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.     

Photoperiodic response of the hypothalamo-pituitary-gonad axis in male and female canaries,Serinus canaria

Although the gonadal photoperiodic response and its influence upon the song control system in canaries have been extensively studied, photoperiodic regulation of the GnRH system has not been investigated. To examine the relationship between photoperiod and the reproductive neuroendocrine system in male and female canaries, three groups of canaries were exposed to chronic short days (8L:16D; Phsens), acute long days (18L:6D; Phstim) and chronic long days (also 18L:6D; Phrefr) to induce the reproductive states of photosensitivity, photostimulation, and photorefractoriness, respectively. Brain sections were processed for GnRH immunocytochemistry. The canaries in this study did not demonstrate consistent or uniform responses to different photoperiodic treatments. In males, gonad size varied with photoperiod; Phstim males had larger gonads than either the Phsens or Phrefr males. In contrast, there was no difference between groups in female gonad size as a result of photoperiodic treatment. Brain GnRH cell number, cell size, and fiber density were similar in all groups. The results suggest that canaries are not as obligatory photoperiodic as previously thought (or at least not all varieties of domestic canaries are). This could be a result of many years of domestication, the natural history of the species, phylogenetic constraint, or a combination of these factors.     

Stimulatory effects on the reproductive axis in female songbirds by conspecific and heterospecific male song

Courtship vocalizations of male songbirds can profoundly enhance the reproductive physiology and behavior of conspecific females. However, no study has fully investigated the selectivity of conspecific song effects on reproductive development in birds. We studied the effects of conspecific and heterospecific song on reproductive development in domesticated (canaries) and wild songbirds (song sparrows). As expected, conspecific song enhanced follicular development. Unexpectedly, however, birds exposed to heterospecific song also underwent enhanced follicular development (compared to birds exposed to no song); conspecific and heterospecific songs were equally effective in enhancing ovarian development. In canaries exposed to 18L:6D, conspecific song induced oviposition earlier and at a greater frequency than in heterospecific and no song groups, with the fewest eggs being laid in the no song group. These results indicate that conspecific and heterospecific male song can enhance reproductive activity in female songbirds. Whether or not activation of the reproductive axis in female songbirds by heterospecific song occurs in the wild remains unclear. It is also unclear as to whether the ability of the reproductive axis to respond to heterospecific song performs a specific function, or whether it is simply a consequence of greater selection pressure acting upon behavioral responses to song.     

Inhibition of reproductive maturation and somatic growth of Fischer 344 rats by photoperiods shorter than L14:D10 and by gradually decreasing photoperiod

Photoperiod is the major regulator of reproduction in temperate-zone mammals. Laboratory rats are generally considered to be nonphotoresponsive, but young male Fischer 344 (F344) rats have a uniquely robust response to short photoperiods of 8 h of light. Rats transferred at weaning from a photoperiod of 16 h to photoperiods of < 14 h of light slowed in both reproductive development and somatic growth rate. Those in photoperiods < 13 h of light underwent the strongest responses. The critical photoperiod of F344 rats can be defined as 13.5 h of light, but photoperiods of 相似文献   

Adult Female Canaries Respond to Male Song by Calling

We describe a new assay for measuring the response to song playback by adult female domesticated canaries, Serinus canaria . We tested song perception and discrimination by measuring the frequency of particular female calls (`single calls') given in response to male song playbacks. We observed that females responded differently to songs of different species (canaries vs. pine siskin, Carduelis spinus ) and to songs of different canary strains (domesticated vs. wild canaries). In addition, females were especially responsive to songs containing a particular type of song phrase (`A' phrases).
This new assay provides equivalent results to the standard method (copulation solicitation displays) traditionally used to assess female song preferences. Our new assay has the advantage that it allows one to measure female song responsiveness without having to use estradiol implants and during both long and short day photoperiods. However, females responded differently in long and short days. We suggest that, by calling, females could both provide information about their sexual interest and attract the attention of particular males.     

