Eran Gefen

Parasitoid wasp affects metabolism of cockroach host to favor food preservation for its offspring

Unlike predators, which immediately consume their prey, parasitoid wasps incapacitate their prey to provide a food supply for their offspring. We have examined the effects of the venom of the parasitoid wasp Ampulex compressa on the metabolism of its cockroach prey. This wasp stings into the brain of the cockroach causing hypokinesia. We first established that larval development, from egg laying to pupation, lasts about 8xa0days. During this period, the metabolism of the stung cockroach slows down, as measured by a decrease in oxygen consumption. Similar decreases in oxygen consumption occurred after pharmacologically induced paralysis or after removing descending input from the head ganglia by severing the neck connectives. However, neither of these two groups of cockroaches survived more than six days, while 90% of stung cockroaches survived at least this long. In addition, cockroaches with severed neck connectives lost significantly more body mass, mainly due to dehydration. Hence, the sting of A. compressa not only renders the cockroach prey helplessly submissive, but also changes its metabolism to sustain more nutrients for the developing larva. This metabolic manipulation is subtler than the complete removal of descending input from the head ganglia, since it leaves some physiological processes, such as water retention, intact.

Heart rate in developing ostrich embryos

1. A non-invasive condenser microphone was used to detect cardiogenic, acoustic pressure changes (acoustocardiogram, ACG) over the eggshell in order to determine embryonic heart rate (HR) of ostriches in a commercial hatchery. 2. HR measured for 36 eggs at 36.3C was maintained at about 185 bpm during the middle stage of development (days 19 to 23) and then decreased with embryonic development. 3. The daily changes in HR were not related to egg mass, but HR of high water vapour conductance (GspH2O) eggs was found to decrease less during the last stages of incubation relative to low and medium GspH2O groups. 4. The averaged HR at 80% of incubation period was close to the value predicted from the allometric equation determined previously for embryos of domesticated precocial birds.

Red foliage color reliably indicates low host quality and increased metabolic load for development of an herbivorous insect

Plant chemical defense and coevolved detoxification mechanisms in specialized herbivorous insects are fundamental in determining many insect–plant interactions. For example, Brassicale plants protect themselves from herbivory by producing glucosinolates, but these secondary metabolites are effectively detoxified by larvae of Pierid butterflies. Nevertheless, not all Brassicales are equally preferred by these specialist herbivores. Female Pieris butterflies avoid laying eggs on anthocyanin-rich red foliage, suggesting red color is a visual cue affecting oviposition behavior. In this study, we reared P. brassicae larvae on green and red cabbage leaves, to determine whether foliage color reliably indicates host plant quality. We did not find a difference in survival rates or maximal larval body mass in the two food treatments. However, larvae feeding on red cabbage leaves exhibited significantly lower growth rates and longer durations of larval development. Interestingly, this longer development was coupled with a higher consumption rate of dry food matter. The lower ratio of body mass gain to food consumption in larvae feeding on red cabbage leaves was coupled with significantly higher (ca. 10xa0%) larval metabolic rates. This suggests that development on red foliage may incur an increased metabolic load associated with detoxification of secondary plant metabolites. Energy and oxygen allocation to detoxification could come at the expense of growth and thus compromise larval fitness as a result of extended development. From an evolutionary perspective, red foliage color may serve as an honest defensive cue, as it reliably indicates the plant’s low quality as a substrate for larval development.

Comparative water relations of four species of scorpions in Israel: evidence for phylogenetic differences

SUMMARY In an attempt to determine the nature of possible interspecific differences in osmotic responses to dehydration, the following species of two scorpion families were examined: Scorpio maurus fuscus (Scorpionidae) and Buthotus judaicus (Buthidae) from the mesic Lower Galilee (mean annual precipitation ∼525 mm); and Scorpio maurus palmatus (Scorpionidae) and Leiurus quinquestriatus (Buthidae) from the xeric Negev Desert (mean annual precipitation ∼100 mm). When sampled in the laboratory following their capture, B. judaicus (548±38 mOsm l–1; mean ± s.d.) and L. quinquestriatus (571±39 mOsm l–1) had higher and less variable haemolymph osmolarities than the scorpionids occupying the same habitats (511±56 and 493±53 mOsm l–1 for S. m. fuscus and S. m. palmatus, respectively). In response to 10% mass loss when desiccated at 30°C, the haemolymph osmolarity of the two buthids increased by 5–9%, compared to ca. 23% in the two scorpionids. Buthids had lower water loss rates than scorpionids. The similar oxygen consumption rates, when converted to metabolic water production, imply a higher relative contribution of metabolic water to the overall water budget of buthids. This could explain why the osmoregulative capabilities exhibited by buthids are better than those of scorpionids. We conclude that the observed interspecific differences in water and solute budgets are primarily phylogenetically derived, rather than an adaptation of the scorpions to environmental conditions in their natural habitat.

