Egg recognition and counting reduce costs of avian conspecific brood parasitism

Birds parasitized by interspecific brood parasites often adopt defences based on egg recognition but such behaviours are puzzlingly rare in species parasitized by members of the same species. Here I show that conspecific egg recognition is frequent, accurate and used in three defences that reduce the high costs of conspecific brood parasitism in American coots. Hosts recognized and rejected many parasitic eggs, reducing the fitness costs of parasitism by half. Recognition without rejection also occurred and some hosts banished parasitic eggs to inferior outer incubation positions. Clutch size comparisons revealed that females combine egg recognition and counting to make clutch size decisions--by counting their own eggs, while ignoring distinctive parasitic eggs, females avoid a maladaptive clutch size reduction. This is clear evidence that female birds use visual rather than tactile cues to regulate their clutch sizes, and provides a rare example of the ecological and evolutionary context of counting in animals.     

A brood parasitic catfish of mouthbrooding cichlid fishes in Lake Tanganyika

Brood parasitism, where a brood of the parasitic species is fostered by the parents of another species, is well known among birds. In most cases, such offspring show a complete reliance upon their host parents for food, protection and warmth until their independence. In other vertebrate groups, however, such total dependence upon a host species is unknown. I report here the first example of true brood parasitic behaviour discovered among fishes. In Lake Tanganyika, an endemic mochokid catfish, Synodontis multipunctatus Boulenger, is a brood parasite of mouthbrooding fishes of the family Cichlidae. The eggs of the catfish are incubated in the mouths of any of several host species together with the host's eggs, but hatch earlier. Following absorption of their yolk sacs, the catfish fry feed upon the fry of the host while still in its mouth. Thus the early stages of development of this catfish not only depend upon their hosts for food and protection, but exploit almost their entire parental investment.     

Escalation of a coevolutionary arms race through host rejection of brood parasitic young

Cuckoo nestlings that evict all other young from the nest soon after hatching impose a high reproductive cost on their hosts. In defence, hosts have coevolved strategies to prevent brood parasitism. Puzzlingly, they do not extend beyond the egg stage. Thus, hosts adept at recognizing foreign eggs remain vulnerable to exploitation by cuckoo nestlings. Here we show that the breach of host egg defences by cuckoos creates a new stage in the coevolutionary cycle. We found that defences used during the egg-laying period by host superb fairy-wrens (Malurus cyaneus) are easily evaded by the Horsfield's bronze-cuckoo (Chrysococcyx basalis), a specialist fairy-wren brood parasite. However, although hosts never deserted their own broods, they later abandoned 40% of nests containing a lone Horsfield's bronze-cuckoo nestling, and 100% of nests with a lone shining bronze-cuckoo nestling (Chrysococcyx lucidus), an occasional fairy-wren brood parasite. Our experiments demonstrate that host discrimination against evictor-cuckoo nestlings is possible, and suggest that it has selected for the evolution of nestling mimicry in bronze-cuckoos.     

Parasitoid secretions provoke ant warfare

Insect social parasites are extreme specialists that typically use mimicry or stealth to enter ant colonies to exploit the rich, but fiercely protected, resources within their nests. Here we show how a parasitic wasp (parasitoid) contrives to reach its host, itself an endangered species of social parasite that lives inside the brood chambers of ant nests, by releasing semiochemicals to induce in-fighting between worker ants, locking the colony in combat and leaving it underprotected. Four of these chemicals are new to biology and have the potential to control pest species by inducing different agonistic behaviours in ants.     

A host parasite interaction rescues Drosophila oogenesis defects

The cytoplasmically inherited bacterium Wolbachia pipientis is a widespread parasite of arthropods that manipulates the reproductive biology of its hosts, often to their detriment, in order to foster its own transmission through egg cytoplasm. Here we report that infection by Wolbachia restores fertility to Drosophila melanogaster mutant females prevented from making eggs by protein-coding lesions in Sex-lethal (Sxl), the master regulator of sex determination. Suppression of sterility by Wolbachia discriminates markedly among similar germline-specific Sxl alleles, and is not observed for mutations in other genes that produce similar 'tumorous ovary' phenotypes, including one that blocks Sxl germline expression. This allele and gene specificity indicates that suppression probably results from a specific interaction with Sxl protein, rather than from a bypass of the normal germline requirement for this developmental regulator or from an effect on Sxl expression. The Sxl-Wolbachia interaction provides a rare opportunity to explore host-parasite relationships at the molecular level in a model insect. Furthermore, demonstration that a parasite infection can counteract the deleterious effects of mutations in host genes illustrates how hosts might become dependent on parasites.     

