ABSTRACT Animal size affects the energetics of locomotion. Using female caste dimorphism in bumblebees, we assessed how body mass impacts morphological and physiological traits linked with flight. The allometric relationships obtained for wing surface area, wingbeat frequency, and flight and resting metabolic rates of workers could predict the trait values of queens that were more than fourfold larger. Flight success of queens decreased over time in part because of a large increase in body mass and a decrease in traits linked with flight, namely wingbeat frequency and metabolic rate, and the activity of metabolic enzymes tended to decrease. After taking into account temporal changes, body mass, flight wingbeat frequency and metabolic rate were repeatable. Finally, we found significant family resemblance for all traits measured, indicating that shared genes and/or environmental effects impact phenotypic variation. Together, our results show that the functional association between body morphology and flight physiology is robust, providing further insights into the mechanistic basis of metabolic rate scaling patterns during locomotion in animals.

ABSTRACT Glycosides are a major group of plant secondary compounds characterized by one or more sugars conjugated to a lipophilic, possibly toxic aglycone, which is released upon hydrolysis. We compared small intestinal homogenate hydrolysis activity of three rodent and two avian species against four substrates: amygdalin and sinigrin, two plant-derived glucosides, the sugar lactose, whose hydrolysis models some activity against flavonoid and isoflavonoid glucosides, and the disaccharide sugar maltose (from starch), used as a comparator. Three new findings extend our understanding of physiological processing of plant glucosides: (1) the capacity of passerine birds to hydrolyze plant glucosides seems relatively low, compared with rodents; (2) in this first test of vertebrates' enzymic capacity to hydrolyze glucosinolates, sinigrin hydrolytic capacity seems low; (3) in laboratory mice, hydrolytic activity against lactose resides on the enterocytes' apical membrane facing the intestinal lumen, but activity against amygdalin seems to reside inside enterocytes.

The evolution of flight energetics requires that phenotypes be variable, repeatable and heritable. We studied intraspecific variation in flight energetics in order to assess the repeatability of flight metabolic rate and wingbeat frequency, as well as the functional basis of phenotypic variation in workers and drones of the bumblebee species Bombus impatiens . We showed that flight metabolic rate and wingbeat frequency were highly repeatable in workers, even when controlling for body mass variation using residual analysis. We did not detect significant repeatability in drones, but a smaller range of variation might have prevented us from finding significant values in our sample. Based on our results and previous findings, we associated the high repeatability of flight phenotypes in workers to the functional links between body mass, thorax mass, wing size, wingbeat frequency and metabolic rate. Moreover, differences between workers and drones were as predicted from these functional associations, where drones had larger wings for their size, lower wingbeat frequency and lower flight metabolic rate. We also investigated thoracic muscle metabolic phenotypes by measuring the activity of carbohydrate metabolism enzymes, and we found positive correlations between mass-independent metabolic rate and the activity of all enzymes measured, but in workers only. When comparing workers and drones that differ in flight metabolic rate, only the activity of the enzymes hexokinase and trehalase showed the predicted differences. Overall, our study indicates that there should be correlated evolution among physiological phenotypes at multiple levels of organization and morphological traits associated with flight.

SUMMARY The migration of Arctic char Salvelinus alpinus from freshwater to seawater requires a substantial reorganization of the osmoregulatory tissues to regulate plasma ion levels. These modifications have an inherent metabolic cost, which must be met through the upregulation of intermediary metabolism. Arctic char intermediary metabolism was monitored during the initial 96 h of seawater acclimation through measurement of key enzymes in gill, liver, red and white muscle as well as tissue and blood free amino acid (FAA) levels, and plasma glucose and non-esterified fatty acid content. In general, seawater exposure stimulated large changes in amino acid metabolism, but no change in lipid or carbohydrate metabolism. White muscle FAA content increased significantly following seawater exposure, with levels of essential FAAs doubling after 96 h. Similar increases were seen in the plasma, suggesting a rapid mobilization of FAAs to the circulation. These changes were accompanied by significant increases in the activities of enzymes involved in amino acid metabolism in the gill, liver, red and white muscle, suggesting seawater-acclimated fish have an enhanced capacity for energy production from amino acids. Increased energy requirements were evident in the gill of seawater-acclimated char, as citrate synthase activity increased significantly. The results of this study suggest a rapid upregulation of amino acid metabolism may be critical for the successful acclimation of Arctic char to seawater.

SUMMARY To test the hypothesis that the preference for ketone bodies rather than lipids as oxidative fuel in elasmobranchs evolved in response to the appearance of urea-based osmoregulation, we measured total non-esterified fatty acids (NEFA) in plasma as well as maximal activities of enzymes of intermediary metabolism in tissues from marine and freshwater elasmobranchs,including: the river stingray Potamotrygon motoro (<1 mmol l –1 plasma urea); the marine stingray Taeniura lymma , and the marine shark Chiloscyllium punctatum (>300 mmol l –1 plasma urea); and the euryhaline freshwater stingray Himantura signifer , which possesses intermediate levels of urea. H. signifer also were acclimated to half-strength seawater(15‰) for 2 weeks to ascertain the metabolic effects of the higher urea level that results from salinity acclimation. Our results do not support the urea hypothesis. Enzyme activities and plasma NEFA in salinity-challenged H. signifer were largely unchanged from the freshwater controls, and the freshwater elasmobranchs did not show an enhanced capacity for extrahepatic lipid oxidation relative to the marine species. Importantly, and contrary to previous studies, extrahepatic lipid oxidation does occur in elasmobranchs, based on high carnitine palmitoyl transferase (CPT) activities in kidney and rectal gland. Heart CPT in the stingrays was detectable but low,indicating some capacity for lipid oxidation. CPT was undetectable in red muscle, and almost undetectable in heart, from C. punctatum as well as in white muscle from T. lymma . We propose a revised model of tissue-specific lipid oxidation in elasmobranchs, with high levels in liver,kidney and rectal gland, low or undetectable levels in heart, and none in red or white muscle. Plasma NEFA levels were low in all species, as previously noted in elasmobranchs. D-β-hydroxybutyrate dehydrogenase( d -β-HBDH) was high in most tissues confirming the importance of ketone bodies in elasmobranchs. However, very low d -β-HBDH in kidney from T. lymma indicates that interspecific variability in ketone body utilization occurs. A negative relationship was observed across species between liver glutamate dehydrogenase activity and tissue or plasma urea levels, suggesting that glutamate is preferentially deaminated in freshwater elasmobranchs because it does not need to be shunted to urea production as in marine elasmobranchs.

SUMMARY In the flight muscles of European bumblebees, high activities of fructose-1,6-bisphosphatase (FbPase) relative to phosphofructokinase (PFK)have suggested a thermogenic `futile cycle' important for regional endothermy. We find generally low activities of FbPase (0.7-19.7 units g -1 thorax) in North American Bombus species, with the exception of Bombus rufocinctus , where activity (43.1 units g -1 thorax)is comparable with that of European congeners. These data, taken with estimates of maximal rates of heat production by cycling, do not support a significant thermogenic role for the PFK/FbPase cycle. In agreement with earlier studies, both PFK and FbPase activities were found to scale allometrically with body size (allometric exponents -0.18 and -1.33,respectively). The cycle may serve to supplement thermogenesis or amplify glycolytic flux in rest-to-flight transitions, especially in smaller bees.