Small Ca2+ releases enable hour-long high-frequency contractions in midshipman swimbladder muscle

A tale of two males: Behavioral and neural mechanisms of alternative reproductive tactics in midshipman fish

An amalgam of investigations at the interface of neuroethology and behavioral neuroendocrinology first established the most basic behavioral, neuroanatomical, and neurophysiological characters of vocal-acoustic communication morphs in the plainfin midshipman fish, Porichthys notatus Girard. This foundation has led, in turn, to the repeated demonstration that neuro-behavioral mechanisms driving reproductive-related, vocal-acoustic behaviors can be uncoupled from gonadal state for two adult male phenotypes that follow alternative reproductive tactics (ARTs).

California singing fish

Bass describes the fascinating life history, behavior, and neurobiology of the California singing fish, including its remarkable vocal abilities.

Ca2+ entry units in a superfast fish muscle

Over the past two decades, mounting evidence has demonstrated that a mechanism known as store-operated Ca2+ entry (SOCE) plays a crucial role in sustaining skeletal muscle contractility by facilitating Ca2+ influx from the extracellular space during sarcoplasmic reticulum (SR) Ca2+ depletion. We recently demonstrated that, in exercised fast-twitch muscle from mice, the incidence of Ca2+ entry units (CEUs), newly described intracellular junctions between dead-end longitudinal transverse tubular (T-tubule) extensions and stacks of sarcoplasmic reticulum (SR) flat cisternae, strictly correlate with both the capability of fibers to maintain contractions during fatigue and enhanced Ca2+ influx via SOCE. Here, we tested the broader relevance of this result across vertebrates by searching for the presence of CEUs in the vocal muscles of a teleost fish adapted for extended, high-frequency activity. Specifically, we examined active vs. inactive superfast sonic muscles of plainfin midshipman (Porichthys notatus). Interestingly, muscles from actively humming territorial males had a much higher incidence of CEU SR stacks relative to territorial males that were not actively vocalizing, strengthening the concept that assembly of these structures is dynamic and use-dependent, as recently described in exercised muscles from mice. Our results support the hypothesis that CEUs represent a conserved mechanism, across vertebrates, for enabling high levels of repetitive muscle activity, and also provide new insights into the adaptive mechanisms underlying the unique properties of superfast midshipman sonic muscles.

Evolutionary and Biomechanical Basis of Drumming Behavior in Woodpeckers

Understanding how and why behavioral traits diversify during the course of evolution is a longstanding goal of organismal biologists. Historically, this topic is examined from an ecological perspective, where behavioral evolution is thought to occur in response to selection pressures that arise through different social and environmental factors. Yet organismal physiology and biomechanics also play a role in this process by defining the types of behavioral traits that are more or less likely to arise. Our paper explores the interplay between ecological, physiological, and mechanical factors that shape the evolution of an elaborate display in woodpeckers called the drum. Individuals produce this behavior by rapidly hammering their bill on trees in their habitat, and it serves as an aggressive signal during territorial encounters. We describe how different components of the display—namely, speed (bill strikes/beats sec–1), length (total number of beats), and rhythm—differentially evolve likely in response to sexual selection by male-male competition, whereas other components of the display appear more evolutionarily static, possibly due to morphological or physiological constraints. We synthesize research related to principles of avian muscle physiology and ecology to guide inferences about the biomechanical basis of woodpecker drumming. Our aim is to introduce the woodpecker as an ideal study system to study the physiological basis of behavioral evolution and how it relates to selection born through different ecological factors.

To hum or not to hum: Neural transcriptome signature of male courtship vocalization in a teleost fish

For many animal species, vocal communication is a critical social behavior and often a necessary component of reproductive success. Additionally, vocalizations are often demanding motor acts. Wanting to know whether a specific molecular toolkit might be required for vocalization, we used RNA-sequencing to investigate neural gene expression underlying the performance of an extreme vocal behavior, the courtship hum of the plainfin midshipman fish (Porichthys notatus). Single hums can last up to 2 h and may be repeated throughout an evening of courtship activity. We asked whether vocal behavioral states are associated with specific gene expression signatures in key brain regions that regulate vocalization by comparing transcript expression levels in humming versus non-humming males. We find that the circadian-related genes period3 and Clock are significantly upregulated in the vocal motor nucleus and preoptic area-anterior hypothalamus, respectively, in humming compared with non-humming males, indicating that internal circadian clocks may differ between these divergent behavioral states. In addition, we identify suites of differentially expressed genes related to synaptic transmission, ion channels and transport, neuropeptide and hormone signaling, and metabolism and antioxidant activity that together may support the neural and energetic demands of humming behavior. Comparisons of transcript expression across regions stress regional differences in brain gene expression, while also showing coordinated gene regulation in the vocal motor circuit in preparation for courtship behavior. These results underscore the role of differential gene expression in shifts between behavioral states, in this case neuroendocrine, motor and circadian control of courtship vocalization.

Sound production in piranhas is associated with modifications of the spinal locomotor pattern

In piranhas, sounds are produced through the vibration of the swim bladder wall caused by the contraction of bilateral sonic muscles. Because they are solely innervated by spinal nerves, these muscles likely evolved from the locomotor hypaxial musculature. The transition from a neuromuscular system initially shaped for slow movements (locomotion) to a system that requires a high contraction rate (sound production) was accompanied with major peripheral structural modifications, yet the associated neural adjustments remain to this date unclear. To close this gap, we investigated the activity of both the locomotor and the sonic musculature using electromyography. The comparison between the activation patterns of both systems highlighted modifications of the neural motor pathway: (1) a transition from a bilateral alternating pattern to a synchronous activation pattern, (2) a switch from a slow- to a high-frequency regime, and (3) an increase in the synchrony of motor neuron activation. Furthermore, our results demonstrate that sound features correspond to the activity of the sonic muscles, as both the variation patterns of periods and amplitudes of sounds highly correspond to those seen in the sonic muscle electromyograms (EMGsonic). Assuming that the premotor network for sound production in piranhas is of spinal origin, our results show that the neural circuit associated with spinal motor neurons transitioned from the slow alternating pattern originally used for locomotion to a much faster simultaneous activation pattern to generate vocal signals.

Gap junction-mediated glycinergic inhibition ensures precise temporal patterning in vocal behavior

Precise neuronal firing is especially important for behaviors highly dependent on the correct sequencing and timing of muscle activity patterns, such as acoustic signaling. Acoustic signaling is an important communication modality for vertebrates, including many teleost fishes. Toadfishes are well known to exhibit high temporal fidelity in synchronous motoneuron firing within a hindbrain network directly determining the temporal structure of natural calls. Here, we investigated how these motoneurons maintain synchronous activation. We show that pronounced temporal precision in population-level motoneuronal firing depends on gap junction-mediated, glycinergic inhibition that generates a period of reduced probability of motoneuron activation. Super-resolution microscopy confirms glycinergic release sites formed by a subset of adjacent premotoneurons contacting motoneuron somata and dendrites. In aggregate, the evidence supports the hypothesis that gap junction-mediated, glycinergic inhibition provides a timing mechanism for achieving synchrony and temporal precision in the millisecond range for rapid modulation of acoustic waveforms.