Quantitative Genetics of Food Intake in Drosophila melanogaster

Food intake is an essential animal activity, regulated by neural circuits that motivate food localization, evaluate nutritional content and acceptance or rejection responses through the gustatory system, and regulate neuroendocrine feedback loops that maintain energy homeostasis. Excess food consumption in people is associated with obesity and metabolic and cardiovascular disorders. However, little is known about the genetic basis of natural variation in food consumption. To gain insights in evolutionarily conserved genetic principles that regulate food intake, we took advantage of a model system, Drosophila melanogaster, in which food intake, environmental conditions and genetic background can be controlled precisely. We quantified variation in food intake among 182 inbred, sequenced lines of the Drosophila melanogaster Genetic Reference Panel (DGRP). We found significant genetic variation in the mean and within-line environmental variance of food consumption and observed sexual dimorphism and genetic variation in sexual dimorphism for both food intake traits (mean and variance). We performed genome wide association (GWA) analyses for mean food intake and environmental variance of food intake (using the coefficient of environmental variation, CV_E, as the metric for environmental variance) and identified molecular polymorphisms associated with both traits. Validation experiments using RNAi-knockdown confirmed 24 of 31 (77%) candidate genes affecting food intake and/or variance of food intake, and a test cross between selected DGRP lines confirmed a SNP affecting mean food intake identified in the GWA analysis. The majority of the validated candidate genes were novel with respect to feeding behavior, and many had mammalian orthologs implicated in metabolic diseases.     

Sympathetic neural influences on muscle blood flow in rats during submaximal exercise

These experiments were designed to estimate the involvement of the sympathetic innervation in regulation of hindlimb muscle blood flow distribution among and within muscles during submaximal locomotory exercise in rats. Blood flows to 32 hindlimb muscles and 13 other selected tissues were measured using the radiolabeled microsphere technique, before exercise and at 0.5, 2, 5, and 15 min of treadmill exercise at 15 m/min. The two groups of rats studied were 1) intact control, and 2) acutely sympathectomized (hindlimb sympathectomy accomplished by bilateral section of the lumbar sympathetic chain and its connections to the spinal cord at L2-L3). There were no differences in total hindlimb muscle blood flow among the two groups during preexercise or at 30 s or 2 min of exercise. However, flow was higher in eight individual muscles at 2 min of exercise in the sympathectomized rats. At 5 and 15 min of exercise there was higher total hindlimb muscle blood flow in the denervated group compared with control. These differences were also present in many individual muscles. Our results suggest that 1) sympathetic nerves do not exert a net influence on the initial elevations in muscle blood flow at the beginning of exercise, 2) sympathetic nerves are involved in regulating muscle blood flow during steady-state submaximal exercise in conscious rats, and 3) these changes are seen in muscles of all fiber types.     

Conservation genetics of Boelen’s python (Morelia boeleni) from New Guinea: reduced genetic diversity and divergence of captive and wild animals

Boelen’s python (Morelia boeleni) is a montane New Guinea endemic found in highlands above 1000 m and below the tree line. The ecology, natural history, distribution, population size, and conservation status of this species are largely unknown. It has a protected status in Papua New Guinea but not in Indonesian Papua and several US and European zoos have active captive breeding programs that have been largely unsuccessful. To understand the degree of genetic diversity in wild and captive animals we undertook a genetic analysis of 90 M. boeleni for which we sequenced two mtDNA loci and one nuclear locus for a total of 1,418 bp of sequence data per individual. All 16 wild-caught M. boeleni from Indonesia and all captive M. boeleni are genetically uniform for all three loci. The single wild-caught animal from Papua New Guinea showed extremely low levels of genetic divergence and diversity from the Indonesian and captive samples. Data from two congeners, M. amethistina and M. viridis, suggests that M. boeleni have reduced genetic variation with a small effective population size possibly due to historical bottlenecks. These data demonstrate the need for further studies of genetic diversity of M. boeleni from across its range and raise particular concern for the limited genetic diversity of M. boeleni used captive breeding programs in zoological parks.     

Assessing Risk of Unintended Antigen Occurrence in Food: A Case Instance for Maize-Expressed LT-B

Plant-based antigen production represents an innovative strategy for low cost vaccine production and delivery. Successfully advancing plant-made antigen production in open field systems requires understanding of confinement integrity and consequences of inadvertent occurrence in the food supply. The food safety implications of confinement loss and inadvertent antigen occurrence in the food supply can be effectively addressed using quantitative exposure assessment along with knowledge of properties of specific antigens. We report here a food safety risk assessment for the maize-expressed heat-labile enterotoxin subunit B of Escherichia coli (LT-B). In addition to dietary exposure assessment, food safety considerations for maize-expressed LT-B included assessment of allergenic potential, levels and sites of transgenic protein expression, history of use, post-translational glycosylation, protein processing and digestive stability, mammalian functionality and toxicity, and compositional characteristics of the transformed plant. As shown for LT-B, inadvertent occurrence in the food supply of a plant-produced antigen constitutes a minimal human health concern principally because of limited exposure potential.     

