Gill size of trichopteran larvae and oxygen supply in streams along a 4000-m gradient of altitude

Abstract:

It is a common belief that mountain streams are richer in oxygen than lowland streams and, as a result, macroinvertebrates inhabiting streams at high altitudes are thought to have smaller gills than invertebrates from lowland streams. I examined gill development of assemblages of trichopteran larvae in relation to water temperature, oxygen concentration, and oxygen supply in a number of small streams along a 4000-m gradient of altitude in tropical Ecuador. Oxygen concentration was almost independent of altitude and followed the pattern pbkp_redicted from considering the changes in solubility of oxygen with water temperature and atmospheric pressure. The estimated oxygen supply, however, was higher in warm lowland streams than in cold highland streams because the oxygen partial pressure decreases with increasing altitude, the diffusion coefficient of oxygen in water increases with increasing temperature, and the kinematic viscosity of water and thus the thickness of the diffusive sublayer decreases with increasing temperature. Allometric scaling showed that total body surface area (including gills) increased with body volume at a rate β = 0.72 (±0.01 SE), suggesting that total body surface area reflects metabolic oxygen demand. Mean body volume of larvae with gills was independent of altitude, whereas mean body volume of gill-less larvae increased with altitude. Overall, high-altitude larvae had slightly smaller gill surface area relative to body volume than low-altitude larvae. This pattern mainly reflected the predominance of relatively large-gilled, caseless Hydropsychidae at low altitudes. Gill size of case-bearing larvae actually increased, although not significantly, with altitude. The study showed that taxa with small gills did not generally replace taxa with large gills as stream altitude increased and stream temperature decreased. The nearly constant mean gill size can be explained by a balance between increased metabolic oxygen demand and increased oxygen supply in warm lowland streams.

Año de publicación:

2000

Keywords:

• Trichopteran larvae
• Oxygen concentration
• Gill size
• ECUADOR
• oxygen supply
• streams
• Andes
• aquatic insects
• altitudinal gradients
• Allometric scaling

Fuente:

scopus