Embryonic heart rate measurements during artificial incubation of emu eggs

1. Daily changes in embryonic heart rate (HR) of emu were determined non-invasively at 36°C by acoustocardiography (ACG) during the last 30% of artificial incubation (predicted incubation time is 50 d). 2. The pattern of daily changes in mean HR of hatched embryos decreased from about 175 bpm to about 140 bpm towards the end of incubation. 3. The mean HR at 80% of incubation (ca. 170 bpm) was close to the value predicted from an allometric equation reported previously for precocial domesticated birds. 4. ACG could measure embryonic HR even during the external pipping period. 5. If the artificial external pipping procedure is timed correctly after internal pipping, it might aid the embryos in hatching. However, further investigation into this aspect is needed.

The effect of discontinuous gas exchange on respiratory water loss in grasshoppers (Orthoptera: Acrididae) varies across an aridity gradient

ABSTRACT The significance of discontinuous gas-exchange cycles (DGC) in reducing respiratory water loss (RWL) in insects is contentious. Results from single-species studies are equivocal in their support of the classic ‘hygric hypothesis’ for the evolution of DGC, whereas comparative analyses generally support a link between DGC and water balance. In this study, we investigated DGC prevalence and characteristics and RWL in three grasshopper species (Acrididae, subfamily Pamphaginae) across an aridity gradient in Israel. In order to determine whether DGC contributes to a reduction in RWL, we compared the DGC characteristics and RWL associated with CO2 release (transpiration ratio, i.e. the molar ratio of RWL to CO2 emission rates) among these species. Transpiration ratios of DGC and continuous breathers were also compared intraspecifically. Our data show that DGC characteristics, DGC prevalence and the transpiration ratios correlate well with habitat aridity. The xeric-adapted Tmethis pulchripennis exhibited a significantly shorter burst period and lower transpiration ratio compared with the other two mesic species, Ocneropsis bethlemita and Ocneropsis lividipes. However, DGC resulted in significant water savings compared with continuous exchange in T. pulchripennis only. These unique DGC characteristics for T. pulchripennis were correlated with its significantly higher mass-specific tracheal volume. Our data suggest that the origin of DGC may not be adaptive, but rather that evolved modulation of cycle characteristics confers a fitness advantage under stressful conditions. This modulation may result from morphological and/or physiological modifications. Highlighted Article: Comparative analysis of respiratory gas exchange in grasshoppers shows interspecific variation in DGC contribution to body water conservation, which is correlated with tracheal system dimensions.

Gas exchange and energy metabolism of the ostrich (Struthio camelus) embryo

We measured oxygen consumption (V(O(2))) and carbon dioxide emission (V(CO(2))) rates, air-cell gas partial pressures of oxygen (P(A)O(2)) and CO(2) (P(A)CO(2)), eggshell water vapour conductance and energy content of the ostrich (Struthio camelus) egg, true hatchling and residual yolk, and calculated RQ and total oxygen consumption (V(O(2)tot)) for ostrich eggs incubated at 36.5 degrees C and 25% relative humidity. The V(O(2)) pattern showed a drop of approximately 5% before internal pipping. V(O(2)) just prior to internal pipping agrees with allometric calculations. Despite the higher incubation temperature compared to other studies, and the resultant shorter incubation duration (42 days), V(O(2)tot) (91.7 l kg(-1)) was similar to a previously reported value. RQ values during the second half of incubation (approx. 0.68) were lower than expected for lipid catabolism. Prior to internal pipping, P(A)O(2) and P(A)CO(2) were 98 and 48.3 torr (13.1 and 6.4 kPa), respectively. The growth pattern of the ostrich embryo is different from the typical precocial pattern, showing a time delay in the rapid growth phase. As a result, the lowered overall energy expenditure for tissue maintenance, as compared to other species, is reflected in the low yolk utilization and high residual yolk fraction of the whole hatchling dry mass. These could also result from the relatively short incubation period of the ostrich egg, thereby evading desiccation by excess water loss.

