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Hypermetric Tracheal Scaling as a Factor in Insect Gigantism
Author(s) -
Wagner Julian,
Duell Meghan,
Harrison Jon
Publication year - 2016
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.30.1_supplement.lb646
Subject(s) - biology , scaling , anatomy , isometric exercise , extant taxon , geometry , evolutionary biology , mathematics , physiology
Why are insects small? In the Paleozoic Era, atmospheric oxygen levels peaked significantly higher than the current level. Along with this oxygen peak came giant insects, many times larger than those currently observed. This suggests that oxygen transport may inhibit insects from becoming giants. If this were the case, then one would expect to observe an increase of investment in gas exchange structures in larger insects, i.e. hypermetric scaling. This has been observed in tenebrionid beetle trachea. In this study, we look at scarab beetles, since they have a large range of sizes including the largest extant insect species. Using sets of micro‐CT images of freshly dead scarabs taken at 180 degrees around the beetle, 3d reconstructions of the specimens were made. Using Aviso Fire, the eight spiracles, coxal‐trochantal areas, and the mesothoracic femoral tracheal volumes were measured. The spiracle areas showed isometric scaling with a slope of 0.70. However, spiracle area over spiracle depth showed a steeper slope in the proximal abdominal and thoracic spiracles as compared to the distal abdominal spiracles, suggesting that larger beetles may exhibit different dimensions in their spiracles to promote the spiracle's diffusive abilities (larger area compared to depth allows more air to flow a shorter distance via diffusion). The scaling of the area of the coxal‐trochantal trachea showed a larger slope than the scaling of the area of the coxa with a p value of 0.09 in a t test. The femur structure showed isometric scaling, whereas the femoral trachea showed hypermetry with a slope of 1.46, which differed from a slope of 1 with a p value of 0.0012 in a t test. These indicate that structures far from oxygen intake at the spiracles scale hypermetrically in scarabs. Support or Funding Information This research was supported in part by funds from the School of Life Sciences Undergraduate Research (SOLUR) Program through the School of Life Sciences at Arizona State University, Tempe Campus, and by NSF 1122157