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1. Galanin immunoreactivity is sexually polymorphic in neuroendocrine and vocal‐acoustic systems in a teleost fish

   https://doi.org/10.1002/cne.24765  

   Tripp, Joel A. ; Bass, Andrew H. ( September 2019 , Journal of Comparative Neurology)

   Galanin is a peptide that regulates pituitary hormone release, feeding, and reproductive and parental care behaviors. In teleost fish, increased galanin expression is associated with territorial, reproductively active males. Prior transcriptome studies of the plainfin midshipman (Porichthys notatus), a highly vocal teleost fish with two male morphs that follow alternative reproductive tactics, show that galanin is upregulated in the preoptic area‐anterior hypothalamus (POA‐AH) of nest‐holding, courting type I males during spawning compared to cuckolding type II males. Here, we investigate possible differences in galanin immunoreactivity in the brain of both male morphs and females with a focus on vocal‐acoustic and neuroendocrine networks. We find that females differ dramatically from both male morphs in the number of galanin‐expressing somata and in the distribution of fibers, especially in brainstem vocal‐acoustic nuclei and other sensory integration sites that also differ, though less extensively, between the male morphs. Double labeling shows that primarily separate populations of POA‐AH neurons express galanin and the nonapeptides arginine‐vasotocin or isotocin, homologues of mammalian arginine vasopressin and oxytocin that are broadly implicated in neural mechanisms of vertebrate social behavior including morph‐specific actions on vocal neurophysiology in midshipman. Finally, we report a small population of POA‐AH neurons that coexpress galanin and the neurotransmitter γ‐aminobutyric acid. Together, the results indicate that galanin neurons in midshipman fish likely modulate brain activity at a broad scale, including targeted effects on vocal motor, sensory and neuroendocrine systems; are unique from nonapeptide‐expressing populations; and play a role in male‐specific behaviors.

    

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2. Centris pallida (Hymenoptera: Apidae) male body size decreases across five decades

   https://doi.org/10.1111/een.13210  

   Barrett, Meghan ; Johnson, Meredith G. ( November 2022 , Ecological Entomology)

   Historical data suggest that many bee species have declined in body size. Larger‐bodied bees with narrow phenological and dietary breadth are most prone to declines in body size over time. This may be especially true in solitary, desert‐adapted species that are vulnerable to climate change such asCentris pallida(Hymenoptera: Apidae). In addition, body size changes in species with size‐linked behaviours could threaten the prevalence of certain behavioural phenotypes long‐term.C. pallidasolitary bees are found in the Sonoran Desert. Males use alternative reproductive tactics (ARTs) and are dimorphic in both morphology and behaviour.C. pallidamale body size has been studied since the 1970s in the same population. The authors collected body size data in 2022 and combined it with published records from 1974–2022. The authors find a persistent decline in the mean head width of patrolling males, and shifts towards smaller body sizes in the populations of males found foraging and hovering. Both morphs declined in average body size, and the proportion of large‐morph males in the population decreased by 8%. Mating males did not decline in mean body size over the last five decades. The authors discuss hypotheses related to the decline inC. pallidamale head width. Finally, the authors advocate forC. pallidaas an excellent study system for understanding the stability of ARTs with size‐linked behavioural phenotypes.

    

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3. Evolutionary divergence of developmental plasticity and learning of mating tactics in Trinidadian guppies

   https://doi.org/10.1111/1365-2656.14043  

   Yang, Yusan ; Axelrod, Caleb J. ; Grant, Elly ; Earl, Shayna R. ; Urquhart, Ellen M. ; Talbert, Katie ; Johnson, Lauren E. ; Walker, Zakiya ; Hsiao, Kyle ; Stone, Isabel ; et al ( December 2023 , Journal of Animal Ecology)

   Behavioural plasticity is a major driver in the early stages of adaptation, but its effects in mediating evolution remain elusive because behavioural plasticity itself can evolve.

   In this study, we investigated how male Trinidadian guppies (Poecilia reticulata) adapted to different predation regimes diverged in behavioural plasticity of their mating tactic. We reared F2 juveniles of high‐ or low‐predation population origins with different combinations of social and predator cues and assayed their mating behaviour upon sexual maturity.

   High‐predation males learned their mating tactic from conspecific adults as juveniles, while low‐predation males did not. High‐predation males increased courtship when exposed to chemical predator cues during development; low‐predation males decreased courtship in response to immediate chemical predator cues, but only when they were not exposed to such cues during development.

   Behavioural changes induced by predator cues were associated with developmental plasticity in brain morphology, but changes acquired through social learning were not.

