Supercooling Differences in the Eastern Subterranean Termite (Isoptera: Rhinotermitidae)

Abstract

Supercooling points were determined for untreated field-collected and untreated laboratory-maintained Reticulitermes flavipes (Kollar) workers and soldiers. Workers treated with antibiotics or had their hindgut-protozoa removed by exposing them to oxygen under pressure to determine the effects of absence of the hindgut fauna on supercooling. Supercooling points were compared between live and freshly-killed workers to determine whether supercooling in this species might be simply due to the biochemical properties of body fluids. Laboratory-maintained workers were also subjected to desiccation, starvation, or atmospheric pressure to determine their effects on supercooling. Supercooling points were lowest for laboratory workers treated with antibiotics and those that fed on brown paper-toweling for 7 d. Untreated field-collected workers had significantly higher supercooling points than untreated laboratory-maintained workers (−6.06 ± 0.79°C vs −9.29 ± 2.38°C, P < 0.0001). Both untreated field-collected and laboratory soldiers had significantly lower supercooling points than their respective workers (−7.39 ± 2.01°C vs −6.06 ± 0.79°C, P < 0.0001; and −11.60 ± 2.53°C vs −9.29 ± 2.38°C, P< 0.0001, respectively). There was no significant association between termite body mass and supercooling points for both laboratory and field termites (P= 0.0523 and P = 0.6242) or water content of laboratory termites and supercooling points (P = 0.1425). Defaunated workers had significantly lower supercooling points (−10.34 ± 2.38°C) than normally faunated workers (−9.48 ± 1.85°C)(P= 0.0095) suggesting that the symbiotic fauna may have higher supercooling points and act as ice nucleators in the termite hindgut. Starved and desiccated workers had significantly lower supercooling points (−10.38 ± 2.70°C and −10.39 ± 2.38°C, respectively) than their corresponding control groups (−9.87 ± 2.11°C and −9.89 ± 1.94°C; P = 0.0454; P = 0.0234, respectively) and untreated workers (−9.29 ± 2.38°C; P= 0.0021; P= 0.0011) suggesting that some forms of physical stress might lower the supercooling point.

Discovery of an underground chamber to protect kings and queens during winter in temperate termites

“…The other potential cause of caste differences in cold tolerance may be due to different symbiotic microbes. Reticulitermes termites are known to harbour obligate symbiotic microbes in their hindgut 48 – 50 , which reduces the cold tolerance in R. flavipes workers 51 . There is a caste difference in the abundance of gut microbes 52 – 55 , and kings and queens are the sole castes that lack them 52 .…”

Seasonal movement of royal chambers: where are the kings and queens of temperate termites in winter?

“…The other potential cause of caste differences in cold tolerance is symbiotic microbes. Reticulitermes termites are known to harbor obligate symbiotic microbes in their hindgut [48][49][50], which reduces the cold tolerance in R. flavipes workers [51]. There is a caste difference in the abundance of gut microbes [52][53][54][55], and kings and queens are the sole castes that lack them [52].…”

Experimental Warming Reduces Survival, Cold Tolerance, and Gut Prokaryotic Diversity of the Eastern Subterranean Termite, Reticulitermes flavipes (Kollar)

“…Accordingly, lower SCP values in the other two temperature groups may be the result of reduction or shift in gut microbiota that would otherwise act as ice nucleating agents. Cabrera and Kamble (2004) showed antibiotic-treated R. flavipes workers to have the lowest SCP values and suggest this may be the result of removing ice-nucleating microorganisms. The significance of these results remains to be determined but could hint at one possible transition by which freeze intolerant insects, such as termites, may evolve to become freeze tolerant.…”

“…A number of researchers dating back to the 1920s have examined the effect of temperature on termites (Esenther, 1969;Haverty and Nutting, 1974;Sponsler and Appel, 1991;Davis and Kamble, 1994;Cabrera and Kamble, 2001;Hu and Appel, 2004;Hu and Song, 2007;Gautam and Henderson, 2011), as well as on their symbiotic gut protozoa (Cleveland, 1923(Cleveland, , 1924Cook and Smith, 1942;Mannesmann, 1969;Smythe and Williams, 1972;Belitz and Waller, 1998;Cabrera and Kamble, 2004). Cleveland (1924) showed that all gut protozoa were killed after 24-h incubation at 36 • C in Reticulitermes flavipes (Kollar).…”

“…Smythe and Williams (1972) observed no effect on protozoa at 29 • C and report the highest tolerable temperature range for R. flavipes survival to be between 31.5 and 33 • C. Despite this abundance of research relating to the effect of temperature on protozoa, the effect on gut bacteria has been mostly ignored. One exception to this is a study of termite cold tolerance, where Cabrera and Kamble (2004) found the supercooling point (SCP) to be the lowest in R. flavipes workers treated with antibiotics, and hypothesized that symbionts (either protists or bacteria) may be acting as ice nucleators in the termite hindgut.…”