Impact of intraspecific variation on measurements of thermal tolerance in bumble bees

Abstract

Climate change is an important driver of bee decline despite the fact that many species might respond to climate change differently. One method to predict how a species will respond to climate change is to identify its thermal tolerance limits. However, differences in thermal tolerance might also occur among distant populations of the same species based on their local environment or even among castes of social insects. Here, we investigated intraspecific differences in thermal tolerance among subspecies of the large earth bumble bee, Bombus terrestris (Apidae). We determined the critical thermal minima and maxima (CT min and CT max , respectively) of workers and queens from three lab-reared B. terrestris subspecies (B. t. terrestris, B. t. audax, and B. t. canariensis) which originated from different thermal environments. Our results showed that caste has an influence on critical thermal minima, with queens being most cold-tolerant, but the values of critical thermal maxima were not correlated to caste or size. The thermal tolerance of workers did not differ among the subspecies. Although heat tolerance was similar in queens, B. t. canariensis queens (originating from the warmest environments) were the least cold tolerant. Overall, we showed that B. terrestris may be generally robust against climate warming, but that particular subspecies and/or populations may be more vulnerable to extreme temperature variability. Future research should focus on responses of B. terrestris populations to short, extreme thermal events.

Effects of Heat Stress on Mating Behavior and Colony Development in Bombus terrestris (Hymenoptera: Apidae)

“…Different threats have been identified to explain the global decline of bumblebees. For several years, many studies have explored effects of microbiota, diet, temperature, and pesticide exposure on bumblebee's health in lab conditions (Gill and Raine, 2014;Vanderplanck et al, 2019;Barraud et al, 2020;Rothman et al, 2020;Maebe et al, 2021a;Oyen et al, 2021). However, most of these studies used commercially available bumblebee species (i.e., Bombus impatiens in North America and B. terrestris in Europe, and Bombus hypocrita in Asia) which are known to be tolerant and resistant to environmental changes (Oyen and Dillon, 2018;Maebe et al, 2021b;Martinet et al, 2021a).…”

Bumblebee resilience to climate change, through plastic and adaptive responses

“…These objective measures are helpful in determining the physiological vulnerability of a species to climate change and to predict species responses to thermal stress (Burdine & McCluney, 2019; Deutsch et al, 2008; Hamblin et al, 2017; Kellermann et al, 2012). However, it seems that thermal sensitivity in bumblebees is species‐specific (Hamblin et al, 2017; Martinet, Dellicour et al, 2021; Martinet, Zambra et al, 2021; Oyen et al, 2016; Zambra et al, 2020), and even intraspecific variation between subspecies and castes has been reported (Maebe et al, 2020). Furthermore, Penick et al (2016) note that the negative effects of temperature extremes can be observed before the limits of CT MIN and CT MAX are reached while selection for thermal tolerance strongly depends on rare but extreme thermal events.…”

“…As with most insects, cold temperatures in bumblebees induce a typical sequence that starts with slowed behavioural responses and impaired coordination before a burst of muscle activity, followed by total paralysis in a chill coma (e.g. Maebe et al, 2020; Oyen & Dillon, 2018). Although the mechanisms for this response have not been investigated in bumblebees, they are likely to be very similar to those described in other insects.…”

“…Leading edge range shifts, depending on dispersal and migration patterns, may be accompanied by founder effects, bottlenecking the ability of future populations to adapt further (Hill et al, 2011). Although genetic population structure occurs among European bumblebee populations (Ghisbain et al, 2021; Lecocq et al, 2017; Maebe et al, 2020), species that have wide distributions are less vulnerable to climate change, as individual populations are exposed to different climatic parameters, and thus overall the species will have genes/variants appropriate to diverse environmental conditions for selective pressure to act upon (Bonebrake & Deutsch, 2012; Kingsolver & Buckley, 2017). Recent research associated the intraspecific heat tolerance among bumblebees with species’ diversity in habitat occupation (Martinet, Dellicour et al, 2021).…”

The Holobiont as a Key to the Adaptation and Conservation of Wild Bees in the Anthropocene

“…Both holobiont partners (i.e., bees and microbiome) contribute to its plasticity: the microbiome is primarily involved in processing food, toxins and promoting immunity, while the bee host contributes to thermal tolerance and mobility. Some bee species seem to be able to face environmental changes through plasticity in their thermoregulation (e.g., Martinet et al, 2021a,b), thermal tolerance (Maebe et al, 2021a), phenology (Duchenne et al, 2020;Gérard et al, 2020a), size (Gérard et al, 2020b(Gérard et al, , 2021, nesting behavior (Ghisbain et al, 2021) or diet (Scheper et al, 2014), which might partly explain their contrasting population trends (reviewed by Maebe et al, 2021b).…”