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

We identify a novel histochemical fibre type that is correlated with a uniq ue myosin heavy chain isoform in the pectoralis muscle of the two bats Arti beus litaratus and Carollia perspicillata (Phyllostomidae). Pectoralis musc les sampled from four other species (Phyllostomus hastatus, Platyrrhinus he lleri, Glossophaga soricina, and Diaemus youngi) exhibited myosin heavy cha in isoforms with electrophoretic properties identical with those of A. litu ratus and C. perspicillata. The pectoralis muscles of A. lituratus and C. p erspicillata consisted mainly of the newly described type IIe fibre. Diaemu s youngi differed from the other species studied by having an FM5 native my osin 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 sy napomorphy. The distribution of fibre types and myosin isoforms correlated with family-level phylogenetic affinity rather than with functional charact eristics. 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 fi bre type, which we call type IIe, had a histochemical and immunocytochemica l pattern inconsistent with interpretation as a type IIb muscle fibre. Elec trophoretic analysis confirmed that isoforms correlated with IIe fibres mig rated at different rates from type I, IIa, IIb, and IIx isoforms. The IIe f ibres had a fast oxidative metabolic pattern and were at least twice as num erous as IIa fibres. Thus, a novel type IIe fibre is predominant in the pec toralis of six phyllostomid species that exhibit highly divergent body size s and (or) flight styles.