Reproductive success and mate choice in Long-Evans rats

In the present study, mating behavior was observed in female rats that were given the opportunity to mate with two male rats simultaneously. Eleven sexually na?ve, naturally cycling rats were assigned to one pair of sexually experienced cohabitating male rats. Each female rat was mated during proestrous with her assigned pair of males. Eight females successfully became pregnant and gave birth to healthy pups (approximately 9 pups/litter). After the offspring were weaned, paternity of each pup was determined using microsatellite DNA markers. Based on this analysis, it was determined that one male in each pair sired the majority of the pups in the litter. No male sexual behaviors or characteristics distinguished male rats that sired the majority of pups from those that sired few or none of the pups. Furthermore, neither female mate preference nor measures of paced mating behavior differed between male rats that had a reproductive advantage from those that did not. Finally, ejaculation order also failed to predict reproductive success of the male rats. Together, these results suggest that reproductive success of some male rats may not depend on specific mating behaviors, but rather their success may depend on physiological or genetic traits that make them unique.     

"Some guys have all the luck": mate preference influences paced-mating behavior in female rats

In the present study, mating behavior was observed in female rats that were given the opportunity to mate with two males simultaneously. Three groups of females were tested: 1) sexually na?ve, naturally cycling rats in proestrous; 2) sexually na?ve, hormone-primed, ovariectomized (OVX) rats; and 3) hormone-primed, OVX rats tested 1 week after sexual receptivity testing. One male rat was determined to be the preferred male for each female, if she spent more time with him during a mating test. Independent of sexual experience, female rats were less likely to leave their preferred male than their non-preferred male following intromissions. However, when they left their preferred male, they returned to him faster than to their non-preferred male. This effect of preference was slightly more robust in the OVX rats. When female rats from Group 2 were tested with the same pair of males for 3 additional tests, each female's preference for a particular male was stable. That is, a female rat preferred the same male in approximately 3 out of the 4 tests, which is more likely than would be expected by chance. In a final experiment, pairs of male rats were tested with different females once weekly to determine if different females would prefer particular males consistently. Although no male rat was preferred by all females, females consistently preferred the same male from each pair during approximately 70% of the tests. In conclusion, female mate preference may have adaptive significance for the reproductive success of rats.     

Emergent patterns of mate choice in human populations

We present a model of human mate choice that shows how realistic population-level patterns of assortative mating can self-organize and emerge from the behavior of individuals using simple mate search rules. In particular, we model plausible psychological mechanisms for mate search and choice in a realistic social ecology. Through individual interactions, patterns emerge that match those observed in typical human societies, particularly with regard to correlated quality levels within couples, distributions of the ages at which couples mate, and effects of skewed sex ratios on these mating age distributions.     

The effect of time of day on sperm competition and male reproductive success in laboratory rats

The study was designed to test the hypothesis that siring success of male rats depends on when during the receptivity period the matings occur. In Experiment 1, females were mated with pairs of males differing in coat colour genetic marker. The males copulated with the female successively, either about 1 hour apart at dusk (schedule AA) or about 1 hour apart around midnight (BB) or one at dusk and the other around midnight (AB). The males mating first had lesser siring success under the schedule AB than under the other two schedules. In Experiment 2, females were mated under the same regimen as in Experiment 1. One male of each competing pair had its spermatozoa labeled by 3H-thymidine. The proportions of spermatozoa of the labeled males were identified in samples from uterine horns and oviducts. Balanced contributions of both males were recorded in uterus in all groups. No definitive conclusion concerning oviductal sperm composition could be reached. In both experiments, night-mating males copulated more quickly. It is suggested that copulation at about midnight is advantageous in intermale reproductive competition and that the function of the diurnal variation in the speed of male sexual behaviour might be clarified on this ground.     

Pubertal decline in maternal responsiveness in Long-Evans rats: maturational influences

Latency to onset of maternal behavior increases progressively from the weanling to the peripubertal period in female and male Long-Evans rats. Gonadectomy or hypophysectomy on day 21 had no influence on the pubertal decline in maternal responsiveness. Apparently, inhibitory neural pathways mature which are independent of pituitary hormonal influences.     

