Digit development and embryonic weight in mice: analysis of sex-related time difference and mating period-related interlitter variability

The embryonic growth and digit formation in limb buds were more advanced in male embryos than in female embryos at a specific time (day 12.0) of midgestation. Furthermore, when the number of digits was compared between the sexes according to their body weight, male embryos were found to be more advanced than females in the differentiation of the digit in limb buds. This is the first demonstration of the presence of a time difference in digit development between the sexes of mouse embryos. In the short-period, morning-mating group, embryonic weights at day 12.0 were lower than those in the overnight-mating group. However, the digit development was not very much delayed in proportion to the difference in body weights, and some "catch-up" phenomena were observed in this group. Interlitter and intralitter variability in body weights of mouse embryos at day 12.0 was greater in the overnight-mating group than in the short-period-mating group. These findings suggest that, in embryonic stage-related teratological experiments in mice, a short-period-mating schedule is advised and that the incidence of developmental anomalies should be analyzed separately for male and female fetuses.     

The impact of founder events on chromosomal variability in multiply mating species

In species with heterogametic males, the relative levels of X chromosome versus autosome diversity hold key information about the evolutionary forces at work in a population. It has been shown that population size changes alter the ratio of X linked to autosomal (X/A) variation, with population size reductions and recent bottlenecks leading to decreased X/A diversity ratios. Here we use theory and simulation to investigate a separate demographic effect-that of founder events involving multiply mated females-and find that it leads to much stronger reductions in X/A diversity ratios than are produced by simple population size changes. Investigating the potential of this process to account for sharply reduced X-linked diversity in European Drosophila melanogaster, we find that this model yields predictions that are compatible with the empirical data.     

The role of mating preferences in shaping interspecific divergence in mating signals in vertebrates

Vertebrates represent one of the best-studied groups in terms of the role that mating preferences have played in the evolution of exaggerated secondary sexual characters and mating behaviours within species. Vertebrate species however, also exhibit enormous interspecific diversity in features of mating signals that has potentially led to reproductive isolation and speciation in many groups. The role that sexual selection has played in interspecific divergence in mating signals has been less fully explored. This review summarizes our current knowledge of how mating preferences within species have shaped interspecific divergence in mate recognition signals among the major vertebrate groups. Certain signal modalities appear to characterize mating signal diversification among different vertebrate taxa. Acoustic signals play an important role in mating decisions in anuran amphibians and birds. Here, different properties of the signal may convey information regarding individual, neighbor and species recognition. Mating preferences for particular features of the acoustic signal have led to interspecific divergence in calls and songs. Divergence in morphological traits such as colouration or ornamentation appears to be important in interspecific diversity in certain groups of fishes and birds. Pheromonal signals serve as the primary basis for species-specific mating cues in many salamander species, most mammals and even some fishes. The evolution of interspecific divergence in elaborate courtship displays may have played an important role in speciation of lizards, and particular groups of fishes, salamanders, birds and mammals. While much research has focused on the importance of mating preferences in shaping the evolution of these types of mating signals within species, the link between intraspecific preferences and interspecific divergence and speciation remains to be more fully tested. Future studies should focus on identifying how variation in mating preferences within a species shapes interspecific diversity in features of mating signals in order to better understand how sexual selection may have led to speciation in vertebrates.     

The role of calcium in the Chlamydomonas reinhardtii mating reaction

The mating reaction of Chlamydomonas reinhardtii entails a rapid series of cell-cell interactions leading to cell fusion. We have demonstrated (Pasquale, S. M., and U. Goodenough. 1987. J. Cell Biol. 105:2279-2293) that cAMP plays a key role in this process: gametic flagellar adhesion elicits a sharp increase in intracellular cAMP, and presentation of dibutyryl-cAMP to unmated gametes elicits all known mating responses. The present study evaluates the role of Ca2+ in this system. We document that the mating-induced increase in cAMP, and hence the mating responses themselves, are blocked by a variety of drugs known to interfere with Ca(2+)-sensitive processes. These data suggest that Ca(2+)-mediated events may couple adhesion to the generation of cAMP. Such events, however, appear to be localized to the flagellar membrane; we find no evidence for the mating-related increase in cytosolic free Ca2+ that has been postulated by others. Indeed, by monitoring the length of the Ca(2+)-sensitive centrin-containing nucleus-basal body connector, we show that cytosolic free Ca2+ levels, if anything, decrease in response to cAMP signaling. We confirm a previous report that Ca2+ levels increase in the mating medium, but document that this represents a response to augmented cAMP levels and not a prelude. Finally, we show that IP3 levels remain constant throughout the mating reaction. These results are discussed in terms of the various signal transduction systems that have now been identified in Chlamydomonas.     

The role of oxytocin in mating and pregnancy

The hormone oxytocin (OT) is released both centrally and peripherally during and after mating. Although research in humans suggests a central role in sexuality, the most reliable findings to date involve peripheral activation. This review will discuss these results and will particularly focus on understanding the most recent findings from fMRI data and the effects of exogenous peripheral OT administration. We will then consider hypotheses of the roles played by central and systemic OT release as well as their control and modulation in the female, summarizing recent findings from animal research. Finally, we will discuss the contribution of OT to the initiation of pregnancy in rodents. This article is part of a Special Issue entitled Oxytocin, Vasopressin, and Social Behavior.     

