Effects of male courtship and gonadal steroids on pair formation, egg-laying, and serum LH in Canvasback ducks (Aythya valisineria)

The effects of social stimuli on the reproductive physiology of female birds have been widely studied. This study examined the endocrine and behavioural responses of female Canvasbacks ( Aythya valisineria ) to changes in the behavioural and endocrine states of the male, as signalled by his courtship displays. Male Canvasbacks exposed to female conspecifics exhibited a variety of courtship displays which increased significantly with testosterone administration. However, the testosterone-increased courtship displays of males did not increase female receptivity or serum LH, or stimulate reproductive development or egg-laying in unpaired females placed with them. Females confined in cubicles within a pen that held breeding pairs and a free-swimming flock had higher serum LH levels and laid more eggs than did females in cubicles in another pen without breeding pairs or a free-swimming flock. This suggests that social factors, such as vocalizations from a flock and breeding pairs, may increase serum LH and egg-laying in unpaired females. Oestradiol implants in female Canvasbacks did not elevate receptivity to courting drakes, nor did they stimulate pair formation, nesting activity, or egg-laying behaviour. Testosterone implants in drakes and oestradiol implants in females decreased serum LH in each group. These results show that increasing the amount of courtship is not adequate to stimulate pairing behaviour or increases in reproductive hormones. Thus, our results suggest that female receptivity to male courtship may be a key determinant of pair formation and consequent synchronization of the behaviour patterns between members of a pair of wild birds. Our results may further suggest a dissociation between effects of courtship and pair formation in wild Canvasbacks.     

The Influence of Physical and Acoustic Experience on Sequential Mate Preference in the Cricket Gryllus bimaculatus. Is Song Important?

Female Gryllus bimaculatus alter their mate choice based on size depending on previous experience with males. Male crickets sing to attract mates and several studies have identified call parameters important in female choice. We tested the hypotheses that exposure to acoustic stimuli before and/or after mating, from males of different sizes, in isolation and together with physical exposure influences female choice (willingness to mate and spermatophore retention time [SRT]). Females exposed to ad lib. song of multiple males post-mating had a shorter SRT than females in acoustic isolation. Exposure to ad lib. song of multiple males prior to mating had no effect on SRT. Females did not alter SRT depending on exposure to acoustic stimuli from males of different sizes either post or ante mating. Females exposed to acoustic and physical stimuli (though gauze) from large males had a shorter SRT than those exposed to small males but only when the exposure was post-mating. We were unable to identify any correlation between call parameters and body size in G. bimaculatus. Females use male song to locate potential mates but physical exposure to males is needed to allow females to judge male size and this exposure only influences SRT if it takes place post-mating.     

Effects of egg-production and of exposure to males on female survival in Drosophila melanogaster

Female Drosophila melanogaster whose rate of egg-laying was lowered by removal of a suitable substrate or additionally by reduction in protein intake had longer lifespans than control females. The association between lifespan and egg-laying rate could not be accounted for in terms of variation in either exposure to males or nutritional status. Females continuously exposed to males lived less long than intermittently exposed females, and this longevety difference could not be explained in terms of differences in either rate of egg-production or egg-hatchability.     

Testing for Links Between Female Urine Odor and Male Sexual Behaviors in Japanese Macaques (<Emphasis Type="Italic">Macaca fuscata</Emphasis>)

Urine is involved in sexual communication in New World monkeys and lemurs, but most studies of the role of olfaction in sexual communication in Old World monkeys have focused on vaginal secretions rather than urine. We investigated whether female urine promotes male sexual behaviors (approaches and inspections of genital area) in Japanese macaques (Macaca fuscata). We used a sequential presentation paradigm in behavioral experiments, presenting unfamiliar female urine and control cotton swabs to males living in a social group with cycling females. We tested whether males (N = 3) showed more processing behaviors (licking, sniffing, tasting) toward female urine (22 stimuli per male from prefertile, fertile, and postfertile phases, based on urinary estrone and progesterone conjugate profiles) than control odor (8 stimuli per male). We then compared male sexual behaviors toward resident females pre- and post-exposure to stimuli and in relation to the females’ reproductive status (perifertile, nonfertile, and pregnancy periods, based on fecal estrone and progesterone conjugate profiles). We found that males showed significantly more processing behaviors toward urine stimuli than to controls but that male behavior did not vary across urine samples from prefertile, fertile, and postfertile phases. Exposure to unfamiliar female urine stimuli did not modulate male approaches to and inspections of resident females at any stage of the female reproductive cycle. Although our study is limited by its small sample size, the results suggest that female urine contains compounds that males detect, but we found no evidence that female urine is related to male sexual behaviors.     