Scorpions regulate their energy metabolism towards increased carbohydrate oxidation in response to dehydration

Scorpions successfully inhabit some of the most arid habitats on earth. During exposure to desiccating stress water is mobilized from the scorpion hepatopancreas to replenish the hemolymph and retain hydration and osmotic stability. Carbohydrate catabolism is advantageous under these conditions as it results in high metabolic water production rate, as well as the release of glycogen-bound water. Hypothesizing that metabolic fuel utilization in scorpions is regulated in order to boost body water management under stressful conditions we used a comparative approach, studying energy metabolism during prolonged desiccation in four species varying in resistance performance. We used respirometry for calculating respiratory gas exchange ratios, indicative of metabolic fuel utilization, and measured metabolic fuel contents in the scorpion hepatopancreas. We found that hydrated scorpions used a mixture of metabolic fuels (respiratory exchange rates, RER~0.9), but a shift towards carbohydrate catabolism was common during prolonged desiccation stress. Furthermore, the timing of metabolic shift to exclusive carbohydrate oxidation (RER not different from 1.0) was correlated with desiccation resistance of the respective studied species, suggesting triggering by alterations to hemolymph homeostasis.

The Relative Importance of Respiratory Water Loss in Scorpions Is Correlated with Species Habitat Type and Activity Pattern

Scorpions exhibit some of the lowest recorded water loss rates compared with those of other terrestrial arthropods of similar body size. Evaporative water loss (EWL) includes cuticular transpiration and respiratory water loss (RWL) from gas exchange surfaces, that is, book lung lamellae. Estimated fractions of cuticular and respiratory losses currently available from the literature show considerable variation, at least partly as a result of differences in methodology. This study reports RWL rates and their relative importance in scorpions from two families (Buthidae and Scorpionidae), including both xeric and mesic species (or subspecies). Two of the included Buthidae were surface-dwelling species, and another inhabits empty burrows of other terrestrial arthropods. This experimental design enabled correlating RWL importance with scorpion phylogeny, habitat type, and/or homing behavior. Buthidae species exhibited significantly lower EWL rates compared with those of Scorpionidae, whereas effects of habitat type and homing behavior were not significant. Resting RWL rates were not significantly affected by scorpion phylogeny, but rates for the xeric species (totaling ∼10% of EWL rates at 30°C) were significantly lower compared with those of mesic species. These lower RWL values were correlated with significantly lower H2O/CO2 emission rates in xeric species. The experimental setup and ∼24-h duration of each individual recording allowed estimating the effect of interspecific variation in activity on RWL proportions. The high respiratory losses in active hydrated Scorpio maurus fuscus, totaling 30% of EWL, suggest that behavioral discretion in this species is a more likely mechanism for body water conservation under stressful conditions when compared with the responses of other studied species.

Neural Control of Gas Exchange Patterns in Insects: Locust Density-Dependent Phases as a Test Case

The adaptive significance of discontinuous gas exchange cycles (DGC) in insects is contentious. Based on observations of DGC occurrence in insects of typically large brain size and often socially-complex life history, and spontaneous DGC in decapitated insects, the neural hypothesis for the evolution of DGC was recently proposed. It posits that DGC is a non-adaptive consequence of adaptive down-regulation of brain activity at rest, reverting ventilatory control to pattern-generating circuits in the thoracic ganglia. In line with the predictions of this new hypothesis, we expected a higher likelihood of DGC in the gregarious phase of the desert locust (Schistocerca gregaria, Orthoptera), which is characterized by a larger brain size and increased sensory sensitivity compared with the solitary phase. Furthermore, surgical severing of the neural connections between head and thoracic ganglia was expected to increase DGC prevalence in both phases, and to eliminate phase-dependent variation in gas exchange patterns. Using flow-through respirometry, we measured metabolic rates and gas exchange patterns in locusts at 30°C. In contrast to the predictions of the neural hypothesis, we found no phase-dependent differences in DGC expression. Likewise, surgically severing the descending regulation of thoracic ventilatory control did not increase DGC prevalence in either phase. Moreover, connective-cut solitary locusts abandoned DGC altogether, and employed a typical continuous gas exchange pattern despite maintaining metabolic rate levels of controls. These results are not consistent with the predictions of the neural hypothesis for the evolution of DGC in insects, and instead suggest neural plasticity of ventilatory control.