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.     

Effects of Song Experience and Song Quality on Immediate Early Gene Expression in Female Canaries (Serinus canaria)

Female songbirds are thought to make mate choices based on aspects of male song quality. Male canaries (Serinus canaria) produce songs with “special” syllables that have been shown to be highly salient to female listeners – eliciting high rates of sexual displays and enhanced immediate early gene (IEG) expression. Immunohistochemistry for the IEG ZENK was used to examine the effects of experience with these syllables on activity in the caudal mesopallium (CMM) and nidocaudal mesopallium (NCM), two auditory areas important in processing conspecific song. Photostimulated female canaries were housed in sound attenuated chambers and played pseudosongs containing either three special syllables or three non‐special syllables, an intro, and an outro sequence. Females that heard special syllable pseudosongs exhibited higher ZENK expression in CMM. To assess the effects of experience, photostimulated females were pair housed and exposed to playback of song with or without special syllables for 14 days. After transfer to individual housing, birds were played one of the aforementioned stimuli or silence. ZENK expression in CMM and NCM was equivalent for song with and without special syllables, but significantly lower for silence. Females who experienced song with special syllables had lower plasma estradiol concentrations after final song playback. This study indicates that CMM exhibits an IEG response bias to special syllables in limited acoustic contexts, but not in full song, which may contain additional biologically relevant information. Furthermore, estradiol concentrations may mediate changes in song responses, serving as a mechanism for modulating mate choice in differing song environments.     

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.     

Male Song Quality, Egg Size and Offspring Sex in Captive Canaries (Serinus canaria)

Life history theory predicts that females should vary their investment in offspring according to the quality of their mate. In birds, several studies have now shown that females do vary investment according to perceived male quality, by producing larger eggs, investing more in parental care or by manipulating the sex of their offspring. In a captive breeding colony of canaries, we first show that under normal conditions larger eggs in a clutch are more likely to hatch male offspring. In canaries, male song functions in female attraction and females respond more to complex structures in male song called sexy syllables. In a series of experiments, we go on to show first, that females exposed to playback of male song produce larger eggs than those who heard no song. Next, using synthetic songs, we show that females exposed to playback of more attractive songs containing sexy syllables, produced larger eggs than those exposed to simpler songs containing no sexy syllables. However, in a final analysis, we found no evidence from our experiments that females exposed to playback of more attractive songs also produced more male offspring.     

Prolactin Induces Apoptosis of Lactotropes in Female Rodents

Anterior pituitary cell turnover occurring during female sexual cycle is a poorly understood process that involves complex regulation of cell proliferation and apoptosis by multiple hormones. In rats, the prolactin (PRL) surge that occurs at proestrus coincides with the highest apoptotic rate. Since anterior pituitary cells express the prolactin receptor (PRLR), we aimed to address the actual role of PRL in the regulation of pituitary cell turnover in cycling females. We showed that acute hyperprolactinemia induced in ovariectomized rats using PRL injection or dopamine antagonist treatment rapidly increased apoptosis and decreased proliferation specifically of PRL producing cells (lactotropes), suggesting a direct regulation of these cell responses by PRL. To demonstrate that apoptosis naturally occurring at proestrus was regulated by transient elevation of endogenous PRL levels, we used PRLR-deficient female mice (PRLRKO) in which PRL signaling is totally abolished. According to our hypothesis, no increase in lactotrope apoptotic rate was observed at proestrus, which likely contributes to pituitary tumorigenesis observed in these animals. To decipher the molecular mechanisms underlying PRL effects, we explored the isoform-specific pattern of PRLR expression in cycling wild type females. This analysis revealed dramatic changes of long versus short PRLR ratio during the estrous cycle, which is particularly relevant since these isoforms exhibit distinct signaling properties. This pattern was markedly altered in a model of chronic PRLR signaling blockade involving transgenic mice expressing a pure PRLR antagonist (TG^{Δ1–9-G129R-hPRL}), providing evidence that PRL regulates the expression of its own receptor in an isoform-specific manner. Taken together, these results demonstrate that i) the PRL surge occurring during proestrus is a major proapoptotic signal for lactotropes, and ii) partial or total deficiencies in PRLR signaling in the anterior pituitary may result in pituitary hyperplasia and eventual prolactinoma development, as observed in TG^{Δ1–9-G129R-hPRL} and PRLRKO mice, respectively.     