Influence of male gonadal hormones and familiarity on pregnancy interruption in prairie voles

Pregnancy interruption (PI) was examined in female prairie voles, Microtus ochrogaster, exposed to stimuli from males 7 to 12 days after pairing. Urine from unfamiliar males interrupted pregnancy when placed directly on the external nares of newly mated females, but urine from familiar stud males was without effect. Castration of males did not reduce the efficacy of unfamiliar male urine in interrupting pregnancy. The neuroendocrine system of female prairie voles responded selectively to male urine as a function of its familiarity; the efficacy of male stimuli leading to PI was not dependent on gonadal hormones.     

Playback of colony sound alters the breeding schedule and clutch size in zebra finch (Taeniopygia guttata) colonies

The hypothesis that social stimulation, derived from the presence and activities of conspecifics, can hasten and synchronize breeding in colonies of birds was tested. A modified playback/recorder system was used to continuously exaggerate the amount of colony sound available to zebra finches throughout their courtship period. Males that heard 'sound supplements' generated from their own colony sang more than males in control colonies that did not receive playback; males that heard samples from a different colony, sang at an intermediate level. Females that were exposed to the vocalizations of their mate and playback from a colony other than their own, laid eggs earlier and more synchronously than females in control colonies. Females that heard the vocalizations of their mate along with playback samples generated from their own colony, laid eggs more synchronously but not earlier than control females. Both acoustic treatments caused females to lay larger clutches. Social stimulation influences the breeding schedule and clutch size in zebra finch colonies. If there are advantages associated with these effects, social stimulation may contribute to the maintenance of colonial breeding systems.     

Modulation of behavior in zebrafish,Danio rerio,according to female reproductive status and visual and chemical cues

Zebrafish, Danio rerio, is one of the most studied vertebrate models. However, there are still many aspects of its reproductive behavior to be elucidated. The aim of this work was to clarify whether males and females of this species display different behaviors according to sexual status, and the kind of cues they were exposed to (visual and/or chemical). Females in two different sexual status, pre- (PreS) or post-spawning (PostS), were exposed to single males cues (visual or chemical) or complementary cues (visual and chemical together). PreS females spent more time near the male’s compartment than PostS when they were exposed to complementary cues, but no differences were found when only one cue was present. Males showed a higher proximity to females when they were exposed to visual, and both cues together, but no difference was found according to females’ reproductive status. When no barrier was present, males and PreS females spent more time swimming together than males with PostS females. These results showed that females’ reproductive status, and the kind of cues to which females and males are exposed to, can modulate behaviors related to reproduction. Particularly, both cues together (visual and chemical) are necessary to trigger different behaviors in females according to their reproductive status.     

Exposure to Advertisement Calls of Reproductive Competitors Activates Vocal-Acoustic and Catecholaminergic Neurons in the Plainfin Midshipman Fish,Porichthys notatus

While the neural circuitry and physiology of the auditory system is well studied among vertebrates, far less is known about how the auditory system interacts with other neural substrates to mediate behavioral responses to social acoustic signals. One species that has been the subject of intensive neuroethological investigation with regard to the production and perception of social acoustic signals is the plainfin midshipman fish, Porichthys notatus, in part because acoustic communication is essential to their reproductive behavior. Nesting male midshipman vocally court females by producing a long duration advertisement call. Females localize males by their advertisement call, spawn and deposit all their eggs in their mate’s nest. As multiple courting males establish nests in close proximity to one another, the perception of another male’s call may modulate individual calling behavior in competition for females. We tested the hypothesis that nesting males exposed to advertisement calls of other males would show elevated neural activity in auditory and vocal-acoustic brain centers as well as differential activation of catecholaminergic neurons compared to males exposed only to ambient noise. Experimental brains were then double labeled by immunofluorescence (-ir) for tyrosine hydroxylase (TH), an enzyme necessary for catecholamine synthesis, and cFos, an immediate-early gene product used as a marker for neural activation. Males exposed to other advertisement calls showed a significantly greater percentage of TH-ir cells colocalized with cFos-ir in the noradrenergic locus coeruleus and the dopaminergic periventricular posterior tuberculum, as well as increased numbers of cFos-ir neurons in several levels of the auditory and vocal-acoustic pathway. Increased activation of catecholaminergic neurons may serve to coordinate appropriate behavioral responses to male competitors. Additionally, these results implicate a role for specific catecholaminergic neuronal groups in auditory-driven social behavior in fishes, consistent with a conserved function in social acoustic behavior across vertebrates.     