Effects of lactation on sodium intake in Fischer-344 and Long-Evans rats

Rats of most strains are attracted to salt in low concentrations, and this attraction is increased by pregnancy and lactation. Nonreproducing Fischer-344 (F344) rats are unusual in that they avoid saline at all concentrations, raising the question of whether lactation alters their sodium appetite. Therefore, lactating and cycling Long-Evans and F344 rats were compared in their relative consumption of water and several concentrations of saline. We found that Long-Evans rats preferred saline, but F344 rats preferred plain water. In comparison with cycling rats, lactating Long-Evans rats markedly increased saline intake whereas F344 rats exhibited only a modest increase. Lactating rats of both strains increased total fluid intake, but this increase was primarily from water in F344 rats and from saline in Long-Evans rats. It was concluded that the aversion to saline characteristic of nonreproducing adult F344 rats continues during lactation. Their aversion to sodium in pup urine may account for the low levels of maternal anogenital licking observed in the F344 strain. © 1998 John Wiley & Sons, Inc. Dev Psychobiol 32: 51–56, 1998     

Does the choice of catheter for embryo transfer influence the success rate of in-vitro fertilization?

The performance of two different transfer catheters has been evaluated in 193 consecutive embryo transfers. Forty pregnancies were achieved, corresponding to a pregnancy rate of 21% of all embryo transfers. The Frydman catheter was used in 123 attempts whereas 70 embryo transfers were performed with the Tom Cat catheter. The Tom Cat catheter yielded a significantly higher pregnancy rate than the Frydman catheter (28% versus 16%; P = 0.03). The mean number of embryos transferred per attempt was similar in the two groups (2.9 +/- 0.1 and 3.0 +/- 0.1 in the Tom Cat and Frydman groups respectively) as was the quality. When more than three embryos were transferred, a pregnancy rate of 37% per embryo transfer was achieved using the Tom Cat versus 20% using the Frydman catheters (P = 0.03). A higher frequency of difficult transfer procedures was observed when the Frydman catheter was used while the Tom Cat performed much better in difficult cases. An alternate use of the two catheters suggests a significantly better performance of the Tom Cat catheter in relation to the efficiency of establishing pregnancy.     

Embryonic origin of mate choice in a lizard with temperature-dependent sex determination

Individual differences in the adult sexual behavior of vertebrates are rooted in the fetal environment. In the leopard gecko (Eublepharis macularius), a species with temperature-dependent sex determination (TSD), hatchling sex ratios differ between incubation temperatures, as does sexuality in same-sex animals. This variation can primarily be ascribed to the temperature having direct organizing actions on the brain. Here we demonstrate that embryonic temperature can affect adult mate choice in the leopard gecko. Given the simultaneous choice between two females from different incubation temperatures (30.0 and 34.0 degrees C), males from one incubation temperature (30.0 degrees C) preferred the female from 34.0 degrees C, while males from another incubation temperature (32.5 degrees C) preferred the female from 30.0 degrees C. We suggest that this difference in mate choice is due to an environmental influence on brain development leading to differential perception of opposite-sex individuals. This previously unrecognized modulator of adult mate choice lends further support to the view that mate choice is best understood in the context of an individual's entire life-history. Thus, sexual selection results from a combination of the female's as well as the male's life history. Female attractiveness and male choice therefore are complementary.     

Variability of bregma in 300 gram Long-Evans and Sprague-Dawley rats

Bregma is used as an anatomical reference point for most freehand and some stereotaxic injections into the rat brain. The variability of bregma with respect to the intraaural line has been examined previously for rats of a wide range of weights. We examined this variability in 282-326 gram male rats of the Long-Evans and Sprague-Dawley strains. In both strains, mean bregma was less than that stated in a widely used stereotaxic atlas. Furthermore, the mean bregma of the Sprague-Dawley rats was significantly greater than that for the Long-Evans strain. The results suggest that bregma is inadequate as an anatomical reference for intraventricular injections in rats unless the volume injected is a substantial fraction of ventricular volume.     

Studies of HLA, fertility and mate choice in a human isolate.

