Histochemical and electrophoretic analysis of the primary flight muscle of several phyllostomid bats

We identify a novel histochemical fibre type that is correlated with a unique myosin heavy chain isoform in the pectoralis muscle of the two bats Artibeus lituratus and Carollia perspicillata (Phyllostomidae). Pectoralis muscles sampled from four other species (Phyllostomus hastatus, Platyrrhinus helleri, Glossophaga soricina, and Diaemus youngi) exhibited myosin heavy chain isoforms with electrophoretic properties identical with those of A. lituratus andC. perspicillata. The pectoralis muscles of A. lituratus and C. perspicillata consisted mainly of the newly described type IIe fibre. Diaemus youngi differed from the other species studied by having an FM5 native myosin isoform, a feature shared with Desmodus rotundus. We hypothesize that the two-fibre-type composition of the pectoralis muscle in the phyllostomid bats may be related to a "two-gear" locomotor strategy and represents a synapomorphy. The distribution of fibre types and myosin isoforms correlated with family-level phylogenetic affinity rather than with functional characteristics. One of the fibre types was identical with type IIa of terrestrial mammals and a correlated IIa isoform pattern upon electrophoretic analysis. The IIa fibres had high oxidative and glycolytic potential. The second fibre type, which we call type IIe, had a histochemical and immunocytochemical pattern inconsistent with interpretation as a type IIb muscle fibre. Electrophoretic analysis confirmed that isoforms correlated with IIe fibres migrated at different rates from type I, IIa, IIb, and IIx isoforms. The IIe fibres had a fast oxidative metabolic pattern and were at least twice as numerous as IIa fibres. Thus, a novel type IIe fibre is predominant in the pectoralis of six phyllostomid species that exhibit highly divergent body sizes and (or) flight styles.