Cornelia Voigt

Seasonal changes in the song pattern of the non-domesticated island canary (Serinus canaria), a field study.

[The domesticated canary ( Serinus canaria ) is one of the most widely used songbird species to study (1) neural mechanisms of behavioural plasticity and (2) mechanisms of song based female mate choice. Despite numerous studies of the singing and seasonal changes in the song of these animals under laboratory conditions, the present paper describes the results of the first systematic study of the song of the non-domesticated, free-living relatives of the domesticated canary, the island canary ( Serinus canaria ). The songs of ringed males of the canary population Ilheu Chao (Madeira) were studied at different times of the year including the spring breeding and autumnal non-breeding season. In the breeding season songs are on average longer and the repetition rate of syllables is higher compared to the non-breeding season. The syllable repertoire size does not change seasonally. Longitudinal studies of individual males confirm these results of the population average. Further, this approach showed that the repertoire composition of individual males changes seasonally with a significant increase of fast-frequency modulated syllables and a decrease of whistle-type syllables during the breeding season. Playback experiments showed that the fastfrequency modulated syllables of the male island canaries are sexually attractive, if used in standard courtship solicitation tests with female canaries under laboratory conditions. This suggests that seasonal changes in the song temporal pattern are a general feature of canaries, domesticated or not while seasonal changes in repertoire composition is an adaptive feature of island canaries, most likely lost during domestication., The domesticated canary ( Serinus canaria ) is one of the most widely used songbird species to study (1) neural mechanisms of behavioural plasticity and (2) mechanisms of song based female mate choice. Despite numerous studies of the singing and seasonal changes in the song of these animals under laboratory conditions, the present paper describes the results of the first systematic study of the song of the non-domesticated, free-living relatives of the domesticated canary, the island canary ( Serinus canaria ). The songs of ringed males of the canary population Ilheu Chao (Madeira) were studied at different times of the year including the spring breeding and autumnal non-breeding season. In the breeding season songs are on average longer and the repetition rate of syllables is higher compared to the non-breeding season. The syllable repertoire size does not change seasonally. Longitudinal studies of individual males confirm these results of the population average. Further, this approach showed that the repertoire composition of individual males changes seasonally with a significant increase of fast-frequency modulated syllables and a decrease of whistle-type syllables during the breeding season. Playback experiments showed that the fastfrequency modulated syllables of the male island canaries are sexually attractive, if used in standard courtship solicitation tests with female canaries under laboratory conditions. This suggests that seasonal changes in the song temporal pattern are a general feature of canaries, domesticated or not while seasonal changes in repertoire composition is an adaptive feature of island canaries, most likely lost during domestication.]

Seasonal activation and inactivation of song motor memories in wild canaries is not reflected in neuroanatomical changes of forebrain song areas.

Seasonal, testosterone-dependent changes in sexual behaviors are common in male vertebrates. In songbirds such seasonal changes occur in a learned behavior--singing. Domesticated male canaries (Serinus canaria) appear to lose song units (syllables) after the breeding season and learn new ones until the next breeding season. Here we demonstrate in a longitudinal field study of individual, free-living nondomesticated (wild) canaries (S. canaria) a different mode of seasonal behavioral plasticity, seasonal activation, and inactivation of auditory-motor memories. The song repertoire composition of wild canaries changes seasonally: about 25% of the syllables are sung seasonally; the remainder occur year-round, despite seasonal changes in the temporal patterns of song. In the breeding season, males sing an increased number of fast frequency-modulated syllables, which are sexually attractive for females, in correlation with seasonally increased testosterone levels. About 50% of the syllables that were lost after one breeding season reappear in the following breeding season. Furthermore, some identical syllable sequences are reactivated on an annual basis. The seasonal plasticity in vocal behavior occurred despite the gross anatomical and ultrastructural stability of the forebrain song control areas HVc and RA that are involved in syllable motor control.

