Poor nutrition and landscape changes are regularly cited as key factors causing the decline of wild and managed bee populations. However, what constitutes ‘poor nutrition’ for bees currently is inadequately defined. Bees collect and eat pollen: it is their only solid food source and it provides a broad suite of required macro- and micronutrients. Bees are also generalist foragers and thus the different pollen types they collect and eat can be highly nutritionally variable. Therefore, characterizing the multidimensional nutrient content of different pollen types is needed to fully understand pollen as a nutritional resource. Unfortunately, the use of different analytical approaches to assess pollen nutrient content has complicated between-studies comparisons and blurred our understanding of pollen nutrient content. In the current study, we start by reviewing the common methods used to estimate protein and lipids found in pollen. Next, using monofloral
Brassica
and
Rosa
pollen, we experimentally reveal biases in results using these methods. Finally, we use our collective data to propose a unifying approach for analysing pollen nutrient content. This will help researchers better study and understand the nutritional ecology—including foraging behaviour, nutrient regulation and health—of bees and other pollen feeders.
This article is part of the theme issue ‘Natural processes influencing pollinator health: from chemistry to landscapes’.
International audienceMany species show a transient group life, and dispersal often coincides with the onset of agonistic behaviors. Changes in the nature of interactions among conspecifics can rely on a variation in the production of communication cues and/or on a switch in the processing of social information. The relative contribution of each process on the initiation of aggression still remains to be investigated. Spiders constitute relevant models to address this issue since all solitary species undergo a transient gregarious phase prior dispersal. In this study, we developed a combination of behavioral and physiological assays to examine the mechanisms accompanying the onset of agonistic interactions in spiderlings of the solitary species Agelena labyrinthica. Juveniles of different developmental stages were supplied with diets differing in prey availability. We showed that unfed spiderlings never molted, retained their cuticular lipid signature, and did not behave aggressively. This contrasted with fed individuals that molted, changed their cuticular profiles, and displayed agonistic interactions and cannibalism. We demonstrated that depletion in lipid stores was not sufficient to elicit aggression or cannibalism. Our analysis also revealed that major shifts in cuticular profiles only occurred after the first molt outside the cocoon. The lack of agonistic interactions in unfed spiderlings suggests an absence of behavioral plasticity in response to food shortage at the earliest developmental stages. We propose that the initiation of aggression relies more on a shift in the production of cuticular cues accompanying molting rather than on changes in information processing depending on the physiological state of individuals
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