Kleptoparasitism as an explanation for paradoxical oviposition decisions of the parasitoid Asobara tabida

It is known that the braconid Asobara tabida, a parasitoid of Drosophila larvae, takes oviposition decisions in accordance with survival probabilities in several host species. Nevertheless, larvae of D. simulans, in which the survival probability is virtually zero, are readily accepted for oviposition by searching females. This even happens when they are offered together with D. melanogaster larvae, in which the parasitoid can develop. Here I show that A. tabida can act as a kleptoparasitoid in D. simulans larvae: it can develop in D. simulans larvae, once these larvae are parasitized by another parasitoid, the eucoilid Leptopilina boulardi. Analysis with an optimal foraging model suggests that the increase in survival probability and the occurrence of L. boulardi in the field are high enough to make this kleptoparasitic behaviour of A. tabida pay.     

Maize based diets and possible neurobehavioural after-effects among some populations in the world

Maize is a cereal particularly lacking in tryptophan, which is the precursor of serotonin, an important neurotransmitter. Altough complementary foods may eliminate tryptophan deficiency, serotonin deficiency may often continue to exist because of competition made by other Large Neutral Amino Acids (LNAA) against tryptophan for neuron access, since they use the same carrier to cross the blood-brain barrier. Thus serotonin synthesis depends on two variables: the amount of tryptophan and the trp/LNAA ratio (R). “R” is lowest for common maize, low for beans and, as a rule, for most vegetable foods, higher for meat. So, when maize is the preponderant food in the meal, the “R” value lowers and so in parallel serotonin synthesis does. Serotonin deficiency involves several behavioural consequences, such as the tendency towards aggressive behaviour or the religious fanaticism. Among native american populations, these consequences appear, as a rule, positively correlated with maize alimentary dependence (Aztecs appear as those who greatly suffered from serotonin deficiency). In the world these are thinkable for some african populations (i.e. Zulu) or european (i.e. Balkan peoples).     

Properties of a plasticised starch blend. Part 1: Influence of moisture content on fracture properties

The effect of moisture content on tensile and fracture properties of a plasticised starch/high molecular weight polyol blend was investigated. A wide range of mechanical behaviour was achieved by varying slightly the water uptake of this material. At low moisture content, the Young’s modulus was 3800 MPa and the yield stress, 54 MPa. When the moisture content reached 15 wt%, their values dropped, respectively, to around 1500 MPa and 21 MPa. As the material behaviour varies greatly over the moisture content range, two fracture mechanics techniques were employed: the linear elastic fracture mechanics approach to characterise brittle behaviour and the essential work of fracture method to investigate a more ductile material. At low moisture content, the measured strain energy release rate at fracture, J_Q was very low and showed little dependency on the moisture content. As the moisture content increases, the material becomes increasingly ductile and displayed a brittle-to-ductile transition at 12% of moisture content, which corresponded to the glass transition temperature of the added polyol.     

Pro-sociality without empathy

Empathy, the capacity to recognize and share feelings experienced by another individual, is an important trait in humans, but is not the same as pro-sociality, the tendency to behave so as to benefit another individual. Given the importance of understanding empathy''s evolutionary emergence, it is unsurprising that many studies attempt to find evidence for it in other species. To address the question of what should constitute evidence for empathy, we offer a critical comparison of two recent studies of rescuing behaviour that report similar phenomena but are interpreted very differently by their authors. In one of the studies, rescue behaviour in rats was interpreted as providing evidence for empathy, whereas in the other, rescue behaviour in ants was interpreted without reference to sharing of emotions. Evidence for empathy requires showing that actor individuals possess a representation of the receiver''s emotional state and are driven by the psychological goal of improving its wellbeing. Proving psychological goal-directedness by current standards involves goal-devaluation and causal sensitivity protocols, which, in our view, have not been implemented in available publications. Empathy has profound significance not only for cognitive and behavioural sciences but also for philosophy and ethics and, in our view, remains unproven outside humans.     

Phospholipase Dα1‐mediated phosphatidic acid change is a key determinant of desiccation‐induced viability loss in seeds

High sensitivity of seeds to water loss is a widespread phenomenon in the world's plant species. The molecular basis of this trait is poorly understood but thought to be associated with critical changes in membrane function. We profiled membrane lipids of seeds in eight species with varying levels of desiccation tolerance and found a close association between reducing seed viability and increasing phosphatidic acid (PA). We applied hydration–dehydration cycles to Arabidopsis seeds, which are normally desiccation tolerant, to mimic the onset of desiccation sensitivity with progression towards germination and examined the role of phospholipase D (PLD) in desiccation stress‐induced production of PA. We found that PLDα1 became more abundant and migrated from the cytosol to the membrane during desiccation, whereas PLDδ did not change, and that all desiccation‐induced PA was derived from PLDα1 hydrolysis. When PLDα1 was suppressed, the germination level after each hydration–dehydration cycle improved significantly. We further demonstrated that PLDα1‐mediated PA formation modulates desiccation sensitivity as applying its inhibitor improved seed desiccation tolerance and its suppression in protoplasts enhanced survival under dehydration. The insights provided by comparative lipidomics enable us to propose a new membrane‐based model for seed desiccation stress and survival.     