Neuroanatomical specificity of sex differences in expression of aromatase mRNA in the quail brain

In birds and mammals, aromatase activity in the preoptic-hypothalamic region (HPOA) is usually higher in males than in females. It is, however, not known whether the enzymatic sex difference reflects the differential activation of aromatase transcription or some other control mechanism. Although sex differences in aromatase activity are clearly documented in the HPOA of Japanese quail (Coturnix japonica), only minimal or even no differences at all were observed in the number of aromatase-immunoreactive (ARO-ir) cells in the medial preoptic nucleus (POM) and in the medial part of the bed nucleus striae terminalis (BSTM). We investigated by in situ hybridization the distribution and possible sex differences in aromatase mRNA expression in the brain of sexually active adult quail. The distribution of aromatase mRNA matched very closely the results of previous immunocytochemical studies with the densest signal being observed in the POM, BSTM and in the mediobasal hypothalamus (MBH). Additional weaker signals were detected in the rostral forebrain, arcopallium and mesencephalic regions. No sex difference in the optical density of the hybridization signal could be found in the POM and MBH but the area covered by mRNA was larger in males than in females, indicating a higher overall expression in males. In contrast, in the BSTM, similar areas were covered by the aromatase expression in both sexes but the density of the signal was higher in females than in males. The physiological control of aromatase is thus neuroanatomically specific and with regard to sex differences, these controls are at least partially different if one compares the level of transcription, translation and activity of the enzyme. These results also indirectly suggest that the sex difference in aromatase enzyme activity that is present in the quail HPOA largely results from differentiated controls of enzymatic activity rather than differences in enzyme concentration.

Sex Differences in the Expression of Sex Steroid Receptor mRNA in the Quail Brain

In Japanese quail, males will readily exhibit the full sequence of male‐typical sexual behaviors but females never show this response, even after ovariectomy and treatment with male‐typical concentrations of exogenous testosterone. Testosterone aromatisation plays a key‐limiting role in the activation of this behavior but the higher aromatase activity in the brain of males compared to females is not sufficient to explain the behavioural sex difference. The cellular and molecular bases of this prominent sex difference in the functional consequences of testosterone have not been identified so far. We hypothesised that the differential expression of sex steroid receptors in specific brain areas could mediate this behavioural sex difference. Therefore, using radioactive in situ hybridisation histochemistry, we quantified the expression of the mRNA coding for the androgen receptor (AR) and the oestrogen receptors (ER) of the α and β subtypes. All three receptors were expressed in an anatomically discrete manner in various nuclei of the hypothalamus and limbic system and, at usually lower densities, in a few other brain areas. In both sexes, the intensity of the hybridisation signal for all steroid receptors was highest in the medial preoptic nucleus (POM), a major site of testosterone action that is related to the activation of male sexual behaviour. Although no sex difference in the optical density of the AR hybridisation signal could be found in POM, the area covered by AR mRNA was significantly larger in males than in females, indicating a higher overall degree of AR expression in this region in males. By contrast, females tended to have significantly higher levels of AR expression than males in the lateral septum. ERα was more densely expressed in females than males throughout the medial preoptic and hypothalamic areas (including the POM and the medio‐basal hypothalamus), an area implicated in the control of female receptivity) and in the mesencephalic nucleus intercollicularis. ERβ was more densely expressed in the medio‐basal hypothalamus of females but a difference in the reverse direction (males > females) was observed in the nucleus taeniae of the amygdala. These data suggest that a differential expression of steroid receptors in specific brain areas could mediate at least certain aspects of the sex differences in behavioural responses to testosterone, although they do not appear to be sufficient to explain the complete lack of activation by testosterone of male‐typical copulatory behaviour in females.

Phylogeography of island canary (Serinus canaria) populations

Island canaries (Serinus canaria) are characterised as a species living exclusively on North Atlantic islands, mainly on the Azores, Madeira and Canary Islands. Although they are very common in their habitats, their behaviour and breeding system has only recently been studied systematically. To advance the understanding of their ecology and to see if the rather isolated archipelagos are already promoting a genetic differentiation, we investigated their phylogeographic relationship as revealed by mtDNA sequences of the cytochrome b gene and investigated whether this measure corresponds to morphological characteristics within the islands. Genetic distances were very low throughout the distribution range of the species. Although the variation of genetic distances within the population of Pico (Azores) was larger than that on Madeira and Canary Islands, the genetic distances between island populations were very low throughout which prevented a clear phylogeographic differentiation. Moreover, morphological measurements did not reveal a consistent pattern to reliably separate the populations, although the measures of beak length and body weight revealed a clear island-specific differentiation. These data lead to the assumption that the colonisation of the Atlantic islands by the canaries occurred very recently, while there is no persisting gene flow between the populations.

