally. We investigated the use of this test with the white-footed mouse, Peromyscus leucopus, in which dispersal is predominantly male-biased, but not extreme. We found that male P. leucopus had significantly lower assignment indices than females. These data suggest that the genetic test for sex bias in dispersal has potential to be used with species that do not have extreme sex-biased dispersal tendencies.

Habitat fragmentation may have significant consequences for population genetic structure because geographic distance and physical barriers may impede gene flow. In this study, we investigated whether habitat fragmentation affects fine-scale genetic structure of populations of the white-footed mouse (Peromyscus leucopus). We studied 27 populations of P. leucopus, 17 in continuous forest and 10 in isolated woodlots. Populations were trapped in pairs that were either 500 or 2000 m apart. We estimated genetic variation at eight P. leucopus specific microsatellite DNA loci. We discovered significant genetic variation within all populations, but no significant differences in numbers of alleles or heterozygosity between populations. For given population pairs, we found significant genetic differentiation even at very short distances, based on multilocus F ST estimates. The amount of genetic differentiation between population pairs was similar in the two habitats. Distance had a marginal effect on genetic differentiation when comparing paired populations separated by 2000 m with those separated by 500 m. However, at a larger geographic scale, there was no evidence of isolation by distance. This study confirms that microsatellite-based studies have the potential to detect interpopulation differentiation at an extremely local scale, and suggests that habitat fragmentation has surprisingly few effects on P. leucopus genetic structure.Résumé : La fragmentation de l'habitat peut avoir des conséquences importantes sur la structure génétique d'une population parce que la distance géographique et les barrières physiques peuvent entraver le flux génique. Dans ce travail, nous avons tenté de déterminer si la fragmentation de l'habitat affecte la structure génétique à petite échelle des populations de Souris à pattes blanches (Peromyscus leucopus). Nous avons étudié 27 populations de P. leucopus, dont 17 en milieu forestier continu et 10 dans des boisés isolés. Les populations ont été soumises à des piégeages appariés à des distances de 500 ou 2000 m. Nous avons estimé que la variation génétique est reliée à huit locus microsatellites d'ADN spécifiques à P. leucopus. Nous avons trouvé de la variation génétique significative au sein de toutes les populations, mais pas de différence significative entre les populations quant au nombre de leurs allèles ou à leur hétéro-zygotie. Chez des paires données de populations, nous avons observé une différenciation génétique significative même à de très courtes distances au moyen d'estimations du F ST multiallélique. L'importance de la différenciation entre les paires de populations s'est avérée la même dans les deux habitats. La distance n'a qu'un effet mitigé sur la différenciation génétique lorsqu'on compare des paires de populations séparées par une distance de 2000 m ou par une distance de 500 m. Cependant, sur une échelle géographique plus grande, nous n'avons trouvé aucun indice d'isolement relié à la distance. Ces résultats confirment que les études basées sur les microsatellites peuvent...

Preferences for male odors by female house mice (Mus domesticus) were examined with respect to age, dominance status, and spatial relationships. Mice were free living in 6 field enclosures. Estrous or nonestrous females were placed in an aquarium with soiled bedding from live traps as the odor source. Females were tested for preferences between (a) adult and juvenile male odors, (b) dominant and subordinate male odors, and (c) "near" and "far" male odors. In dominance odor tests, estrous females preferred odors from dominant males; nonestrous females exhibited no significant preferences. In adult-juvenile and spatial odor tests, there were no significant differences between odor preferences of estrous and nonestrous females. However, most females preferred odors from adult and "near" males. Male dominance status appears to be the strongest influence on female odor preference in these seminatural enclosures.

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Intrauterine position (IUP) of female and male fetuses in litter‐bearing mammals can affect their physiology, morphology and behavior. The relationship between anogenital distance (AGD) and IUP was used as a bioassay for the degree of exposure of female and male fetuses to hormones in utero. Based on laboratory work in several rodent species, the following predictions were made for house mice (Mus musculus domesticus): (1) female mice should prefer odors from males with larger AGDs because such males are more aggressive, could protect more resources, and are better parents than males with smaller AGDs; (2) male mice should prefer odors from females with smaller AGDs because these females produce more offspring and are better parents than females with larger AGDs. We also tested the prediction that within sexes, mice should avoid odors from mice with larger AGDs because such mice are more aggressive. Responses to odors in traps were used to test these predictions for house mice living in outdoor enclosures using odor‐baited traps. Both predictions were confirmed. Furthermore, mice of both sexes tended to avoid odor cues from individuals of the same sex that had larger AGDs, probably to decrease chances of an aggressive encounter that could result in injury.