David L. Lanier

Open-field behavior in muroid rodents.

Open-field behavior was observed in 10-min tests of 10 adult males of each of 12 species of muroid rodents and of the two reciprocal crosses of Peromyscus leucopus and P. gossypinus. Considerable variation was found in number of squares entered, number of fecal boli deposited, and patterns of behavior displayed in the open field. Animals generally showed decreasing ambulation as tests progressed and tended to seek walls. Most measures varied significantly as a function of the general ecology of these species.

The role of prolonged copulatory behavior in facilitating reproductive success in male Syrian golden hamsters (Mesocricetus auratus) in a competitive mating situation

Summary1.The objective of this research was to determine whether the multiple ejaculation pattern of golden hamsters might have a functional consequence in increasing the percentage of offspring sired by a male when the female partner subsequently mates with a second male.2.A risk of displacement by a second male was demonstrated to exist. When two male hamsters mated for five ejaculatory series each, a male was able to sire significantly more offspring when mating second than when mating first. Thus, hamster compulatory plugs do not provide complete protection against subsequent sperm displacement.3.Prolonged copulation can provide protection against sperm displacement. Prolongation afforded no protection to cream males. However, when agouti males mated to satiety prior to a mating by a cream male, the agouti males sired more of the offspring than when they attained just one or five ejaculations.4.The primary mechanism underlying the protective effects of prolongation of copulation was found related to copulations with sperm transfer, presumably stemming from the relative concentrations of sperm from the two males. Neither the mere passage of time nor copulation by a vasectomized male conferred a protective effect.5.Viewed as a reproductive strategy in social context, the multiple ejaculatory pattern can be seen as having functional significance in maximizing individual fitness.

Copulatory behavior and nest building behavior of wild house mice (Mus musculus)

The copulatory behavior and nest building behavior of wild house mice (Mus musculus) were examined in an attempt to study the effects of domestication on these behaviors. In the first experiment, 17 male and 17 female wild house mice were observed on a total of 68 tests of copulatory behavior, each carried to a satiety criterion of 90 min with no intromissions. The basic copulatory pattern was found to be identical to that of domesticated strains of house mice. However, the wild house mice appeared more extreme in certain of the quantitative aspects of copulatory behavior than most inbred strains. In the second experiment, 9 male and 10 female wild house mice and 10 male and 10 female C57BL/6J inbred house mice were tested for nest building behavior for 28 consecutive days. The nest building of wild house mice appeared similar to that of most domesticated house mice, although wild house mice used less cotton in building nests than did domesticated animals.

Copulatory behavior of golden hamsters: Effects on pregnancy

Two experiments were conducted to study the role of male copulatory behavior in initiating physiological responses necessary for pregnancy in female hamsters. In Experiment 1, it was found that copulation beyond the first ejaculatory series is critical to attainment of maximal probabilities of pregnancy. Whereas all females became pregnant when mated to a criterion of sexual satiety, only 20 percent were pregnant after one ejaculatory series. The relationship between increased copulatory stimulation and increased probability of pregnancy was further refined in Experiment 2. Females required more than 4 ejaculatory series to maximize the probability of pregnancy. Mounts without intromission had no effect. Neither parturition number of ova shed, nor little size appeared affected by amount of copulatory stimulation. A coadaptation between the copulatory pattern of the males and the response systems of the females of several rodent species appears to have evolved and to aid successful reproduction.

Food hoarding in muroid rodents.

The hoarding of food pellets was studied in 72 adult male muroid rodents of ten species; Mesocricetus auratus, Microtus ochrogaster, Microtus pennsylvanicus, Microtus montanus, Peromyscus californicus, P. eremicus, P. gossypinus, P. leucopus, Sigmodon hispidus, and Meriones unguiculatus. Seven Oryzomys palutris were also studied. Microtus and hamsters were the only species to show any appreciable hoarding. Six species were tested for the hoarding of sunflower seeds and corn kernels. Data were consistent with those on the hoarding of food pellets. Although information is incomplete, the ease of eliciting hoarding behavior in the laboratory appears roughly correlated with the tendency to hoard in the natural habitat. No other ecological correlates were apparent.

