Wood ants use resin to protect themselves against pathogens

Social life is generally associated with an increased exposure to pathogens and parasites, due to factors such as high population density, frequent physical contact and the use of perennial nest sites. However, sociality also permits the evolution of new collective behavioural defences. Wood ants, Formica paralugubris, commonly bring back pieces of solidified coniferous resin to their nest. Many birds and a few mammals also incorporate green plant material into their nests. Collecting plant material rich in volatile compounds might be an efficient way to fight bacteria and fungi. However, no study has demonstrated that this behaviour has a positive effect on survival. Here, we provide the first experimental evidence that animals using plant compounds with antibacterial and antifungal properties survive better when exposed to detrimental micro-organisms. The presence of resin strongly improves the survival of F. paralugubris adults and larvae exposed to the bacteria Pseudomonas fluorescens, and the survival of larvae exposed to the entomopathogenic fungus Metarhizium anisopliae. These results show that wood ants capitalize on the chemical defences which have evolved in plants to collectively protect themselves against pathogens.     

Odour-mediated long-range avoidance of interspecific competition by a solitary endoparasitoid: a time-saving foraging strategy

1. In studies on optimal foraging strategies, long-range decisions in the pursuit of resource are rarely considered. This is also the case for sympatric parasitoids, which may be confronted with the decision to accept or reject host larvae that are already parasitized by a competing species. They can be expected to reject already parasitized hosts if it is likely that they will lose the resulting intrinsic competition. However, examples of such interspecific host discrimination are rare. 2. We propose that parasitoids that are not egg-limited should reject inferior hosts only if it saves them time, and that this will be achieved mainly when the parasitoids are able to detect competitors from a distance. We tested this hypothesis using the sympatric parasitoids Cotesia marginiventris (Cresson) and Campoletis sonorensis (Cameron). 3. C. sonorensis was found to be the superior intrinsic competitor but, upon contact with a host larva, both wasps readily accepted hosts that had already been parasitized by the other species. However, in an olfactometer experiment, C. marginiventris females were found to strongly avoid the odour of their superior competitor. 4. These results are in accordance with a time optimization scenario, whereby the inferior competitor accepts competition if it costs only an egg, but avoids competition if it may save time that can be allocated to the search for more profitable hosts. 5. Models on host discrimination strategies in parasitoids had not yet considered discrimination from a distance. Long-range foraging decisions can also be expected for other organisms that have to choose between resources of varying suitability and profitability.     

Is there a fixed number of niches for endoparasites of fish?

Kennedy and Guégan, based on Cornell and Lawton (J Anim Ecol 1992;61:1–12), found a curvilinear relationship (the fundamental form of the relationship for parasite communities) between infracommunity and component community richness, and interpreted this as meaning that only processes acting within the infracommunities can explain the limitation in the number of parasite species in a given host. The research described here shows that an asymptotic relationship is the consequence of the differential likelihoods of parasite species to appear in an infracommunity as determined by transmission rates and intrinsic lifespans. Processes operating at the infracommunity level are not necessary to explain the curvilinear relationship. Even communities much richer than those found in European freshwater fishes cannot be assumed to be saturated in the sense that further species cannot be added over evolutionary time.     

斑痣悬茧蜂对不同寄主密度斑块的选择和最优搜寻行为

在圆柱形透明有机玻璃罩内,观察了斑痣悬茧蜂对不同寄主密度斑块的选择和滞留时间,并用Cox比例风险模型分析了寄主密度、产卵次数和搜寻特征对斑痣悬茧蜂在斑块上的驻留时间及其影响因素.结果表明:斑痣悬茧蜂对高密度寄主斑块的初次选择次数、访问次数均高于低密度寄主斑块,导致在高密度斑块上具有更高的寄生率;斑痣悬茧蜂在各斑块的驻留时间随寄主密度的增加而增加.Cox模型分析结果显示,斑块内寄主密度和产卵数均对其离开斑块的倾向起消极作用,即随寄主密度和产卵数的增加而倾向于留在斑块上;而寄主密度与产卵数的互作反而对寄生蜂离开斑块倾向具有促进作用,这两种作用可使寄生蜂利用寄主斑块获得最大适合度.     

