Characteristics of Muscle Fiber‐Type Distribution in Moles

Abstract

Moles are a strictly fossorial Soricomorpha species and possess a suite of specialized adaptations to subterranean life. However, the contractile function of skeletal muscles in moles remains unclear. We compared muscle fiber‐type distribution in two mole species (the large Japanese mole and lesser Japanese mole) with that in four other Soricomorpha species that are semi‐fossorial, terrestrial, or semi‐aquatic (the Japanese shrew‐mole, house shrew, Japanese white‐toothed shrew, and Japanese water shrew). For a single species, the fiber‐type distribution in up to 38 muscles was assessed using immunohistochemical staining and/or gel electrophoresis. We found that slow and fatigue‐resistant Type I fibers were absent in almost all muscles of all species studied. Although, the two methods of determining the fiber type did not give identical results, they both revealed that fast Type IIb fibers were absent in mole muscles. The fiber‐type distribution was similar among different anatomical regions in the moles. This study demonstrated that the skeletal muscles of moles have a homogenous fiber‐type distribution compared with that in Soricomorpha species that are not strictly fossorial. Mole muscles are composed of Type IIa fibers alone or a combination of Type IIa and relatively fast Type IIx fibers. The homogenous fiber‐type distribution in mole muscles may be an adaptation to structurally simple subterranean environments, where there is no need to support body weight with the limbs, or to move at high speeds to pursue prey or to escape from predators. Anat Rec, 302:1010–1023, 2019. © 2018 Wiley Periodicals, Inc.

Immunohistochemistry of kangaroo rat hindlimb muscles

“…Type I fibers, which are known for having a postural role (Ichikawa et al, 2018; Meyers, 2019), were found deeply situated in very small percentages ranging from 0.13 to 5.3% in PL, MG, and LG, which is comparable to the percentages reported by Williamson and Frederick (1977). It is commonly reported that Type I fibers are typically found in deeper muscle regions in mammals (Armstrong, 1980; Ryan et al, 1992).…”

Muscle architecture and muscle fibre type composition in the forelimb of two African mole‐rat species, Bathyergus suillus and Heterocephalus glaber

“…In the current study, the differences observed in the muscle fibre type composition of the forelimb muscles may not be due to functional strains or environmental demands, but rather the phylogeny of the species (Álvarez & Pérez, 2019). Ichikawa et al (2019) discovered the absence of MHC IIb fibres within the muscles of two species of subterranean true moles (Eulipotyphla), whereas all subtypes of fast MHC II fibres were present in the semi‐fossorial, terrestrial and semi‐aquatic Eulipotyphla species. This suggests that the subterranean habitat may have an influence on the MHC II fibre compositions in species belonging to the same phylogenetic order.…”

“…However, the fast movements produced for digging in subterranean mammals may influence the percentages of the subtypes of MHC II fibres, which were not evaluated in the present study. Furthermore, Ichikawa et al (2019) indicated the absence of MHC I fibres in two subterranean mole species within the order Eulipotyphla (Douady et al, 2002). Other studies performed on species belonging to Eulipotyphla confirmed the absence of slow MHC I fibres within species with different locomotor habits and suggest that it may be due to phylogenetic effects and not locomotor adaptations (Peters et al, 1999; Savolainen & Vornanen, 1995; Suzuki, 1990).…”

Hind foot drumming: Myosin heavy chain muscle fiber distribution in the hind limb muscles of three African mole‐rat species (Bathyergidae)

“…This may be due to phylogenetic differences between the rodent species as myosin isoform expression can be constrained by phylogeny (Nov ak et al, 2010). Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis in two non-drumming, T A B L E 3 The muscle fiber composition (%) of slow (type I) and fast (type II) fibres in the hind limb muscles of Georychus capensis, Bathyergus suillus, and Cryptomys hottentotus natalensis (fibers that did not stain positively were considered fast) subterranean Japanese mole species revealed that both species only had type II fibers in their front and hind limb muscles (Ichikawa et al, 2019). Avivi, Band, Joel, Shenzer, and Coleman (2009) demonstrated that the m. gastrocnemius muscles in the subterranean, nondrumming blind mole rat (Spalax ehrenbergi) had mainly type II muscle fibers which is consistent with the results in the present study.…”

“…The fiber type composition of individual muscles varies within groups of the same species as well as different species. Where some species such as sloths (Xenarthra; Spainhower et al, 2021) and Japanese moles (Mogera species; Ichikawa et al, 2019) express a single MHC isoform within a whole muscle, other species express all four muscle isoforms with variations in proportion in a single muscle. These differences in muscle fiber phenotype can be attributed to sex, age, hormonal, neural and phylogenetic influences (Nov ak, Zacharova, & Soukup, 2010;Schianffino & Reggiani, 2011).…”