Examining the disconnect between prolactin and parental care in avian brood parasites.

Prolactin is often referred to as the "parental hormone" but there are examples in which prolactin and parental behavior are disconnected. One intriguing example is in avian obligate brood parasites; species exhibiting high circulating prolactin but no parental care. To understand this disconnect, we examined transcriptional and behavioral responses to prolactin in brown-headed (Molothrus ater) and bronzed (M aeneus) brood parasitic cowbirds. We first examine prolactin-dependent regulation of transcriptome wide gene expression in the preoptic area (POA), a brain region associated with parental care across vertebrates. We next examined prolactin-dependent abundance of seven parental care-related candidate genes in hypothalamic regions that are prolactin-responsive in other avian species. We found no evidence of prolactin sensitivity in cowbirds in either case. To understand this prolactin insensitivity, we compared prolactin receptor transcript abundance between parasitic and nonparasitic species and between prolactin treated and untreated cowbirds. We observed significantly lower prolactin receptor transcript abundance in brown-headed but not bronzed cowbird POA compared with a nonparasite and no prolactin-dependent changes in either parasitic species. Finally, estrogen-primed female brown-headed cowbirds with or without prolactin treatment exhibited significantly greater avoidance of nestling begging stimuli compared with untreated birds. Taken together, our results suggest that modified prolactin receptor distributions in the POA and surrounding hypothalamic regions disconnect prolactin from parental care in brood parasitic cowbirds.

HVC lesions modify immediate early gene expression in auditory forebrain regions of female songbirds.

It is well established that auditory forebrain regions of oscine birds are essential for the encoding of species-typical songs and are, therefore, vital for recognition of song during sociosexual interactions. Regions such as the caudal medial nidopallium (NCM) and the caudal medial mesopallium (CMM) are involved in perceptual processing of song and the formation of auditory memories. There is an additional telencephalic nucleus, however, that has also been implicated in species recognition. This nucleus is HVC, a prominent nucleus that sits at the apex of the song system, and is well known for its critical role in song learning and song production in male songbirds. Here, we explore the functional relationship between auditory forebrain regions (i.e., NCM and CMM) and HVC in female canaries (Serinus canaria). We lesion HVC and examine immediate early gene responses to conspecific song presentation within CMM and NCM to explore whether HVC can modulate auditory responses within these forebrain regions. Our results reveal robust deficits in ZENK-ir in CMM and NCM of HVC-lesioned females when compared with control- and sham-lesioned females, indicating that functional connections exists between HVC and NCM/CMM. Although these connected regions have been implicated in song learning and production in males, they likely serve distinct functions in female songbirds that face the task of song recognition rather than song production. Identifying functional connections between HVC and auditory regions involved in song perception is an essential step toward developing a comprehensive understanding of the neural basis of song recognition.

Noradrenergic deficits alter processing of communication signals in female songbirds.

During acoustic communication, animals must attend to sounds from a particular source while simultaneously rejecting intrusion from other sources. One possible candidate mechanism for this process is the noradrenergic system. Noradrenaline is a neuromodulator that tunes sensory processing systems and regulates attention. We examined whether pharmacological degradation of the noradrenergic system using N-(2-chloroethyl)-N-2-bromobenzyl-amine hydrochloride (DSP-4) modifies processing of species-typical auditory signals in female canaries (Serinus canaria). We measured auditory responses to conspecific and heterospecific songs using ZENK protein expression within the caudomedial nidopallium (NCM) and the mesopallium caudomedial (CMM). Song-induced ZENK expression in these auditory forebrain areas is typically higher in birds exposed to conspecific songs as opposed to heterospecific songs. Our results reveal that this differential ZENK induction is abolished specifically within dNCM and CMM in female canaries treated with DSP-4. Furthermore, in DSP-4-treated birds, conspecific song-induced ZENK expression is significantly reduced when compared to saline-treated birds. This suggests that the noradrenergic system modifies auditory processing by enhancing neuronal responses to signals relevant to survival and reproduction rather than inhibiting neuronal responses to signals that are less relevant. Overall, our results reveal that noradrenaline plays a significant neuromodulatory role during the reception of species-typical communication signals.

Social regulation of plasma estradiol concentration in a female anuran.

The behavior of an individual within a social aggregation profoundly influences behavior and physiology of other animals within the aggregation in such a way that these social interactions can enhance reproductive success, survival and fitness. This phenomenon is particularly important during the breeding season when males and female must synchronize their reproductive efforts. We examined whether exposure to conspecific social cues can elevate sex steroid levels, specifically estradiol and androgens, in female túngara frogs (Physalaemus pustulosus). We compared plasma estradiol and androgen concentrations in wild-caught females before and after exposure to either natural mate choruses or random tones. After exposure to mate choruses for 10 consecutive nights, estradiol concentrations were significantly elevated whereas there was no significant elevation in estradiol concentrations in the group of females exposed to random tones for 10 nights. Plasma androgen concentrations were not significantly changed after exposure to either natural mate choruses or random tones for 10 consecutive nights. Social modulation of estradiol concentrations may be important in maintaining a female's reproductive state while males are chorusing. To our knowledge, this is the first study to demonstrate social regulation of estradiol concentration in female anurans.