Dr James Gilbert
Speaker: Dr James Gilbert, Lecturer in Zoology, University of Hull
Escaping a nutritional trap: how do bees achieve a balanced diet in a changing landscape?
Ecosystem stability and global food security depend upon healthy populations of bees, our foremost pollinators, to the tune of many hundreds of billions of dollars annually. However, human activity is changing animal habitats, and bee populations are rapidly declining. Partly this is due to changing nutritional landscapes: modern intensive farming means that bees face fractured landscapes where floral resources exist as oases within green deserts.
Solitary bees face a particular problem: adults provide all larval nutrition before eggs are even laid, giving no opportunity for parent-offspring feedback. Solitary bees account for over 80% of bee species in the UK; collectively they perform just as much pollination as social bees, but are sadly undergoing similarly catastrophic declines. Unfortunately we know little of the nutritional rules governing how offspring are fed, or how they process variable diets, so it is hard to predict the effects of landscape change. Understanding how parental and larval behaviour combine to ensure a balanced diet for solitary bee larvae is of paramount importance.
Using Nutritional Geometry, a method for establishing how animals balance their diets, we investigated the effect of manipulating larval nutrition (i.e. protein:carbohydrate ratio) in the solitary bee Osmia bicornis. The optimal larval diet for growth was not high-protein as often assumed, but high carbohydrate. Larvae did balance their diet to a degree, by eating different amounts: they pupated after eating a fixed amount of carbohydrate (C), regardless of protein (P). To an extent larvae can therefore buffer the effects of different nutrition brought by parents; this buffering may carry later fitness costs from e.g. processing excess protein – costs which we are assessing. The critical question to address now is whether parents can regulate nutrition in the pollen they deliver to larvae. If they cannot, human-induced landscape change may represent a “nutritional trap” for bees.