Parasite adaptation to locally common host genotypes

According to the Red Queen hypothesis--which states that interactions among species (such as hosts and parasites) lead to constant natural selection for adaptation and counter-adaptation--the disproportionate evolutionary success of parasites on common host genotypes leads to correlated selection for sexual reproduction and local adaptation by the parasite population. Here we determined whether local adaptation is due to disproportionate infection of common host genotypes, and, if so, whether infection of common host genotypes is due to commonness per se, or some other aspect of these genotypes. In a reciprocal cross-inoculation experiment parasites occupying the same geographical area (sympatric) infected locally common host genotypes significantly more often than rare host genotypes, whereas parasites occupying separate geographical areas (allopatric) showed no such significant difference. A mixed source of parasites (containing F1 hybrids) also showed no difference in infection between rare and common host genotypes. These results show that local adaptation results from parasite tracking of locally common host genotypes, and, as such, a necessary condition of the Red Queen hypothesis is met.     

The role of parasites in sympatric and allopatric host diversification

Exploiters (parasites and predators) are thought to play a significant role in diversification, and ultimately speciation, of their hosts or prey. Exploiters may drive sympatric (within-population) diversification if there are a variety of exploiter-resistance strategies or fitness costs associated with exploiter resistance. Exploiters may also drive allopatric (between-population) diversification by creating different selection pressures and increasing the rate of random divergence. We examined the effect of a virulent viral parasite (phage) on the diversification of the bacterium Pseudomonas fluorescens in spatially structured microcosms. Here we show that in the absence of phages, bacteria rapidly diversified into spatial niche specialists with similar patterns of diversity across replicate populations. In the presence of phages, sympatric diversity was greatly reduced, as a result of phage-imposed reductions in host density decreasing competition for resources. In contrast, allopatric diversity was greatly increased as a result of phage-imposed selection for resistance, which caused populations to follow divergent evolutionary trajectories. These results show that exploiters can drive diversification between populations, but may inhibit diversification within populations by opposing diversifying selection that arises from resource competition.     

Genetic evidence for female host-specific races of the common cuckoo

The common cuckoo Cuculus canorus is divided into host-specific races (gentes). Females of each race lay a distinctive egg type that tends to match the host's eggs, for instance, brown and spotted for meadow pipit hosts or plain blue for redstart hosts. The puzzle is how these gentes remain distinct. Here, we provide genetic evidence that gentes are restricted to female lineages, with cross mating by males maintaining the common cuckoo genetically as one species. We show that there is differentiation between gentes in maternally inherited mitochondrial DNA, but not in microsatellite loci of nuclear DNA. This supports recent behavioural evidence that female, but not male, common cuckoos specialize on a particular host, and is consistent with the possibility that genes affecting cuckoo egg type are located on the female-specific W sex chromosome. Our results also support the ideas that common cuckoos often switched hosts during evolution, and that some gentes may have multiple, independent origins, due to colonization by separate ancestral lineages.     

Adaptation varies through space and time in a coevolving host-parasitoid interaction

One of the central challenges of evolutionary biology is to understand how coevolution organizes biodiversity over complex geographic landscapes. Most species are collections of genetically differentiated populations, and these populations have the potential to become adapted to their local environments in different ways. The geographic mosaic theory of coevolution incorporates this idea by proposing that spatial variation in natural selection and gene flow across a landscape can shape local coevolutionary dynamics. These effects may be particularly strong when populations differ across productivity gradients, where gene flow will often be asymmetric among populations. Conclusive empirical tests of this theory have been particularly difficult to perform because they require knowledge of patterns of gene flow, historical population relationships and local selection pressures. We have tested these predictions empirically using a model community of bacteria and bacteriophage (viral parasitoids of bacteria). We show that gene flow across a spatially structured landscape alters coevolution of parasitoids and their hosts and that the resulting patterns of adaptation can fluctuate in both space and time.     