Female canaries produce eggs with greater amounts of testosterone when exposed to preferred male song

Male birdsong has a great influence in the stimulation of female reproduction. However, female physiological responsiveness to song may depend on the degree of complexity of male song. This is expected because females of iteroparous organisms may increase their fitness by matching their reproductive investment to the predicted value of each reproductive attempt. To the extent that the expression of male ornaments is a signal of male quality, we expect females to increase their investment when paired to highly ornamented males. However, female investment may be cryptic and difficult to detect, such as androgen content in the eggs. In this study, we exposed female canaries (Serinus canaria) to attractive and unattractive song repertoires using a crossover design. As predicted, females invested greater concentrations of testosterone in their eggs when exposed to attractive repertoires than when exposed to unattractive repertoires. This implies that song repertoires convey important information about the reproductive value of a given male and suggests that testosterone deposition in egg yolk may be costly.     

Effects of unilateral lesions of HVC on song patterns of male domesticated canaries

Bird song is a model for studying neural control and lateralization of a learned behavior. Adult male canary develops large and varied song repertoires. Particular features of the male are well known to stimulate the reproductive activities of the female. We report here on the effect of lesions of either the left or right HVC, a key nucleus of the descending vocal control network of songbirds, on different song parameters of common domesticated male canaries of an European outbred strain. These canaries are useful to evaluate the question of central versus peripheral lateralization because they do not show syringeal dominance for syllable production compared to the previously studied canary strains. Right-sided lesions reduced the highest frequency and the widest frequency band. Left-sided lesion increased the lowest frequency. The size of the left-sided lesions correlated with the reduction of the repertoire of simple syllables, of the total repertoire and of the highest repetition rate, and with the increase of the lowest frequency. These results suggest a lateralized specialization of both left and right vocal pathways for particular features of the song, especially those that are known to elicit a great number of copulation solicitation displays (CSD). Lesions of both left and right pathways affected, however, sound amplitude of all syllables. Because this effect was more sever following left-sided lesions, and because the syrinx morphology of canaries has a left-right asymmetry, we suggest a peripheral mechanism for the observed lateralized specializations.     

Relationship between Song Repertoire and Age in the Canary,Serinus canarius

We recorded the song of six male canaries during their first and second year of life to see if we could detect systematic age-related changes. Soundspectrographic analysis revealed that many syllables from the previous year were omitted and many new ones were added. There was a significant increase in syllable repertoire during the second year. The proportion of single-element syllables increased between year 1 and year 2. These results indicate that neural pathways responsible for song learning in canaries remain plastic in adulthood. We suggest that the larger song repertoires of older ♂♂ confer a reproductive advantage by acting as a more potent stimulus on ♀♀.     

Social cues attenuate photoresponsiveness of the male reproductive system in Siberian hamsters (Phodopus sungorus)

Transfer of adult Siberian hamsters (Phodopus sungorus) from long (16 h light and 8 h dark, 16L:8D) to short (8L:16D) daily photoperiods induces an involution of the gonads and a cessation of reproductive behavior 8 to 10 weeks later. However, when male and female long-day hamsters were paired on transfer to short photoperiods, the males' gonads did not undergo the typical short-day response. Similarly, when male long-day hamsters were paired with refractory females (i.e., females housed in short photoperiods for at least 28 weeks so that they became unresponsive to short photoperiods), the response of the males' reproductive system to short photoperiods also was attenuated. Thus, social cues can override or delay the effects of photoperiod on the testes of this species. These results suggest that the inhibitory effects of long durations of melatonin secretion (in response to short photoperiods) on the male hypothalamic-pituitary-gonadal axis may be attenuated by social cues such as contact with the opposite sex.     