The role of human leukocyte antigen (HLA) genes in pregnancy and in human mate choice has been investigated in the Hutterites, an inbred population of European origins. High-resolution HLA haplotypes were defined by alleles at 16 loci in >1000 Hutterites. Prospective studies of pregnancy outcome previously demonstrated increased fetal loss rates among Hutterite couples matching for HLA-B antigens (P = 0.033) or for the entire 16-locus haplotype (P = 0.002). Among living children of couples matching for HLA-B or for the haplotype, there was a non-significant deficit of children who were heterozygous and compatible with the mother; the number of living children who were compatible and homozygous or incompatible and heterozygous was not different than expectations (HLA-B, P = 0.095; haplotype, P = 0.376). Mate choice among 411 couples was non-random with respect to the HLA haplotype, assessed by a variety of methods (P = 0.020 to <0.001). These combined data indicate a role for HLA region genes in both pregnancy outcome and mate choice, and suggest that selection acting on these genes occurs pre-conceptually as well as during pregnancy. This review outlines previously published studies on HLA, fertility and mate choice in the Hutterites.     

The effect of pregnancy and stress on the onset of placentophagia in Long-Evans rats

Most virgin rats do not eat placenta when it is presented to them; virtually all parturient rats do. This study was designed to examine the role of the duration and termination of pregnancy on the induction of placentophagia. Time-bred rats determined by a pretest not to be attracted to placenta (nonplacentophages), were tested for placentophagia on one of a number of days of pregnancy. A comparable group was tested for placentophagia after surgical termination of pregnancy on Day 21. Groups of virgins were run controlling for the time interval between the pretest and the placentophagia test, and for a time interval that included a “stressful” event. The results were that (a) the incidence of placentophagia rose gradually from Day 7 to Day 15 of pregnancy, then remained stable, at about 0.4, until delivery; (b) pregnancy termination did not produce an effect on placentophagia greater than that of unterminated pregnancy; (c) a pretest-test interval containing a “stressful” event produced significantly more placentophagia than one that did not contain such an event; and (d) the maximum level of placentophagia observed during pregnancy was the same as that produced in virgins by a “stressful” event.     

Measuring informed choice in population-based reproductive genetic screening: a systematic review

Genetic screening and health-care guidelines recommend that programmes should facilitate informed choice. It is therefore important that accurate measures of informed choice are available to evaluate such programmes. This review synthesises and appraises measures used to evaluate informed choice in population-based genetic screening programmes for reproductive risk. Databases were searched for studies offering genetic screening for the purpose of establishing reproductive risk to an adult population sample, in which aspects of informed choice were measured. Studies were included if, at a minimum, measures of uptake of screening and knowledge were used. Searches identified 1462 citations and 76 studies were reviewed in full text; 34 studies met the inclusion criteria. Over 20 different measures of informed choice were used. Many measures lacked adequate validity and reliability data. This systematic review will inform future evaluation of informed choice in population genetic screening programmes.     

Simmondsin: effects on meal patterns and choice behavior in rats

Simmondsin, a glycoside from jojoba meal, decreases food intake after oral administration. The present experiments are designed to clarify the mechanism of simmondsin's anorectic activity. The meal pattern analysis shows that simmondsin supplementation at different doses results in a dose-dependent food intake reduction, which is more pronounced after prior simmondsin experience. The effect of simmondsin on meal patterns (decreased meal size, meal duration and eating rate, increased latency to eat) is most severe at the highest concentration. Rats familiar with simmondsin more seriously postpone their first meal than with first contact, resulting in a decrease of the meal frequency and the day/night feeding ratio.Rats given the choice between a control diet and a simmondsin-supplemented (0.5%) diet, after half an hour, have a significant preference for the control diet. Simmondsin seems to have a specific flavor when mixed in the food since rats recognise the feeder containing simmondsin.The ability of simmondsin to induce conditioned taste aversion (CTA) was also investigated. Rats receiving simmondsin at concentrations of 0.15%, 0.25% or 0.5% during their conditioning develop significant taste aversions to the saccharin solutions.The performed experiments indicate that the simmondsin activity shows some analogy with the satiating molecule cholecystokinin (CCK) at first contact, but shows more analogy with the illness-inducing agent lithium chloride (LiCl) after prior experience with simmondsin. Rats familiar with simmondsin avoid simmondsin-supplemented food by directly monitoring its presence, and by learning to relate it to the postingestive consequences of consumption.     