Influence of time of mating and paced copulation on induction of pseudopregnancy in cyclic female rats

The present experiment was designed to examine whether changes occur during the course of behavioural oestrus in the sensitivity of the female to copulatory stimulation and in patterns of sexual behaviour which might influence the likelihood of luteal maintenance. Cyclic female rats were mated on the evening of pro-oestrus (21:00 h) or early on the morning of oestrus (05:00 h) and received either 5 or 10 intromissions from males under conditions which allowed or did not allow pacing of contacts with males to occur. During mating, the levels of sexual receptivity, the timing of sexual mounts from males, and pacing behaviours were measured. The occurrence of pseudopregnancy or pregnancy in each animal was determined by examining vaginal smears for 14 days after mating and by examining the uterus for the presence of fetuses at the end of the experiment. At both mating times, pacing of copulation with males increased the likelihood of prolonged luteal activity. However, females were more likely to become pseudopregnant following non-paced mating at 05:00 h than at 21:00 h the previous evening. Of those females receiving an ejaculation during mating, no difference were seen between groups in the incidence of pregnancy. This change in sensitivity to cervical-vaginal stimulation during oestrus was not associated with changes in sexual receptivity or pacing behaviour. The ability of cervical-vaginal stimulation to induce pseudopregnancy therefore increases toward the end of the period of oestrus, but the behavioural mechanisms which regulate receipt of such stimulation remain constant during that time.     

The role of degradation of fetal haemoglobin in the energy supply of very low body weight pre-term babies

Low body weight premature babies born before the 32nd gestational week were studied to analyse the postnatal fall in plasma haemoglobin and in quantitative changes in amino acid levels. Red blood cells of premature low body weight infants were found to disintegrate more rapidly than those of mature newborns. Thin-layer ion-exchange chromatographic studies showed that amino acids originating from the degrading haemoglobin-F lead to rise in plasma amino acids. These amino acids might play a role as substrates for gluconeogenesis in the energy supply of low body weight premature babies during the special fasting state just after birth.     

The role of the placenta in variability of fetal exposure to cocaine and cannabinoids: a twin study.

There is wide variability in the reported adverse fetal effects of cocaine and cannabinoids. The causes of this variability are largely unknown. We hypothesized that variability in placental handling of drugs affect fetal exposure. We used twin pregnancies as a paradigm to address the role of the placenta in this variability. We analyzed hair or meconium samples taken from dizygotic and monozygotic twins exposed in utero to illicit drugs. Out of 12 pairs, 5 had negative levels in both twins, and seven pairs of twins had chemical evidence of fetal exposure to cocaine (n = 5) or cannabinoids (n = 2). The one known monozygotic pair of twins had almost identical levels of cocaine. In contrast, the six dizygotic pairs had large disparities in either cocaine or cannabinoid concentrations. In three of these six dizygotic pairs, levels of cocaine (n = 2) or canabinoids (n = 1) were undetectable in one twin while positive in the other. Given that twins are theoretically exposed to similar maternal drug levels, our findings suggest that the placenta may have a major role in modulating the amounts of drug reaching the fetus.     

The influence of conditions at the time of mating on reproduction of commercial pigs

The objective of this study was to compare a new mating system, called the Detection-Mating Area (DM Area), and a conventional mating system on the long-term reproductive performance of commercial pigs. The DM Area treatment basically involved detecting oestrous females in an arena closely surrounded on two sides by boars and mating these females in this arena. This mating system was designed to improve the physical and sexual environments of the pigs at mating. In contrast, the conventional treatment involved conducting oestrus detection and mating in the boar's accommodation pen. The study was conducted over an 18-month period at a commercial farm that housed 2400 breeding female pigs.

In order to control for the effects of the stockperson, an analysis was conducted on the reproductive performance of female pigs in which one stockperson assisted the matings in both treatments over a 12-month period. Gilts mated in the DM Area treatment had a higher (P<0.05) total litter size and a higher (P<0.01) litter size born alive than gilts mated in the conventional treatment (10.31 vs. 8.96 and 9.50 vs. 8.29, respectively). Although gilts in the DM Area treatment had a higher farrowing rate (93.2 vs. 87.9%), this difference was not significant (P>0.05). There were no significant (P>0.05) differences found between the reproductive performance of sows in the two treatments; however this comparison was confounded by sows in the DM Area treatment having a lower number of matings per oestrus than those in the other treatment. Observations on the sexual behaviour of pigs at 145 matings indicated that the boars in the DM Area treatment displayed a higher (P<0.05) number of bouts of courting behaviour directed towards the female than boars in the conventional treatment (8.3 and 6.4, respectively). These very limited observations on sexual behaviour suggest that changes in the courting behaviour of bears may be associated with changes in litter size. While there was some indication from the results of progesterone analysis of blood samples taken from unmated gilts that there may have been some differences between treatments in the sexual age of gilts at matings, these differences are unlikely to explain the differences in litter size between treatments. Further research is required to identify the component (s) of the DM Area treatment that are responsible for the improvement in litter size in gilts and to further examine the effects of the two treatments on the reproductive performance of sows.     

