Isolation of the abdomen releases oviposition behaviour in females of the cricket, Acheta domesticus

Upon isolation, abdomens of adult female house crickets (Acheta domesticus) produced abdominal and ovipositor movements characteristic of normal oviposition. Oviposition behaviour was thus released even in reproductively mature or immature virgins where under normal conditions it was never observed. Decapitation was not sufficient to release oviposition behaviour but transection of the ventral nerve cord between the thorax and the abdomen of immobilized females evoked the response. These observations indicate that the motor programmes for certain components of the oviposition sequence reside in the abdominal ganglia. Moreover, the prerequisite circuitry for ovipositional posturing of the abdomen and ovipositor appears to be functional prior to sexual maturity and insemination, primed by mating, and subject to inhibition by the thoracic ganglia.     

Additive and non-additive responses of seedlings to simulated herbivory and drought

Drought is a global threat, increasing in severity and frequency throughout tropical ecosystems. Although plants often face drought in conjunction with biotic stressors, such as herbivory or disease, experimental studies infrequently test the simultaneous effects of drought and biotic stress. Because multiple simultaneous stressors may have non-additive and complex effects on plant performance, it is difficult to predict plant responses to multiple threats from research examining one stress at a time. Using an experimental approach in the greenhouse, we investigated potential non-additivity in seedling growth and survival to simulated drought and herbivory across a phylogenetically diverse pool of ten Hawaiian plant species. Overall, seedlings showed limited tolerance, defined as similar growth and survival in stressed compared with control (non-stressed) plants, to simulated herbivory and drought, with the combined effects of both stressors to be generally additive and negative across species. Significant variation in stress tolerance was detected among species, and species variation was explained, at least in part, by functional traits such that species with larger root/shoot ratios and smaller seeds, tended to demonstrate greater herbivory and drought tolerance. Future research incorporating additional trait analysis and different stressors could shed light on mechanisms underlying seedling stress tolerance and clarify whether additivity, as detected in this study, extends across other combinations of stressors. Such work will provide needed insights into the regeneration of seedlings in tropical forests under threats of herbivory and climate change.     

Clipping defoliation and nitrogen addition shift competition between a C3 grass (Leymus chinensis) and a C4 grass (Hemarthria altissima)

• Human‐induced disturbances, including grazing and clipping, that cause defoliation are common in natural grasslands. Plant functional type differences in the ability to compensate for this tissue loss may influence interspecific competition.
• To explore the effects of different intensities of clipping and nitrogen (N) addition on compensatory growth and interspecific competition, we measured accumulated aboveground biomass (AGB), belowground biomass (BGB), tiller number, non‐structural carbohydrates concentrations and leaf gas exchange parameters in two locally co‐occurring species (the C₃ grass Leymus chinensis and the C₄ grass Hemarthria altissima) growing in monoculture and in mixture.
• For both grasses, the clipping treatment had significant impacts on the accumulated AGB, and the 40% clipping treatment had the largest effect. BGB gradually decreased with increasing defoliation intensity. Severe defoliation caused a significant increase in tiller number. Stored carbohydrates in the belowground biomass were mobilised and transported aboveground for the growth of new leaves to compensate for clipping‐induced injury. The net CO₂ assimilation rate (A) of the remaining leaves increased with clipping intensity and peaked under clipping intensities of 20% or 40%. Nitrogen addition, at a rate of 10 g·N·m^?2·year^?1, enhanced A of the remaining leaves and non‐structural carbohydrate concentrations, which benefited plant compensatory growth, especially for the C₃ grass. Under the mixed planting conditions, the clipping and N addition treatments lowered the competitive advantage of the C₄ grass.
• The results suggest that a combination of defoliation and N deposition have the potential to benefit the coexistence of C₃ and C₄ grasses.