Chemosensory Recognition of Familiar and Unfamiliar Conspecifics by the Scincid Lizard Eumeces laticeps

The ability of broad-headed skinks (Eumeces laticeps) to distinguish familiar from unfamiliar individuals of the opposite sex and themselves from other individuals of the same sex using only chemical stimuli was examined experimentally. Cloacal chemical stimuli were presented to lizards on moistened cotton swabs and numbers of tongue-flicks performed in 60 s were recorded. Males emitted significantly greater numbers of tongue-flicks in response to chemical cues from unfamiliar females than of female cagemates. Response rates of males housed with females and males housed alone to chemical stimuli from unfamiliar females did not differ. Chemical stimuli from unfamiliar males elicited significantly more tongue flicks from males than their own or deionized water, but their own stimuli elicited no more than the odourless control. Females tongue-flicked significantly more in response to cloacal chemical stimuli from unfamiliar males than from male cagemates. The findings indicate that both sexes of broad-headed skinks can discriminate between chemical stimuli of familiar and unfamiliar individuals of the opposite sex and that males can distinguish their own cloacal chemicals from those of unfamiliar males. The possible functions of these chemosensory capacities, including location of mates by scent-trailing and assessment of the presence of sexual competitors, are discussed in relation to the social behaviour of E. laticeps.     

Sub‐lethal effects of monoterpenes on reproduction by mountain pine beetles

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Recent social history alters male courtship preferences

Phenotypically plastic mating behavior may allow males to modify their reproductive behavior to suit the prevailing social conditions, but we do not know if males only react to immediate social stimuli or change their inherent mate preferences according to their social history. Here we examine the effect of social experiences on the subsequent reproductive behavior of male guppies under standard conditions, allowing us to distinguish the effect of past and immediate social conditions. Males experienced experimental conditioning periods during which they interacted with three females, either of variable size or of similar size. Females arrived either simultaneously or consecutively. In subsequent standard assays, only males that had experienced females of variable size preferentially courted large females. Further, males exposed to sequential female arrival courted subsequent females more vigorously than males that had experienced simultaneous female arrival. In contrast, males did not alter their coercive mating attempts in relation to their recent social history. These results demonstrate that males use past experiences to modify their subsequent reproductive behavior rather than reacting only to immediate stimuli, and reveal the sophisticated ways in which males alter their reproductive tactics to suit the social environment and maximize fitness across changing selective landscapes.     

Exposure to a novel male during late pregnancy influences subsequent growth of offspring during lactation

In mammals, allocation to reproduction can either be primed or suppressed in relation to cues from other individuals. Some conspecifics (e.g. potential mates) may enhance an individual's ability to reproduce but others may have a detrimental effect on reproductive success. One widely studied response to conspecific cues, the ‘Bruce effect’, occurs when pregnant females abort their pregnancies after exposure to a novel male. It has been suggested that this response has evolved as a counter‐tactic to the threat of infanticide posed by novel males. In some species, like mice, pregnancy termination will only occur if females are exposed to the unfamiliar male during a brief critical period early in pregnancy, which is surprising considering that an unfamiliar male threatens infanticide whenever present, and in particular near to birth. We demonstrate that female mice experiencing novel males during late pregnancy also alter their investment in progeny, but in a more subtle manner than previously observed. Females exposed to an unfamiliar male during late pregnancy give birth to offspring of a comparable weight to those produced by females exposed to the paternal male, but these offspring grow more slowly over lactation. As a consequence, offspring from these females weigh less at weaning. Modification of their growth trajectory, however, allows these offspring to catch up to normal weights by adulthood. Thus, cues of unfamiliar males, and possibly their associated threat of infanticide, can produce more wide‐ranging effects on maternal investment than previously recognized.     

