Harrison Jon F, Lafreniere Jessie J, Greenlee Kendra J
Section of Organismal, Integrative, and Systems Biology, School of Life Sciences, Arizona State University, PO Box 874501, Tempe, AZ 85287-4501, USA.
Comp Biochem Physiol A Mol Integr Physiol. 2005 Aug;141(4):372-80. doi: 10.1016/j.cbpb.2005.05.055.
How does body size affect the structure and gas exchange capacities of insect tracheae? Do insects become more oxygen-limited as they grow? We addressed these questions by measuring the dimensions of two transverse tracheae within the abdomen of American locusts of different ages, and evaluating the potential for diffusion or convection to provide adequate gas exchange. The grasshopper abdomen has longitudinal tracheae that run along the midgut, heart, nerve cord, and lateral body wall. Transverse tracheae run from each spiracle to the longitudinal tracheae. Dorsal air sacs attach near each spiracle. In both transverse tracheae studied, diffusive capacities increased more slowly than metabolic rates with age, and calculated oxygen gradients necessary to supply oxygen by diffusion increased exponentially with age. However, surgical studies demonstrated that transport of gas through these transverse tracheae occurred by convection, at least in adults. Convective capacities paralleled metabolic rates with age, and the calculated pressure gradients required to sustain oxygen consumption rates by convection were independent of age. Thus, in growing grasshoppers, tracheal capacities matched tissue oxygen needs. Our morphological and physiological data together suggest that use of convection allows older grasshoppers to overcome potential limitations on size imposed by diffusion through tracheal systems.
体型如何影响昆虫气管的结构和气体交换能力？昆虫在生长过程中是否会受到更多的氧气限制？我们通过测量不同年龄的美洲蝗虫腹部两根横向气管的尺寸，并评估扩散或对流提供充足气体交换的潜力，来解决这些问题。蝗虫腹部有沿着中肠、心脏、神经索和体侧壁分布的纵向气管。横向气管从每个气门通向纵向气管。背气囊附着在每个气门附近。在所研究的两根横向气管中，随着年龄增长，扩散能力的增加比代谢率的增加更为缓慢，并且通过扩散供应氧气所需的计算氧梯度随年龄呈指数增加。然而，外科手术研究表明，至少在成虫中，气体通过这些横向气管的运输是通过对流进行的。对流能力与年龄的代谢率平行，并且通过对流维持氧气消耗率所需的计算压力梯度与年龄无关。因此，在生长中的蝗虫中，气管能力与组织氧气需求相匹配。我们的形态学和生理学数据共同表明，对流的利用使老龄蝗虫能够克服气管系统扩散对体型造成的潜在限制。
