CO2 emission was always cyclic, sometimes on the verge of continuous respiration ( Fig. 2D). Fig. 3 shows the duration Bosutinib mouse of cycles, and of open, closed and flutter phases (where present)
as a function of experimental ambient temperature. The course of all components of DGC follows exponential curves. With rising ambient temperature the open phase decreased slower in duration than the flutter and the closed phases at low to medium Ta. Closed phases were only detectable up to Ta ⩽ 26.3 °C. Fig. 4 shows the duration of the respiration cycles and cycle phases in dependence on resting metabolic rate (RMR). However, the courses of data points indicate a higher order of dependence than a simple exponential decrease. Good linear regression in a double logarithmic graph (inset) strengthens this finding. With rising Ta the cycle frequency (f) increased ( Fig. 1, Fig. 2) following an exponential curve ( Fig. 5). Data fitted best with an exponential function of the type f = y0 + A1Ta/t1, with y0 = 0.12716, A1 = 2.18932, t1 = 11.2997 (R2 = 0.51337, P < 0.0001, N = 37). Respiration cycle frequency was 2.55 ± 3.58 mHz at 4.7 °C, 9.33 ± 13.2 mHz at 9.8 °C, 13.0 ± 24.66 mHz at 19.8 °C, 39.92 ± 25.35 mHz at 31.1 °C selleck inhibitor and 73.97 ± 28.85 mHz at 39.7 °C. Data at 42.4 °C were not included in the fitting curve because single CO2 “peaks”
merged to “plateaus”. Comparison of variances of cycle frequency at the same Ta revealed significant differences between individuals (P < 0.05, N = 2–10, ANOVA). Over the entire temperature range these tests indicated significant differences in 69.5% of comparisons. An ANOVA with the means per animal and Ta (of both species) indicated a slight negative temperature dependence of CO2 release per cycle (P < 0.05; R2 = 0.06685, N = 62, F = 5.36977, DF = 60). The correlation was more pronounced in an analysis with all cycles of all animals, which includes the intra-individual variation ( Fig. 6). CO2 release per cycle as estimated from
the regression line changed from 39.51 μl g−1 cycle−1 at 2.9 °C to 25.4 μl g−1 cycle−1 at 42.4 °C, Single individuals compared at the same temperature showed significant differences Selleck Y 27632 in the variances of mean CO2 emission per cycle and animal (P < 0.05, N = 2–8, ANOVA; see large circles in Fig. 6). Over the entire temperature range these within-Ta comparisons showed inter-individual differences in 56.8% of cases. This implies that the other 43.2% of cases indicated no difference. However, measurements where data of only one individual could be evaluated indicate also considerable intra-individual variance ( Fig. 6, Ta = 22.5 and 42.4 °C). In direct comparison, wasps differed from honeybees significantly in slope and intercept (P < 0.0001 in both cases, ANOVA; see Fig. 6). Cycle frequency (f) increased linearly with the mass specific RMR ( Fig. 7, f (mHz) = −2.54647 + 0.65394 * RMR CO2 (μl g−1 min−1), R2 = 0.976, P < 0.0001, N = 37, means per animal).