Field evidence for non-host predator avoidance in a manipulated amphipod

Manipulative parasites are known to alter the spatial distribution of their intermediate hosts in a way that enables trophic transmission to definitive hosts. However, field data on the ecological implications of such changes are lacking. In particular, little is known about the spatial coexistence between infected prey and dead-end predators after a parasite-induced habitat shift. Here, we used an Amphipoda (Gammarus roeseli)–Acanthocephala (Polymorphus minutus) association to investigate how infection with a manipulative parasite affects the predation risk by non-hosts within the invertebrate community. First, we collected invertebrates by sampling various natural habitats and calculated the distribution amplitude of amphipods according to their infection status. Infection with P. minutus significantly reduced the habitat breadth in G. roeseli, parasitised individuals being mainly found in floating materials whereas uninfected ones were widespread throughout the sampled habitats. Second, to test if these changes also affect the risk for P. minutus to be ingested by non-hosts, we estimated the predation risk experienced by G. roeseli within the macro-invertebrate community. The habitat overlap between potential invertebrate predators and G. roeseli showed that the spatial probability of encounter was lower for P. minutus-infected amphipods than for uninfected conspecifics. For the first time, to our knowledge, a study used ecological tools to bring field evidence for the spatial avoidance of dead-end predators in a manipulated amphipod.     

Nest defenses and egg recognition of yellow-bellied prinia against cuckoo parasitism

Parasites may, in multi-parasite systems, block the defenses of their hosts and thus thwart host recognition of parasites by frequency-dependent selection. Nest defenses as frontline may block or promote the subsequent stage of defenses such as egg recognition. We conducted comparative studies of the defensive strategies of a host of the Oriental cuckoo Cuculus optatus, the yellow-bellied prinia Prinia flaviventris, in mainland China with multiple species of cuckoos and in Taiwan with a single cuckoo species. Cuckoo hosts did not exhibit aggression toward cuckoos in the presence of multiple cuckoo species but showed strong aggressive defenses of hosts directed toward cuckoos in Taiwan. Furthermore, the cuckoo host in populations with a single cuckoo species was able to distinguish adults of its brood parasite, the Oriental cuckoo, from adult common cuckoos (Cuculus canorus). This represents the first case in which a cuckoo host has been shown to specifically distinguish Oriental cuckoo, from other Cuculus species. Hosts ejected eggs at a higher rate in a single cuckoo species system than in a multi-species cuckoo system, which supports the strategy facilitation hypothesis. Granularity analysis of variation in egg phenotype based on avian vision modeling supported the egg signature hypothesis in hosts because Taiwanese prinias increased consistency in the appearance of their eggs within individual hosts thus favoring efficient discrimination against cuckoo eggs. This study significantly improves our knowledge of intraspecific variation in antiparasitism behavior of hosts between single- and multi-cuckoo systems.     

Effects of life-history traits on parasitism in a monogamous mammal, the eastern rock sengi (Elephantulus myurus)

The distribution of parasites is often characterised by substantial aggregation with a small proportion of hosts harbouring the majority of parasites. This pattern can be generated by abiotic and biotic factors that affect hosts and determine host exposure and susceptibility to parasites. Climate factors can change a host’s investment in life-history traits (e.g. growth, reproduction) generating temporal patterns of parasite aggregation. Similarly, host age may affect such investment. Furthermore, sex-biased parasitism is common among vertebrates and has been linked to sexual dimorphism in morphology, behaviour and physiology. Studies exploring sex-biased parasitism have been almost exclusively conducted on polygynous species where dimorphic traits are often correlated. We investigated the effects of season and life-history traits on tick loads of the monogamous eastern rock sengi (Elephantulus myurus). We found larger tick burdens during the non-breeding season possibly as a result of energetic constraints and/or climate effects on the tick. Reproductive investment resulted in increased larval abundance for females but not males and may be linked to sex-specific life-history strategies. The costs of reproduction could also explain the observed age effect with yearling individuals harbouring lower larval burdens than adults. Although adult males had the greatest larval tick loads, host sex appears to play a minor role in generating the observed parasite heterogeneities. Our study suggests that reproductive investment plays a major role for parasite patterns in the study species.     

Short-sighted evolution of virulence in parasitic honeybee workers (Apis mellifera capensis Esch.)