The effects of photoperiod on androgen-induced reproductive behavior in male ring doves, Streptopelia risoria

The effect of photoperiod on reproductive behavior in male ring doves (Streptopelia risoria) was studied in androgen-injected castrates maintained under long (16L:8D) or short (86:16D) photoperiods. Behavioral recordings were made over a 2-week period during which each male was paired with a female for 6.5 hr/day. There was some indication that males held on long days display higher levels of courtship activity during the initial period following pairing, but the evidence was not conclusive. Day length had no effect upon copulatory behavior. Long-day males exhibited consistently higher levels of nest building than short-day males, indicating that photoperiod affects building through some mechanism other than changes in endogenous androgen levels.     

Eavesdropping on Male Singing Interactions Leads to Differential Allocation in Eggs

Females invest differently in their eggs depending on the quality of their mates. In oscines, female investment is influenced by the quality of male song. In domestic canaries Serinus canaria, as well as in black‐capped chickadees Poecile atricapillus, females pay attention not only to the intrinsic quality of male song but can also gather information, by eavesdropping on male–male singing interactions, on the relative quality of males. During these interactions, overlapping the song of the rival is more threatening than alternating. Moreover eavesdropping female canaries have been shown to prefer the overlapping song rather than the overlapped song. The present study was designed to assess the effect of the information gathered by eavesdropping on female investment in eggs. First, we broadcasted overlapping interactions to female canaries. Then, we broadcasted to each female one of the two songs previously heard and collected eggs. Females exposed to overlapping songs laid eggs with greater yolk ratio than females exposed to overlapped songs. In contrast, yolk testosterone quantity and concentration were not affected by the treatment. Moreover, we found a variation between eggs with regard to the testosterone deposited in yolk: both quantity and concentration increased with laying order. Our results suggest that female canaries use information gathered by eavesdropping to differentially allocate resources into the eggs. They suggest that singing interactions could influence chick quality via female investment.     

Effects of age and photoperiod on reproduction and the spleen in the marsh rice rat (Oryzomys palustris)

To examine the interactions between age and photoperiod on reproduction and spleen weights, we exposed adult male and female rice rats of various ages to photoperiods of 16:8-h light-dark photoperiods (16L:8D) or 12L:12D. After 10 wk, animals were killed and the following data were recorded: weights of testes, seminal vesicles, uterus, ovaries, body, and spleen and, in addition, vaginal patency. Young adult males displayed a greater degree of testicular and seminal vesicle regression in short photoperiods than did older males; the testes of most older males did not regress in response to short photoperiods. Spleen weight was unresponsive to short photoperiods in all males, but was affected by age. Females, however, exhibited reproductive organ regression and decreased vaginal patency in response to short photoperiods at all ages examined. Body weights were affected by photoperiod in young females, and, as in males, photoperiod had no effect on spleen weights. These data suggest that the reproductive response to photoperiod in adult male rice rats declines with age, whereas in adult females it does not.     

Coordinated and dissociated effects of testosterone on singing behavior and song control nuclei in canaries (Serinus canaria)

Temperate zone songbirds that breed seasonally exhibit pronounced differences in reproductive behaviors including song inside and outside the breeding season. Springlike long daylengths are associated with increases in plasma testosterone (T) concentrations, as well as with increases in singing and in the volume of several brain nuclei known to control this behavior. The mechanisms whereby T can induce changes in behavior and brain, and whether or not these effects are differentially regulated, have recently begun to be examined, as has the question of the relative contributions of T and its androgenic and estrogenic metabolites to the regulation of this seasonal behavioral and neural plasticity. In this experiment, we examined the effects of T, 5alpha-dihydrotestosterone, or 17beta-estradiol treatment on castrated male canaries housed on short days and compared neural and behavioral effects in these males to similarly-housed males given only blank implants. We observed that only T treatment was effective in eliciting significant increases in singing behavior after 11 days of hormone exposure. In addition, T alone was effective in increasing the volume of a key song production nucleus, HVC. However, at this time, none of the steroids had any effects on the volumes of two other song control nuclei, Area X of the medial striatum and the robust nucleus of the arcopallium (RA), that are efferent targets of HVC, known to be regulated by androgen in canaries and also to play a role in the control of adult song. T can thus enhance singing well before concomitant androgen-induced changes in the song control system are complete.     

