Termites have wider thermal limits to cope with environmental conditions in savannas

Abstract

The most diverse and abundant family of termites, the Termitidae, evolved in African tropical forests. They have since colonised grassy biomes such as savannas. These open environments have more extreme conditions than tropical forests, notably wider extremes of temperature and lower precipitation levels and greater temporal fluctuations (of both annual and diurnal variation). These conditions are challenging for soft‐bodied ectotherms, such as termites, to survive in, let alone become as ecologically dominant as termites have. Here, we quantified termite thermal limits to test the hypothesis that these physiological limits are wider in savanna termite species to facilitate their existence in savanna environments. We sampled termites directly from mound structures, across an environmental gradient in Ghana, ranging from wet tropical forest through to savanna. At each location, we quantified both the Critical Thermal Maxima (CTmax) and the Critical Thermal Minima (CTmin) of all the most abundant mound‐building Termitidae species in the study areas. We modelled the thermal limits in two separate mixed‐effects models against canopy cover at the mound, temperature and rainfall, as fixed effects, with sampling location as a random intercept. For both CTmax and CTmin, savanna species had significantly more extreme thermal limits than forest species. Between and within environments, areas with higher amounts of canopy cover were significantly associated with lower CTmax values of the termite colonies. CTmin was significantly positively correlated with rainfall. Temperature was retained in both models; however, it did not have a significant relationship in either. Sampling location explained a large proportion of the residual variation, suggesting there are other environmental factors that could influence termite thermal limits. Our results suggest that savanna termite species have wider thermal limits than forest species. These physiological differences, in conjunction with other behavioural adaptations, are likely to have enabled termites to cope with the more extreme environmental conditions found in savanna environments and facilitated their expansion into open tropical environments.

Sublethal doses of insecticide reduce thermal tolerance of a stingless bee and are not avoided in a resource choice test

“…We ramped bees from an acclimation temperature of 26.2 (± 0.2 SD)°C by increments of 0.5°C every 2 min until the CT max was reached for all individuals. We identified CT max as the temperature at which an individual became unresponsive to a stimulus [81,82], which was in this case a single flick of the vial (vial was removed from water bath to administer stimulus and replaced if bee responded [81,83,84]). During the temperature ramp, bees exhibited typical indicators of heat stress, initially including wing fluttering, or extending and holding still a single or both wings [82].…”

Predicting the Habitat Suitability and Distribution of Two Species of Mound-Building Termites in Nigeria Using Bioclimatic and Vegetation Variables

“…Species within the genus Macrotermes, which are mound builders and fungus growers, are mostly found in tropical and subtropical regions of the world [9,10]. The presence of termites in an environment means the habitat is suitable for the termites to inhabit, with temperature having a key role in defining the type of species found in the habitat [11][12][13][14][15]. Termites are no exception to the effects caused by the changing climate as they have to adopt different means of surviving…”