Genetic Architecture of Sexual Selection: QTL Mapping of Male Song and Female Receiver Traits in an Acoustic Moth

Models of indirect (genetic) benefits sexual selection predict linkage disequilibria between genes that influence male traits and female preferences, owing to non-random mate choice or physical linkage. Such linkage disequilibria can accelerate the evolution of traits and preferences to exaggerated levels. Both theory and recent empirical findings on species recognition suggest that such linkage disequilibria may result from physical linkage or pleiotropy, but very little work has addressed this possibility within the context of sexual selection. We studied the genetic architecture of sexually selected traits by analyzing signals and preferences in an acoustic moth, Achroia grisella, in which males attract females with a train of ultrasound pulses and females prefer loud songs and a fast pulse rhythm. Both male signal characters and female preferences are repeatable and heritable traits. Moreover, female choice is based largely on male song, while males do not appear to provide direct benefits at mating. Thus, some genetic correlation between song and preference traits is expected. We employed a standard crossing design between inbred lines and used AFLP markers to build a linkage map for this species and locate quantitative trait loci (QTL) that influence male song and female preference. Our analyses mostly revealed QTLs of moderate strength that influence various male signal and female receiver traits, but one QTL was found that exerts a major influence on the pulse-pair rate of male song, a critical trait in female attraction. However, we found no evidence of specific co-localization of QTLs influencing male signal and female receiver traits on the same linkage groups. This finding suggests that the sexual selection process would proceed at a modest rate in A. grisella and that evolution toward exaggerated character states may be tempered. We suggest that this equilibrium state may be more the norm than the exception among animal species.     

Female Canaries (Serinus canaria) Associate more with Males that Contrast Strongly against the Background

Male birds with bright plumage colors which entail production costs and increased predation risks should be able to emphasize the handicap function of their ornaments when they present themselves against a contrasting background. Contrast with the background may accentuate the signal's costliness and make the male more conspicuous to predators. Both effects should contribute to increase male attractiveness. It is therefore conceivable that the extent to which the male plumage contrasts against the background modifies female choice behavior as it improves the discrimination of mates. We tested this hypothesis in domesticated canaries (Serinus canaria). In the first experiment, yellow females could choose between two yellow males presented in front of a yellow and a white background, respectively. In the second experiment we replaced the yellow males with white ones. In experiment 1 females associated significantly more with yellow males which contrasted strongly against the white background. In experiment 2 there was at least a trend for preferred associations with the white male in front of the yellow background. We found no support that male properties per se were chosen. We could further clarify that females associated with the contrasting male and not with a particular background color. Thus, our study demonstrates that not only inherent properties of the sender but also the interaction of bird color with the signaling environment may influence mate choice.     

Copulation-solicitation Displays in Female Canaries (Serinus canaria): are Oestradiol Implants Necessary?

The aim of this study was twofold: 1. To study the timing of copulation-solicitation displays (CSD) in female canaries during a natural breeding cycle; 2. To address the question of the adequacy of invasive methods such as oestradiol treatment. Towards these ends, we compared seven oestradiol-implanted and eight control females. Moreover, temporal relationships between reproductive behaviour and plasma concentrations of luteinizing hormone and oestradiol were investigated. The results showed that: 1. CSD appeared about 3 d before egg laying, after the peak of nest building. The maximum number of CSD was observed at the beginning of egg laying. CSD disappeared when the last egg was laid, at the very beginning of incubation; 2. No significant difference was found between the two groups for any behavioural criterion, particularly CSD. No significant difference appeared between control and oestradiol-treated females for luteinizing hormone concentrations. In contrast, oestradiol-implanted females presented higher levels of oestradiol during nest building and during egg laying, 9–13 d after implantation (median 2.53 and 1.47 ng/ml for implanted females vs 0.57 ng/ml and undetectable levels for controls). Implantation had no effect on the progress of nest building, CSD exhibition, egg laying and incubation. Our results suggest that implantation with oestradiol is not necessary in female canary to obtain CSD since they breed readily in captivity and already have enough oestradiol. The similar results in both groups lead one to question the necessity of oestradiol priming in some female choice experiments.     

