Successful Copulation Research Articles

LEKKING BEHAVIOR OF ANASTREPHA FRATERCULUS (DIPTERA: TEPHRITIDAE)

Anastrepha fraterculus (Wiedemann) (Diptera: Tephritidae) displays a lek mating system. Males form groups in which they simultaneously display signals (acoustical, visual, or chemical) to attract females with the purpose of mating. Females visit the lek and choose among signaling and courting males to mate. Scarce information is available in A. fraterculus about the main factors involved in female choice and the behavior of displaying males. This information could be important within the context of pest control programs with a sterile insect technique (SIT) component, because departures from normal sexual behavior caused by artificial rearing could affect males’ performance in the field. In this study we assessed A. fraterculus male behavior within the leks and analyzed the importance of behavioral and morphological traits on their copulatory success. The existence of preferred places for lek formation was evaluated in field cages with trees inside and analyzed by dividing the trees in sectors according to a 3-dimensional system. Males were individually weighed, marked, and observed every 15 min. Morphometric and behavioral characteristics of successful and unsuccessful males were compared. Most successful males grouped in a region of the tree characterized by the highest light intensity in the first 2 h of the morning. Results showed that pheromone calling activity is positively associated with copulatory success. Copulations were more frequent for males calling inside the lek, indicating that pheromone calling activity and presence in the lek are key factors for copulatory success. A positive association between copulatory success and eye length was found; some characteristics of the face were also associated with copula duration and latency.

SEXUAL SELECTION ON MULTIVARIATE PHENOTYPES IN ANASTREPHA FRATERCULUS (DIPTERA: TEPHRITIDAE) FROM ARGENTINA

Despite the interest in applying environmentally friendly control methods such as sterile insect technique (SIT) against Anastrepha fraterculus (Wiedemann) (Diptera: Tephritidae), information about its biology, taxonomy, and behavior is still insufficient. To increase this information, the present study aims to evaluate the performance of wild flies under field cage conditions through the study of sexual competitiveness among males (sexual selection). A wild population from Horco Molle, Tucumán, Argentina was sampled. Mature virgin males and females were released into outdoor field cages to compete for mating. Morphometric analyses were applied to determine the relationship between the multivariate phenotype and copulatory success. Successful and unsuccessful males were measured for 8 traits: head width (HW), face width (FW), eye length (EL), thorax length (THL), wing length (WL), wing width (WW), femur length (FL), and tibia length (TIL). Combinations of different multivariate statistical methods and graphical analyses were used to evaluate sexual selection on male phenotype. The results indicated that wing width and thorax length would be the most probable targets of sexual selection. They describe a nonlinear association between expected fitness and each of these 2 traits. This nonlinear relation suggests that observed selection could maintain the diversity related to body size.

Competition moderates the benefits of thermal acclimation to reproductive performance in male eastern mosquitofish

The reproductive behaviour of the sexually coercive male eastern mosquitofish (Gambusia holbrooki) offers an excellent model system for testing the benefits of reversible thermal acclimation responses to mating success. We acclimated male mosquitofish to either 18 or 30 degrees C (14 h light:10 h dark) for six weeks and tested their ability to obtain coercive copulations in the presence and the absence of male-male competition. Based on the beneficial acclimation hypothesis, we predicted for both sets of experiments that 18 degrees C acclimated males would outperform 30 degrees C acclimated males when tested at 18 degrees C, and vice versa when tested at 30 degrees C. We found that copulation success was greater for acclimated than non-acclimated males at both temperatures when individual males were tested without competing males. In contrast, when males from the different acclimation treatments were competed against each other for copulations with a single female, the 30 degrees C acclimated males were more aggressive and obtained a greater number of copulations at both test temperatures. Thus, we found a clear benefit for acclimation when fish were tested in a non-competitive environment, but acclimation to cool temperatures was associated with a decrease in aggressive behaviour that reduced mating performance at both test temperatures in a competitive environment. In contrast with the long-held assumption that reversible plasticity is beneficial, the adaptive significance of reversible physiological plasticity is affected by a variety of other ecological factors and is more complex than previously suggested.