The stimulus to egg-laying in the Bengalese finch

The effects of mate and nesting facilities on the occurrence of egg-laying were examined in the Bengalese finch.
Egg-laying is unusual in isolated females and those kept in large groups. It is more common in monosexual pairs, and its incidence in them is not markedly altered by whether males can be heard or not. Females in heterosexual pairs usually lay within three weeks of pairing. A similar lag was found in pairs separated by bars, pointing to copulation being unnecessary.
Carrying of nest material to the nest box is mainly done by males. It is unusual in isolated birds, but occurs in monosexual and heterosexual pairs, and in pairs separated by bars.
Egg-laying is delayed in the absence of hay for nest building. A delay was also found in pairs separated by bars, when only the male was given nest material: this indicates that personal experience by the female is important. Heterosexual pairs deprived of nest boxes, but given nest material, were not recorded as laying.
It is concluded that egg-laying is stimulated by mate and nest material in a complex fashion. The various stimuli these provide interact to a greater or lesser degree to give the physiological and behavioural changes observed.     

Male Song Stimulation of Female Reproduction in Canaries: Features Relevant to Sexual Displays are not Relevant to Nest-building or Egg-laying

Recent studies conducted in our laboratory have demonstrated that a special type of song phrase (‘sexy’ phrases) containing bipartite syllables composed of abrupt frequency falls and short silences stimulate female canaries to solicit for copulation. The study was undertaken to determine whether sexy phrases also facilitated other aspects of the reproductive activity of the female canary, namely, nest-building and egg-laying. During the first experiment, we studied the effect of sexy and non-sexy songs on copulation solicitation displays in 1-year-old females without reproductive experience and in mature females with previous reproductive experience. We confirmed that sexy songs elicited more sexual responses than did non-sexy songs in yearlings and in mature females. During the second experiment, we studied the effect of male songs on nest-building activities and egg-laying in 1-year-old inexperienced females, and in mature, experienced females. The songs of conspecific males significantly triggered and increased nest-building behaviour in female canaries whatever their age or reproductive experience. In contrast, song effects on egg-laying were only found in young females. One-year-old inexperienced females exposed to sexy or non-sexy songs laid more eggs and laid earlier than did 1-year-old inexperienced controls; no such differences were observed in mature, experienced females. The efficiency of songs in promoting nest-building or egg-laying appeared to be unrelated to their efficiency in eliciting sexual responses. No difference was found between females exposed to sexy songs and females exposed to non-sexy songs; differences were only found between control and the two groups of song-exposed females. This result demands further experiments in order to determine whether other song phrase types may account for the stimulating effects of male song on female nest-building and egg-laying.     

Age at mating and male quality influence female patterns of reproductive investment and survival

The trade‐off between the allocation of resources toward somatic maintenance or reproduction is one of the fundamentals of life history theory and predicts that females invest in offspring at the expense of their longevity or vice versa. Mate quality may also affect life history trade‐offs through mechanisms of sexual conflict; however, few studies have examined the interaction between mate quality and age at first mating in reproductive decisions. Using house crickets (Acheta domesticus), this study examines how survival and reproductive trade‐offs change based on females’ age at first reproduction and exposure to males of varying size. Females were exposed to either a large (presumably high‐quality) or small male at an early (young), middle (intermediate), or advanced (old) age, and longevity and reproductive investment were subsequently tracked. Females mated at a young age had the largest number of eggs but the shortest total lifespans while females mated at older ages produced fewer eggs but had longer total lifespans. The trade‐off between age at first mating and eggs laid appears to be mediated through higher egg‐laying rates and shorter postmating lifespans in females mated later in life. Exposure to small males resulted in shorter lifespans and higher egg‐laying rates for all females indicating that male manipulation of females, presumably through spermatophore contents, varies with male size in this species. Together, these data strongly support a trade‐off between age at first reproduction and lifespan and support the role of sexual conflict in shaping patterns of reproduction.     

Sex differences in common Marmosets (<Emphasis Type="Italic">Callithrix jacchus</Emphasis>) in response to an unfamiliar food task

There is a growing body of information on sex differences in callitrichid behaviour that includes the animals performance in food tasks. For example, both reproductive and non-reproductive adult females have been found to be more successful than adult males in solving food tasks. In this study ten adult male and ten adult female common marmosets (Callithrix jacchus), housed individually, were tested with an unfamiliar task that involved the extraction of an embedded food. The task was to open a plastic canister that contained a raisin; the open end was covered with parchment paper. Each marmoset was given 15 trials in three blocks of 5 consecutive days. We measured the latency for each animal to open the lid and get the raisin—by one of five strategies that spontaneously emerged. The females learned the task faster and more efficiently than males; all the females opened the canister on day 1, for instance, in contrast to seven of the males on the same day. Females also progressively decreased the time that they took to open the tube. The final latency on day 15, for instance, was significantly shorter for the females. These results are consistent with relevant literature for callitrichids and cannot be accounted for in terms of differences in mental abilities, strength, hand morphology, or energy requirements. Further investigation is necessary to clarify the reasons for these differences.     