Predators marked with chemical cues from one prey have increased attack success on another prey species

1. To reduce the risk of being eaten by predators, prey alter their morphology or behaviour. This response can be tuned to the current danger if chemical or other cues associated with predators inform the prey about the risks involved. 2. It is well known that various prey species discriminate between chemical cues from predators that fed on conspecific prey and those that fed on heterospecific prey, and react stronger to the first. It is therefore expected that generalist predators are more successful in capturing a given prey species when they are contaminated with chemical cues from another prey species instead of cues from the same prey species. 3. Here, a generalist predatory mite was studied that feeds on thrips larvae as well as on whitefly eggs and crawlers. Mites were marked with cues (i.e. body fluids) of one of these two prey species and were subsequently offered thrips larva. 4. Predators marked with thrips cues killed significantly fewer thrips than predators marked with whitefly cues, even though the predator's tendency to attack was the same. In addition, more thrips larvae sought refuge in the presence of a predatory mite marked with thrips cues instead of whitefly cues. 5. This suggests that generalist predators may experience improved attack success when switching prey species.     

小鼠异常行为及其继代遗传特性

实验室条件下小鼠常表现多种异常行为,通过对跳跃爬行鼠和非跳跃爬行鼠的亲代及F1代的行为观察,研究小鼠异常行为在继代过程中的变化规律以及皮质醇浓度与异常行为的关系。结果表明:两代跳跃爬行鼠和非跳跃爬行鼠的异常行为差异显著(P<0.05),在正常行为中跳跃爬行鼠的平均睡眠时间和修饰行为的次数明显少于非跳跃爬行鼠(P<0.05),而探究行为的次数明显高于非跳跃爬行鼠(P<0.05)。F1代跳跃爬行鼠的异常行为类型基本和母体一致,异常行为的发生次数明显高于亲代,说明异常行为具有遗传基础。通过测定皮质醇浓度,发现跳跃爬行鼠的皮质醇平均浓度明显高于非跳跃爬行鼠(P<0.05),说明皮质醇的分泌量影响着异常行为的发生频率。     

Rapid expansion of the cane toad (Bufo marinus) invasion front in tropical Australia

Abstract Cane toads (Bufo marinus) are large toxic anurans that have spread through much of tropical Australia since their introduction in 1935. Our surveys of the location of the toad invasion front in 2001 to 2005, and radiotracking of toads at the front near Darwin in 2005, reveal much faster westwards expansion than was recorded in earlier stages of toad invasion through Queensland. Since reaching the wet‐dry tropics of the Northern Territory, the toads have progressed an average of approximately 55 km year⁻¹ (mean rate of advance 264 m night⁻¹ along a frequently monitored 55‐km road transect during the wet season of 2004–2005). Radiotracking suggests that this displacement is due to rapid locomotion by free‐ranging toads rather than human‐assisted dispersal; individual toads frequently moved >200 m in a single night. One radiotracked toad moved >21 800 m in a 30‐day period; the fastest rate of movement yet recorded for any anuran. Daily displacements of radiotracked toads varied with time and local weather conditions, and were highest early in the wet season on warm, wet and windy nights. The accelerated rate of expansion of the front may reflect either, or both: (i) evolved changes in toads or (ii) that toads have now entered an environment more favourable to spread. This accelerated rate of expansion means that toads will reach the Western Australian border and their maximal range in northern Australia sooner than previously predicted.     

Behaviour of drifting insect larvae

The larval drift behaviour of 23 species representing Ephemeroptera, Plecoptera and Trichoptera was investigated in the laboratory using different current regimes. Mayfly nymphs often performed swimming, while caddis larvae were reluctant to do so. Stonefly nymphs were intermediate. In mayflies swimming seemed to be used to reach the substrate as soon as possible. In contrast most stonefly nymphs by swimming prolonged the time spent in the water column. Modes of swimming and sinking posture differed markedly between the orders. Living passively sinking animals often reached bottom faster than dead control specimens, so consequently behaviour did not always express itself in activity. Some caddis larvae spun adherent anchor lines. Differences among taxa seemed more important in explaining swimming activity compared to preferred habitats (as stream, river and lake) in each species. However, observed differences among closely related species indicated subtle differences related to microhabitat to be of profound importance in explaining the alternative behavioural strategies used.