Sexual maturity of the edible crab (Cancer pagurus) in the Skagerrak and the Kattegat, based on reproductive and morphometric characters

Abstract Ungfors, A. 2007. Sexual maturity of the edible crab (Cancer pagurus) in the Skagerrak and the Kattegat, based on reproductive and morphometric characters. – ICES Journal of Marine Science, 64: 318–327. The size at the onset of sexual maturity of female and male edible crab (Cancer pagurus) from the Skagerrak and the Kattegat and the fecundity of females were estimated. Physiological maturity of females, i.e. ovary development, was at a larger size than behavioural maturity (indications of successful copulation). The carapace width (CW) at which 50% of females were mature (CW50), based on development of the gonads, was 132 mm, sperm presence gave a CW50 of 107 mm, and the presence of sperm plugs a CW50 of 118 mm. Changes in relative abdominal width were found at approximately 100 and 130 mm, and CW50 was 104 mm. A smaller fraction (25%) of the females is functionally mature at sizes <140 mm. However, male physiological and functional maturity was more synchronized: CW50s based on advanced sperm production and allometric changes in the chelae were within 5 mm (117–122 mm). Size-specific fecundity increases with CW (0.5–2.5 million eggs). Recommendations for a minimum landing size (MLS) of 140 mm and a change of escape gap size to 90 mm are given. Legislation of a MLS of 140 mm CW for females and males will reduce future potential landings more in the Skagerrak than in the Kattegat.

Fertility and early embryonic development toxicity of penequine hydrochloride in mice

Penequine hydrochloride, a novel anticholinergic agent, was developed as an effective treatment for organophosphorus intoxication. The potential for penequine hydrochloride to induce fertility and early embryonic developmental toxicity was evaluated in AMMS-1 mice. Totally 320 healthy, sexual mature and nulliparous AMMS-1 mice were orally treated with the chemical in drinking water at dose levels of 0, 2.5, 12.5 and 62.5 mg/L from 60 days before cohabitation to successful copulation in 160 males and from two weeks before cohabitation to GD 6 in 160 females, respectively. All the parental mice were observed for body weights, water consumption and any abnormal change during treatment period. Caesarean sections were carried out on day 14 of pregnancy in half assumed-pregnant females, and all the intrauterine data were recorded. Pups naturally delivered by the other half females were weighed, and examined for viability, sex ratio and gross malformations. About 7 days after cohabitation period, all the paternal males were examined for epididymal and testicular weights, sperm number and sperm motility. The decreases in fertility/fecundity indices and maternal weight gain were found at high-dose level in both caesarean sections and natural delivery observations. The primary developmental toxicity of the chemical included decreases in relative organ (epididymis, liver and lung) weights at mid- and high-dose levels in pups on postnatal day (PND) 35. The cause of both the decreased fertility/fecundity indices in F0 males and the decreased relative organ weights in F1 pups are not well known but are presently under investigation. Under the experimental conditions, penequine hydrochloride did not produce any adverse effects (expect the decreases in certain relative organ weights) up to and including 12.5 mg/L (2.53 mg/kg/day in males and 2.19 mg/kg/day in females) corresponding to approximately 72 times above anticipated dosage in human.

