Meeting Abstract

P2-4    Lattice structure of mandible closer muscles in leaf-cutter ants (Atta vollenweideri) Ahmed, S*; Kang, V; Labonte, D; Holt, N; University of California, Riverside ; Imperial College London; Imperial College London; University of California, Riverside sahme040@ucr.edu

A cross sectional view of sarcomeres in vertebrate skeletal muscle reveals a hexagonal lattice structure in which six thin actin filaments surround a single thick myosin filament, giving a packing ratio of 2:1. In contrast, sarcomeres of invertebrate skeletal muscle show a lattice structure in which the packing ratio of actin to myosin filaments varies widely across different muscle types even within the same organism, with common ratios of 3:1 or 6:1. However, the potential functional consequences of this variation in packing ratios in invertebrate muscle remain unclear. It has previously been suggested that muscles with longer actin and myosin lengths have higher packing ratios. We will take a comparative approach to add to this body of literature by determining sarcomere length and packing ratio in the high-force capacity mandibular closer muscle of the leaf-cutter ants Atta vollenweideri. The heads of seven worker ants (body mass 3.8-7.6 mg) were fixed, embedded in resin, sectioned, and imaged using transmission electron microscopy (TEM). TEM images and preliminary data concerning sarcomere length and packing ratios will be presented. Examination of the lattice structure in this specialized muscle will contribute to our understanding of the functional role of the three-dimensional ultrastructure of invertebrate striated muscle. This and future TEM work on these muscles will contribute to a body of literature exploring how aspects of muscle ultrastructure co-vary in invertebrates, so helping us determine whether stereotyped collections of muscle features – analogous to vertebrate fiber types – exist in invertebrates.