     

Compensatory light utilization of Phalaris arundinacea within the Phalaris arundinacea–Phragmites australis compound community

This study investigated the light utilization characteristics of Phalaris arundinacea within the Phalaris arundinacea-Phragmites australis compound community. The investigation was based on the response curve equation of the net photosynthetic rate-photosynthetic photon flux density (Pn-PPFD) of P. arundinacea and on the distribution of PPFD on the surface canopy of P. arundinacea within the compound community. Results showed that P. arundinacea was able to compensate for substantial reduction in available light, and utilize the weak light within the lower part of the compound community. On the one hand, the density of P. australis within the compound community determined the compensatory light utilization rate (CLUR) of P.arundinacea. On the other hand, the CLUR amplitude of P. arundinacea within the compound community with the same P. australis density was relatively small in a day. The results can help people to regulate P. arundinacea-P. australis compound communities to maintain a long-term, stable coexistence in the constructed wetlands.

Abbreviations: CK – control; CLUR, compensatory light utilization rate; LER, light extinction rates; Pn, net photosynthetic rate; PPFD, photosynthetic photon flux density.     

Plane of nutrition during the rearing phase for replacement ewes of four genotypes: I – effects on growth and development,and on ovulation rate at first joining

Plane of nutrition (PN) offered to ewe replacements during the rearing phase (8 to 17 months) affects BW at joining and may affect reproductive performance when joined at ~19 months. The effects of PN offered to ewe replacements during their first winter (winter_1) and second summer (summer_2) were evaluated over 3 consecutive years, using 287 spring-born ewe lambs, representing four genotypes (Belclare (Bel), Charmoise×Scottish Blackface (C×SBF), Bel×SBF (Bel×SBF), Bel×SBF that were heterozygous either FecG^H or FecX^G mutations that increase ovulation rate (OR) (BelMG×SBF)). During extended (deferred) grazing in winter_1 (November to March) the lambs were offered herbage DM allowances (HA) of 0.75 (L) or 1.75 (H) kg/day. During summer_2 (March to August) the replacements were set stocked to maintain sward heights of 4 (L) or 6 (H) cm, thus yielding a 2×2 factorial design for the nutrition treatments (71 to 73 animals/treatment). Increasing HA during winter_1, and residual sward height during summer_2, increased (P<0.001) BW and body size at joining (19 months) but had no effect (P>0.05) on OR. Mean BW at joining was 53.3, 56.8, 56.6 and 61.7 (SEM 0.74) kg for ewes offered the LL, LH, HL and HH treatments, respectively. Mean OR of C×SBF and BelMG×SBF differed (P<0.001) from that of Bel×SBF by −0.58 and +0.47, respectively. Correlations between linear measurements (LMs) of body size and BW at 7, 12 and 17 months were all positive and significant (P<0.001). The precision of the set of LMs as a predictor of BW at joining improved with age (R² 0.46, 0.54 and 0.74 at 7, 12 and 17 months) but BW at a given age was a better predictor at all age time points. Chest girth was the best predictor, among the LMs, of BW at joining and its explanatory power increased with age. Equations developed using LMs at 7, 12 or 17 months, to predict BW at joining exhibited biases of −2.1, −1.5 and +0.9 kg, respectively. It is concluded that whilst altering PN during the rearing phase changed BW by 16% it had no effect on OR. There was no interaction (P>0.05) between the PN offered during winter_1 and summer_2, or PN and ewe genotype for BW at joining or OR. LMs, either at 7, 12 or 17 months of age, are useful predictors of BW at joining.     

Pea leaf weevil herbivory on pea seedlings: effects on growth response and yield

Field experiments were conducted to determine growth and yield responses ofPisum sativum L. to defoliation by adultSitona lineatus (L.). Seedlings grown under conventional (moldboard plowed) and conservation (chisel plowed) tillage treatments were infested for a 1-week period with 0, 1 and 8 weevils per plant at two times: at 75% field emergence and 1 week later. After the early infestation, defoliation for the control, low and high weevil densities was about 0,15 and 50%, respectively, while defoliation after the late infestation was about 0, 10 and 35%. An undercompensatory growth response was observed in one experiment after seedlings were subjected to moderate levels of early defoliation. Exact compensation was observed in two experiments after early infestations of low and highSitona densities.Sitona defoliation reduced the number of pods per plant and pod length in two experiments. However, seed biomass was never significantly reduced. Averaged over all experiments, reduction in seed biomass due to highSitona densities was 10 and 5% for early and late infestations, respectively. Tillage treatments did not affectPisum compensatory growth response, although yield components were sometimes greater in conservation tillage than in conventional tillage, possibly due to slightly greater soil moisture in the conservation tillage plots.     

