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1. Vocal and electric fish: Reprising a comparison of two teleost models in the neuroethology of social behavior.

   https://doi.org/10.3389/fncir.2021.713105  

   Dunlap, K; Chagnaud BP.; Zakon HH.; Bass AH. (August 2021, Frontiers in neural circuits)

   Edward S Ruthhazer Takao K Hensch (Ed.)

   The communication behaviors of vocal fish and electric fish are among the vertebrate social behaviors best understood at the level of neural circuits. Both forms of signaling rely on midbrain inputs to hindbrain pattern generators that activate peripheral effectors (sonic muscles and electrocytes) to produce pulsatile signals that are modulated by frequency/repetition rate, amplitude and call duration. To generate signals that vary by sex, male phenotype, and social context, these circuits are responsive to a wide range of hormones and neuromodulators acting on different timescales at multiple loci. Bass and Zakon (2005) reviewed the behavioral neuroendocrinology of these two teleost groups, comparing how the regulation of their communication systems have both converged and diverged during their parallel evolution. Here, we revisit this comparison and review the complementary developments over the past 16 years. We (a) summarize recent work that expands our knowledge of the neural circuits underlying these two communication systems, (b) review parallel studies on the action of neuromodulators (e.g., serotonin, AVT, melatonin), brain steroidogenesis (via aromatase), and social stimuli on the output of these circuits, (c) highlight recent transcriptomic studies that illustrate how contemporary molecular methods have elucidated the genetic regulation of social behavior in these fish, and (d) describe recent studies of mochokid catfish, which use both vocal and electric communication, and that use both vocal and electric communication and consider how these two systems are spliced together in the same species. Finally, we offer avenues for future research to further probe how similarities and differences between these two communication systems emerge over ontogeny and evolution. 

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2. The calling songs of some katydids (Orthoptera, Tettigonioidea) from the tropical forests of Southeast Asia

   https://doi.org/10.3897/jor.32.84563  

   Tan, Ming Kai; Duncan, Jacob; Wahab, Rodzay bin; Lee, Chow-Yang; Japir, Razy; Chung, Arthur Y.; Baroga-Barbecho, Jessica B.; Yap, Sheryl A.; Montealegre-Z, Fernando (January 2023, Journal of Orthoptera Research)

   Katydids produce sound for signaling and communication by stridulation of the tegmina. Unlike crickets, most katydids are known to sing at ultrasonic frequencies. This has drawn interest in the investigation of the biophysics of ultrasonic sound production, detection, evolution, and ecology (including predator–prey interactions) of these katydids. However, most of these studies are based on species from the Neotropics, while little is known about katydid species from the hyperdiverse region of Southeast Asia. To address this, a concerted effort to document, record, and describe the calling songs of Southeast Asian katydids, especially species that call at ultrasonic frequencies, was made. A study spanning two years (2018–2020) in the Malay Peninsula (Singapore and Malaysia), Borneo (Brunei Darussalam and Sabah), and the Philippines revealed previously unknown calls of 24 katydid species from four subfamilies. The calling songs of Southeast Asian katydid species are highly diversified in terms of time and frequency. Call structure can range from isolated syllables (e.g.,Holochlora), continuous trills (e.g.,Axylus philippinus), to short pulse-trains (e.g.,Euanisous teuthroides) and complex echemes (e.g.,Conocephalusspp.), with 87.5% of species having ultrasonic peak frequencies and 12.5% being considered extreme ultrasonic callers (peak frequency >40 kHz). The call spectrum ranges from tonal (e.g., spectral entropy is 6.8 inCasignetasp. 2) to resonant (entropy is 8.8 inConocephalus cognatus). Of the 24 species whose calls are described here, we imaged and described the sound-producing structures of 18. This study provides a preliminary overview of the acoustic diversity of katydids in Southeast Asia, and the authors hope to inspire further investigation into the bioacoustics of little-known katydids from these areas. Amassing a database of calling songs and sound-producing organ illustrations from different species is important to address taxonomic impediments while advancing our knowledge about the bioacoustics of Southeast Asian katydids. 

