Allometry and growth in the adult stalk-eyed fly, Teleopsis dalmanni

Eyespan in the stalk-eyed fly, Teleopsis dalmanni, is sexually dimorphic, and both sexes exhibit considerable variation in eyespan which may impact moment of inertia, maneuverability and flight behavior. T. dalmanni are not sexually mature until approximately 4 weeks post-eclosion, suggesting that investment into gonads may further increase abdominal mass and overall body mass across age. The purpose of this study was to investigate morphological compensation across age and between sexes in adult flies. Twenty-four groups of approximately 30 1-day old flies were collected and housed in separate 3L chambers so that the age of each fly was known at the time of the morphometric analysis. Male (n=175) and female (n=189) flies from these groups were collected over a 2-month period, anesthetized with CO₂, photographed and weighed, then immediately dissected and their heads, thoraces and abdomens individually weighed. Images were analyzed to determine eyespan, thorax width and length, and wing length. Males were heavier and had longer eyespans and wings than females. Wing length and thorax width varied proportional to eyespan in both sexes. Total body mass, abdominal and thorax mass increased logarithmically across age in both sexes; body mass increased 48% during the first week post-eclosion, then increased an additional 31% over the following 7 weeks. However, the ratio of thorax-to-body mass did not vary across age, suggesting that investment into abdominal tissues is met by proportional, compensatory growth of thorax tissues, presumably to maintain flight performance as flies become heavier with age.