An official website of the United States government
ABSTRACT Androgens mediate the expression of many reproductive behaviors, including the elaborate displays used to navigate courtship and territorial interactions. In some vertebrates, males can produce androgen-dependent sexual behavior even when levels of testosterone are low in the bloodstream. One idea is that select tissues make their own androgens from scratch to support behavioral performance. We first studied this phenomenon in the skeletal muscles that actuate elaborate sociosexual displays in downy woodpeckers and two songbirds. We show that the woodpecker display muscle maintains elevated testosterone when the testes are regressed in the non-breeding season. Both the display muscles of woodpeckers, as well as the display muscles in the avian vocal organ (syrinx) of songbirds, express all transporters and enzymes necessary to convert cholesterol into bioactive androgens locally. In a final analysis, we broadened our study by looking for these same transporters and enzymes in mammalian muscles that operate at different speeds. Using RNA-seq data, we found that the capacity for de novo synthesis is only present in ‘superfast’ extraocular muscle. Together, our results suggest that skeletal muscle specialized to generate extraordinary twitch times and/or extremely rapid contractile speeds may depend on androgenic hormones produced locally within the muscle itself. Our study therefore uncovers an important dimension of androgenic regulation of behavior.
more »
« less
This content will become publicly available on November 1, 2026
Endocrine and skeletal muscle physiology optimizing avian migratory capabilities
The long‐distance migrations of thousands of bird species and their billions of individuals are feats of astounding physiological specialization and plasticity. Whereas numerous organ systems require modification to achieve successful fueling and navigation capabilities, given their overarching importance for movement and contribution to body mass, skeletal muscles are subject to exceptional performance optimization and anatomical plasticity. To express the appropriate changes throughout the complicated life history of migration, while remaining in synchrony with the environment, skeletal muscles must receive preparatory signals and express transcriptional and biochemical modifications required for full expression of the migratory phenotype. In all likelihood, these muscles must also temporally signal their state and needs to other organ systems. By considering other well‐studied avian skeletal muscle systems, this review explores how endocrine signaling likely impacts skeletal muscles involved in migration and, conversely, how those muscles might relay their condition elsewhere throughout the bird's body. Systems biology offers exceptional modeling for capturing this complex biology.
more »
« less
- PAR ID:
- 10656621
- Publisher / Repository:
- Journal of Avian Biology
- Date Published:
- Journal Name:
- Journal of Avian Biology
- Volume:
- 2025
- Issue:
- 6
- ISSN:
- 0908-8857
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Studies of vertebrate feeding have predominantly focused on the bones and muscles of the head, not the body. Yet, postcranial musculoskeletal structures like the spine and pectoral girdle are anatomically linked to the head, and may also have mechanical connections through which they can contribute to feeding. The feeding roles of postcranial structures have been best studied in ray-finned fishes, where the body muscles, vertebral column, and pectoral girdle attach directly to the head and help expand the mouth during suction feeding. Therefore, I use the anatomy and motion of the head–body interface in these fishes to develop a mechanical framework for studying postcranial functions during feeding. In fish the head and body are linked by the vertebral column, the pectoral girdle, and the body muscles that actuate these skeletal systems. The morphology of the joints and muscles of the cranio-vertebral and hyo-pectoral interfaces may determine the mobility of the head relative to the body, and ultimately the role of these interfaces during feeding. The postcranial interfaces can function as anchors during feeding: the body muscles and joints minimize motion between the head and body to stabilize the head or transmit forces from the body. Alternatively, the postcranial interfaces can be motors: body muscles actuate motion between the head and body to generate power for feeding motions. The motor function is likely important for many suction-feeding fishes, while the anchor function may be key for bite- or ram-feeding fishes. This framework can be used to examine the role of the postcranial interface in other vertebrate groups, and how that role changes (or not) with morphology and feeding behaviors. Such studies can expand our understanding of muscle function, as well as the evolution of vertebrate feeding behaviors across major transitions such as the invasion of land and the emergence of jaws.more » « less
-