Carbon dioxide-induced changes in beech foliage cause female beech weevil larvae to feed in a compensatory manner

The phenology of Fagus sylvatica was unaffected by exposure to an atmosphere of elevated CO₂ (600 μL L^-1) after two years of fumigation. Non-significant changes in nitrogen and phenolic content of the leaves decreased the nutritional status of beech for female larvae in elevated CO₂ such that they responded by eating in a compensatory manner; males were unaffected. Rates of development, mortality and adult biomass of Rhynchaenus fagi were no different from those in ambient CO₂ concentrations (355 μL L ^-1). It is possible that, with the changes in leaf chemistry affecting the females, fecundity will be altered, with important consequences for populations of beech weevil.     

Tonic and modulatory subsystems of the complex gravity receptor system in crickets, Gryllus bimaculatus

The gravity receptor system of crickets Gryllus bimaculatus is composed of antennal, cercal and leg subsystems. The cercal gravity receptors are the club-shaped sensilla. Each of these subsystems elicits compensatory head movements during passive roll.The extent of compensatory head movements depends on the strength of the gravitational stimulus applied to the leg subsystem. Amputation of 2 legs never causes a decrease in reflex amplitude. Unilateral amputation of 1 to 3 legs always induces a roll movement of the head to the intact body side. Therefore, the leg gravity receptor system exerts a modulatory and tonic effect on the neck muscles.The gravity receptors of 1 cercus or 1 antenna only elicit compensatory head movements. They exert no tonic effect on the neck muscles.The results are discussed with respect to (i) the proposed connectivity of the cercus-neck muscle pathway, (ii) mutual inhibitory interactions between the sensory pathways originating in the leg gravity receptors, and (iii) the influence of non-gravitationally induced excitation on the occurrence of compensatory head movements during passive roll of the crickets.     

Density‐dependent growth in hatchery‐reared brown trout released into a natural stream

Hatchery‐reared brown trout Salmo trutta stocked in a natural stream in addition to resident wild brown trout grew more slowly than those stocked with an experimentally reduced density of brown wild trout. In both cases, hatchery‐reared brown trout grew more slowly than resident wild fish in control sections. Mortality and movements did not differ among the three categories of fish. The results showed that growth of stocked hatchery‐reared brown trout parr was density‐dependent, most likely as a consequence of increased competition. Thus, supplementary release of hatchery‐reared fish did not necessarily increase biomass.     

The Mendelian inheritance of rare flesh and shell colour variants in the black‐lipped pearl oyster (Pinctada margaritifera)

Pinctada margaritifera is French Polynesia's most economically important aquaculture species. This pearl oyster has the specific ability to produce cultured pearls with a very wide range of colours, depending on the colour phenotypes of donor oysters used. Its aquaculture is still based on natural spat collection from wild stocks. We investigated three rare colour variants of P. margaritifera – orange flesh, and red and white shell colour phenotypes – in comparison with the wild‐type black flesh and shell commonly found in this species. The study aimed to assess the geographic distribution and genetic basis of these colour variants. Colour frequencies were evaluated during transfer and graft processes of pearl oyster seed captured at collector stations. Among the collection locations studied, Mangareva Island showed the highest rate of the orange flesh phenotype, whereas Takaroa and Takume atolls had relatively high rates of red and white shell phenotypes respectively. Broodstocks were made of these rare colour variants, and crosses were performed to produce first‐ and second‐generation progenies to investigate segregation. The results were consistent with Mendelian ratios and suggest a distinct model with no co‐dominance: (i) a two‐allele model for flesh trait, whereby the orange allele is recessive to the black fleshed type, and (ii) a three‐allele model for shell trait, whereby the black wild‐type allele is dominant to the red coloration, which is dominant to the white shell. Furthermore, the proposed model provides the basis for producing selected donor pearl oyster lines through hatchery propagation.