Age-related sperm transfer and sperm competitive ability in the male hide beetle

The influence of male age on reproductive success after a single mating has been explored widely; however, few studies have investigated whether quantitative or qualitative differences in male sperm are responsible for the observed patterns. Moreover, the role of male age on sperm competitive ability has been largely ignored. We examined the importance of male age on the probability and amount of sperm transferred during a single mating and explored whether sperm competitive ability varies with male age in the hide beetle Dermestes maculatus, a species where sperm viability does not vary with male age. We also investigated whether sperm transfer rates varied with female age. We found that the probability of sperm transfer and the amount of sperm transferred varied with male, but not female, age. All males performed behaviorally successful copulations, but intermediate-age and old males were more likely to transfer sperm successfully and also transferred a greater quantity of sperm than young males. Old males were less likely to transfer sperm than intermediate-age males, but if they did transfer sperm successfully, they transferred comparable amounts. Sperm competitive ability varied with male age and reflected the quantity of sperm transferred. On average, intermediate-age males achieved greater fertilization success when competing against young or old males than when competing against other intermediate-age males. Old males were poor competitors against intermediate-age males, but they achieved significantly higher rates of fertilization when competing against young males. Our findings suggest that quantitative differences in the amount of sperm transferred determine male success in sperm competition in the hide beetle.

MATING AND PARENTAL CARE IN CAPTIVE PYGMY RABBITS

As part of a captive-breeding program to restore extirpated Columbia Basin pygmy rabbits (Brachylagus idahoensis) to their native habitat in Washington, we documented mating and parental care behavior of these lagomorphs, which was previously unknown. Pygmy rabbits bred from late February through early June, and mating behavior consisted of chasing and brief copulations. Although presented with 1–4 mating partners and 1–6 mating opportunities annually, only 74% of females became pregnant each year. Unlike other lagomorphs, females dug a 16- to 35-cm natal burrow, usually separate from the residential burrow system, an average of 13 days after a successful copulation. Twenty-four days after copulation, females gave birth to 2–7 young at the entrance of the natal burrow and then covered the entrance. Females returned to nurse 1 or 2 times per day, until young emerged from burrows about 15 days after birth. Females averaged 1.3 litters per year, rarely (2%) producing 4 litters. Except for digging a natal burrow, mating and parental care in pygmy rabbits is similar to that of other lagomorphs. Understanding reproductive behavior is critical for captive breeding and reintroduction of pygmy rabbits, and efforts to reduce the consequences of genetic bottlenecks and inbreeding in captivity.

Insemination does not affect female mate choice in a nuptial feeding spider

Nuptial feeding is an important part of mating in several arthropods including some spiders. A male can contribute via the nuptial gift to his own offspring (paternal investment) and/or the nuptial gift may allow him to better transfer sperm or to make the female more willing to copulate (mating effort). From the female's perspective, however, weighing a male's quality according to the presence of a gift should coincide with her mating status, because male rejection by the virgin female may decrease her fitness by increasing the likelihood of remaining unmated. Therefore, female mate choice would depend on her mating status and virgin females are expected to be less choosy than mated females. I examined this hypothesis in the nursery web spider, Pisaura mirabilis, in which females are polyandrous and mate both with males with and without a gift. I found no support for my hypothesis; instead the presence of a gift was crucial in accomplishing successful copulation regardless of female mating status. Interestingly, sexual size dimorphism was found to be a significant predictor for duration of copulation.

Gestational stage sensitivity to ultrasound effect on postnatal growth and development of mice

An experiment was conducted to find out whether ultrasound exposure leads to changes in postnatal growth and development in the mouse. A total of 15 pregnant Swiss albino mice were exposed to diagnostic levels of ultrasound (3.5 MHz, 65 mW/cm2, I(SPTP) = 1 mW/cm2 Intensity(Spatial Peak-Temporal Peak), I(SATA) = 240 mW/cm2 Intensity(Spatial Average-Temporal Average)) for 30 min for a single day between days 10 and 18 of gestation (GD 10-18). Virgin female mice were placed with same age group males for mating in the ratio 2 females : 1 male and examined the next morning for the presence of vaginal plug, a sign of successful copulation. The females with vaginal plugs were separated and labeled as 0-day pregnant. Maternal vaginal temperature was also measured. A sham exposed control group of 15 pregnant mice was maintained for comparison. All exposed as well as control animals were left to complete gestation and parturition. Their offspring were used in our further studies. They were monitored during early postnatal life for standard developmental markers, postnatal mortality, body weight, body length, head length, and head width, and growth restriction was recorded up to 6 weeks of age. An exposure to ultrasound induced nonsignificant deviations in the maternal vaginal temperature or developmental markers. Significant low birth weight was observed in the present study, after exposure at GD 11, 12, 14, and 16. However, 14 and 16 days postcoitus during the fetal period appears to be the most sensitive to the ultrasound effect, in view of the number of different effects as well as severity of most of the observed effects when exposed on these gestation days. The results indicate that diagnostic ultrasound can induce harmful effects on mouse growth and development when given at certain critical periods of gestation.