The role of female dominance hierarchies in the mating behaviour of mosquitofish

While studies of sexual selection focus primarily on female choice and male-male competition, males should also exert mate choice in order to maximize their reproductive success. We examined male mate choice in mosquitofish, Gambusia holbrooki, with respect to female size and female dominance. We found that the number of mating attempts made by a male was predicted by the dominance rank of females in a group, with dominant females attracting more mating attempts than subordinates. The number of mating attempts made by males was independent of the female size. The observed bias in the number of mating attempts towards dominant females may be driven either by straightforward male mate choice, since dominance and female fecundity are often closely related, or via the dominant females mediating male mating behaviour by restricting their access to subordinate females.     

Pupariation time as a source of variability in mating performance in mass-reared Anastrepha ludens (Diptera: Tephritidae)

The effect of time of pupariation on pupal weight and adult sexual competitiveness under field cage conditions was studied in mass-reared Anastrepha ludens (Loew) males. Larvae that took 72 h to pupariate after separation from diet resulted in lighter pupae than those that took 24 and 48 h. Wild pupae were heavier than the 48- and the 72-h pupae but not the 24-h pupae. Interestingly, no differences in mating performance were found between males of the 24- and 48-h pupae despite differences in pupal weight. In general, lower-than expected levels of mating compatibility between sterile and wild A. ludens resulted from the interaction of both strains as more homotypic pairs were observed. Discussion focuses on the effect of the mass-rearing process on male fruit fly mating performance.     

Selection for fresh weight in Arabidopsis thaliana under two mating systems

Summary Four races of Arabidopsis thaliana were used to produce two F ₂ populations and these constituted the base populations of an artifical selection study. All plants were grown under aseptic culture conditions in a controlled environment and the character studied was fresh weight after 15 days' growth. For one section of the study, two selection intensities were applied to each F ₂ population and the selected parents were randomly mated. In addition to the high selections a group of random selections were maintained as a control. In the second section of the study the procedure differed only in that mating was by self-fertilization.For one population the selection response was as expected for a character of low heritability. A regular response was also observed for the other population when mating was at random, but the results for selection with self-fertilization indicated the presence of dominance effects. The overall conclusion was that selection with random mating and selection with self-fertilization produced approximately equal genetic gains.

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Zusammenfassung Vier Rassen von Arabidopsis thaliana wurden verwendet, um zwei F ₂-Populationen herzustellen, die als Ausgangspopulationen für Untersuchungen über künstliche Selektion dienten. Alle Pflanzen wurden unter sterilen Kulturbedingungen in kontrollierter Umwelt gezogen, das untersuchte Merkmal war das Frischgewicht nach 15tägigem Wachstum. In einem Teil des Versuchs wurden zwei Selektionsintensitäten auf jede der F ₂-Populationen angewandt und die selektierten Eltern zufällig gepaart. Zusätzlich zur strengen Selektion wurde eine Gruppe zufallsgemäß ausgewählter Individuen als Kontrolle gezogen. Im zweiten Teil des Versuchs unterschied sich das Vorgehen vom vorigen nur dadurch, daß die zufällige Paarung durch Selbstbefruchtung ersetzt wurde.Für eine Population war der Selektionserfolg wie für ein Merkmal mit niedriger Heritabilität zu erwarten. Eine reguläre Antwort wurde auch für die andere Population beobachtet, wenn die Paarung zufällig erfolgte, jedoch zeigten die Ergebnisse der Selektion mit Selbstbefruchtung das Vorkommen von Dominanzeffekten an. Insgesamt wird gefolgert, daß Selektion verbunden mit zufälliger Paarung und Selektion verbunden mit Inzucht näherungsweise gleiche genetische Gewinne zur Folge hatten.

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Paper number 3497 of the Journal Series of the North Carolina State University Agricultural Experiment Station, Raleigh, N.C. This investigation was supported in part by Public Health Service Research Grant GM11546 from the Division of General Medical Sciences. The support for computing was provided by the National Institutes of Health Grant FR-00011. The use of trade names in this publication does not imply endorsement by the North Carolina Agricultural Experiment Station of the products named, nor criticism of similar ones not mentioned.     

Interlitter variability in fetal body weight in mouse offspring from continuous, overnight, and short-period matings

When female mice of the Jcl:ICR strain were mated with a male either (1) continuously throughout the day or (2) overnight or (3) during 2 hours in the morning at light period, the interlitter variability of fetal body weight on the 18th day of gestation was smallest in the group with short-period mating. Thus, in the embryonic stage-specific teratological experiments, this mating schedule is advised. Even for routine reproductive toxicity testing protocols, the short-period mating may be preferable for the purpose of increasing test sensitivity.