The Development of Geographic Song Preferences in Female Song Sparrows Melospiza melodia

Previous work suggests that early learning plays a role in auditory preferences of female songbirds. We explored whether early experience shapes preferences for local geographic song in female song sparrows ( Melospiza melodia ), a species that prefers local geographic song in adulthood. We hand-reared females from two locations 450 km apart and controlled song exposure early in life. To examine the effects of experience and inherited factors on geographic song preferences, we used a counterbalanced design. Females from each location were tutored with either natal song (recorded from their location of capture) or non-natal song (recorded from the other location) and their preferences for tutor vs. non-tutor song assessed in adulthood. We also examined song preferences in isolate females reared with no song experience. We found that tutored females preferred their tutor song over non-tutor song, regardless of their capture location. Furthermore, birds not exposed to song (isolates) had no geographic song preferences. Thus, song exposure early in life clearly plays an important role in adult female preferences for local song in this species.     

Testosterone Affects Neural Gene Expression Differently in Male and Female Juncos: A Role for Hormones in Mediating Sexual Dimorphism and Conflict

Despite sharing much of their genomes, males and females are often highly dimorphic, reflecting at least in part the resolution of sexual conflict in response to sexually antagonistic selection. Sexual dimorphism arises owing to sex differences in gene expression, and steroid hormones are often invoked as a proximate cause of sexual dimorphism. Experimental elevation of androgens can modify behavior, physiology, and gene expression, but knowledge of the role of hormones remains incomplete, including how the sexes differ in gene expression in response to hormones. We addressed these questions in a bird species with a long history of behavioral endocrinological and ecological study, the dark-eyed junco (Junco hyemalis), using a custom microarray. Focusing on two brain regions involved in sexually dimorphic behavior and regulation of hormone secretion, we identified 651 genes that differed in expression by sex in medial amygdala and 611 in hypothalamus. Additionally, we treated individuals of each sex with testosterone implants and identified many genes that may be related to previously identified phenotypic effects of testosterone treatment. Some of these genes relate to previously identified effects of testosterone-treatment and suggest that the multiple effects of testosterone may be mediated by modifying the expression of a small number of genes. Notably, testosterone-treatment tended to alter expression of different genes in each sex: only 4 of the 527 genes identified as significant in one sex or the other were significantly differentially expressed in both sexes. Hormonally regulated gene expression is a key mechanism underlying sexual dimorphism, and our study identifies specific genes that may mediate some of these processes.     

RESEARCH PAPER: Multiple Sexual Ornamentation Signals Male Quality and Predicts Female Preference in Minnows

Sexual ornamentation often consists of multiple components. Different sexual signals may indicate different aspects of mate quality or reflect quality in different time scales. On the other hand, same signals can have a dual function and are used both in male–male competition and courtship. Many fish species are capable of rapidly altering their colouration (ephemeral colour changes), but this capability is usually ignored in sexual selection studies. Here, we used experimentally manipulated social environments to study the ephemeral colour changes in multicomponent sexual signals of male minnows (Phoxinus phoxinus) during male–male competition and female choice. We found that the dominant males courted the females more actively and had redder and/or darker skin colouration than the subordinate males. Furthermore, darkness difference between subordinate and dominant males increased in the presence of female, which suggests that the male–male competition may increase the honesty of signalling and thus facilitate female choice. In support of this hypothesis, females had a strong behavioural preference towards the more colourful males, which may indicate female choice. As colourful males often had a higher social status than paler individuals, it is possible that females base their preference on male status, not only the colouration per se. In any case, our results suggest that sexual ornamentation of male minnows may signal status, courting activity and superior quality of the males and that these signals may have a dual function in both male–male competition and female choice. Females preferred different ornamental traits (dark and red colour patterns) relatively equally, indicating that mate choice is based on multiple cues.     

