The adipokinetic hormones of African water bugs of the Heteropteran families Nepidae and Belostomatidae

Four African species of true water bugs (Nepomorpha: Hemiptera: Heteroptera) are studied by mass spectrometry and biological assays to gain information on the presence, structure and function of peptides from the adipokinetic hormone (AKH) family, which are produced in the corpora cardiaca (CC). The water scorpion Laccotrephes fabricii Stål (Nepidae) has the peptide code‐named Peram‐CAH‐I with the sequence pGlu‐Val‐Asn‐Phe‐Ser‐Pro‐Asn‐Trp amide, whereas Appasus grassei Poisson (Belostomatidae) produces Anaim‐AKH, which is a Ser⁷ analogue of Peram‐CAH‐I (pGlu‐Val‐Asn‐Phe‐Ser‐Pro‐Ser‐Trp amide). The giant water bug Hydrocyrius columbiae Spinola (Belostomatidae) has two adipokinetic hormone family members: Anaim‐AKH and Letin‐AKH, which again differ only at position 7 (Ser⁷ versus Tyr⁷). When the sequence data are compared with current molecular phylogenetic analyses of Nepomorpha, they are essentially in agreement with the newest ideas on phylogenetic relationships among the families. Functional investigation of these peptides reveals a mainly lipid‐based energy metabolism in these insects, as demonstrated by a hyperlipaemic response after injecting crude CC extract or the appropriate peptide into the respective species. The carbohydrate concentration in the haemolymph is not affected by such injections, and the carbohydrate level in most cases is lower than that of the circulating lipids. During physical exercise, such as swimming for 1 h, carbohydrates may contribute to some extent to the provision of energy; the substantial increase in the concentration of lipids in the haemolymph, however, is a strong indicator that the peptides are released from the CC and act primarily as true adipokinetic hormones during this period of intense muscular activity.     

Reduced humoral and cellular cytotoxic sensitivity in major histocompatibility variants of the YAC (Moloney) lymphoma

Previously we have reported that two sublines of the YAC lymphoma selected for reduced expression of H-2^a and Moloney-virus determined cell-surface (MCSA) antigens are, in contrast to YAC, allotransplantable in H-2-incompatible recipients, and resistant to rejection by preimmunized semisyngeneic hosts. A third YAC variant with reduced MCSA but unchanged H-2-antigen expression, was not allotransplantable and showed only a slight decrease in its immunosensitivity in preimmunized semisyngeneic hosts in vivo. This suggested that H-2-antigen expression may be more important than MCSA expression for recognition and rejection by semisyngeneic mice. We have now tested the sublines expressing low H-2^a for their in vitro sensitivity to humoral and cell-mediated lysis. — The variants were more resistant than YAC to complement lysis by anti-H-2^a, anti-MCSA, anti-Thy 1.2 and antispecies sera. Absorption tests with antispecies serum indicated that the decreased cytolytic sensitivity of the variants was not related to the concentration of the relevant antigens, which was similar to that of the original YAC tumor. As expected from the low amount of H-2^a the variants showed a decreased sensitivity to the killing effect of allogeneic cytotoxic T lymphocytes (CTL). They were also lysed to a lesser extent than YAC by semisyngeneic CTL, probably directed against virally determined antigens. However, they were also less sensitive to lysis by natural killer (NK) cells, although NK lysis is probably unrelated to MHC expression. In conclusion, our selection for reduced H-2-expression appears to have resulted in the isolation of variants with a generally increased resistance to various humoral and cell-mediated lytic functions.On leave from Instituto Venezolano de Investigaciones Cientificas (IVIC), Caracas, Venezuela.     

