Fuels for flight in the fruit beetle,Pachnoda Sinuata, and control of flight metabolism

Bibliography: p. 131-143.Isolated flight muscle mitochondria of Pachnoda sinuata, Decapotoma lunata, Trichostetha fascicularis, Lepithrix sp. and Camenta innocua prefer the oxidation of proline, pyruvate and α- glycerophosphate, while those of Locusta migratoria prefer the oxidation of palmitoyl-carnitine,pyruvate and α-glycerophosphate. Palmitoyl-carnitine cannot be oxidised directly by P. sinuata flight muscle mitochondria, while proline is oxidised at low rates in locust mitochondria. At low concentrations of proline, the respiration rate during co-oxidation of proline and pyruvate is additive, while at high proline concentrations it is equal to the respiration rates of sole proline oxidation. Flight muscles of P. sinuata and D. lunata were found to have high activities of the enzymes alanine aminotransferase and NAD-dependent malic enzyme which are involved in proline metabolism, while the activities of these enzymes were lower in locust flight muscles. The activity of 3-hydroxyacyl-CoA dehydrogenase, an enzyme used in fatty acid oxidation, is low in the flight muscles of P. sinuata and D. lunata, but high in locust flight muscles. Enzymes involved In carbohydrate breakdown (glyceraldehyde-3-phosphatedehydrogenase, glycogen phosphorylase) were found to have high activities in flight muscles of P. sinuata, D. lunata and L. migratoria. Two methods of tethered flight were investigated. One of these allowed the animals to produce lift. During lift generating flight, proline concentrations in haemolymph and flight muscles of P. sinuata decrease sharply with concomitant increases in alanine concentrations. During recovery after flight, proline concentrations increase while concentrations of alanine decrease. Haemolymph carbohydrate concentrations increase during the first seconds off light but decline consistently thereafter. During a subsequent rest period concentrations again increase. Glycogen concentration in the flight muscles decrease sharply in the first few seconds of flight, gradually declining thereafter. During subsequent recovery, flight muscle glycogen concentrations increase. Lipid haemolymph concentration increase only slightly during flight and rest thereafter. Two distinct metabolic phases were observed during lift generating flight

Insect neuropeptides regulating substrate mobilisation

Insect flight muscles perform their work completely aerobically, and working flight muscles are known to be the most metabolically active tissue in nature with respect to oxygen uptake. Various substrates can be oxidised and utilised as fuels for flight. Insects such as Diptera and Hymenoptera power their flight muscles by the breakdown of carbohydrates, whereas lipids are the predominant fuel for the contracting flight muscles of Lepidoptera and Orthoptera during long-distance flight. The amino acid proline can also be used as a substrate for flight, especially in tsetse flies and beetles (Colorado potato beetle, blister beetles, certain dung beetles). Neuropeptides from the corpus cardiacum are well-known to be responsible for carbohydrate and lipid mobilisation from the fat body. In this short overview, we show that peptides belonging to the large adipokinetic hormone/red pigment-concentrating hormone family are also thought to be the chemical messengers for initiating proline homeostasis. The peptides isolated and sequenced so far from glands of beetles from the genera Pachnoda, Scarabaeus and Onitis all have a tyrosine residue (at position 2 or 4) and seem to be related to each other

A temperature‐controlled, circular maintenance system for studying growth and development of pelagic tunicates (salps)

Salps have attracted attention as zooplankton organisms that may be able to expand their habitat range and increase their ecological importance in the face of ongoing global warming. Due to their gelatinous nature, unique feeding strategy, and reproductive ecology such changes could have profound impacts on regional marine ecosystems. While their role in the regional carbon cycle is receiving attention, our knowledge of their physiology and life cycle is still limited. This knowledge gap is mainly due to their fragile gelatinous nature, which makes it difficult to capture and maintain intact specimen in the laboratory. We present here a modified kreisel tank system that has been tested onboard a research vessel with the Southern Ocean salp Salpa thompsoni and at a research station with Salpa fusiformis and Thalia democratica from the Mediterranean Sea. Successful maintenance over days to weeks allowed us to obtain relative growth and developmental rates comparable to in situ field samples of S. thompsoni and S. fusiformis, and provided insights into previously unknown features of their life cycle (e.g., testes development). Our results show that traditional methods of estimating growth, such as cohort analysis, may lead to a general overestimation of growth rates and neglect individual strategies (e.g., shrinkage), which can affect the results and conclusions drawn from population dynamic models. By providing a starting point for the successful maintenance of different species, comparable experiments on the physiology of salps is made possible. This will contribute to refining model parameters and improving the reliability of the predictions

Physiological response of adult Antarctic krill, Euphausia superba, to long-term starvation

