Comparative Biochemistry and Physiology Part A: Physiology最新文献

Hemagglutinins were determined in six species of mosquitoes that are susceptible and refractory to Brugia malayi (Filarioidea: Nematoda). High titers of hemagglutinins were found in the salivary gland extract and in the body fluid of a completely refractory species, Aedes taeniorhynchus, and in partially refractory species, Anopheles quadrimculatus; but low levels of hemagglutinins were also present in the body fluid of Aedes aegypti (Black-eye, Liverpool strain), a susceptible species. Hemagglutinating activity was not found in the other three completely refractory species of mosquitoes, Culex quinquefasciatus, Culex nigripalpus, and Aedes albopictus in which blood coagulated rapidly after ingestion. High titers of hemagglutinins in the salivary glands of Ae. taeniorhynchus and An. quadrimaculatus facilitated rapid movement of sheathed microfilariae from the midgut to the hemocoel. It is suggested that high titers of hemagglutinins present in the hemocoel bound to the glycoconjugates with exposed carbohydrate moieties present on the microfilarial sheaths and developing abnormal larvae (L₁) in the thoracic muscle cells. These hemagglutinin-bound glycoconjugates formed capsules that subsequently stimulated the immune response and resulted in melanization of microfilarial sheaths and sheathed microfilariae in the hemocoel and intracellularly developing abnormal L₁ in the thoracic muscles. Only minimal encapsulation and melanization of B. malayi microfilariae was observed in the hemocoel of the other four species of mosquitoes that lacked hemagglutinins in the salivary glands. The results suggest that tissue specific hemagglutinins are one of several factors of vector susceptibility/refractoriness through immune reactions (encapsulation, activation of prophenoloxidases).

The sex- and developmental stage-specific occurrence of gelatin-degrading enzymes has as yet never been systematically investigated in any insect species. By way of zymographic analysis, gelatinolytic activity was analyzed in the hemolymph and homogenates of the gray fleshfly Neobellieria bullata. Gelatinolytic activity was detected in feeding larvae and disappeared from both hemolymph and total body extracts during the wandering stage. An increase in gelatinolytic activity is observed around the third day after pupariation and again in late pharate adults. In adult females, gelatinolytic activity is only present in the hemolymph during the vitellogenic stages, whereas it is undetectable in the adult male hemolymph. Gelatinolytic activity is high in the fat body of vitellogenic females but low in that of previtellogenic females and in males. Injection of 20-OH-ecdysone induces gelatinolytic activity in previtellogenic females and in liver-fed males. In vitro, this hormone triggers gelatinase production by the fat body of liver-fed males but surprisinly not by that of sugar-fed (previtellogenic) females, which indicates that ecdysteroids are not the only regulatory molecules involved. Our data suggest that in Neobellieria, and perhaps in other insects as well, gelatinolytic activity is indirectly involved in growth, metamorphosis and reproduction.

Plasma cortisol in wild kahawai (Arripis trutta), an active pelagic marine fish, immediately after capture by hook and line was 8 ± 5 ng/ml (capture time, 4.9 ± 0.8 min, range 1–11 min). Capture by angling was accompanied by high levels of lactate in the white muscle (46.6 ± 2.8 μmol/g) and moderate plasma lactate levels (8.4 ± 1.0 mmol/l). Peak plasma cortisol concentration in fish after transport to shore in live tanks aboard a boat (1–2 hr post-capture) was 161 ± 31 ng/ml. Cortisol levels in wild-caught kahawai had returned to basal values within 3 days of introduction to a shore-based holding pool. Kahawai reacted violently to confinement in still water in darkened enclosed boxes. This prompted the design and construction of a swim tunnel for holding individual kahawai. Confinement of chronically cannulated kahawai in the swim tunnel resulted in a progressive increase in plasma cortisol; 2 hr after cannulation and confinement in the swim tunnel, plasma cortisol concentration was 112 ± 31 ng/ml. This increased to 233 ± 55 ng/ml after 2 days of confinement. Thus, confinement and cannulation do not appear to be suitable approaches for studying the physiology of this species.

The tropical marine sponge Acanthella cavernosa (Dendy) converts potassium [¹⁴C] cyanide to axisonitrile-3 (1); this precursor is also used for the synthesis of axisothiocyanate-3 (2) suggesting that isocyanides are precursors to isothiocyanates in A. cavernosa. Likewise, potassium [¹⁴C] thiocyanate is used for the synthesis of axisothiocyanate-3; unexpectedly this precursor also labelled axisonitrile-3. These results demonstrate either an interconversion between cyanide and thiocyanate prior to secondary metabolite formation or that the secondary metabolites can themselves be interconverted. Specimens of the dorid nudibranch Phyllidiella pustulosa, preadapted to a diet of A. cavernosa, fed on ¹⁴C-labelled sponges and were subsequently found to contain the radioactive terpenes (1) and (2). Specimens of P. pustulosa, which had not expressed a dietary preference for A. cavernosa in the field, did not generally feed in aquarium test with ¹⁴C-labelled sponges and, therefore, provided non-radioactive extracts. Since control experiments demonstrated the inability of P. pustulosa to synthesise the metabolites de novo, we therefore conclude that P. pustulosa acquires secondary metabolites by dietary transfer from A. cavernosa.

We investigated the effect of sucrose concentration on the patterns of feeding, gut function, and energy management in the nectar-eating Chilean hummingbird Sephanoides sephanoides. We interpreted these results using a simple model of digestive function. The predictions of this model are: (a) Hummingbirds should exhibit 100% assimilation efficiency of sugars at all sugar concentrations; (b) Daily rates of energy intake should be positively correlated with sugar concentration; and (c) Increased sugar concentration should lead to linearly increasing meal retention times, and, therefore, to linearly increasing time intervals between meals. In agreement with the model, hummingbirds exhibited almost complete assimilation of sugars and increased meal retention times and intermeal intervals with increased sugar concentration. Hummingbirds did not, however, show any significant differences in daily energy intake when fed different sugar concentrations. Birds differed in their temporal pattern of feeding when fed solutions with sucrose solutions of contrasting concentrations. At low food sucrose concentrations (0.25 M), birds showed a burst of feeding before dark. In contrast, birds feeding on higher sucrose concentrations (0.5 M and 0.75 M) showed steadily declining feeding activity throughout the day. In addition to measuring the behavior and gut function of hummingbirds, we also measured their daily patterns of energy use using respirometry. Hummingbirds showed considerable flexibility in their patterns of energy use. The amount of energy used at night was positively correlated with the surplus of energy (intake minus diurnal expenditures) at dusk. Although birds exhibited only small variation in total daily energy budgets as a function of sugar concentration, birds feeding at the lowest sucrose concentration (0.25 M) seemed to rely on nocturnal torpor with more frequency than those fed on higher concentrations. We conclude that energy maximization is probably an inappropriate assumption for birds that are not growing, storing fat, or reproducing. We present a modification of the original model that allows assuming that birds do not maximize energy intake, but rather maintain constant rates of energy intake. We describe experiments and criteria that allow discriminating among the two models.