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Physiology of heartbeat reversal in diapausing pupae of the tobacco hornworm, Manduca sexta (Lepidoptera: Sphingidae)

2001; Institute of Entomology; Volume: 98; Issue: 4 Linguagem: Inglês

10.14411/eje.2001.061

1802-8829

K. Sláma, Thomas A. Miller,

Insect and Arachnid Ecology and Behavior

Pulsations o f dorsal vessel were monitored by the noninvasive techniques o f contact thermography on the dorsal cuticle and by strain gauge detection o f abdominal elongation movements.Diapausing pupae exhibited periods o f forward-oriented, or anterograde pulsations (average duration o f each pulsation 5 -8 min, frequency o f individual systolic strokes 10-15 per min) alter nating with somewhat slower, backward-oriented or retrograde cardiac pulsations (average duration o f each pulsation 6-10 min, fre quency o f systolic strokes 7-1 2 per min).The highest rate o f hemolymph flow was associated with the anterograde pulsations.We studied cardiac functions in diapausing pupae because o f the almost complete absence o f extracardiac hemocoelic pulsations, which are much stronger and could interfere with the recordings o f heartbeat in all other developing stages.The movement o f abdomen associated with the heartbeat was extremely small, only some 0.14 to 0.9 pm (i.e. from one 428000th to one 66000th o f the body length) and thus was not practical for routine recordings ofheartbeat.Simultaneous recordings from multiple thermographic sensors revealed the complete absence o f retrograde cardiac pulsations in the head region.There are some indications that the retrograde pulsations were also lacking in the thoracic region o f the aorta.The retrograde peristalsis appeared to be used for circulatory functions in the abdomen alone.By contrast, the anterograde cardiac pulsa tions underwent a profound amplification in the anterior part o f the abdomen, entering thoracic aorta with considerable strength before reaching the final destination in the head region.The amplification o f anterograde peristalsis was manifested by enhanced hemolymph flow towards the head associated with a two-fold increase in frequency o f anterograde heartbeat before reaching the head region.The sensors distributed along the dorsal vessel revealed that the rate o f the backward-oriented, retrograde cardiac flow o f the hemolymph was also location specific.The rate o f flow was lowest at the front o f the abdomen, medium in the middle and highest close to the end o f the abdomen.The finding o f lowest hemolymph circulation at the beginning o f the cardiac peristaltic waves suggested that the physiological "raison d ' être" for heartbeat reversal was a need for differential enhancement o f hemolymph flow towards the extremities o f the immobile pupal body.The switchovers from the retrograde to anterograde cardiac pulsations were usually immediate, while the reciprocal, antero-to retro-switchovers were mostly associated with a brief cardiac arrest.Increasing temperature gradients (in 5°C steps) progressively diminished duration o f both reciprocal heartbeat periods.The ampli tudes o f the cardiac systolic strokes also decreased with increasing temperature while the frequencies were substantially elevated.