Neuropeptide Y and sympathetic vascular control in man

A parallel increase in systemic plasma levels of neuropeptide Y (NPY)-like immunoreactivity (LI) and noradrenaline (NA) was found during thoracotomy and surgery involving cardiopulmonary bypass in man. Thus, plasma levels of NPY-LI increased from 29 +/- 4 pmol/l before anaesthesia to 59 +/- 10 after thoracotomy and to 87 +/- 8 pmol/l upon cardiopulmonary bypass. The corresponding NA levels increased from 1.3 +/- 0.1 nmol/l before anaesthesia to 3.0 +/- 0.6 and 4.2 +/- 5 nmol/l after thoracotomy and cardiopulmonary bypass, respectively. A significant correlation was found between plasma levels of NPY-LI and NA during the operation but not between NPY-LI and adrenaline. The NPY-LI in human plasma was found to be similar to synthetic porcine NPY on reversed phase high performance liquid chromatography. Human submandibular arteries contained high levels of NPY-LI (24 +/- 3 pmol/g). In in vitro experiments on isolated human submandibular arteries, NPY in low concentrations (1000 pmol/l) was found to potentiate the contractile effects of NA or transmural nerve stimulation and to exert vasoconstrictor activity per se in higher concentrations. The calcium-entry antagonist nifedipine abolished both the NPY-induced contractions and the enhancement of NA-evoked contractions. NPY depressed the nerve stimulation-evoked 3H-NA release from human submandibular arteries via a prejunctional mechanism which was resistant to nifedipine. NPY contracted human mesenteric veins and renal arteries, but not mesenteric arteries. In conclusion, NPY seems to be co-released with NA upon sympathetic activation in man. Furthermore, NPY exerts both pre- and postjunctional effects on sympathetic control of human blood vessels.     

Mass fragmentographic determination of prostaglandin F2α in human and rabbit urine

Analysis of prostaglandin F_2α (PGF_2α) in urine is a useful indicator of renal prostaglandin synthesis. A mass fragmentographic method for PGF_2α analysis in human urine was developed using [3,3,4,4-²H₄]PGF_2α as an internal standard and carrier. PGF_2α was extracted from urine (20 ml) with chloroform, purified by preparative thin-layer chromatography and converted to the methyl ester trimethylsilyl ether before analysis by gas chromatograph—mass spectrometry. The specificity of the urine analysis was demonstrated by retention time and the use of two pairs of fragments m/e 494/498 and 513/517 with the same results. The coefficient of variation for duplicate analysis averaged 12.6%, n = 17. Urine from recumbent women contained 4.9 ± 2.6 (S.D.) ng/ml or 4.1 ± 1.0 ng PGF_2α per mg creatinine (n = 10) with little diurnal variation. Male urine contained 5.0 ± 2.7 (S.D.) ng/ml or 3.7 ± 2.1 ng/mg creatinine (n = 10). Similar concentrations were found in boys and in girls. These observations indicate that urinary PGF_2α originates from the kidneys with little contribution from the male accessory sexual glands. This method can also be applied to analysis of PGF_2α in rabbit urine.     

Food discrimination and induction of preference for artificial diets in the tobacco hornworm, Manduca sexta

ABSTRACT. Feeding discrimination of Manduca larvae reared on leaves and a variety of artificial media was tested against leaves, various media, solvent fractions of leaves and media, and media components, including pure chemicals. Field-collected animals showed the same preferences as did animals cultured in the laboratory for many generations. Rearing larvae on a leaf species, an artificial diet, or homogenized leaves added to artificial diet induced a preference for that food in subsequent choice tests. Extracts of these foods using organic solvents (particularly hexane) elicited feeding choices resembling those evoked by the foods themselves: water extracts were effective as stimulants or deterrents, but responses to them differed considerably from responses to the foods. Animals raised on a defined artificial diet showed an increased preference (or decreased deterrence) for the lipid component (linolenic acid) of that diet in behavioural tests. Thus induction of preference was shown to be influenced by a specific nutrient compound. Fifteen artificial diets were tested; three were successful, including a completely defined medium. Various components of the diets were tested for feeding preferences, both as omissions from the main diet and as pure compounds. Some were stimulatory, most were neutral or slightly deterrent; a few were strongly deterrent. With the exception of linolenic acid, preferences for pure compounds were not significantly correlated with the food on which the animals were reared. The data suggest that food discrimination depends on the perception of a complex chemical message comprised of both polar and non-polar compounds, with the latter being of somewhat greater importance. The results are consistent with the explanation of the induction of feeding preferences being due to a reduced responsiveness to deterrents, to an increased preference for feeding stimulants or to both.     