The short-sighted selection hypothesis for parasite virulence predicts that winners of within-host competition are poorer at transmission to new hosts. Social parasitism by self-replicating, female-producing workers occurs in the Cape honeybee Apis mellifera capensis, and colonies of other honeybee subspecies are susceptible hosts. We found high within-host virulence but low transmission rates in a clone of social parasitic A. m. capensis workers invading the neighbouring subspecies A. m. scutellata. In contrast, parasitic workers from the endemic range of A. m. capensis showed low within-host virulence but high transmission rates. This suggests a short-sighted selection scenario for the host-parasite co-evolution in the invasive range of the Cape honeybee, probably facilitated by beekeeping-assisted parasite transmission in apiaries.     

An acanthocephalan parasite increases the salinity tolerance of the freshwater amphipod <Emphasis Type="Italic">Gammarus roeseli</Emphasis> (Crustacea: Gammaridae)

Studies of the influence of parasites on host fitness generally conclude that parasites have a strong negative effect on their hosts. In this study, we have investigated experimentally the role of Polymorphus minutus, an acanthocephalan parasite, on the salinity tolerance of the freshwater amphipod Gammarus roeseli, one of its intermediate hosts. Unexpectedly, P. minutus-infected gammarids were more tolerant to salinity stress than uninfected ones. The mean lethal salt concentrations for 50% mortality of hosts tested were 17.3 (infected) and 9.7 g/L (uninfected). The parasitic load (one or two parasites per host) did not affect the result. The size of hosts had no significant influence on the salinity tolerance of either infected or uninfected gammarids. The mobility of all types of gammarid decreased when the salinity exceeded 9.0 g/L, but there was no significant difference between infected and uninfected gammarids. We discuss the higher salinity tolerance of infected amphipods in relation to O₂ consumption and osmoregulation. Finally, we demonstrate that the salinity tolerance is enhanced in the parasitized amphipod but without a significant change in behavior or an osmoregulatory adjustment.     

Explaining postnatal growth plasticity in a generalist brood parasite

Selection of a particular host has clear consequences for the performance of avian brood parasites. Experimental studies showed that growth rate and fledging mass of brood parasites varied between host species independently of the original host species. Finding correlates of this phenotypic plasticity in growth is important for assessing adaptiveness and potential fitness consequences of host choice. Here, I analyzed the effects of several host characteristics on growth rate and fledging mass of the young of brown-headed cowbird (Molothrus ater), a generalist, non-evicting brood parasite. Cowbird chicks grew better in fast-developing host species and reached higher fledging mass in large hosts with fast postnatal development. A potential proximate mechanism linking fast growth and high fledging mass of cowbird with fast host development is superior food supply in fast-developing foster species. So far, we know very little about the consequences of the great plasticity in cowbird growth for later performance of the adult parasite. Thus, cowbird species could become interesting model systems for investigating the role of plasticity and optimization in the evolution of growth rate in birds.     

Deviance partitioning of host factors affecting parasitization in the European brown hare (Lepus europaeus)

Deviance partitioning can provide new insights into the ecology of host-parasite interactions. We studied the host-related factors influencing parasite prevalence, abundance, and species richness in European brown hares (Lepus europaeus) from northern Spain. We defined three groups of explanatory variables: host environment, host population, and individual factors. We hypothesised that parasite infection rates and species richness were determined by different host-related factors depending on the nature of the parasite (endo- or ectoparasite, direct or indirect life cycle). To assess the relative importance of these components, we used deviance partitioning, an innovative approach. The explained deviance (ED) was higher for parasite abundance models, followed by those of prevalence and then by species richness, suggesting that parasite abundance models may best describe the host factors influencing parasitization. Models for parasites with a direct life cycle yielded higher ED values than those for indirect life cycle ones. As a general trend, host individual factors explained the largest proportion of the ED, followed by host environmental factors and, finally, the interaction between host environmental and individual factors. Similar hierarchies were found for parasite prevalence, abundance, and species richness. Individual factors comprised the most relevant group of explanatory variables for both types of parasites. However, host environmental factors were also relevant in models for indirect life-cycle parasites. These findings are consistent with the idea of the host as the main habitat of the parasite; whereas, for indirect life-cycle parasites, transmission would be also modulated by environmental conditions. We suggest that parasitization can be used not only as an indicator of individual fitness but also as an indicator of environmental quality for the host. This research underlines the importance of monitoring parasite rates together with environmental, population, and host factors.     