The Effects of Inbreeding on Male Courtship Behaviour and Coloration in Guppies

AbstractDespite an extensive literature on inbreeding depression in a variety of traits, relatively little is known about the effects of inbreeding on patterns of sexual behaviour. In this study, we use the guppy Poecilia reticulata to investigate the influence of parental relatedness (full‐sib. vs. unrelated matings) on sexual behaviour and colour pattern variation in adult male offspring. Our results revealed that one generation of full‐sibling mating resulted in a strong decline in male sexual motivation (courtship intensity and following behaviour) and mating success (number of successful copulations and insemination success – as estimated by the frequency of post‐copulatory jerks after mating), but we detected no significant influence of inbreeding on colour pattern variation. Our finding that sexual ornamentation (colour) did not show similar inbreeding depression to courtship behaviour may be due to differences in the genetic basis of these traits. Our findings indicate that courtship can be a sensitive indicator of genetic stress and add to an emerging picture that sexually selected traits can be severely affected by inbreeding depression.

Sperm transfer during mating in the pharaoh’s ant, Monomorium pharaonis

Abstract Sperm transfer in the pharaoh’s ant Monomorium pharaonis (L.) is studied by making longitudinal sections through the gasters of mating pairs fixed in copula. Sperm is transferred inside a spermatophore similar to those found in two other ants, Diacamma sp. from Japan and Carebara vidua. Sharp teeth‐ridges are present on the penis valves and, during copulation, these teeth make contact with a thick and soft cuticular layer covering the bursa copulatrix. This ensures an attachment long enough for the successful transfer of the spermatophore to the right position inside the female oviduct. The thick cuticle also protects the queen from serious damage by the male’s sharp claspers. After a first successful copulation, sperm is still present inside the male’s seminal vesicles, suggesting that males can mate multiply. Additional experiments, where single, initially virgin males are presented to several virgin females, confirm this.

Age at maturity in cavies and guinea‐pigs (Cavia aperea and Cavia aperea f. porcellus): influence of social factors

AbstractAge at maturity, a particularly important parameter in the life history of small mammals, contributes greatly to fitness. Social influences on age at maturity have been demonstrated for altricial rodents, in particular, mice. Nothing is known about such effects in precocial small mammals. Wild cavies Cavia aperea are born in a highly precocial state and mature early in life, briefly after weaning. We investigated whether the wild cavy C. aperea and the domestic guinea‐pig Cavia aperea f. porcellus reach maturity earlier in the presence of adults of the opposite sex. Juvenile females kept in pairs without males showed first vaginal opening (=oestrus) when 59 days old in cavies and at about 40 days in the guinea‐pig. However, in the company of adult males, cavy females kept in pairs reached maturity when about 30 days old, and guinea‐pig females when 26 days old. Most cavy females experienced successful pregnancy following first vaginal opening. In cavies, female mass at birth and at first oestrus was not correlated with age at first oestrus. In guinea‐pigs, birth mass predicted age at maturity only when a male was present. The growth rate from birth to first oestrus related to age at first oestrus. In the wild cavy, the presence of a male appeared to influence maturation more between days 25 and 30 than earlier in life. Male C. aperea matured and had fully descended testes when about 65–70 days old. All male cavies produced abundant motile sperm from day 75. First successful copulations occurred at about the same age. Surprisingly, the priming effect of the presence of an adult male on female maturation proved stronger in these highly precocial caviomorphs than in altricial rodents investigated so far.

