Sharoni Shafir | Search bioRxiv

bioRxiv2014

Amino acid and carbohydrate tradeoffs by honey bee nectar foragers and their implications for plant-pollinator interactions

Honey bees are important pollinators, requiring floral pollen and nectar for nutrition. Nectar is rich in sugars, but contains additional nutrients, including amino acids (AAs). We tested the preferences of free-flying foragers between 20 AAs at 0.1% w/w in sucrose solutions in an artificial meadow. We found consistent preferences amongst AAs, with essential AAs preferred over nonessential AAs. The preference of foragers correlated negatively with AA induced deviations in pH values, as compared to the control. Next, we quantified tradeoffs between attractive and deterrent AAs at the expense of carbohydrates in nectar. Bees were attracted by phenylalanine, willing to give up 84 units sucrose for 1 unit AA. They were deterred by glycine, and adding 100 or more units of sucrose could resolve to offset 1 unit AA. In addition, we tested physiological effects of AA nutrition on forager homing performance. In a no-choice context, caged bees showed indifference to 0.1% proline, leucine, glycine or phenylanaline in sucrose solutions. Furthermore, flight tests gave no indication that AA nutrition affected flight capacity directly. In contrast, low carbohydrate nutrition reduced the performance of bees, with important methodological implications for homing studies that evaluate the effect of substances that may affect imbibition of sugar solution. In conclusion, low AA concentrations in nectar relative to pollen suggest a limited role in bee nutrition. Most of the 20 AAs evoked a neutral to a mild deterrent response in bees, thus it seems unlikely that bees respond to AAs in nectar as a cue to assess nutritional quality. Nonetheless, free choice behavior of foraging bees is influenced, for instance by phenylalanine and glycine. Thus, AAs in nectar may affect plant-pollinator interactions and thereby exhibit a selective pressure on the flora in the honey bee habitat.\n\nO_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=83 SRC=\"FIGDIR/small/008516_ufig1.gif\" ALT=\"Figure 1\">\nView larger version (31K):\norg.highwire.dtl.DTLVardef@8fde04org.highwire.dtl.DTLVardef@138fdd3org.highwire.dtl.DTLVardef@a05775org.highwire.dtl.DTLVardef@cde793_HPS_FORMAT_FIGEXP M_FIG C_FIG HIGHLIGHTS- Amino acids in artificial nectar elicit preferences from honey bee foragers\n- Amino acid identity, pH, and essentiality explain preferences of bees\n- A honey bee forager is willing to pay a premium of carbohydrates for amino acids\n- Carbohydrate nutritional state affects flight performance of foraging bees

Animal Behavior and Cognition↗

bioRxiv2014

Nutritional aspects of honey bee-collected pollen and constraints on colony development in the eastern Mediterranean

*Graphical Abstract (for review)\n\nO_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=78 SRC=\"FIGDIR/small/008524_ufig1.gif\" ALT=\"Figure 1\">\nView larger version (25K):\norg.highwire.dtl.DTLVardef@5beae8org.highwire.dtl.DTLVardef@9b33e3org.highwire.dtl.DTLVardef@16ba880org.highwire.dtl.DTLVardef@103a08b_HPS_FORMAT_FIGEXP M_FIG C_FIG *Highlights (for review)O_LIHoney bee colonies in Israel collect a mean 7 kg protein and 0.7 kg fat per year\nC_LIO_LIAt maximal colony development, honey bee queens lay up to 3,300 eggs per day\nC_LIO_LIAmount and content of collected pollen differ between sites and seasons\nC_LIO_LIPollen linoleic acid and protein levels best describe bee production cost\nC_LIO_LIColonies seem limited first by climate, then protein and finally specific nutrients\nC_LI\n\nABSTRACTPollen is the main protein and lipid source for honey bees (Apis mellifera), and nutritionally impoverished landscapes pose a threat to colony development. To determine colony nutritional demands, we analyzed a yearly cycle of bee-collected pollen from colonies in the field and compared it to colony worker production and honey bee body composition, for the first time in social insects. We monitored monthly bee production in ten colonies at each of seven sites throughout Israel, and trapped pollen bi-monthly in five additional colonies at each of four of these sites. Pollen mixtures from each sampling date and site were analyzed for weight, total protein, total fatty acids (FAs), and FA composition. Compared to more temperate climates, the eastern Mediterranean allows a relatively high yearly colony growth of ca. 300,000 to 400,000 bees. Colonies at higher elevation above sea level showed lower growth rates. Queen egg-laying rate did not seem to limit growth, as peaks in capped brood areas showed that queens lay a prolific 2,000 eggs a day on average, with up to 3,300 eggs in individual cases. Pollen uptake varied significantly among sites and seasons, with an overall annual mean total 16.8 kg per colony, containing 7.14 kg protein and 677 g fat. Overall mean pollen protein content was high (39.8%), and mean total FA content was 3.8%. Production cost, as expressed by the amount of nutrient used per bee, was least variable for linoleic acid and protein, suggesting these as the best descriptive variables for total number of bees produced. Linolenic acid levels in pollen during the autumn were relatively low, and supplementing colonies with this essential FA may mitigate potential nutritional deficiency. The essentiality of linoleic and linolenic acids was consistent with these FAs tendency to be present at higher levels in collected pollen than in the expected nutrients in bee bodies, demonstrating a well-developed adjustment between pollinator nutritional demands and the nutritional value of food offered by pollinated plants.

Ecology↗