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1. Forebrain nuclei linked to woodpecker territorial drum displays mirror those that enable vocal learning in songbirds

   https://doi.org/10.1371/journal.pbio.3001751  

   Schuppe, Eric R.; Cantin, Lindsey; Chakraborty, Mukta; Biegler, Matthew T.; Jarvis, Electra R.; Chen, Chun-Chun; Hara, Erina; Bertelsen, Mads F.; Witt, Christopher C.; Jarvis, Erich D.; et al (September 2022, PLOS Biology)

   Townsend, Simon W. (Ed.)

   Vocal learning is thought to have evolved in 3 orders of birds (songbirds, parrots, and hummingbirds), with each showing similar brain regions that have comparable gene expression specializations relative to the surrounding forebrain motor circuitry. Here, we searched for signatures of these same gene expression specializations in previously uncharacterized brains of 7 assumed vocal non-learning bird lineages across the early branches of the avian family tree. Our findings using a conserved marker for the song system found little evidence of specializations in these taxa, except for woodpeckers. Instead, woodpeckers possessed forebrain regions that were anatomically similar to the pallial song nuclei of vocal learning birds. Field studies of free-living downy woodpeckers revealed that these brain nuclei showed increased expression of immediate early genes (IEGs) when males produce their iconic drum displays, the elaborate bill-hammering behavior that individuals use to compete for territories, much like birdsong. However, these specialized areas did not show increased IEG expression with vocalization or flight. We further confirmed that other woodpecker species contain these brain nuclei, suggesting that these brain regions are a common feature of the woodpecker brain. We therefore hypothesize that ancient forebrain nuclei for refined motor control may have given rise to not only the song control systems of vocal learning birds, but also the drumming system of woodpeckers. 

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2. A distinct neurogenomic response to a trade-off between social challenge and opportunity in male sticklebacks ( Gasterosteus aculeatus )

   https://doi.org/10.1098/rsbl.2023.0253  

   Barbasch, T. A.; Behrens, C.; McLain, M.; Arredondo, E.; Bell, A. M. (November 2023, Biology Letters)

   Animals frequently make adaptive decisions about what to prioritize when faced with multiple, competing demands simultaneously. However, the proximate mechanisms of decision-making in the face of competing demands are not well understood. We explored this question using brain transcriptomics in a classic model system: threespined sticklebacks, where males face conflict between courtship and territorial defence. We characterized the behaviour and brain gene expression profiles of males confronted by a trade-off between courtship and territorial defence by comparing them to males not confronted by this trade-off. When faced with the trade-off, males behaviourally prioritized defence over courtship, and this decision was reflected in their brain gene expression profiles. A distinct set of genes and biological processes was recruited in the brain when males faced a trade-off and these responses were largely non-overlapping across two brain regions. Combined, these results raise new questions about the interplay between the neural and molecular mechanisms involved in decision-making. 

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3. Solitude and serotonin: juvenile isolation alters the covariation between social behavior and cFos expression by serotonergic neurons

   https://doi.org/10.3389/fnins.2024.1446866  

   Hutchens, Sarah_E D; Khurram, Izza; Hurley, Laura M (October 2024, Frontiers in Neuroscience)

   Variation in the mutual responsiveness of social partners to each other can be reflected in behavioral suites that covary with neural activity in ways that track the salience or valence of interactions. Juvenile social isolation alters social behavior and neural activity during social interaction, but whether and how it alters the covariation between behavior and neural activity has not been as well explored. To address this issue, four classes of experimental subjects: isolated males, socially housed males, isolated females, and socially housed females, were paired with an opposite-sex social partner that had been socially housed. Social behaviors and c-Fos expression in the serotonergic dorsal raphe nucleus (DRN) were then measured in subjects following the social interactions. Relative to social housing, postweaning isolation led to a decrease in the density of neurons double-labeled for tryptophan hydroxylase and c-Fos in the dorsomedial subdivision of the DRN, regardless of sex. Vocal and non-vocal behaviors were also affected by isolation. In interactions with isolated males, both ultrasonic vocalization (USVs) and broadband vocalizations (squeaks) increased in conjunction with greater male investigation of females. Neural and behavioral measures also correlated with each other. In the isolated male group, the density of double-labeled neurons in the dorsomedial DRN was negatively correlated with USV production and positively correlated with a principal component of non-vocal behavior corresponding to greater defensive kicking by females and less investigation and mounting behavior. This correlation was reversed in direction for socially housed males, and for isolated males versus isolated females. These findings confirm that the dynamics of social interactions are reflected in c-Fos activation in the dorsomedial DRN, and suggest an altered responsiveness of serotonergic neurons to social interaction following social isolation in males, in parallel with an altered male response to female cues. 