Effect of acute respiratory acidosis on multimodality sensory evoked potentials of Long-Evans rats

Auditory, visual and somatosensory evoked potentials (EPs), recorded epidurally from 31 chronically implanted male Long-Evans rats, were studied to examine the pattern of sensory effects caused by hypercapnia. Recordings were obtained before exposures, 10-20 min after the beginning of exposure to CO2 in synthetic air, and 30 min after the end of exposure. Previous recordings revealed no substantial effects of the extended recording period itself. Blood pH during an average exposure of 18.8% CO2 was about 7.1. During this level of CO2 exposure the somatosensory response was almost completely abolished, but the latencies of early detectable components were not affected. In contrast, the latencies of all brainstem auditory evoked response components and the 1-5 interwave time increased, whereas amplitudes were only slightly affected. Amplitudes and latencies of early and late components of the flash EP were decreased and lengthened, but the after-discharge components appeared to be most sensitive to CO2. Concentration-response relationships were examined by exposure of rats to 8 and 16% CO2. The most sensitive EP parameter was average amplitude of the late somatosensory EP components. These results suggest that EPs might be useful for assessing acute metabolic disturbances as well as more commonly assessed neurologic disorders.     

Effects of anthracyclines on reproductive function in rats

A single injection of antitumor anthracycline antibiotic in a maximum tolerated dose decreased mating capacity in male rats (doxorubicin, farmorubicin) and decreased the efficiency of mating (farmorubicin). In female rats mating capacity did not decrease, but some of them became sterile. The majority of toxic effects were reversible. The incidence of embryonal death before implantation was increased in intact females mated with males treated with farmorubicin. In females treated with anthracycline antibiotics high incidence of pre- and postimplantation embryonal deaths was noted. Translated fromByulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 130, No. 11, pp. 527–530, November, 2000     

Effects of anthracyclines on reproductive function in rats

A single injection of antitumor anthracycline antibiotic in a maximum tolerated dose decreased mating capacity in male rats (doxorubicin, farmorubicin) and decreased the efficiency of mating (farmorubicin). In female rats mating capacity did not decrease, but some of them became sterile. The majority of toxic effects were reversible. The incidence of embryonal death before implantation was increased in intact females mated with males treated with farmorubicin. In females treated with anthracycline antibiotics high incidence of pre- and postimplantation embryonal deaths was noted.     

Morphologic effects of bromocriptine on spontaneously occurring pituitary prolactin-cell hyperplasia in old Long-Evans rats.

The effect of bromocriptine (BEC), a dopaminergic agonist, on nontumorous pituitary prolactin (PRL) cells of aging female Long-Evans rats, was studied histologically, immunocytologically, electron-microscopically, and morphometrically. Rats were arbitrarily divided into two control groups, one with normal (less than 20 ng/ml) and one with elevated serum PRL concentrations, and into four BEC-treated groups, all of which had increased serum PRL levels prior to commencement of BEC administration. In hyperprolactinemic control rats, compared with normoprolactinemic control rats, pituitary weight and percentage of pituitary PRL cells were increased. The morphologic features of PRL cells in these two groups did not differ markedly, which suggested that hyperprolactinemia was due to increased PRL-cell number and not increased PRL-cell function. Compared with age-matched hyperprolactinemic control rats, hyperprolactinemic rats treated with BEC showed a reversible decrease in serum PRL levels, pituitary weight as well as percentage of pituitary PRL cells, and by ultrastructural morphometry an increase in the volume density of lysosomes. BEC caused no striking changes in nuclear and cytoplasmic areas, volume densities of RER, Golgi regions, mitochondria, lipid droplets, and size and volume densities of forming and storage granules. Since spontaneously hyperplastic PRL cells show less conspicuous morphologic changes following BEC treatment than PRL cells rendered hyperplastic by estrogen administration or pituitary transplantation, it is suggested that PRL cells with no increased endocrine function respond less markedly to dopaminergic suppression than endocrinologically hyperactive PRL cells. It can be concluded that BEC suppresses spontaneous proliferation of PRL cells which occurs with aging.