Repertoire and structure of duet and solo songs in cooperatively breeding white-browed sparrow weavers

Summary White-browed sparrow weavers (Plocepasser mahali) are cooperatively breeding songbirds of eastern and southern Africa that live in small groups year-round consisting of a dominant breeding pair, and subordinate, non-breeding males and females. This species possesses an elaborate vocal communication system: solo songs are exclusively produced by the dominant male, duet songs are mainly produced by the dominant pair, and chorus songs, similar in syllable structure and temporal pattern to duet songs, are produced by all group members. We analysed songs of males and females with known social status recorded from different colonies in Zimbabwe and complemented these data by studying songs of captive birds at our institute. Solo songs are produced in one performance at dawn during the breeding season. Recordings of captive males on consecutive days revealed that males sing in a single solo performance 88.4 ± 4.1% of their total solo song repertoire. This suggests that dominant males recorded in Zimbabwe have a solo song repertoire of 67.0 ± 4.0 syllables, which is similar in size to those of captive males (58.3 ± 3.7 syllables). Repertoire sizes of both free-living and captive males are not correlated with the length of the solo song performance. Duetting is both antiphonal and in unison. Dominant males and females appear to have similar sized duet repertoires (51.9 ± 2.1 syllables). Recordings from captive pairs suggest that 7598% of the repertoire is shared with higher syllable sharing in more experienced pairs. Since all group members engage in duets and chorus singing, we estimate that each subordinate male and female shares the duet syllable repertoire with the breeding pair. For dominant males, the duet syllables are widely distinct from those of the solo songs; of their total syllable repertoire only 2.1% occur in both repertoires. Further, solo song and duet song differ in the temporal organisation.

Green matters! Growing vegetation stimulates breeding under short-day conditions in wild canaries (Serinus canaria).

JOURNAL OF BIOLOGICAL RHYTHMS, Vol. 22 No. 6, December 2007 554-557 DOI: 10.1177/0748730407306928

Mate fidelity in a population of Island Canaries (Serinus canaria) in the Madeiran Archipelago

Previous studies have shown that extra-pair paternity occurs less frequently in island populations than in mainland populations. This is thought to be due mainly to the low genetic variability in island populations but non-genetic factors have also been discussed. Here we report the results of a parentage analysis in a population of island canaries (Serinus canaria) on a small uninhabited island in the Madeiran archipelago. Island canaries are socially monogamous, non-migratory seasonal breeders where biparental care is essential for offspring survival. Multilocus DNA-fingerprinting provided no evidence of extra-pair-paternity in 15 families comprising 45 juveniles. The band sharing coefficient for presumably unrelated breeding pairs was low (0.17 ± 0.03), an indication that genetic variability within the population is similar to most non-island populations of other species. Females did not seek extra-pair copulations and actively rejected sexual approaches from males other than their mate. We propose that female island canaries assess the quality of males during a perid outside the breeding season and optimise their mate choice according to learned preferences. Vorangegangene Untersuchungen haben gezeigt, dass Vaterschaften außerhalb des Paarbundes bei Inselpopulationen weniger häufig vorkommen als bei Festlandpopulationen. Dieses Phänomen wird hauptsächlich mit der bei Inselpopulationen auftretenden geringeren genetischen Variabilität begründet, aber auch nicht-genetische Faktoren werden diskutiert. Wir stellen in der vorliegenden Studie die Ergebnisse einer Vaterschaftsanalyse in einer Kanarengirlitz-Population auf einer kleinen, unbewohnten Insel im Madeira-Archipel vor. Kanarengirlitze sind sozial monogame Standvögel, die saisonal brüten. Die Brutpflege beider Eltern ist entscheidend für das überleben der Jungvögel. Multilocus-DNA-Fingerprinting ergab keinen Fall von Vaterschaften außerhalb des Paarbundes in 15 untersuchten Familien mit insgesamt 45 Jungvögeln. Der Anteil gemeinsamer Banden zwischen den unverwandten Elterntieren war niedrig (0.17 ± 0.03, Mittelwert ± s. d.), was darauf hindeutet, dass die genetische Variabilität dieser Population ähnlich der von Festlandpopulationen anderer Arten ist. Es konnte kein Fall beobachtet werden, in dem Weibchen Kopulationen mit fremden Männchen zu erlangen versuchten. Vielmehr verweigerten sie aktiv Kopulationsversuche fremder Männchen. Wir schlagen vor, dass die Kanarengirlitz-Weibchen die Zeit außerhalb der Brutzeit nutzen, um die Qualität der Männchen festzustellen und anhand gelernter Präferenzen ihre Partnerwahl optimieren.

