Hypoxia and Ventilation of the Marsupium in the Amphipod, Gammarus Pseudolimnaeus Bousfield

Date of Graduation

Fall 1998


Master of Science in Biology



Committee Chair

M. Chris Barnhart


Amphipod crustaceans brood their eggs and young within a marsupium formed by the oostegites of the thoracic legs. I investigated the processes that deliver oxygen and food into the marsupium of Gammarus pseudolimnaeus, a freshwater amphipod common in eastern North America. Dissolved oxygen (DO) in the marsupium measured directly using a micro-oxygen electrode that was inserted between the oostegites. DO in the marsupium of gravid females, in air-saturated water, averaged approximately 30% of air saturation. Marsupium DO varied with position. DO was highest at the ventral margin of the marsupium and was lowest near the ventral body wall of the female. DO was lowest in females brooding late stage embryos, and increased after hatching. DO in the marsupium was closely associated with the female's pleopod movements, indicating that most oxygen enters the marsupium by convection created by maternal ventilatory movements. When the pleopods were manually restrained, and also during natural pauses in ventilation, marsupium DO fell near zero. Acute changes in ambient DO were accompanaied by compensatory change in the rate of pleopod movements. However, these changes were not sustained over 5 hours, and marsupium DO was not well compensated. Females exposed to prolonged hypoxia did not induce brood release from the marsupium. Newly released juveniles were prone to become trapped hydrophobically on the water surface. Brooding of hatchlings may protect hatchlings from this hazard, although hatchlings removed prematurely from the marsupium were not more likely to become trapped than those released normally. The probability of trapping decreased with increasing size of the juveniles. Juveniles were observed to feed within the marsupium. Female ventilatory movements cause suspended food particles to enter the marsupium. Fragmentation of food by the female allows access to foods not otherwise available.

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