Variation of food hoarding with the estrous cycle of Syrian golden hamsters (Mesocricetus auratus)

Food hoarding was assessed in 16 adult female Syrian golden hamsters (Mesocricetus auratus) across the stages of the estrous cycle. Results show that food hoarding is depressed on the day of behavioral estrus but does not vary among the other days of the cycle. Decreases in food hoarding appear to be correlated with high levels of estrogen and progesterone. The data are consistent with the hypothesis that food hoarding, food intake, and weight gain are controlled either by the same mechanism or by similar mechanisms in some female rodents.

A Laboratory Study of Climbing Behavior in 11 Species of Muroid Rodents

The tendency to climb was examined in a laboratory study of 11 species of muroid rodents {Peromyscus gossypinus, P. tnaniculMus b air di, P. eremicus, P. polionotus, P. leucopus, Microtus canicaudus, M. montanus, M. ochrogaster, M. pennsylvanicus, Rhabdomys pumilio and Mus musculus). Differences among species were found, with species such as P. gossypinus, P. maniculatus and Mus musculus spending approximately one-third to one-half of their time off the ground and R. pumilio, Microtus pennsylvanicus and M. ochrogaster displaying virtually no climbing. Although the performance of some species was consistent with reports of their behavior in the field, several exceptions were noted. Significant positive correlations were found between time spent off the ground in the present study and the hind foot length ratio, number of square entries in the open field, and the amount of jumping in the open field as found in previous laboratory studies.

Copulatory behavior of Syrian golden hamsters in a one-male two-female test situation

Eighteen male hamsters each completed two tests of copulatory behavior: one with one female present and one with two females. Males displayed only relatively small, quantitative alterations of their typical copulatory pattern in the two-female vs. the one-female situation. All males mated with both females. Shifts between females tended to occur at predictable times-particularly after ejaculations and those long intromissions that did not immediately precede ejaculations. When mating in the two-female situation, males sired more offspring than with one female. Females in the two-female situation received less copulatory stimulation than in the one-female situation, but there were no detectable deleterious effects of this reduced stimulation on reproduction. Should copulation occur between one male and two females in the natural habitat, it would appear to be of reproductive advantage to the male, with no detriment to the female.

Studies of copulatory behaviour in northern grasshopper mice (Onychomys leucogaster)

Abstract Onychomys leucogaster display a copulatory pattern characterized by locking, no intravaginal thrusting, ejaculation on a single insertion, and multiple ejaculations. Ten pairs of mice received a total of 50 tests with females in hormone-induced oestrus. A mean of 3·8 locks with a mean duration of 69·4 s preceded attainment of a satiety criterion. In a second experiment, pregnancies were found in approximately 25 per cent of females tested to sexual satiety in natural oestrus, but no female mated for just one lock. There was a positive relationship between number of locks and probability of pregnancy. Supplementary observations on attempts to increase pregnancy rates and on effects of mode of oestrus induction on copulatory behaviour are reported.

Effects of variations in copulatory behavior on pregnancy in two species of Peromyscus

Stimulation requirements for the initiation of pregnancy were studied in cotton mice, Peromyscus gossypinus, and white-footed mice, P. leucopus. Mating to satiety rather than for one ejaculatory series significantly increased the per cent of P. gossypinus females pregnant (63% vs 0%). Among females mated to satiety, those which became pregnant received significantly more copulations than those which did not. While no P. leucopus female mated for one ejaculatory series became pregnant, the increase in the probability of pregnancy following tests continued to satiety (or satiety plus overnight) was not significant, as just 20% of females in the satiety groups became pregnant. The multiple ejaculation pattern in these species appears to be an integral part of pregnancy initiation.