Higher developmental temperature increases queen production and decreases worker body size in the bumblebee Bombus terrestris

Abstract

Climate change and increasing average temperatures are now affecting most ecosystems. Social insects such as bumblebees are especially impacted because these changes create spatial, temporal and morphological mismatches that could impede their ability to find food resources and mate. However, few studies have assessed how the colony and life cycle are affected when temperatures rise above optimal rearing temperature. It has become imperative to understand how heat stress affects the life history traits of insect pollinators as well as how changes in life history interact with other traits like morphology. For example, a decrease in the number of foraging workers could be balanced by producing larger workers, able to forage at longer distances and gather more resources. Here, we investigated the impact of temperature on colony production and body size in the bumblebee Bombus terrestris. Colonies were exposed to two temperatures: 25 °C, which is around the optimal temperature for larval development and 33 °C, which is slightly above the set-point that is considered stressful for bumblebees. Although the production of males and workers wasn’t significantly affected by these different temperatures, queen production and reproductive investment were much higher for colonies placed in 33 °C than in 25 °C. We also found that, in agreement with the temperature-size rule, workers were significantly smaller in the higher temperature. The decrease in worker body size could affect resource collection and pollination if their foraging distance and the quantity of food they are taking back to the colony decreases. While in our controlled conditions the bumblebees were fed ad libitum, the decrease of resource collection in field conditions could prevent colonies from producing as many queens as in our study. Together with the decrease of worker body size, our results suggest that elevated temperatures could ultimately have a negative impact on bumblebee colony fitness. Indeed, smaller workers are known to have weaker flight performance which could affect foraging performance and consequently colony development.

Short‐term exposure to heatwave‐like temperatures affects learning and memory in bumblebees

“…The impact of high ambient temperature could even be accentuated by potential effects of stressful temperatures experienced during development. While it is already known that elevated developmental temperature can impact bee morphology (Gérard et al, 2018; Guiraud et al, 2021), its effects on cognition remain unclear. In honeybees, exposure to temperatures just outside the optimum for larval development can affect the learning and memory capacity of adults (Jones et al, 2005; Tautz et al, 2003), suggesting that exposure to temperatures that cause heat‐stress in honeybee colonies may also have quite detrimental effects on the cognition of adults.…”

Morphological Variation in Bumblebees (Bombus terrestris) (Hymenoptera:Apidae) After Three Decades of an Island Invasion

“…Because body size varies within colonies (up to 10-fold) and across locations, it is considered to be a plastic trait ( Chole et al 2019 ) that is responsive to different environmental conditions ( Theodorou et al 2020 ). Body size in social bees is also affected by variation in growth conditions during ontogeny ( Schmid-Hempel et al 2007 , Rotheray et al 2017 , Gerard et al 2018 , Malfi et al 2019 , Guiraud et al 2021 ). Body size may indirectly affect competition between invasive and native bees if it is related to key fitness components, as suggested by Inoue (2011) who observed selection for larger body size in invasive Bombus terrestris (L. 1758) (Hymenoptera: Apidea) 20 yr after its invasion to Japan.…”

Elevated developmental temperatures impact the size and allometry of morphological traits of the bumblebeeBombus terrestris

“…Still, the TSR has regularly been observed among bees (e.g. Radmacher and Strohm, 2011 ; Guiraud et al, 2021 ). Part of the relationship between developmental temperature and body size could be linked to juvenile hormone ( Radmacher and Strohm, 2010 ; 2011 ).…”