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First published online July 26, 2004
Journal of Experimental Biology 207, 2925-2933 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.01121

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Thermal stability and muscle efficiency in hovering orchid bees (Apidae: Euglossini)

Brendan J. Borrell^*, and Matthew J. Medeiros^*

Section of Integrative Biology, University of Texas, Austin, TX 78712, USA

View larger version (20K): [in a new window]   Fig. 1. (A) Filtered optical tachometer signal of three wingbeats from a Euglossa imperialis hovering over a chemical bait. (B) Histogram of wingbeat frequency determinations from the complete record sampled in A.

View larger version (17K): [in a new window]   Fig. 2. Thorax (Tth), head (Th) and abdomen (Tab) temperatures plotted against air temperature (Ta) in hovering Euglossa imperialis. Least-squares regressions: Tth=0.574Ta+22.9, r2=0.596, P<0.0001; Th=0.418Ta+22.6, r2=0.497, P<0.0001; Tab=0.675Ta+13.5, r2=0.745, P<0.0001.

View larger version (15K): [in a new window]   Fig. 3. Head temperature excess ratio (Rh) and abdominal temperature excess ratio (Rab) decline with air temperature (Ta) in hovering Euglossa imperialis. Least-squares regressions: Rab=-0.016Ta+0.846, r2=0.16, P=0.0213; Rh=-0.032Ta+1.475, r2=0.395, P<0.0001.

View larger version (19K): [in a new window]   Fig. 4. Wingbeat frequency (WBF) declines at higher operative temperatures (Top) in hovering Euglossa imperialis (13 experimental bees shown as filled circles; 139 additional bees from Costa Rica and Panama shown as open circles). Least-squares regression: WBF=-0.115Top2+5.00Top+127.

View larger version (15K): [in a new window]   Fig. 5. Thoracic temperature excess increases linearly with wingbeat frequency (WBF) in hovering Euglossa imperialis. Least-squares regression: Texcess=0.128WBF-11.6, r2=0.240, P=0.0038.

View larger version (18K): [in a new window]   Fig. 6. Metabolic power (P*met), non-evaporative heat loss (P*heat) and mechanical power output (P*zero and P*per) plotted against air temperature (Ta) in hovering Euglossa imperialis. The equation for metabolic rate is: P*met=-30.6Ta+1780. The equation for heat loss is: P*heat=-29.9Ta+1490.

View larger version (17K): [in a new window]   Fig. 7. Muscle efficiency () increases with air temperature (Ta) in hovering Euglossa imperialis. Data points are mean values for each individual from respirometry and heat loss experiments. The equation for the least-squares regression line assuming perfect elastic energy storage is =0.006Ta+0.009 and for zero elastic energy storage is =0.007Ta+0.027.

View larger version (23K): [in a new window]   Fig. 8. Wingbeat frequency declines linearly with operative temperature in four species of orchid bees hovering in the field.

View larger version (17K): [in a new window]   Fig. 9. Wingbeat frequency (WBF) declines at higher operative temperatures (Top) in hovering Euglossa purpurea. Least-squares regression: WBF=-0.163Top2+8.09Top+125.