Photoperiodic modulation of sexual and aggressive behavior in female golden hamsters (Mesocricetus auratus): role of the pineal gland

Pinealectomized female hamsters (Mesocricetus auratus) housed in a short-day photoperiod were ovariectomized and tested for hormone-induced sexual receptivity in order to investigate the role of the pineal gland in the control of behavioral sensitivity to exogenous ovarian steroid hormones (Experiment 1). Behavioral sensitivity to hormones was further investigated in females maintained in a long-day photoperiod and rendered acyclic by daily administration of exogenous melatonin (Experiment 2). Female aggressive behavior was also monitored in all tests. Pinealectomy did not affect the reduced behavioral sensitivity to exogenous estrogen (E) induced by short days. These animals were also partially refractory to the effects of E when combined with low doses of progesterone. In addition, although melatonin administration mimicked the effects of short days on estrous cyclicity, the expression of hormone-dependent behaviors in these animals resembled the pattern displayed by control animals kept in long days. Thus, these findings suggest that the pineal gland plays a negligible role in the photoperiodic modulation of hormone-dependent sociosexual behaviors in female hamsters.     

Melatonin Binding in the House Sparrow Song Control System: Sexual Dimorphism and the Effect of Photoperiod

Avian song is a sexually dimorphic behavior which is regulated seasonally. This regulation involves the construction and growth of song control structures: the high vocal center (HVC),nucleus robustus archistrialis(RA),nucleus magnocellularis anterior(MAN), and Area X. Song behavior and its neural correlates are controlled by steroid-dependent and independent processes. The avian circadian system is known to be involved in both daily processes and seasonal reproduction. A major part of this system is the circadian secretion of melatonin by the pineal gland. To determine possible interactions of the circadian and song control systems, the distribution and density of 2-[¹²⁵I]iodomelatonin (IMEL) binding, an indicator of melatonin sensitivity, were determined in male and female house sparrow brains. Specific binding was found in visual system centers of both genders, but binding in HVC, RA, and Area X was present only in males. Binding in MAN was present in both sexes. Although the effects of short and long photoperiods on male house sparrow IMEL binding in song structures revealed no systematic changes, there were significant differences in binding under different photoperiods in HVC and RA. IMEL binding in the tectofugalnucleus rotundus,however, was consistently highest under short day conditions. IMEL binding in song control nuclei was independent of testicular influence, since castration did not affect it significantly. The data point to a role for the circadian system of house sparrows in song control, but a specific role for melatonin in the daily or seasonal regulation of the song control system in birds, could not be determined.     

Temporal relations of brood patch development, nest-building and egg-laying in domesticated canaries

Relationships were assessed between brood patch development, nest-building and egg-laying in 20 female canaries in the natural breeding season. Twelve of these were unpaired; eight were provided with males after two months of being kept singly. The later laying of some females was due to their more protracted development rather than to their later start. The completion of brood patch defeathering, a certain stage of its vascularity, and the start of intensive nest-building occurred within a few days of each other whatever the date of egg-laying. Differences from an earlier study of paired females which had only limited access to nest material can be understood in terms of the known effects of the male and the nest-cup on reproductive development.
All birds showed a period of intensive nest-building beginning about eight days before egg-laying, with a peak about three days before. In those females in which the period of intensive building lasted for more than eight days, there was an earlier peak about seven days previously. This, and also the building behaviour of many females even earlier in the season, are in harmony with the view that reproductive development is not progressive, but intermittent.     

