Functional neurogenomic responses to acoustic threats, including a heterospecific referential alarm call and its referent, in the auditory forebrain of red-winged blackbirds.

In animal communication, functionally referential alarm calls elicit the same behavioral responses as their referents, despite their typically distinct bioacoustic traits. Yet the auditory forebrain in at least one songbird species, the black-capped chickadee Poecile atricapillus, responds similarly to threat calls and their referent predatory owl calls, as assessed by immediate early gene responses in the secondary auditory forebrain nuclei. Whether and where in the brain such perceptual and cognitive equivalence is processed remains to be understood in most other avian systems. Here, we studied the functional neurogenomic (non-) equivalence of acoustic threat stimuli perception by the red-winged blackbird Agelaius phoeniceus in response to the actual calls of the obligate brood parasitic brown-headed cowbird Molothrus ater and the referential anti-parasitic alarm calls of the yellow warbler Setophaga petechia, upon which the blackbird is known to eavesdrop. Using RNA-sequencing from neural tissue in the auditory lobule (primary and secondary auditory nuclei combined), in contrast to previous findings, we found significant differences in the gene expression profiles of both an immediate early gene, ZENK (egr-1), and other song-system relevant gene-products in blackbirds responding to cowbird vs. warbler calls. In turn, direct cues of threats (including conspecific intruder calls and nest-predator calls) elicited higher ZENK and other differential gene expression patterns compared to harmless heterospecific calls. These patterns are consistent with a perceptual non-equivalence in the auditory forebrain of adult male red-winged blackbirds in response to referential calls and the calls of their referents.

The mate choice brain: comparing gene profiles between female choice and male coercive poeciliids.

Genes that mediate mate preferences potentially play a key role in promoting and maintaining biological diversity. In this study, we compare mate preference behavior in two related poeciliid fishes with contrasting behavioral phenotypes and relate these behavioral differences to gene profiles in the brain. Results reveal that one poeciliid fish, the Northern swordtail, exhibits robust mate preference as compared to the Western mosquitofish, which utilizes a coercive mating system. Female swordtails display no significant difference in association time between male- and female-exposure trials, whereas female mosquitofish spend significantly less time associating with males relative to females. Furthermore, the preference strength for large males is significantly lower in female mosquitofish relative to swordtails. We then examine expression of three candidate genes previously shown to be associated with mate preference behavior in female swordtails and linked to neural plasticity in other vertebrates: neuroserpin (NS), neuroligin-3 (NLG-3) and N-methyl-d-aspartate receptor (NMDA-R). Whole brain gene expression patterns reveal that two genes (NS and NLG-3) are positively associated with mate preference behavior in female swordtails, a pattern opposing that of the mosquitofish. In mosquitofish females, these genes are downregulated when females express biases toward males yet are elevated in association with total motor activity patterns under asocial conditions, suggesting that the presence of males in mosquitofish species may inhibit expression of these genes. Both gene expression and female behavioral responses to males exhibit opposing patterns between these species, suggesting that this genetic pathway may potentially act as a substrate for the evolution of mate preference behavior.

Cloning of gonadotropin-releasing hormone I complementary DNAs in songbirds facilitates dissection of mechanisms mediating seasonal changes in reproduction.

Temperate zone animals exhibit seasonal variation in reproductive physiology. In most cases, seasonal changes in reproductive states are regulated by changes in GnRH1 secretion, rather than synthesis, from the preoptic area (POA)/anterior hypothalamus. An important exception occurs in some songbirds that become photorefractory to the stimulatory effects of long days and show profound decreases in brain GnRH1 protein content. Whether this decline reflects changes in gene expression is unknown because of past failures to measure GNRH1 mRNA levels, due in large part to the absence of available GNRH1 gene sequence in this taxon. Here, we report the first cloning of GNRH1 cDNAs in two songbirds: European starlings and zebra finches. Consistent with the size of the prepro-hormone in other avian and non-avian species, the open-reading frames predict proteins of 91 and 92 amino acids, respectively. Whereas the decapeptide in both species is perfectly conserved with chicken GnRH1, the amino acid identity in the signal peptide and GNRH associated peptide subdomains are significantly less well conserved. At the nucleotide level, the starling and zebra finch coding sequences are approximately 88% identical to each other but only approximately 70% identical to chicken GNRH1. In situ hybridization using radiolabeled cRNA probes demonstrated GNRH1 mRNA expression primarily in the POA, consistent with previous studies on the distribution of the GnRH1-immunoreactive cell bodies. Furthermore, we provide evidence for photoperiod-dependent regulation of GNRH1 mRNA in male starlings. Declines in GNRH1 mRNA levels occur in parallel with testicular involution. Thus, photorefractoriness is associated with decreases in GNRH1 gene expression in the medial POA.