Sexual Selection and the Psychophysics of Female Choice

Woodland birds of 20 species were captured in mist-nets in winter (September to February) and summer (April—August) and scored for whether or not they made distress calls while being handled. Birds of only two species showed significant tendencies to be consistent in calling or failing to call when recaptured, but most species had weak trends in. the same direction. Some species changed seasonally in the tendency to call, but there was no general pattern. In winter, but not summer, the incidence of calling was correlated across species with an index of the number of conspecifics likely to hear the call, but there was no comparable correlation with variations within species. In the long-tailed tit, calling was associated with struggling, and with eyelid colour, which reflects a bird's mood. This implies that calling may be directed at a captor as well as at flock companions.     

Intromission Induces and Insemination Reduces Female Immune Response in the Medfly

Sexual reproduction exposes females to immune threats. The immune response of females to these threats may conflict with male reproductive interests. We examine the hypothesis that in the Mediterranean fruit fly, Ceratitis capitata, female immune activity during and after copulation reflects this conflict, and its resolution. By comparing the temporal changes in immune status of females paired with normal males to virgin females of the same age, or to those paired with surgically altered males (that perform normal courtship without intromission), we determined the specific effects of courtship, intromission and insemination on female immune response. At the initiation of mating, levels of the immune enzyme Phenoloxidase (PO) were higher in mated females compared to virgin females. Females who copulated with normal males, compared to females paired with males lacking external genitalia, had significantly higher levels of PO. However, 2 h after the beginning of mating PO levels decreased significantly, and increased again 24 h later. These changes may be interpreted as a sequential resolution of the ongoing conflict of interest between males and females, with the advantage shifting from one sex to another.     

Nest Defence Behaviour and Testosterone Levels in Female Pied Flycatchers

Nesting holes are a scarce resource for obligated cavity‐nesting birds and an important selective force for the evolution of aggressive female behaviours, which may be mediated by testosterone (T) levels. It is known that during periods of intense intrasexual competition such as initial breeding stages, females are highly aggressive towards intruding females. Here, we studied the implications of T levels for female–female competition by comparing levels of aggressiveness towards simulated female intruders (decoys) in two populations of the pied flycatcher (Ficedula hypoleuca) with a marked difference in breeding density. To this end, we exposed free‐living females to simulated territorial intrusions during 30 min when nest construction was almost complete. T levels of females were measured at the beginning of incubation under the assumption that they are positively associated with T levels during nest building. We also related aggressiveness to T levels in both populations. Furthermore, we aimed at detecting whether variation of T levels may explain female incubation attendance. Females showed higher T levels in the populations where pied flycatchers were exposed to a higher likelihood of conspecific interactions (high breeding density) than in the population with low breeding density. Female territorial presence, vigilance at the nest box and proximity to decoys were negatively related to circulating T levels in the high‐density population, but not in the low‐density population. Differences in T levels between populations did not result in differences in female incubation attendance, but T levels were negatively related to the incubation attendance in females from the population showing high T levels. In our populations, T levels in females prior to laying reflect the need to defend nesting cavities which is higher at high breeding density and in subdominant females. High T levels are costly in terms of incubation attendance.     