   We thus show that guppy populations diverged in their response to social and ecological cues during development, and correlational evidence suggests that different cues can shape the same behaviour via different neural mechanisms. Our study demonstrates that behavioural plasticity, both environmentally induced and socially learnt, evolves rapidly and shapes adaptation when organisms colonize ecologically divergent habitats.

    

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4. Predation risk drives long‐term shifts in migratory behaviour and demography in a large herbivore population

   https://doi.org/10.1111/1365-2656.14022  

   Williams, S. ; Hebblewhite, M. ; Martin, H. ; Meyer, C. ; Whittington, J. ; Killeen, J. ; Berg, J. ; MacAulay, K. ; Smolko, P. ; Merrill, E. H. ( November 2023 , Journal of Animal Ecology)

   Migration is an adaptive life‐history strategy across taxa that helps individuals maximise fitness by obtaining forage and avoiding predation risk. The mechanisms driving migratory changes are poorly understood, and links between migratory behaviour, space use, and demographic consequences are rare.

   Here, we use a nearly 20‐year record of individual‐based monitoring of a large herbivore, elk (Cervus canadensis) to test hypotheses for changing patterns of migration in and adjacent to a large protected area in Banff National Park (BNP), Canada.

   We test whether bottom‐up (forage quality) or top‐down (predation risk) factors explained trends in (i) the proportion of individuals using 5 different migratory tactics, (ii) differences in survival rates of migratory tactics during migration and whilst on summer ranges, (iii) cause‐specific mortality by wolves and grizzly bears, and (iv) population abundance.

   We found dramatic shifts in migration consistent with behavioural plasticity in individual choice of annual migratory routes. Shifts were inconsistent with exposure to the bottom‐up benefits of migration. Instead, exposure to landscape gradients in predation risk caused by exploitation outside the protected area drove migratory shifts. Carnivore exploitation outside the protected area led to higher survival rates for female elk remaining resident or migrating outside the protected area.

   Cause‐specific mortality aligned with exposure to predation risk along migratory routes and summer ranges. Wolf predation risk was higher on migratory routes than summer ranges of montane‐migrant tactics, but wolf predation risk traded‐off with heightened risk from grizzly bears on summer ranges. A novel eastern migrant tactic emerged following a large forest fire that enhanced forage in an area with lower predation risk outside of the protected area.

   The changes in migratory behaviour translated to population abundance, where abundance of the montane‐migratory tactics declined over time. The presence of diverse migratory life histories maintained a higher total population abundance than would have been the case with only one migratory tactic in the population.

   Our study demonstrates the complex ways in which migratory populations change over time through behavioural plasticity and associated demographic consequences because of individuals balancing predation risk and forage trade‐offs.

    

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5. Neurogenomic landscape associated with status‐dependent cooperative behaviour

   https://doi.org/10.1111/mec.17327  

   Bolton, Peri E. ; Ryder, T. Brandt ; Dakin, Roslyn ; Houtz, Jennifer L. ; Moore, Ignacio T. ; Balakrishnan, Christopher N. ; Horton, Brent M. ( March 2024 , Molecular Ecology)

   The neurogenomic mechanisms mediating male–male reproductive cooperative behaviours remain unknown. We leveraged extensive transcriptomic and behavioural data on a neotropical bird species (Pipra filicauda) that performs cooperative courtship displays to understand these mechanisms. In this species, the cooperative display is modulated by testosterone, which promotes cooperation in non‐territorial birds, but suppresses cooperation in territory holders. We sought to understand the neurogenomic underpinnings of three related traits: social status, cooperative display behaviour and testosterone phenotype. To do this, we profiled gene expression in 10 brain nuclei spanning the social decision‐making network (SDMN), and two key endocrine tissues that regulate social behaviour. We associated gene expression with each bird's behavioural and endocrine profile derived from 3 years of repeated measures taken from free‐living birds in the Ecuadorian Amazon. We found distinct landscapes of constitutive gene expression were associated with social status, testosterone phenotype and cooperation, reflecting the modular organization and engagement of neuroendocrine tissues. Sex‐steroid and neuropeptide signalling appeared to be important in mediating status‐specific relationships between testosterone and cooperation, suggesting shared regulatory mechanisms with male aggressive and sexual behaviours. We also identified differentially regulated genes involved in cellular activity and synaptic potentiation, suggesting multiple mechanisms underpin these genomic states. Finally, we identified SDMN‐wide gene expression differences between territorial and floater males that could form the basis of ‘status‐specific’ neurophysiological phenotypes, potentially mediated by testosterone and growth hormone. Overall, our findings provide new, systems‐level insights into the mechanisms of cooperative behaviour and suggest that differences in neurogenomic state are the basis for individual differences in social behaviour.

    

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