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Herein, the dataset generated for Queeno et al. [1] is presented and described. Mammalian skeletal muscle slow (MyHC-I) fiber composition data was collated from 269 eligible studies identified via a systematic literature search and meta-analysis, following a structure similar to PRISMA [2]. Academic search systems were queried with terms relating to mammalian skeletal muscle fiber content and reference lists of selected articles were thoroughly investigated for additional studies. Eligible studies were those that provided skeletal muscle fiber composition data from mammalian species that were not subjected to experimental manipulations. Taxonomic information, sex, age, number of individuals sampled, average body mass (kg), average slow fiber content (%) of each skeletal muscle under investigation and fiber-typing methodology were collated from eligible studies when available. Muscle fiber composition data was collected from more than 200 skeletal muscles across 174 mammalian species, which will be of value to those interested in muscle physiology, interspecific muscle comparisons, and connections between muscle physiology, taxonomy, body mass, ecomorphology and locomotor strategy (among others). 

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. 

Humans are unique among terrestrial mammals in our manner of walking and running, reflecting 7 to 8 Ma of musculoskeletal evolution since diverging with the genus Pan. One component of this is a shift in our skeletal muscle biology towards a predominance of myosin heavy chain (MyHC) I isoforms (i.e. slow fibers) across our pelvis and lower limbs, which distinguishes us from chimpanzees. Here, new MyHC data from 35 pelvis and hind limb muscles of a Western gorilla (Gorilla gorilla) are presented. These data are combined with a similar chimpanzee dataset to assess the MyHC I content of humans in comparison to African apes (chimpanzees and gorillas) and other terrestrial mammals. The responsiveness of human skeletal muscle to behavioral interventions is also compared to the human-African ape differential. Humans are distinct from African apes and among a small group of terrestrial mammals whose pelvis and lower limb muscle is slow fiber dominant, on average. Behavioral interventions, including immobilization, bed rest, spaceflight and exercise, can induce modest decreases and increases in human MyHC I content (i.e. -9.3% to 2.3%, n = 2033 subjects), but these shifts are much smaller than the mean human-African ape differential (i.e. 31%). Taken together, these results indicate muscle fiber content is likely an evolvable trait under selection in the hominin lineage. As such, we highlight potential targets of selection in the genome (e.g. regions that regulate MyHC content) that may play an important role in hominin skeletal muscle evolution. 

Genomic data are being produced and archived at a prodigious rate, and current studies could become historical baselines for future global genetic diversity analyses and monitoring programs. However, when we evaluated the potential utility of genomic data from wild and domesticated eukaryote species in the world’s largest genomic data repository, we found that most archived genomic datasets (87%) lacked the spatiotemporal metadata necessary for genetic biodiversity surveillance. Labor-intensive scouring of a subset of published papers yielded geospatial coordinates and collection years for only 39% (51% if place names were considered) of these genomic datasets. Streamlined data input processes, updated metadata deposition policies, and enhanced scientific community awareness are urgently needed to preserve these irreplaceable records of today’s genetic biodiversity and to plug the growing metadata gap.