Trade‐offs in the evolution of bumblebee colony and body size: a comparative analysis

Abstract

Trade‐offs between life‐history traits – such as fecundity and survival – have been demonstrated in several studies. In eusocial insects, the number of organisms and their body sizes can affect the fitness of the colony. Large‐than‐average body sizes as well as more individuals can improve a colony's thermoregulation, foraging efficiency, and fecundity. However, in bumblebees, large colonies and large body sizes depend largely on high temperatures and a large amount of food resources. Bumblebee taxa can be found in temperate and tropical regions of the world and differ markedly in their colony sizes and body sizes. Variation in colony size and body size may be explained by the costs and benefits associated with the evolutionary history of each species in a particular environment. In this study, we explored the effect of temperature and precipitation (the latter was used as an indirect indicator of food availability) on the colony and body size of twenty‐one bumblebee taxa. A comparative analysis controlling for phylogenetic effects as well as for the body size of queens, workers, and males in bumblebee taxa from temperate and tropical regions indicated that both temperature and precipitation affect colony and body size. We found a negative association between colony size and the rainiest trimester, and a positive association between the colony size and the warmest month of the year. In addition, male bumblebees tend to evolve larger body sizes in places where the rain occurs mostly in the summer and the overall temperature is warmer. Moreover, we found a negative relationship between colony size and body sizes of queens, workers, and males, suggesting potential trade‐offs in the evolution of bumblebee colony and body size.

The converse to Bergmann's rule in bumblebees, a phylogenetic approach

“…), the results do not suggest a positive effect of climatic temperatures on body size, even though we previously found a positive effect of precipitation during the warmest trimester of the year on the body size of males (for a smaller number of eusocial species) (Cueva del Castillo et al. ).…”

“…; Cueva del Castillo and Fairbairn ; Cueva del Castillo et al. ), but we also incorporate unpublished measurements for twenty species, including 12 cuckoo bumblebees. In these cases, measurements were taken considering the methods reported by Cueva del Castillo & Fairbairn (Cueva del Castillo and Fairbairn ).…”

“…Similarly, as moisture affects flowering (Rathcke and Lacey ), we used precipitation parameters as indicators of food availability, as in other comparative studies (Yom‐Tov and Geffen ; Branson ; Cueva del Castillo et al. ). We used Google Earth 7.1.5 (Google Inc ) to obtain the geographic coordinates and BioClim (Hijmans et al.…”

“…Nonetheless, in eusocial species, the body size of bumblebees is constrained by the size of the colonies (Cueva del Castillo et al. ). Body size could be related to a higher extent to the size of food rewards to be harvested, than to the energetic advantages of thermoregulation (Heinrich ).…”

Intraspecific variation in body size of bumblebee workers influences anti‐predator behaviour

“…Within a population, morphological variation of bumblebee workers is, primarily, the result of indirect selection pressures on colony success (Linksvayer & Wade, ). In this way, bumblebee workers' body size can be positively associated with the nutritional level of the colony (Cartar, ) and/or negatively correlated with colony population size (Couvillon, Jandt, Duong, & Dornhaus, ; Cueva del Castillo, Sanabria‐Urbán, & Serrano‐Meneses, ), and can also be affected by environmental conditions such as temperature (Kelemen & Dornhaus, ).…”