P O 2 of the metathoracic ganglion in response to progressive hypoxia in an insect

Mammals regulate their brain tissue P O 2 tightly, and only small changes in brain P O 2 are required to elicit compensatory ventilation. However, unlike the flow-through cardiovascular system of vertebrates, insect tissues exchange gases through blind-ended tracheoles, which may involve a more prominent role for diffusive gas exchange. We tested the effect of progressive hypoxia on ventilation and the P O 2 of the metathoracic ganglion (neural site of control of ventilation) using microelectrodes in the American locust, Schistocerca americana . In normal air (21 kPa), P O 2 of the metathoracic ganglion was 12 kPa. The P O 2 of the ganglion dropped as air P O 2 dropped, with ventilatory responses occurring when ganglion P O 2 reached 3 kPa. Unlike vertebrates, insects tolerate relatively high resting tissue P O 2 levels and allow tissue P O 2 to drop during hypoxia, activity and discontinuous gas exchange before activating convective or spiracular gas exchange. Tracheated animals, and possibly pancrustaceans in general, seem likely to generally experience wide spatial and temporal variation in tissue P O 2 compared with vertebrates, with important implications for physiological function and the evolution of oxygen-using proteins.

Incidence of the thermal transition in the range of 45-5°C in chromatophores present in the wings of Schistocerca americana

The variation of the color intensity of the chromatophores present in the wings of Schistocerca americana was analyzed by exposing 31 specimens to thermal transitions within the range of 45 - 5 °C. The adult specimens were collected using a mini-terrarium of dimensions 40x40x30 cm. As a substrate, a layer of soil, stones, and finally a layer of grass were used along with branches of bushes and leaves; hydroponic lettuce, cabbage and the grass were used as food for the specimens. Optical microscopy of the wings of the insects was used for live observation without coverslips or contrasting substances. At 45°C, degradation of color intensity was observed in the chromatophores present in the wings. At 5°C, chromatophores intensify their color to brownish-black. This temperature was the extreme minimum that S. americana could tolerate. We found negative correlation between the temperature and the degree of darkness (R2 = 0.8038). Our results are in accordance with a previously published study in which Phaulacridium vittatum was examined, as the decrease of temperature caused darkening color change in melanin-type chromatophores. The present investigation can be considered as the first initial study of its kind for S. americana, in terms of examining the changes in the color intensity of the chromatophores present in the wings caused by thermal transition under laboratory conditions.