Abstract Muscle-based movement is a hallmark of animal biology, but the evolutionary origins of myocytes are unknown. Although believed to lack muscles, sponges (Porifera) are capable of coordinated whole-body contractions that purge debris from internal water canals. This behavior has been observed for decades, but their contractile tissues remain uncharacterized with respect to their ultrastructure, regulation, and development. We examine the spongeEphydatia muelleriand find tissue-wide organization of a contractile module composed of actin, striated-muscle myosin II, and transgelin, and that contractions are regulated by the release of internal Ca2+stores upstream of the myosin-light-chain-kinase (MLCK) pathway. The development of this contractile module appears to involve myocardin-related transcription factor (MRTF) as part of an environmentally inducible transcriptional complex that also functions in muscle development, plasticity, and regeneration. As an actin-regulated force-sensor, MRTF-activity offers a mechanism for how the contractile tissues that line water canals can dynamically remodel in response to flow and can re-form normally from stem-cells in the absence of the intrinsic spatial cues typical of animal embryogenesis. We conclude that the contractile module of sponge tissues shares elements of homology with contractile tissues in other animals, including muscles, indicating descent from a common, multifunctional tissue in the animal stem-lineage.more » « less
-
Skeletal muscle slow fiber (MyHC-I) content varies across muscles and taxa and is one of the traits that distinguishes humans from other apes, yet no study to date has compiled this interspecific data into a single, usable format. Thus, the goal of this study was to collate mammalian skeletal muscle slow fiber composition data from published, peer-reviewed articles into a single, open-access Excel sheet for interspecific comparison and analysis (as in Queeno et al., 2023). A systematic literature search and review was conducted between June 1 2021 and November 30 2022 following a structure similar to PRISMA. Terms relating to mammalian skeletal muscle fiber composition were queried using academic search systems (e.g. Google Scholar) and library databases for relevant primary articles. Reference lists in relevant articles were thoroughly investigated for eligible studies. In total, 269 primary articles were deemed eligible for inclusion in the meta-analysis (i.e. these studies provided skeletal muscle fiber composition data from mammalian species that were not subjected to experimental manipulations). Relevant metadata (e.g. taxonomic information, sex, age, fiber-typing methodology, average body mass, and average percent slow fiber content) was then extracted from the text, figures, tables, and supplementary materials of eligible studies when available. Muscle fiber composition data was collected from more than 200 skeletal muscles across 174 mammalian species, which will be of immense value to those interested in muscle physiology, interspecific muscle comparisons, and connections between muscle physiology, taxonomy, body mass, ecomorphology and locomotor strategy (among others). These data highlight certain species, taxonomic orders, and muscles for which fiber composition data is lacking and needs investigation. Hopefully, these data will spark interest in gathering muscle fiber composition data from underrepresented species and muscles, and generate interest in pursuing questions relating to muscle physiology and evolution, as well as analyses based on interspecific datasets.more » « less
-
ABSTRACT Drilling and tapping behaviors in woodpeckers have long garnered significant attention, given their extreme, high-impact nature. However, how these birds integrate neuromuscular and respiratory systems to produce such high-force, high-frequency behaviors remains poorly understood. Here, we combined electromyography with measures of respiratory air-sac pressure and syringeal airflow to investigate the neuromuscular and ventilatory mechanisms of forceful pecking in downy woodpeckers. We found that both types of pecking behaviors tested engage skeletal muscles across the head, neck, hips, tail and abdomen. In-depth analysis of EMG timing and activity point to a hammer-like model associated with drilling, whereby head and neck muscles contract to create a stiffened cephalo-cervical lever arm that efficiently transfers kinetic energy from the swinging bill into the wood. Moreover, hip flexors help power protraction of the head and body for drilling, whereas tail muscles presumably help brace the bird's body against the tree. Respiratory analyses show that woodpeckers actively exhale with each bill strike of the substrate, resembling the ‘grunting’ behavior that human athletes use to stabilize their core and enhance force output. These effects persist at high tapping frequencies, indicating that individuals take mini-breaths between successive taps. Altogether, our results highlight the way motor and respiratory systems are leveraged to facilitate the production of extreme behavior, which hinges on biomechanical specializations and extraordinary performance abilities.more » « less