Self-induced Increase of Gut Motility and the Control of Parasitic Infections in Wild Chimpanzees

When physiological adaptation is insufficient, hosts have developed behavioral responses to avoid or limit contact with parasites. One such behavior, leaf-swallowing, occurs widely among the African great apes. This behavior involves the slow and deliberate swallowing without chewing of whole bristly leaves. Folded one at a time between tongue and palate, the leaves pass through the gastro-intestinal (GI) tract visibly unchanged. Independent studies in two populations of chimpanzees (Pan troglodytes schweinfurthii) showed significant correlations between the swallowing of whole leaves and the expulsion of the nodule worm Oesophagostomum stephanostomum and a species of tapeworm (Bertiella studeri). We integrate behavioral, parasitological and physiological observations pertaining to leaf-swallowing to elucidate the behavioral mechanism responsible for the expulsion and control of nodule worm infections by the ape host. Physical irritation produced by bristly leaves swallowed on an empty stomach, increases motility and secretion resulting in diarrhea which rapidly moves leaves through the GI tract. In the proximal hindgut, the site of third-stage larvae (L3) cyst formation and adult worm attachment, motility, secretion and the scouring effect of rough leaves is enhanced by haustral contractions and peristalsis-antiperistalsis. Frequently, at the peak of reinfection, a proportion of nonencysted L3 is also predictably vulnerable. These factors should result in the disruption of the life cycle of Oesophagostomum spp. Repeated flushing during peak periods of reinfection is probably responsible for long-run reduction of worm burdens at certain times of the year. Accordingly, leaf-swallowing can be viewed as a deliberate adaptive behavioral strategy with physiological consequences for the host. The expulsion of worms based on the activation of basic physiological responses in the host is a novel hitherto undescribed form of parasitic control.     

鱼类三代虫的寄主特异性分析

分析了迄今为止世界范围三代虫的寄主情况。三代虫具有很强的寄主特异性,并且在种、属及科等水平上的特异性均有较明显差异;分析同一种寄主上所寄生的三代虫种类之间的关系,显示大部分寄主只寄生一种三代虫,体现出了三代虫很强的寄主特异性。     

Host fragmentation and helminth parasites: Hedging your bets against extinction

We consider the probability of parasite extinction due to anthropogenic fragmentation of host populations and in the absence of host extinction. We conclude that extinction at infrapopulation and infracommunity levels is both common and trivial. Extinction may occur in communities at higher levels but only if metapopulations or suprapopulations become extinct. Suprapopulations are highly complex and unlikely to become extinct in the face of simple host fragmentation. We acknowledge parasite metapopulations as being the most likely to become extinct, but only locally. Our reasoning for this is that, in the absence of complete host extinction, populations of the parasite in other fragments are likely to serve as sources for reinvasion (e.g. a rescue effect). We identify a number of features that may act as hedges against extinction for many parasites and conclude by attempting to identify what form an extinction might take.     

Social networks and the spread of Salmonella in a sleepy lizard population

Although theoretical models consider social networks as pathways for disease transmission, strong empirical support, particularly for indirectly transmitted parasites, is lacking for many wildlife populations. We found multiple genetic strains of the enteric bacterium Salmonella enterica within a population of Australian sleepy lizards (Tiliqua rugosa), and we found that pairs of lizards that shared bacterial genotypes were more strongly connected in the social network than were pairs of lizards that did not. In contrast, there was no significant association between spatial proximity of lizard pairs and shared bacterial genotypes. These results provide strong correlative evidence that these bacteria are transmitted from host to host around the social network, rather than that adjacent lizards are picking up the same bacterial genotype from some common source.     

Flight Toward a Learned Odor and Factors Inducing Landing of Female Brachymeria intermedia (Hymenoptera: Chalcididae), a Parasitoid of the Gypsy Moth, Lymantria dispar (Lepidoptera: Lymantriidae)

Through a single oviposition experience in the presence of vanilla odor, female Brachymeria intermedia were conditioned to fly toward a source of vanilla odor in a wind tunnel. Conditioning was an associative process, and wasps were able to fly toward odor sources at much lower doses than the dose used in conditioning. Furthermore, upon approaching vanilla-scented paper rolls hung on a vertical cylinder, conditioned wasps landed on them readily, whereas few wasps landed on real pupae. However, more wasps reached pupae or pupal cases than white paper rolls. Visual and olfactory cues appeared to mediate the foraging behavior of wasps in conflicting ways. Therefore, the extent to which olfactory learning mediates foraging success in this species remains unresolved.     

寄生蜂成虫在寄主搜索过程中的学习行为

综述了寄生蜂寄主搜索过程中的学习行为的概念、过程、适应性意义及影响因子。学习是寄生蜂的一种普遍特征,但学习基本上只发生在成虫期,其中联系性学习是一个主要特征。学习可产生启动和嗜好性学习二种效应,在寄生蜂搜索寄主的各个步骤中发挥重要作用,使其在复杂多变的生存环境中可高效地识别和利用各种有用信息,提高搜索效率。学习的潜力及效应可依寄生蜂和寄主的食性专化程度、寄主的发育阶段、寄生蜂自身的生理状态及环境中刺激的性质等因子而变化。对寄生蜂学习行为的了解有助于发展对其行为调控的技术,提高寄生蜂对害虫控制的效能。