Calcium binding to the photosystem II subunit CP29

We have identified a Ca(2+)-binding site of the 29-kDa chlorophyll a/b-binding protein CP29, a light harvesting protein of photosystem II most likely involved in photoregulation. (45)Ca(2+) binding studies and dot blot analyses of CP29 demonstrate that CP29 is a Ca(2+)-binding protein. The primary sequence of CP29 does not exhibit an obvious Ca(2+)-binding site therefore we have used Yb(3+) replacement to analyze this site. Near-infrared Yb(3+) vibronic side band fluorescence spectroscopy (Roselli, C., Boussac, A., and Mattioli, T. A. (1994) Proc. Natl. Acad. Sci. U. S. A. 91, 12897-12901) of Yb(3+)-reconstituted CP29 indicated a single population of Yb(3+)-binding sites rich in carboxylic acids, characteristic of Ca(2+)-binding sites. A structural model of CP29 presents two purported extra-membranar loops which are relatively rich in carboxylic acids, one on the stromae side and one on the lumenal side. The loop on the lumenal side is adjacent to glutamic acid 166 in helix C of CP29, which is known to be the binding site for dicyclohexylcarbodiimide (Pesaresi, P., Sandonà, D., Giuffra, E. , and Bassi, R. (1997) FEBS Lett. 402, 151-156). Dicyclohexylcarbodiimide binding prevented Ca(2+) binding, therefore we propose that the Ca(2+) in CP29 is bound in the domain including the lumenal loop between helices B and C.     

Retirement investment theory explains patterns in songbird nest-site choice

When opposing evolutionary selection pressures act on a behavioural trait, the result is often stabilizing selection for an intermediate optimal phenotype, with deviations from the predicted optimum attributed to tracking a moving target, development of behavioural syndromes or shifts in riskiness over an individual''s lifetime. We investigated nest-site choice by female golden-winged warblers, and the selection pressures acting on that choice by two fitness components, nest success and fledgling survival. We observed strong and consistent opposing selection pressures on nest-site choice for maximizing these two fitness components, and an abrupt, within-season switch in the fitness component birds prioritize via nest-site choice, dependent on the time remaining for additional nesting attempts. We found that females consistently deviated from the predicted optimal behaviour when choosing nest sites because they can make multiple attempts at one fitness component, nest success, but only one attempt at the subsequent component, fledgling survival. Our results demonstrate a unique natural strategy for balancing opposing selection pressures to maximize total fitness. This time-dependent switch from high to low risk tolerance in nest-site choice maximizes songbird fitness in the same way a well-timed switch in human investor risk tolerance can maximize one''s nest egg at retirement. Our results also provide strong evidence for the adaptive nature of songbird nest-site choice, which we suggest has been elusive primarily due to a lack of consideration for fledgling survival.     

Assessing the influence of habitat quality on movements of the endangered shortnose sturgeon

Movements of the endangered shortnose sturgeon Acipenser brevirostrum in the Ogeechee River (Georgia, USA) may be limited by unsuitable habitat conditions during June–September. The research objective was to determine if habitat quality is likely to impede movements and spawning of shortnose sturgeon in this system. We inserted ultrasonic transmitters in 18 adult shortnose sturgeon to monitor their monthly in-stream movements. Water quality data were collected at discrete locations along the Ogeechee River. We used geostatistical models based on Weighted Asymmetric Hydrologic Distance, in place of Euclidean distance, to predict water quality variables along the Ogeechee River, avoiding problems associated with linear distance metrics in a river network. Using ArcGIS, we constructed habitat quality models based on physiological tolerance to water temperature, dissolved oxygen, and salinity. During the summer months, tagged fish remained congregated above the fresh-saltwater interface. However, individuals appeared to move in response to changing water quality conditions. Seasonal habitat availability in other southern rivers should be similarly analyzed to assess potential relationships between the habitat and sturgeon movements. Although further laboratory and field studies are needed to better understand latitudinal variation in life history and environmental tolerances of shortnose sturgeon, the results of our study suggest that temporal and spatial variability in water quality affect habitat availability of southern populations of shortnose sturgeon.