Adult Euphausia superba survive winter without or with little feeding. It is not exactly known whether the scarcity of food or an internal clock, set by the natural Antarctic light regime, are responsible for non-feeding. Our research questions were therefore the following: (1) How will physiological and biochemical conditions of krill change during long-term starvation at constant light regime? (2) If and how do enzyme activities change during such starvation? (3) What is the influence of food availability versus that of light regime? To answer these questions, adult krill were starved under laboratory conditions for 12 weeks with constant light regime (12:12; dark/light) and the impact on physiological functions was studied. Initial experimental condition of krill resembled the condition of late spring krill in the field with fully active metabolism and low lipid reserves. Metabolic activity and activities of enzymes catabolising lipids decreased after the onset of starvation and remained low throughout, whereas lipid reserves declined and lipid composition changed. Mass and size of krill decreased while the inter-moult period increased. Depletion of storage- and structural metabolites occurred in the order of depot lipids and glycogen reserves after onset of starvation until proteins were almost exclusively used after 6–7 weeks of starvation. Results confirmed various proposed overwintering mechanisms such as metabolic slowdown, slow growth or shrinkage and use of lipid reserves. However, these changes were set in motion by food shortage only, i.e.without the trigger of a changing light regime

Effects of chronic hypercapnia and elevated temperature on the immune response of the spiny lobster, Jasus lalandii

The West Coast rock lobster (WCRL), Jasus lalandii, inhabits highly variable environments frequented by upwelling events, episodes of hypercapnia and large temperature variations. Coupled with the predicted threat of ocean acidification and temperature change for the coming centuries, the immune response in this crustacean will most likely be affected. We therefore tested the hypothesis that chronic exposure to hypercapnia and elevated seawater temperature will alter immune function of the WCRL. The chronic effects of four combinations of two stressors (seawater pCO and temperature) on the total number of circulating haemocytes (THC) as well as on the lobsters’ ability to clear (inactivate) an injected dose of Vibrio anguillarum from haemolymph circulation were assessed. Juvenile lobsters were held in normocapnic (pH 8.01) or hypercapnic (pH 7.34) conditions at two temperatures (15.6 and 18.9 °C) for 48 weeks (n = 30 lobster per treatment), after which a subsample of lobsters (n = 8/treatment), all at a similar moult stage, were selected from each treatment for the immune challenge. Baseline levels of haemocytes (THC ml) and bacteria (CFU ml) in their haemolymph were quantified 24 h prior to bacterial challenge. Lobsters were then challenged by injecting 4 × 10 V. anguillarum per g body weight directly into the cardiac region of each lobster and circulating haemocyte and culturable bacteria were measured at 20 min post challenge. No significant differences in THC ml (p normocapnia/high temperature > normocapnia/low temperature > hypercapnia/high temperature. This study demonstrated that despite chronic exposure to combinations of reduced seawater pH and high temperature, the WCRL was still capable of rapidly rendering an injected dose of bacteria non-culturable

Acid–base balance and changes in haemolymph properties of the South African rock lobsters, Jasus lalandii, a palinurid decapod, during chronic hypercapnia

Few studies exist reporting on long-term exposure of crustaceans to hypercapnia. We exposed juvenile South African rock lobsters, Jasus lalandii, to hypercapnic conditions of pH 7.3 for 28 weeks and subsequently analysed changes in the extracellular fluid (haemolymph). Results revealed, for the first time, adjustments in the haemolymph of a palinurid crustacean during chronic hypercapnic exposure: 1) acid-base balance was adjusted and sustained by increased bicarbonate and 2) quantity and oxygen binding properties of haemocyanin changed. Compared with lobsters kept under normocapnic conditions (pH 8.0), during prolonged hypercapnia, juvenile lobsters increased bicarbonate buffering of haemolymph. This is necessary to provide optimum pH conditions for oxygen binding of haemocyanin and functioning of respiration in the presence of a strong Bohr Effect. Furthermore, modification of the intrinsic structure of the haemocyanin molecule, and not the presence of molecular modulators, seems to improve oxygen affinity under conditions of elevated pCO2

Seawater carbonate chemistry and blood acid-base balance and other blood parameters of demersal shark species Haploblepharus edwardsii

Global ocean acidification is expected to chronically lower the pH to 7.3 (>2200 µatm seawater pCO2) by the year 2300. Acute hypercapnia already occurs along the South African west and south coasts due to upwelling- and low-oxygen events, with increasing frequency. In the present project we investigated the impact of hypercapnia on the endemic demersal shark species Haploblepharus edwardsii. Specifically, we experimentally analysed acid-base regulation during acute and chronic hypercapnia, the effects of chronic hypercapnia on growth rates and on denticle structure- and composition. While H. edwardsii are physiologically well adapted to acute and chronic hypercapnia, we observed, for the first time, denticle corrosion as a result of chronic exposure. We conclude that denticle corrosion could increase denticle turnover and compromise hydrodynamics and skin protection