Effects of sex steroids on aromatase mRNA expression in the male and female quail brain.

Castrated male quail display intense male-typical copulatory behavior in response to exogenous testosterone but ovariectomized females do not. The behavior of males is largely mediated by the central aromatization of testosterone into estradiol. The lack of behavioral response in females could result from a lower rate of aromatization. This is probably not the case because although the enzymatic sex difference is clearly present in gonadally intact sexually mature birds, it is not reliably found in gonadectomized birds treated with testosterone, in which the behavioral sex difference is always observed. We previously discovered that the higher aromatase activity in sexually mature males as compared to females is not associated with major differences in aromatase mRNA density. A reverse sex difference (females>males) was even detected in the bed nucleus of the stria terminalis. We analyzed here by in situ hybridization histochemistry the density of aromatase mRNA in gonadectomized male and female quail that were or were not exposed to a steroid profile typical of their sex. Testosterone and ovarian steroids (presumably estradiol) increased aromatase mRNA concentration in males and females respectively but mRNA density was similar in both sexes. A reverse sex difference in aromatase mRNA density (females>males) was detected in the bed nucleus of subjects exposed to sex steroids. Together these data suggest that although the induction of aromatase activity by testosterone corresponds to an increased transcription of the enzyme, the sex difference in enzymatic activity results largely from post-transcriptional controls that remain to be identified.

Breeding status and social environment differentially affect the expression of sex steroid receptor and aromatase mRNA in the brain of female Damaraland mole-rats

IntroductionThe Damaraland mole-rat (Fukomys damarensis) is a eusocial, subterranean mammal, which exhibits an extreme reproductive skew with a single female (queen) monopolizing reproduction in each colony. Non-reproductive females in the presence of the queen are physiologically suppressed to the extent that they are anovulatory. This blockade is thought to be caused by a disruption in the normal gonadotropin-releasing hormone (GnRH) secretion from the hypothalamus. In order to understand the underlying physiological mechanisms of reproductive suppression in subordinate females we studied the expression of steroid hormone receptors and the androgen-converting enzyme aromatase in forebrain regions involved in the control of reproductive behaviour in female breeders and non-breeders from intact colonies. Additionally, we included in our analysis females that experienced the release from social suppression by being removed from the presence of the queen.ResultsWe found expression of androgen receptor, estrogen receptor α and aromatase in several forebrain regions of female Damaraland mole-rats. Their distribution matches previous findings in other mammals. Quantification of the hybridisation signal revealed that queens had increased expression of androgen receptors compared to non-breeders and removed non-breeders in most brain regions examined, which include the medial preoptic area (MPOA), the principal nucleus of the bed nucleus of the stria terminalis (BSTp), the ventromedial nucleus of the hypothalamus (VMH), the arcuate nucleus (ARC) and the medial amygdala (MeA). Furthermore, breeders had increased estrogen receptor α expression in the anteroventral periventricular nucleus (AVPV) and in the MeA, while aromatase expression in the AVPV was significantly reduced compared to non-breeders. Absence of social suppression was associated with increased androgen receptor expression in the ARC, increased estrogen receptor α expression in the MeA and BSTp and reduced aromatase expression in the AVPV.ConclusionThis study shows that social suppression and breeding differentially affect the neuroendocrine phenotype of female Damaraland mole-rats. The differential expression pattern of estrogen receptor α and aromatase in the AVPV between breeders and non-breeders supports the view that this region plays an important role in mediating the physiological suppression in subordinate females.