Aggression, Copulation, and Differential Reproduction of Deer Mice (Peromyscus Maniculatus) in a Semi-Natural Enclosure

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Abstract
This study was designed to analyze the interactions of priority of residence, strain, dominance, male capacity, and sperm competition in relation to aggression, copulation, and differential reproduction in deer mice (Peromyscus maniculatus). Males were wild-type or blonde mutants; females were of the recessive blonde phenotype. There were 20 replicates of a procedure entailing 7-day runs. One male was introduced into a seminatural enclosure on Day 1 and the second male on Day 3. Their interactions were sampled on Days 3-7. In addition, two estrous females were introduced for tests on Day 5 and 6. In the absence of females, levels of male-male aggression were lower than in their presence. Priority of residence led to increased levels of chasing by males. Limitations on male capacity were revealed as decreased numbers of ejaculations and chases in the second of the two tests with females. Dominance was established in 13 of the 20 runs; copulation occurred in 28 of the 41 tests. Dominant males achieved more ejaculations than subordinates. Males copulated with both females on 20 of 41 occasions, with most partner changes (but smaller percentage per opportunity) occurring within ejaculatory series. Females copulated on 44 of the 82 occasions and delivered a total of 30 litters. Determinants of differential reproduction were diffuse. This study was designed to analyze the interactions of priority of residence, strain, dominance, male capacity, and sperm competition in relation to aggression, copulation, and differential reproduction in deer mice (Peromyscus maniculatus). Males were wild-type or blonde mutants; females were of the recessive blonde phenotype. There were 20 replicates of a procedure entailing 7-day runs. One male was introduced into a seminatural enclosure on Day 1 and the second male on Day 3. Their interactions were sampled on Days 3-7. In addition, two estrous females were introduced for tests on Day 5 and 6. In the absence of females, levels of male-male aggression were lower than in their presence. Priority of residence led to increased levels of chasing by males. Limitations on male capacity were revealed as decreased numbers of ejaculations and chases in the second of the two tests with females. Dominance was established in 13 of the 20 runs; copulation occurred in 28 of the 41 tests. Dominant males achieved more ejaculations than subordinates. Males copulated with both females on 20 of 41 occasions, with most partner changes (but smaller percentage per opportunity) occurring within ejaculatory series. Females copulated on 44 of the 82 occasions and delivered a total of 30 litters. Determinants of differential reproduction were diffuse.