Skeletal muscle fiber types in the ghost crab,Ocypode quadrata:implications for running performance

Abstract

SUMMARYGhost crabs possess rapid running capabilities, which make them good candidates for comparing invertebrate exercise physiology with that of more extensively studied vertebrates. While a number of studies have examined various aspects of running physiology and biomechanics in terrestrial crabs, none to date have defined the basic skeletal muscle fiber types that power locomotion. In the current study, we investigated skeletal muscle fiber types comprising the extensor and flexor carpopodite muscles in relation to running performance in the ghost crab. We used kinematic analyses to determine stride frequency and muscle shortening velocity and found that both parameters are similar to those of comparably sized mammals but slower than those observed in running lizards. Using several complementary methods, we found that the muscles are divided into two primary fiber types: those of the proximal and distal regions possess long sarcomeres (6.2±2.3 μm) observed in crustacean slow fibers and have characteristics of aerobic fibers whereas those of the muscle mid-region have short sarcomeres (3.5±0.4 μm) characteristic of fast fibers and appear to be glycolytic. Each fiber type is characterized by several different myofibrillar protein isoforms including multiple isoforms of myosin heavy chain (MHC), troponin I (TnI), troponin T (TnT) and a crustacean fast muscle protein, P75. Three different isoforms of MHC are differentially expressed in the muscles, with fibers of the mid-region always coexpressing two isoforms at a 1:1 ratio within single fibers. Based on our analyses, we propose that these muscles are functionally divided into a two-geared system, with the aerobic fibers used for slow sustained activities and the glycolytic mid-region fibers being reserved for explosive sprints. Finally, we identified subtle differences in myofibrillar isoform expression correlated with crab body size, which changes by several orders of magnitude during an animalʼs lifetime.

Migration-related changes in gene expression in leg muscle of the Christmas Island red crab Gecarcoidea natalis: seasonal preparation for long-distance walking

“…In crustaceans, up to seven isoforms of TnI can be differentially expressed in the various fibre types (Mykles, 1988;Miegel et al, 1992;Neil et al, 1993;Sohn et al, 2000;Medler and Mykles, 2003;Perry et al, 2009). Several contigs allocated to TnI were distinguished in G. natalis, which is not surprising since multiple isoforms of TnI are co-expressed in muscle tissue.…”

“…Several contigs allocated to TnI were distinguished in G. natalis, which is not surprising since multiple isoforms of TnI are co-expressed in muscle tissue. In lobster and ghost crab muscles, different isoforms of troponin T and troponin I provide convenient markers of fibre type, albeit with low consensus between the two decapod species (Perry et al, 2009), most especially with regards to TnI. In the lobster, five TnI isoforms exist and are expressed in different proportions in different fibre types.…”

“…In crustaceans, myofibrillar isoforms allow at least three fibre types to be distinguished; fast, slow phasic (S1) and slow tonic (S2) (Mykles, 1985a;Mykles, 1985b;Silverman et al, 1987;Mykles, 1988;Medler and Mykles, 2003;Medler et al, 2004). These fibre types tend to exhibit a specific suite of muscle protein isoforms, including different myosin heavy chains and isoforms of tropomyosin, troponin T (TnT), troponin I (TnI) and the fast fibre protein P75 (Mykles, 1985a;Mykles, 1985b;Mykles, 1988;Mykles, 1997;Medler and Mykles, 2003;Perry et al, 2009).…”

“…Mykles, 1988;Perry et al, 2009). Crayfish have two types of fast fibres that exhibit differences in sarcomere width, TnI isoform composition and activation properties (Koenders et al, 2004), and differences in isoform expression have been matched to functional properties of slow and fast muscle fibres in ghost crabs (Perry et al, 2009).…”

“…Mellon, 1992;Boyle et al, 2003;Kinsey et al, 2005) as well as mixed phenotype fibres (e.g. Govind et al, 1987;Govind, 1992;Medler and Mykles, 2003;Medler et al, 2004;Perry et al, 2009). Muscle fibre phenotypes can respond to altered functional demands (for a review, see Pette and Staron, 2001), which may be important for the putative seasonal changes in G. natalis muscle physiology.…”