Results of the regression analysis using GLM between abdominal pumping and three explanatory variables: T_abdomen, T_thorax and T_ambient.

<p>SE: Standard Error.</p><p>W: Wald Statistic.</p

Flight thermoregulatory behaviour of <i>Scarabaeus sacer</i>.

<p>(A) Individual variation of T_thorax (in red) and T_abdomen (in blue). Environmental temperature (T_ambient) (in green) was maintained during each experiment. (B) Comparison of slopes of T_thorax, T_abdomen and T_ambient variation during flight (<i>N</i> = 27; Kruskal-Wallis test with the Conover-Inman post hoc test for pairwise comparisons, α<0.05); black dots indicate the median values; temperatures with the same letter did not differ significantly from each other. (C) Thermal image of <i>S. sacer</i> during flight showing the strong contrast between T_thorax and T_abdomen.</p

Heat transfer between the thorax and the abdomen and abdominal pumping behaviour.

<p>Differences between (A) T_thorax and T_abdomen during flight for <i>Scarabaeus sacer</i> (in blue) and <i>S. cicatricosus</i> (in red), and (B) frequency of abdominal pumping. (<i>Scarabaeus cicatricosus</i>, N = 27; and <i>S. sacer</i>, N = 24; U-Mann-Whitney, α<0.05); Boxes labelled with the different letters differ significantly from each other. Black dots indicate the median values.</p

Distribution and development of abdominal air sacs.

<p>(A) <i>Scarabaeus sacer</i> and (B) <i>S. cicatricosus</i>. Abdominal air sacs were coloured in blue. Red lines indicate the separation between the metathorax and the abdomen. Abbreviations: pr: prothorax; ms: mesothorax; mt: metathorax.</p

Flight postures of <i>Scarabaeus</i> species.

<p>(A) <i>S. sacer</i> and (B) <i>S. cicatricosus</i>. Arrows indicate regions in which body temperatures were analysed (T_thorax and T_abdomen) and the abdominal movement to generate heat flow (abdominal pumping). The flight posture adopted by <i>S. cicatricosus</i>, with the posterior legs extended from the body, increase turbulence and convective cooling.</p

Flight thermoregulatory behaviour of <i>Scarabaeus cicatricosus</i>.

<p>(A) Individual variation of T_thorax (in red) and T_abdomen (in blue). Environmental temperature (T_ambient) (in green) was maintained during each experiment. (B) Comparison of the slopes of T_thorax, T_abdomen and T_ambient variation during flight (<i>N</i> = 27; Kruskal-Wallis test with the Conover-Inman post hoc test for pairwise comparisons, α<0.05); black dots indicate the median values; temperatures with the same letter did not differ significantly from each other. (C) Thermal image of <i>S. cicatricosus</i> during flight, showing lower contrast between T_thorax and T_abdomen, relative to <i>S. sacer</i>.</p

Tracheal and air sac volume (V_air) of <i>Scarabaeus sacer</i> and <i>S. cicatricosus</i>.

<p>Total body volume (V_T) was measured using the function proposed by Radtke and Williamson (2005) based on total body mass.</p

The thermal hysteresis activity (THA) of <i>Thorectes lusitanicus</i>.

<p>The differential scanning calorimetry curves of refreezing (rate of 0.1°C/min) of (A) partially melted hemolymph of <i>Thorectes lusitanicus</i>, and (B) partially melted bovine serum albumin (BSA; as control). No thermal hysteresis effect was observed in the curves with a lower heat flow (temperature ranges from –5 to –2°C), whereas THA was observed in temperature ranges oscillating from −2 to −1°C (see curves marked by an arrow). Frozen BSA was heated to partially melt at the different hold temperatures and then cooled to recrystallize. No thermal hysteresis effect was observed in this case.</p

<i>Thorectes lusitanicus</i> eating cork-oak acorns.

<p>During their reproductive period, <i>T. lusitanicus</i> bury and feed on acorns of <i>Quercus</i>, with important ecological implications.</p

The supercooling process in <i>Thorectes lusitanicus</i>.

<p>(A) The prefreezing state when the supercooling point was measured; (B) the exothermic crystallization of the hemolymph contained in the thorax (see black curve below); and (C) the crystallization of the hemolymph contained in the abdomen (see grey curve below) and the rest of the body. The red marks indicate the instant that correspond with each thermography and temperature curves (the thoracic temperature in the black curve, and the abdominal temperature in the grey line).</p