The effect of auditory distractors on song discrimination in male canaries (Serinus canaria)

Male songbirds such as canaries produce complex learned vocalizations that are used in the context of mate attraction and territory defense. Successful mate attraction or territorial defense requires that a bird be able to recognize individuals based on their vocal performance and identify these songs in a noisy background. In order to learn more about how birds are able to solve this problem, we investigated, with a two-alternative choice procedure, the ability of adult male canaries to discriminate between conspecific song segments from two different birds and to maintain this discrimination when conspecific songs are superimposed with a variety of distractors. The results indicate that male canaries have the ability to discriminate, with a high level of accuracy song segments produced by two different conspecific birds. Song discrimination was partially maintained when the stimuli were masked by auditory distractors, but the accuracy of the discrimination progressively declined as a function of the number of masking distractors. The type of distractor used in the experiments (other conspecific songs or different types of artificial white noise) did not markedly affect the rate of deterioration of the song discrimination. These data indicate that adult male canaries have the perceptual abilities to discriminate and selectively attend to one ongoing sound that occurs simultaneously with one or more other sounds. The administration of a noradrenergic neurotoxin did not impair markedly the discrimination learning abilities although the number of subjects tested was too small to allow any firm conclusion. In these conditions, however, the noradrenergic lesion significantly increased the number failures to respond in the discrimination learning task suggesting a role, in canaries, of the noradrenergic system in some attentional processes underlying song learning and processing.     

Seasonal changes in song nuclei and song behavior in Gambel's white-crowned sparrows

In males of several songbird species, the morphology of forebrain nuclei that control song changes seasonally. The only seasonally breeding songbird in which seasonal changes in the structure of song control nuclei have been reported not to occur is the nonmigratory Nuttall's subspecies of white-crowned sparrow. In the present study, we manipulated photoperiod and plasma testosterone concentrations in captive male white-crowned sparrows of the migratory Gambel's subspeices. Males exposed to photoperiods and plasma testosterone concentrations typical of those experienced by wild breeding males had larger song control nuclei than males held on a winter photoperiod. We also found seasonal change in stereotypy of spectral and temporal parameters of song in wild Gambel's white-crowned sparrows. We hypothesize that seasonal changes in song control nuclei may correlate with seasonal changes in song stereotypy. © 1995 John Wiley & Sons, Inc.     

Photoperiodic regulation of reproductive development in male prairie voles: influence of laboratory breeding

Two populations of male prairie voles, one derived from an outbred laboratory colony and the second consisting of F1 offspring of wild-trapped voles, were tested for responsiveness to photoperiod. Animals were reared from birth until 35 days of age either in 16L:8D or 8L:16D photoperiods. Short day lengths did not affect the reproductive apparatus of the laboratory-strain voles; however, offspring of wild-caught voles manifested arrested development of the reproductive system in short photoperiods. These results suggest that selection processes associated with laboratory husbandry can alter responsiveness to photoperiod; the use of wild-trapped animals or their F1 progeny is indicated in photoperiodism research.     

Day length and estradiol affect same-sex affiliative behavior in the female meadow vole

Non-sexual social bonding between adult mammals is poorly understood, despite its importance in many species. Female meadow voles are territorial and nest alone in long summer day lengths when circulating estradiol concentrations are high, but cohabit in groups in short winter photoperiods when estradiol secretion is low. The influence of day length and estradiol on same-sex huddling behavior was assessed in adult female pairs housed together in long day lengths (LDs) or short day lengths (SDs) from weaning. The behavior of intact, ovariectomized, and estradiol-treated ovariectomized females from each photoperiod was assessed during 3 h partner-preference tests. Intact SD voles, unlike intact LD voles, spent the majority of the test in proximity to their cage-mates. Estradiol treatment of SD voles significantly reduced time spent huddling with the partner. Neither ovariectomy nor estradiol treatment significantly affected the amount of time LD females spent in contact with their partners. Low estradiol availability is therefore a necessary but not sufficient condition for maintenance of high levels of huddling. These results establish that ovarian hormones interact with photoperiod to affect same-sex social behavior.