Extra-pair copulations in common murres I: a mate attraction strategy?

AbstractWe investigated the behavioural context of pair (PCs) and extra-pair copulations (EPCs) in individually-marked socially-monogamous, long-lived seabirds, common murres (Uria aalge). Since forced EPCs have been documented for this species, we first examined which sex controls successful (cloacal contact achieved) copulation. The finding that all successful copulations required female cooperation and crouching suggested that benefits of successful EPCs accrue primarily to females. In a group of murres for which paternity analyses indicated no extra-pair paternity, behavioural observations over five breeding seasons showed that individual females engaged in EPCs primarily under two circumstances: (1) before they were reunited with their mates, and (2) when they were in the process of re-pairing. There was no such relationship between EPCs and re-pairing for males. Successful EPCs occurred with familiar neighboring males of apparent high quality, indicated by their high ledge attendance and prior reproductive success rates. Thus, EPCs may be used by females to attract potential high quality mates in situations where females are attempting to re-pair as a result of divorce or mate death.

Early sexual maturity in male hamadryas baboons (Papio hamadryas hamadryas) and its reproductive implications

We present data on sexual maturity in young hamadryas baboon males (Papio hamadryas hamadryas) and its reproductive consequences in a large captive baboon colony. Hamadryas baboons live in a multilevel social system, with one-male units (OMUs) as the smallest social entity. Male leaders of OMUs are believed to monopolize matings within their OMUs; hence mating is believed to be polygynous and monandrous. In a captive colony of hamadryas baboons, we found evidence that young males less than 4 years old fathered at least 2.5% of 121 offspring born subsequent to vasectomy of all adult males, and males aged 4-5 years fathered at least 16.5% of the offspring. Additional evidence that these young males are able to sire offspring came from a morphological comparison of sperm from hamadryas males of different ages. The sperm of a 48-month-old hamadryas baboon were morphologically indistinguishable from viable sperm from adult males, whereas sperm from a 45-month-old male showed some aberrations. If successful copulations by adolescent males constitute a regular pattern even in free-ranging hamadryas baboons, a hamadryas male's chances to reproduce would not be limited to his role as an OMU leader as previously assumed, and a male's reproductive career would consist of two phases: the adolescent phase, and the OMU leader male phase.

Glucocorticoids of bison bulls in relation to social status

A primary response to stress is an increase in circulating adrenal glucocorticoids (GC) such as cortisol. Two hypotheses propose differential stress responses to agonistic and aggressive interactions in social groups. If subordinate animals are subjected to social and psychological stressors leading to chronic GC elevation, the ‘stress of subordination’ hypothesis predicts that GCs will be higher in subordinates than dominants. Alternatively, if dominant animals are subject to physiological stressors (e.g., fight at higher rates than subordinates) or hierarchies are unstable, the ‘stress of domination’ hypothesis predicts higher GCs in dominant individuals. Both models predict that GC levels will peak during the breeding season. We tested these predictions in bison bulls ( Bison bison) using fecal steroid analysis to characterize GC concentration and behavioral observations to determine dominance rank, copulatory success, and tending status of bulls. Fecal samples were collected during 2003 from adult bison bulls during pre-rut (June), rut (July–August), and post-rut (September). Matched sample data indicated that mean GC levels (ng/g feces) of bulls strongly peaked during the 4-week rut, doubling from pre-rut to rut and then declining again during post-rut. High ranked dominant bulls maintained higher GC levels than lower ranked subordinate bulls. Dominance rank was positively correlated with copulatory success and age, and dominant bulls were more likely to tend (guard) cows as they approached estrus. There was a positive correlation between GC level and copulatory success, with prime-aged bulls (≥7 years) obtaining the most copulations. GC levels were positively correlated with bull androgen levels determined in a previous study. These results support the ‘stress of domination’ hypothesis, indicating that dominant bison bulls pay a significant physiological price for high social status and the opportunity to mate.