Control of stream insect assemblages: roles of spatial configuration and local environmental factors

Abstract 1. Current views in ecology emphasise that community structure is the sum of multiple processes, with imprints of both regional and local drivers. However, the degree to which stream insect assemblages are structured by spatial configuration (complying with the dispersal‐based neutral hypothesis) and local environmental features (complying with the niche‐based species sorting hypothesis) has not been rigorously examined based on surveys in multiple years. 2. Stream sites in a boreal drainage system were surveyed during three consecutive years and the relative contribution of spatial configuration and local environmental variables to aquatic insect assemblage structure (characterised by both abundance and presence–absence data) was assessed. Separate analyses were conducted for mayflies (Ephemeroptera), stoneflies (Plecoptera), caddisflies (Trichoptera), and non‐biting midges (Diptera: Chironomidae) in each year. 3. There were no relationships between the spatial location and local environmental features of streams in Mantel tests, facilitating exploration of their independent effects on assemblage structure. The study found virtually no effects of spatial location on stream insect assemblages across the study drainage system, as evidenced by Mantel tests and canonical correspondence analyses (CCA). The environmental variables were also rather weakly associated with assemblage structure, with the total amount of explained variation ranging from 9.8% to 31.7% in the CCAs. There were no appreciable differences in the amount of environment‐related explained variation in assemblage structure between mayflies, stoneflies, caddisflies, and midges, but some between‐year differences were noticeable in most insect groups. The environmental variables that were significantly related to assemblage structure exhibited some between‐group and between‐year variability. In general, patterns shown by abundance and presence–absence data were highly similar. 4. It appears that stream insect assemblages comply with the niche‐based species sorting hypothesis in the context of metacommunity ecology. In contrast, the absence of spatial structuring suggests that stream insect assemblages do not comply with the neutral hypothesis, being not strongly dispersal limited at the within‐drainage basin scale.     

OUGHT WE TO ENHANCE OUR COGNITIVE CAPACITIES?1

Ought we to improve our cognitive capacities beyond the normal human range? It might be a good idea to level out differences between peoples cognitive capacities; and some people's reaching beyond normal capacities may have some good side‐effects on society at large (but also bad side‐effects, of course). But is there any direct gain to be made from having ones cognitive capacities enhanced? Would this as such make our lives go better? No, I argue; or at least there doesn't seem to be any evidence suggesting that it would. And it doesn't matter whether we consider the question from a narrow hedonistic perspective, from a more refined hedonistic perspective, from a desire‐satisfaction view, or from some reasonable objective list view of what makes a life go well. Only an extremely perfectionist – and implausible – view of what makes our lives go well could support any direct value in cognitive enhancement. Finally, our sense of identity gives us no good reasons to enhance even our capacity to remember. So, cognitive enhancement as such would not improve our lives.     

Allometry between leg and body length of insects: lack of support for the size–grain hypothesis

• 1 The size–grain hypothesis ( Kaspari & Weiser, 1999 ) states that (1) as organisms decrease in size, they perceive their environment as being more rugose; (2) long legs allow organisms to step over obstacles but hinder them from entering small gaps; and (3) as the size of an organism decreases, the benefits of long legs begin to be outweighed by the costs of construction. Natural selection should therefore favour proportionally longer legs in larger organisms, thereby leading to a positive allometry between leg and body length (scaling exponent b > 1).
• 2 Here we compare the scaling exponent of leg‐to‐body length relationships among insects that walk, walk and fly, and predominantly fly. We measured the lengths of the hind tibia, hind femur, and body length of each species.
• 3 The taxa varied considerably in the scaling exponent b. In seven out of ten groups (Formicidae, Isoptera, Carabidae, Pentatomidae, Apidae, Lepidoptera, Odonata adult), b was significantly greater than one. However, there was no gradual decrease in b from walking to walking/flying to flying insects.
• 4 The results of the present study provide no support for the size–grain hypothesis. We propose that leg length is not only affected by the rugosity of the environment, but also by (1) functional adaptations, (2) phylogeny, (3) lifestyle, (4) the type of insect development (hemimetabolism or holometabolism), and (5) constraints of gas exchange.