The Influence of Body Size on Metabolic Rates, Scaling, Telomere Dynamics, and Metamorphosis in Megachilid Bees
Grula, Courtney Corinne
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Body size is related to many aspects of a bee’s life history including foraging distance and pollination efficiency. Megachile rotundata, and Osmia lignaria are agriculturally important, solitary pollinators. Adult body size in solitary bees is variable because it is determined by the quantity of food available to the developing larva. The goal of this dissertation was to determine the effect of body size on metabolic rates, scaling, telomere dynamics, and entry into metamorphosis. Body size was manipulated under laboratory conditions by manipulating the amount of food provided during the final larval stage. First, I tested the effect of body size on allometry and amount of energy produced, measured indirectly through CO2 emission. The power required during flight was predicted using biomechanical formulas. I found larger bees had higher absolute metabolic rates at rest and during flight. Smaller bees had higher mass-specific metabolic rates at rest, but not during flight. As bees increased in size, their thorax and abdomens became disproportionately larger, while wings became disproportionately smaller. Smaller bees had more power available during flight as demonstrated by flight biomechanical formulas. Next, I measured telomere length in M. rotundata and O. lignaria throughout development. I also measured telomere length across a variety of body sizes, and life stages in both bee species, and found that body size does not affect telomere length. I found that telomere length increases in later life stages in both bee species. Lastly, I determined the cue for metamorphosis in M. rotundata by determining the critical weight. Entry into metamorphosis involves the insect’s ability to monitor its size. I found the cue for metamorphosis in M. rotundata is a critical weight which is influenced by nutritional condition. This was confirmed by declines in Juvenile Hormone titers, and upregulation of genes involved in metamorphic molts. This study found smaller-sized bees are not always at a disadvantage. Smaller bees had increased flight performance based on flight biomechanical formulas, did not show differences in telomere length based on body size, and enter metamorphosis at small sizes. Advantages to small body size may be a response to declines in resource availability.