Sexual differentiation in three unconventional mammals: Spotted hyenas, elephants and tammar wallabies

The present review explores sexual differentiation in three non-conventional species: the spotted hyena, the elephant and the tammar wallaby, selected because of the natural challenges they present for contemporary understanding of sexual differentiation. According to the prevailing view of mammalian sexual differentiation, originally proposed by Alfred Jost, secretion of androgen and anti-Mullerian hormone (AMH) by the fetal testes during critical stages of development accounts for the full range of sexually dimorphic urogenital traits observed at birth. Jost's concept was subsequently expanded to encompass sexual differentiation of the brain and behavior. Although the central focus of this review involves urogenital development, we assume that the novel mechanisms described in this article have potentially significant implications for sexual differentiation of brain and behavior, a transposition with precedent in the history of this field. Contrary to the “specific” requirements of Jost's formulation, female spotted hyenas and elephants initially develop male-type external genitalia prior to gonadal differentiation. In addition, the administration of anti-androgens to pregnant female spotted hyenas does not prevent the formation of a scrotum, pseudoscrotum, penis or penile clitoris in the offspring of treated females, although it is not yet clear whether the creation of masculine genitalia involves other steroids or whether there is a genetic mechanism bypassing a hormonal mediator. Wallabies, where sexual differentiation occurs in the pouch after birth, provide the most conclusive evidence for direct genetic control of sexual dimorphism, with the scrotum developing only in males and the pouch and mammary glands only in females, before differentiation of the gonads. The development of the pouch and mammary gland in females and the scrotum in males is controlled by genes on the X chromosome. In keeping with the “expanded” version of Jost's formulation, secretion of androgens by the fetal testes provides the best current account of a broad array of sex differences in reproductive morphology and endocrinology of the spotted hyena, and androgens are essential for development of the prostate and penis of the wallaby. But the essential circulating androgen in the male wallaby is 5α androstanediol, locally converted in target tissues to DHT, while in the pregnant female hyena, androstenedione, secreted by the maternal ovary, is converted by the placenta to testosterone (and estradiol) and transferred to the developing fetus. Testicular testosterone certainly seems to be responsible for the behavioral phenomenon of musth in male elephants. Both spotted hyenas and elephants display matrilineal social organization, and, in both species, female genital morphology requires feminine cooperation for successful copulation. We conclude that not all aspects of sexual differentiation have been delegated to testicular hormones in these mammals. In addition, we suggest that research on urogenital development in these non-traditional species directs attention to processes that may well be operating during the sexual differentiation of morphology and behavior in more common laboratory mammals, albeit in less dramatic fashion.

Female resistance and male force: context and patterns of copulation in the New Zealand stitchbird Notiomystis cincta

The New Zealand stitchbird or hihi Notiomystis cincta is unique in that it has two distinct mating positions, in addition to the male standing on the female's back, as is seen in all other birds, it also copulates face‐to‐face. In this study, 43 male stitchbirds first attracted a female to their territory and supplemented their within‐pair matings by intruding into other territories and attempting forced copulations – often resulting in high levels of female harassment. I recorded the temporal variation of both attempted and successful copulations relative to the female's fertile period in order to understand the function of copulation variation in this species. Each of 105 observed copulations were classified according to whether they were: (1) within‐pair or extra‐pair, (2) forced or unforced, and (3) face‐to‐face or standing. Two copulation categories ‘within‐pair unforced standing’ (50%) and ‘extra‐pair forced face‐to‐face’ (27%) accounted for the majority of all observed copulations, and this supported the previous categorisation of face‐to‐face copulation being forced by extra‐pair males in this species. However, in 10% of copulations the female conceded to copulate with an extra‐pair male in a standing position while displaying only subtle signs of resistance, thus, female stitchbirds may show convenience polyandry when the costs of resistance are high. The peak in copulation frequency centred on two days prior to the laying of the first egg and occurred within a period of six days before and seven days after the first egg was laid. Unsuccessful extra‐pair forced copulation attempts closely followed the distribution of all copulations. Male age and morphometrics did not predict whether a female would resist or accept extra‐pair copulation attempts, and female resistance did not appear to depend on male quality. Despite the current trend focussing on female fitness benefits associated with EPCs, it appears that male stitchbirds gain EPCs through forced copulation and females gain no apparent benefit.