危害规模化养猪场的主要寄生虫及其防治措施

危害规模化养猪场的主要寄生虫有猪疥螨、猪线虫和猪血虱 .这些寄生虫感染造成的主要危害是降低饲料报酬和生长速度 ,并可能诱发其他疾病 .胃肠道线虫的最常用诊断方法是粪便检验 ,计算粪便中虫卵种类和数量 ;猪疥螨的诊断则需以临床症状为基础 ,检查皮肤的碎屑或进行血清学检查 .寄生虫病的防治措施主要有 :预防为主 ,加强饲养管理 ,选用适当的抗寄生虫药物 (如通灭 ) ,优化驱虫方案     

厦门海区浮游桡足类卵形态与孵化率的研究

在厦门海区,调查了19种常见的自由产卵的浮游桡足类卵型及其孵化率。发现卵有二种基本型:卵表光滑和具附属刺或鞘结构。卵的形态随种类而异,即使同种也常不同。卵径大小(D)似与产卵雌体大小呈正相关;而与海区水温(t)呈负相关,并可拟合为D=a·t~b。卵孵化率具有明显的季节变化,但和卵型的相关与否则依种的不同而异,这可能与种群不同的生态适应性有关。     

Ecosystem energetic implications of parasite and free-living biomass in three estuaries

Parasites can have strong impacts but are thought to contribute little biomass to ecosystems. We quantified the biomass of free-living and parasitic species in three estuaries on the Pacific coast of California and Baja California. Here we show that parasites have substantial biomass in these ecosystems. We found that parasite biomass exceeded that of top predators. The biomass of trematodes was particularly high, being comparable to that of the abundant birds, fishes, burrowing shrimps and polychaetes. Trophically transmitted parasites and parasitic castrators subsumed more biomass than did other parasitic functional groups. The extended phenotype biomass controlled by parasitic castrators sometimes exceeded that of their uninfected hosts. The annual production of free-swimming trematode transmission stages was greater than the combined biomass of all quantified parasites and was also greater than bird biomass. This biomass and productivity of parasites implies a profound role for infectious processes in these estuaries.     

Predator-induced behaviour shifts and natural selection in field-experimental lizard populations

The role of behaviour in evolutionary change has long been debated. On the one hand, behavioural changes may expose individuals to new selective pressures by altering the way that organisms interact with the environment, thus driving evolutionary divergence. Alternatively, behaviour can act to retard evolutionary change: by altering behavioural patterns in the face of new environmental conditions, organisms can minimize exposure to new selective pressures. This constraining influence of behaviour has been put forward as an explanation for evolutionary stasis within lineages and niche conservatism within clades. Nonetheless, the hypothesis that behavioural change prevents natural selection from operating in new environments has never been experimentally tested. We conducted a controlled and replicated experimental study of selection in entirely natural populations; we demonstrate that lizards alter their habitat use in the presence of an introduced predator, but that these behavioural shifts do not prevent patterns of natural selection from changing in experimental populations.     

Variation in egg size and nestling growth rate in relation to clutch size and laying sequence in great tits Parus major

The objectives of this study were to examine (1) optimal clutch size in great tits (Parus major) nesting in nest boxes; (2) variation in egg morphology and nestling growth rate with position in the laying sequence; and (3) hatching asynchrony and nestling survival as determined by infrared nest cameras. We collected data from 73 clutches in artificial nest boxes in the Zuojia Natural Preserve area in Jilin Province, China, in 2005 and 2006, using infrared cameras to match laying order to hatching order for four nests. Egg morphology and growth rate were significantly affected by clutch size and position in the laying order. Overall, egg size and growth rate increased with position in the laying order. In general, it was difficult to detect asynchronous hatching from observations alone, but data from our infrared cameras showed that early-laid eggs tended to hatch before later-laid eggs, leading to hatching asynchrony. However, females invested more into last-laid eggs and nestlings, reducing size asynchrony among the chicks and leading to higher survival rates of nestlings. Our results, therefore, provide support for the"brood survival"hypothesis rather than for the"brood reduction"hypothesis.     

林木上寄生灌木的重寄生演化

野外调查和形态学研究表明，硬序重寄生(檀香科重寄生属模式种)以桑寄生科半寄生灌木为寄主，具有一些特殊的生活习性和形态结构特征。讨论认为，重寄生链上的一些渐变特征展现林木上寄生灌木具有2个演化阶段，即以自养树木为寄主的半寄生灌木演化阶段，和以树木上半寄生灌木为直接寄主的重寄生灌木演化阶段；重寄生属植物特殊的生活习性和形态结构特征，是与其在寄主桑寄生科半寄生灌木上生活的特殊环境相适应的，是与其寄主、传播花粉蚂蚁类昆虫和传播种子鸟类协同演化的结果。     

Chemical communication: butterfly anti-aphrodisiac lures parasitic wasps

To locate their hosts, parasitic wasps can 'eavesdrop' on the intraspecific chemical communications of their insect hosts. Here we describe an example in which the information exploited by the parasitic wasp Trichogramma brassicae is a butterfly anti-aphrodisiac that is passed from male to female Pieris brassicae butterflies during mating, to render them less attractive to conspecific males. When the tiny wasp detects the odour of a mated female butterfly, it rides on her (Fig. 1) to her egg-laying sites and then parasitizes the freshly laid eggs. If this fascinating strategy is widespread in nature, it could severely constrain the evolution of sexual communication between hosts.     

