Meeting Abstract
One of the challenges in behavioral ecology is an accurate quantification of relatively rare or cryptic behaviors such as copulation. Behaviors that activate skeletal muscles can lead to adaption such as hypertrophy and fiber type switching. Muscles are also damaged during use in a frequency- and intensity-dependent manner. Muscle damage causes the recruitment of inflammatory cells which remove debris and allows the native tissue to regenerate. When viewing muscles in cross section, muscle damage manifests as disruptions of normal muscle architecture, notably invaded muscle fibers and regions of densely packed cells. In anoles, the retractor penis magnus (RPM) is only activated during copulation. Thus, muscle damage in the RPM should be due to mating, and the extent of damage may indicate the extent of muscle use. We tested the hypothesis that observed copulation rate is positively correlated with RPM muscle damage. We used field observations to determine copulation rates for 27 species of anoles across the southern United States and Caribbean islands. Males from each species were captured and tail muscle tissues were dissected, flash-frozen, cross sectioned, and stained with H and E. We outlined each RPM (total cross-sectional area or CSA) and the damaged tissue (damaged CSA). We calculated a ratio of muscle damage (damaged CSA / total CSA) for each RPM and averaged the two sides to give each animal a single value. We then used phylogenic generalized least squares regression to test for a correlation between the ratio of damage in the RPM to the observed copulation rate in the wild. We found that RPM damage was significantly correlated to copulation rate. Our study suggests that RPM damage can be used as a proxy for estimating copulation rates in anoles, and more generally, that muscle damage may be a proxy for estimating muscle use across species.