Female Copulation Calls in Guinea Baboons: Evidence for Postcopulatory Female Choice?

We tested the hypothesis that primate female copulation calls are a form of postcopulatory female choice. We collected data on female sexual swellings, sexual and agonistic behavior, copulation calls and postcopulatory behavioral interactions in a multimale-multifemale captive group of Guinea baboons over a 3-mo period. Males copulated with only a few females, and females copulated with only 1 or 2 different males in the group, suggesting a harem-like mating system similar to that of hamadryas and gelada baboons. Female copulations were most likely to occur at peak sexual swellings and male copulatory success was accounted for by dominance rank and age. Variation in female tendencies to call after copulation is best explained by the copulatory success of the male with which each female copulated the most and by the number of copulating partners. The findings are consistent with predictions that calls are likely to be associated with copulation with preferred males and the risk of sperm competition. The prediction that copulation calls increased the probability of postcopulatory mate guarding is also supported. Taken together, the findings suggest that female copulation calls may play an important role in postcopulatory sexual selection and in particular in the expression of postcopulatory female choice in primate species in which females have little opportunity to choose their mates or female mate choice is costly or both.

Effects of sequential or group exposure to unrestrained estrual females on expression of sexual behavior in sexually experienced beef bulls1,2

We tested the hypothesis that expression of sexual behavior in bulls is affected by the manner in which they are exposed to unrestrained, sexually receptive females. Twelve Angus bulls were used in a crossover design involving two treatments, each tested four times for a total of eight tests for each bull. Sexual interactions were quantified for each of four, 30-min periods under the following treatments: 1) exposure to each of four estrual females in sequence (SEQ); or 2) exposure to four estrual females as a group (GRP). Bulls were blocked into three testing groups, the order of which was stratified across eight test days. The order in which bulls were tested on a particular day had no effect on bulls' expression of mount interactions, or flehmen responses, suggesting that each group of bulls had similar sexual motivation at the beginning of each test. However, the bull testing order x treatment x time interaction influenced mounting interval (P = 0.08), copulation frequency (P <0.05), and copulation success ratio (P <0.05). When bulls were in GRP and tested first on test days, more (P <0.05) copulations were distributed to the first three females encountered compared with either the fourth female (P <0.05) or to each of the other females in SEQ (P <0.05). During later tests, other bulls in GRP were not able to copulate as frequently (P <0.05) with each female, displayed lower (P <0.05) copulation success ratios, and were allowed copulations by fewer (P <0.05) females during each 30-min test. When bulls were in SEQ, they displayed similar numbers of copulations regardless of the order in which they were tested, and had stable mounting intervals; however, copulation success ratio decreased (P <0.05) more rapidly during subsequent tests. Flehmen responses were initially displayed more frequently (P <0.05) when bulls were in GRP, but this effect diminished during subsequent 30-min tests. In conclusion, exposure of bulls to GRP induced greater sexual responsiveness than SEQ; however, this effect was due to enhanced sexual activity during the early stages of sexual encounters and with females that were not recently mated. Interestingly, bulls seem to repeatedly copulate with each individual female until, apparently, female sexual receptivity became attenuated. Thereafter, recently mated females allowed fewer episodes of repeated copulations, but they did not completely cease copulating with novel bulls.

Arousal Mechanisms: Speedy Flies Don’t Sleep at Night

Alertness and behavioral performance depend on an animal's level of arousal. In vertebrates, reinforcement and maintenance of arousal in the cortex are ensured by diffuse inputs from neurons releasing biogenic amine neuromodulators. Fruit flies similarly use dopamine for arousal control, indicating an ancient evolutionary origin of this essential feature of the functioning brain.