The effect of migration on local adaptation in a coevolving host-parasite system

Antagonistic coevolution between hosts and parasites in spatially structured populations can result in local adaptation of parasites; that is, the greater infectivity of local parasites than foreign parasites on local hosts. Such parasite specialization on local hosts has implications for human health and agriculture. By contrast with classic single-species population-genetic models, theory indicates that parasite migration between subpopulations might increase parasite local adaptation, as long as migration does not completely homogenize populations. To test this hypothesis we developed a system-specific mathematical model and then coevolved replicate populations of the bacterium Pseudomonas fluorescens and a parasitic bacteriophage with parasite only, with host only or with no migration. Here we show that patterns of local adaptation have considerable temporal and spatial variation and that, in the absence of migration, parasites tend to be locally maladapted. However, in accord with our model, parasite migration results in parasite local adaptation, but host migration alone has no significant effect.     

Tumour necrosis factor alpha restores granulomas and induces parasite egg-laying in schistosome-infected SCID mice.

Schistosomiasis (bilharzia) is a parasitic disease caused by several species of schistosome worms (blood flukes). The key pathogenic event in this disease is the formation of granulomas around schistosome eggs trapped in portal venules of the liver. Granulomas are a distinctive form of chronic inflammation characterized by localized aggregation of activated macrophages around an inciting stimulus. Each granuloma evolves to form a fibrous scar; in schistosomiasis, the result is widespread hepatic fibrosis and portal hypertension. To identify the specific immune signal molecules necessary for granuloma formation, we studied schistosome infections in severe combined immunodeficient (SCID) mice, which have normal macrophages but lack functional B or T lymphocytes. Here we report that the immunoregulatory cytokine tumour necrosis factor alpha is necessary and sufficient to reconstitute granuloma formation in schistosome-infected SCID mice. Moreover, we find that the parasitic worms require tumour necrosis factor alpha for egg-laying and for excretion of eggs from the host. The implication of this latter result is that the parasite has adapted so successfully to its host that it uses a host-derived immunoregulatory protein as a signal for replication and transmission.     

膝芒寄蝇族昆虫(双翅目:寄蝇科)研究进展

膝芒寄蝇族昆虫属微卵型,其幼虫主要寄生在鳞翅目、鞘翅目、膜翅目和双翅目的幼虫体内;通过触觉和嗅觉寻找寄主;寄生成功率较低,因此产卵量高,导致本族属阶元多,但种类少;寄蝇多样性分布与雌蝇产卵战略相关。世界已知本族88属,中国记录有49属139种。综述了膝芒寄蝇族的研究史和现状,介绍了其系统地位、形态分类、动物区系与分布、系统发育与演化的单系性、寄生生物学与害虫控制等方面的研究进展。分析了目前该类群存在的问题并展望了今后研究工作内容和方向。     

Social parasitism by male-producing reproductive workers in a eusocial insect

The evolution of extreme cooperation, as found in eusocial insects (those with a worker caste), is potentially undermined by selfish reproduction among group members. In some eusocial Hymenoptera (ants, bees and wasps), workers can produce male offspring from unfertilized eggs. Kin selection theory predicts levels of worker reproduction as a function of the relatedness structure of the workers' natal colony and the colony-level costs of worker reproduction. However, the theory has been only partially successful in explaining levels of worker reproduction. Here we show that workers of a eusocial bumble bee (Bombus terrestris) enter unrelated, conspecific colonies in which they then produce adult male offspring, and that such socially parasitic workers reproduce earlier and are significantly more reproductive and aggressive than resident workers that reproduce within their own colonies. Explaining levels of worker reproduction, and hence the potential of worker selfishness to undermine the evolution of cooperation, will therefore require more than simply a consideration of the kin-selected interests of resident workers. It will also require knowledge of the full set of reproductive options available to workers, including intraspecific social parasitism.