Mating affects reproductive investment into eggs,but not the timing of oogenesis in the flesh fly <Emphasis Type="Italic">Sarcophaga crassipalpis</Emphasis>

We examined the effects of mating on reproductive investment and the timing of oogenesis in the flesh fly Sarcophaga crassipalpis by exposing females to males or not. All females exposed to males were mated within a few days and we found that mating affected reproductive investment. Virgin females not exposed to males produced a large clutch of eggs (∼91), but females exposed to males and mated produced 10% more. There was no effect of mating on egg length or mass. There was also no effect of mating on the timing of oogenesis. Females in both treatments provisioned their eggs at the same rate with yolk first becoming visible in the oocytes on day three of adulthood and complete provisioning of eggs occurring by the seventh day of adulthood. We examined the biochemical basis of egg provisioning by identifying the yolk proteins and quantifying their blood titer during the oogenic period in both, females exposed to males and mated and those not exposed to males. There was no difference in the timing of the first appearance, peak titer, or disappearance of yolk proteins in the blood between the two treatments. However, consistent with our observation of greater egg production in mated females, these females contained a greater peak yolk protein titer.     

Do Male and Female Cowbirds See Their World Differently? Implications for Sex Differences in the Sensory System of an Avian Brood Parasite

Background

Male and female avian brood parasites are subject to different selection pressures: males compete for mates but do not provide parental care or territories and only females locate hosts to lay eggs. This sex difference may affect brain architecture in some avian brood parasites, but relatively little is known about their sensory systems and behaviors used to obtain sensory information. Our goal was to study the visual resolution and visual information gathering behavior (i.e., scanning) of brown-headed cowbirds.

Methodology/Principal Findings

We measured the density of single cone photoreceptors, associated with chromatic vision, and double cone photoreceptors, associated with motion detection and achromatic vision. We also measured head movement rates, as indicators of visual information gathering behavior, when exposed to an object. We found that females had significantly lower density of single and double cones than males around the fovea and in the periphery of the retina. Additionally, females had significantly higher head-movement rates than males.

Conclusions

Overall, we suggest that female cowbirds have lower chromatic and achromatic visual resolution than males (without sex differences in visual contrast perception). Females might compensate for the lower visual resolution by gazing alternatively with both foveae in quicker succession than males, increasing their head movement rates. However, other physiological factors may have influenced the behavioral differences observed. Our results bring up relevant questions about the sensory basis of sex differences in behavior. One possibility is that female and male cowbirds differentially allocate costly sensory resources, as a recent study found that females actually have greater auditory resolution than males.     

Sexual Differences in the Behavioral Response of Túngara Frogs, Physalaemus pustulosus, to Cues Associated with Increased Predation Risk

Engaging in mating behaviors usually increases exposure to predators for both males and females. Anti‐predator strategies during reproduction may have important fitness consequences for prey. Previous studies have shown that individuals of several species adjust their reproductive behavior according to their assessment of predation risk, but few studies have explored potential sexual differences in these strategies. In this study, we investigate whether the acoustic cues associated with predatory attacks or those associated with predators themselves affect the mating behavior of female and male túngara frogs, Physalaemus pustulosus. We compared the responses of females approaching a mate and those of calling males when exposed to mating calls associated with sounds representing increased hazard. When presented with mating calls that differed only in whether or not they were followed by a predation‐related sound, females preferentially approached the call without predation‐related sounds. In contrast to females, calling males showed greater vocal response to calls associated with increased risk than to a call by itself. We found significant differences in the responses of females and males to several sounds associated with increased hazard. Females behaved more cautiously than males, suggesting that the sexes balance the risk of predation and the cost of cautious mating strategies differently.     

Mate selection in the fly Scatophaga stercoraria: female choice in a male-controlled system

Sexual pairing in the fly Scatophaga stercoraria involves ‘capture’ of females by males. Sizerelated choice by males and females is considered, because these flies are highly variable in size, and size strongly affects reproductive success. Results show that males do not discriminate among females on the basis of size. Females choose large males when free to select mates. They move toward larger males when contronted by more than one possible mate, and their movement on the oviposition site takes them to areas where large males are more common. Females paired with large males gain from (1) reduced harm in struggles; (2) more rapid copulation and oviposition, with lower risk to the female and her progeny; and (3) greater ability to escape danger during copulation. These benefits may account for female preference for large males.