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4. Melatonin receptor expression in vocal, auditory, and neuroendocrine centers of a highly vocal fish, the plainfin midshipman ( Porichthys notatus )

   https://doi.org/10.1002/cne.24629  

   Feng, Ni Y.; Marchaterre, Margaret A.; Bass, Andrew H. (January 2019, Journal of Comparative Neurology)

   Abstract Melatonin plays a central role in entraining activity to the day–night cycle in vertebrates. Here, we investigate neuroanatomical substrates of melatonin‐dependent vocal–acoustic behavior in the nocturnal and highly vocal teleost fish, the plainfin midshipman (Porichthys notatus). Using in situ hybridization (ISH) and quantitative real‐time PCR (qPCR), we assess the mRNA distribution and transcript abundance of melatonin receptor subtype 1B (mel1b), shown to be important for vocalization in midshipman fish and songbirds. ISH shows robustmel1bexpression in major nodes of the central vocal and auditory networks in the subpallium, preoptic area (POA), anterior hypothalamus, dorsal thalamus, posterior tuberculum, midbrain torus semicircularis and periaqueductal gray, and hindbrain.Mel1blabel is also abundant in secondary targets of the olfactory, visual, and lateral line systems, as well as telencephalic regions that have been compared to the amygdala, extended amygdala, striatum, septum, and hippocampus of tetrapods. Q‐PCR corroboratesmel1babundance throughout the brain and shows significant increases in the morning compared with nighttime in tissue samples inclusive of the telencephalon and POA, but remains stable in other brain regions. Plasma melatonin levels show expected increase at night. Our findings support the hypothesis that melatonin's stimulatory effects on vocal–acoustic mechanisms in midshipman is mediated, in part, by melatonin binding in vocal, auditory, and neuroendocrine centers. Together with robustmel1bexpression in multiple telencephalic nuclei and sensory systems, the results further indicate an expression pattern comparable to that in birds and mammals that is indicative of melatonin's broad involvement in the modulation of physiology and behavior. 

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5. Time-course RNASeq of Camponotus floridanus forager and nurse ant brains indicate links between plasticity in the biological clock and behavioral division of labor

   https://doi.org/10.1186/s12864-021-08282-x  

   Das, Biplabendu; de Bekker, Charissa (January 2022, BMC Genomics)

   Abstract BackgroundCircadian clocks allow organisms to anticipate daily fluctuations in their environment by driving rhythms in physiology and behavior. Inter-organismal differences in daily rhythms, called chronotypes, exist and can shift with age. In ants, age, caste-related behavior and chronotype appear to be linked. Brood-tending nurse ants are usually younger individuals and show “around-the-clock” activity. With age or in the absence of brood, nurses transition into foraging ants that show daily rhythms in activity. Ants can adaptively shift between these behavioral castes and caste-associated chronotypes depending on social context. We investigated how changes in daily gene expression could be contributing to such behavioral plasticity inCamponotus floridanuscarpenter ants by combining time-course behavioral assays and RNA-Sequencing of forager and nurse brains. ResultsWe found that nurse brains have three times fewer 24 h oscillating genes than foragers. However, several hundred genes that oscillated every 24 h in forager brains showed robust 8 h oscillations in nurses, including the core clock genesPeriodandShaggy. These differentially rhythmic genes consisted of several components of the circadian entrainment and output pathway, including genes said to be involved in regulating insect locomotory behavior. We also found thatVitellogenin, known to regulate division of labor in social insects, showed robust 24 h oscillations in nurse brains but not in foragers. Finally, we found significant overlap between genes differentially expressed between the two ant castes and genes that show ultradian rhythms in daily expression. ConclusionThis study provides a first look at the chronobiological differences in gene expression between forager and nurse ant brains. This endeavor allowed us to identify a putative molecular mechanism underlying plastic timekeeping: several components of the ant circadian clock and its output can seemingly oscillate at different harmonics of the circadian rhythm. We propose that such chronobiological plasticity has evolved to allow for distinct regulatory networks that underlie behavioral castes, while supporting swift caste transitions in response to colony demands. Behavioral division of labor is common among social insects. The links between chronobiological and behavioral plasticity that we found inC. floridanus, thus, likely represent a more general phenomenon that warrants further investigation. 

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