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3. Mechanistic insights into gene expression changes and electric organ discharge elongation in mormyrid electric fish

   https://doi.org/10.1101/2024.09.02.610879  

   Losilla, Mauricio; Gallant, Jason R (September 2024, bioRxiv)

   Abstract Electric organ discharge (EOD) duration in African weakly electric fish (Mormyridae) is the most variable waveform component between species and the basis for distinguishing species-specific signals. EOD duration is thought to be influenced by morphological and physiological features of electrocytes (the cells that comprise the electric organ), but the mechanistic details are poorly understood. It has long been known that EOD duration is modulated by androgen hormones, affording an opportunity to identify gene expression correlates of EOD duration differences. We induced EOD elongation in the mormyridBrienomyrus brachyistiusby administering 17α-methyltestosterone (17αMT) to three treatment groups: control (no 17αMT exposure), T1day and T8day (samples taken one and eight days after a single exposure to 17αMT, respectively). We then performed RNAseq, differential gene expression, and functional enrichment analysis to detect gene expression changes during EOD duration change. Our analyses indicate 44 genes whose expression changed in tandem with EOD elongation and include genes responsible for actin filaments and microtubules, extracellular matrix organization, and membrane lipid metabolism. Additionally, we found expression changes in one Na⁺channel beta subunit, and five K⁺voltage-gated channels. Together, these genes point toward specific cellular processes that contribute to morphological and physiological changes that contribute to EOD duration changes. 

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4. Generalization of learned responses in the mormyrid electrosensory lobe

   https://doi.org/10.7554/eLife.44032  

   Dempsey, Conor; Abbott, LF; Sawtell, Nathaniel B (March 2019, eLife)

   Appropriate generalization of learned responses to new situations is vital for adaptive behavior. We provide a circuit-level account of generalization in the electrosensory lobe (ELL) of weakly electric mormyrid fish. Much is already known in this system about a form of learning in which motor corollary discharge signals cancel responses to the uninformative input evoked by the fish’s own electric pulses. However, for this cancellation to be useful under natural circumstances, it must generalize accurately across behavioral regimes, specifically different electric pulse rates. We show that such generalization indeed occurs in ELL neurons, and develop a circuit-level model explaining how this may be achieved. The mechanism involves regularized synaptic plasticity and an approximate matching of the temporal dynamics of motor corollary discharge and electrosensory inputs. Recordings of motor corollary discharge signals in mossy fibers and granule cells provide direct evidence for such matching. 

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5. Cycad-Weevil Pollination Symbiosis Is Characterized by Rapidly Evolving and Highly Specific Plant-Insect Chemical Communication

   https://doi.org/10.3389/fpls.2021.639368  

   Salzman, Shayla; Crook, Damon; Calonje, Michael; Stevenson, Dennis W.; Pierce, Naomi E.; Hopkins, Robin (April 2021, Frontiers in Plant Science)

   null (Ed.)

   Coevolution between plants and insects is thought to be responsible for generating biodiversity. Extensive research has focused largely on antagonistic herbivorous relationships, but mutualistic pollination systems also likely contribute to diversification. Here we describe an example of chemically-mediated mutualistic species interactions affecting trait evolution and lineage diversification. We show that volatile compounds produced by closely related species of Zamia cycads are more strikingly different from each other than are other phenotypic characters, and that two distantly related pollinating weevil species have specialized responses only to volatiles from their specific host Zamia species. Plant transcriptomes show that approximately a fifth of genes related to volatile production are evolving under positive selection, but we find no differences in the relative proportion of genes under positive selection in different categories. The importance of phenotypic divergence coupled with chemical communication for the maintenance of this obligate mutualism highlights chemical signaling as a key mechanism of coevolution between cycads and their weevil pollinators. 

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