Meeting Abstract
P2.93 Sunday, Jan. 5 15:30 Is there a price of being a giant? Body systems scaling in Scarabaeid beetles illustrated by high resolution micro-CT DUELL, M*; CIARLARIELLO, J; KLOK, CJ; VANDENBROOKS, J; HARRISON, JF; Arizona State University meduell@asu.edu
Today’s insects are small in comparison to the giants of the Paleozoic Era when atmospheric oxygen levels were higher than current levels. If tracheal oxygen delivery limits insect size, then larger insects might require larger tracheal systems with respect to body size (hypermetrically scaled) to meet their oxygen demands; this pattern has been found in grasshoppers during ontogeny and across tenebrionid beetle species. Hypermetric scaling of the tracheal system could mean that the price of being giant may be reduced investment in other body systems. We tested these possibilities in the clade of insects including the most massive extant species, scarab beetles ranging in size from 1 mg to 30 g. The beetles were killed using ethyl acetate fumes and scanned within two days to maintain the integrity of internal structures. Using micro-CT scanners at Virginia Tech, Argonne National Laboratory, and UT Austin, beetles were scanned at high resolution. Raw X-rays were reconstructed in 3-D so we could estimates volumes of muscles, airsacs, gut, genitalia, and brain tissue using Avizo Fire software. We measured cuticle volumes after a NaOH digestion of soft tissues. Based on analysis of about a third of the species, air sac contents scaled hypermetrically, as found in prior studies. Gut and genitalia were difficult to distinguish using x-ray density thresholding so they were combined and represent approximately 3-20% of the body volume. Brains were consistently less than 1% of body volume and were proportionally larger in smaller beetles (Haller’s rule). Flight muscle scaled isometrically and was approximately 15-20% of the body. Larger beetles have lower densities due to investing a greater percentage of body volume in airsacs, apparently without trade-offs in other tissues. This work was funded by NSF 1122157.