Developmental Abnormalities of Female Sexual Organs in Swine

One thousand reproductive organs from gilts were collected during the period March-August at a slaughterhouse in central Sweden. The organs were inspected in respect of congenital defects and certain reproductive physiological data. The results are recorded in Tables 1–6. Figs. 1–7 show some types of malformations. The total frequency of malformations was 22.1 %, of which 14 % cysts in mesosalpinx and 4.1 % partial duplication of the vagina. The remainder consisted of general developmental defects and of local defects in the tubular genital tract. Malformations with presumed effect on fertility were found in 4.5 % of all organs examined, of which 0.8 % presumably caused permanent sterility and 3.7 % lowered fertility (small litters). Hydrometra was found in 33 cases, 2 of which in sexually mature gilts. The left ovary contained more corpora lutea than the right, and the mean weight of the left ovary was greater than that of the right, both in sexually mature and prepuberal gilts. Of 202 sexually mature gilts examined 16.9 % had cystic corpora lutea in their ovaries as a rule 2–4 in each ovary.     

Interspecific Differences in the Response of Female Birds to Song Repertoires

The functional significance of the wide variation between bird species in the sizes of individual song repertoires is not understood. We have studied the effects of song repertoires on females. Song triggers copulation solicitation display in female sparrows treated with estradiol. Song sparrow males (Melospiza melodia) have repertoires of about 10 song types, and female song sparrows display significantly more to presentations of large repertoires than to a single song type. By contrast, male field sparrows (Spizella pusilla) and white-throated sparrows (Zonotrichia albicollis) each have only one song type, and their females show no significant increment in responsiveness to repertoires of several song types over a single song type. Swamp sparrows (Melospiza georgiana) fall in between, with male repertoires of three song types. Female swamp sparrows behave in intermediate fashion, responding more to several song types than to one, but the response increment is less than in song sparrows. Thus species differences that males exhibit in song repertoires are paralleled by differences in female responsiveness to multiple song types, implicating variations in female reactivity in the evolution of song repertoires. Female song sparrows respond preferentially to repertoires programmed in eventual variety rather than immediate variety, while field sparrows and white-throated sparrows show no discrimination.     

Purification and Characterization of a Novel Sex Pheromone that Induces the Release of Another Sex Pheromone during Sexual Reproduction of the Heterothallic Closterium peracerosum-strigosum-littorale Complex

A sex pheromone, PR-IP Inducer, which is released from mating-typeminus cells of Closterium, was purified by monitoring its biologicaleffect on the induction of the release of protoplast-release-inducingprotein (PR-IP) from mating-type plus cells. The purified PR-IPInducer had an apparent molecular mass of 22 kDa and of 18.7kDa as determined by SDS-PAGE and mass-spectrometric analysis,respectively. Staining with periodic acid-Schiff reagent indicatedthat PR-IP Inducer included a glycan chain. From the analysisof a dose-response curve, it seemed that PR-IP Inducer was ableto exert its activity over quite wide range of concentrations(1 x 10^–10–3 x 10^–7 M). It appears that PR-IPInducer is a novel glycoproteinaceous pheromone, as is PR-IP,and that it exerts its effect at the earliest stages of thesexual reproduction of the Closterium peracerosum-strigosum-littoralecomplex. ¹Recipient of a Fellowship for Japanese Junior Scientists fromthe Japan Society for the Promotion of Science.     

Sexual Harassment Influences Group Choice in Female Mosquitofish

Male sexual harassment has been demonstrated to result in high costs for females. Male mosquitofish are amongst the most ardent in the animal kingdom and sexual harassment can halve female foraging efficiency. Female mosquitofish have been found to vary their shoaling behaviour when harassed by a male, approaching other males to promote male–male interactions or reducing the distance to another female to dilute male disturbance. The present study tested two predictions about female counterstrategies. As the dilution effect increases with group size, a harassed female was expected to prefer joining a larger group. She should also benefit from joining larger females since males are known to prefer larger mates. When given a choice between a group of two and a group of four females, females harassed by a male spent significantly more time near the larger group. Harassed females also preferred a shoal consisting of larger females over one consisting of smaller females, but no such preferences were observed in the absence of a male. In addition to influencing the individual decision whether to shoal or not, the presence of a harassing male appears to affect group choice. In these fish, sexual harassment might be a powerful factor in shaping both the structure and the composition of shoals.