First evidence of regular common cuckoo, <Emphasis Type="Italic">Cuculus canorus</Emphasis>, parasitism on eastern olivaceous warblers, <Emphasis Type="Italic">Hippolais pallida elaeica</Emphasis>

Coevolution is defined as specialized relationships between species that lead to a reciprocal evolutionary change. A particularly suitable model system for studying coevolution is the interactions between obligate avian brood parasites and their hosts. The common cuckoo (Cuculus canorus, hereafter cuckoo) is a well-known brood parasite, which utilizes a range of smaller passerines as hosts. However, warblers of the genus Hippolais have rarely been reported as being victims of cuckoos, and furthermore, few data exist on the occurrence of antiparasite defenses in these hosts. In this study, we examined possible host–parasite coevolution between cuckoos and eastern olivaceous warblers (Hippolais pallida elaeica, hereafter olivaceous warblers) in three closely situated areas in northwestern Bulgaria. The olivaceous warbler has never been reported to be a regular cuckoo host. However, the present study, carried out in 2001–2003 shows that the olivaceous warbler is regularly and heavily parasitized by the cuckoo in this area. Parasitism rate was high (26.6%, 34/128) and consistent among years, with some variation between areas. The cuckoo egg mimicry was moderately good, and olivaceous warbler rejection rate of such eggs was 50%. Cuckoo eggs laid in olivaceous warbler nests had a whitish to whitish-green ground color, and the majority appeared to be distinctly different from cuckoo eggs found in other host species in the area. The olivaceous warbler proved to be a rather good host for cuckoos as 20.6% (7/34) of cuckoo eggs laid produced fledglings, a breeding success comparable to other suitable hosts in Europe. This is the first in-depth study of brood parasitism in a warbler of the genus Hippolais, and cuckoos parasitizing olivaceous warblers probably represent a previously unknown gens.     

Does contrast between eggshell ground and spot coloration affect egg rejection?

Obligate avian brood parasitic species impose the costs of incubating foreign eggs and raising young upon their unrelated hosts. The most common host defence is the rejection of parasitic eggs from the nest. Both egg colours and spot patterns influence egg rejection decisions in many host species, yet no studies have explicitly examined the role of variation in spot coloration. We studied the American robin Turdus migratorius, a blue-green unspotted egg-laying host of the brown-headed cowbird Molothrus ater, a brood parasite that lays non-mimetic spotted eggs. We examined host responses to model eggs with variable spot coloration against a constant robin-mimetic ground colour to identify patterns of rejection associated with perceived contrast between spot and ground colours. By using avian visual modelling, we found that robins were more likely to reject eggs whose spots had greater chromatic (hue) but not achromatic (brightness) contrast. Therefore, egg rejection decision rules in the American robin may depend on the colour contrast between parasite eggshell spot and host ground coloration. Our study also suggests that egg recognition in relation to spot coloration, like ground colour recognition, is tuned to the natural variation of avian eggshell spot colours but not to unnatural spot colours.     

河鲈锚首吸虫及其宿主鳜鱼组织器官中铅含量的比较

利用原子吸收分光光度计分析了寄生鳜鱼（Sinipercachuatsi）鳃部的河鲈锚首吸虫（Ancyrocephalusmogurndae）及其宿主组织器官,包括肌肉、鳃、头肾和肝脏的铅含量.结果表明,来自三湖连江水库和牛山湖两个采样点的河鲈锚首吸虫的铅含量都显著地高于其宿主组织器官中的铅含量.在所检测的宿主组织器官中,肝脏的铅含量最高,在两个采样点分别为0.138和0.114μg/g（湿重）.河鲈锚首吸虫富集铅的机理及其较高水平铅含量的特点是否与其体外寄生的特性有关,尚有待于进一步研究.     

A colony-level response to disease control in a leaf-cutting ant

Parasites and pathogens often impose significant costs on their hosts. This is particularly true for social organisms, where the genetic structure of groups and the accumulation of contaminated waste facilitate disease transmission. In response, hosts have evolved many mechanisms of defence against parasites. Here we present evidence that Atta colombica, a leaf-cutting ant, may combat Escovopsis, a dangerous parasite of Atta's garden fungus, through a colony-level behavioural response. In A. colombica, garden waste is removed from within the colony and transported to the midden - an external waste dump - where it is processed by a group of midden workers. We found that colonies infected with Escovopsis have higher numbers of workers on the midden, where Escovopsis is deposited. Further, midden workers are highly effective in dispersing newly deposited waste away from the dumping site. Thus, the colony-level task allocation strategies of the Atta superorganism may change in response to the threat of disease to a third, essential party.     

The neglected heart of science policy: reconciling supply of and demand for science

The funding of scientific research is almost always justified in terms of the potential for achieving beneficial societal outcomes. In pursuing a particular societal outcome, how can we know if one research portfolio is better than another? In this paper we conceptualize: (1) science in terms of a “supply” of knowledge and information, (2) societal outcomes in terms of a “demand” function that seeks to apply knowledge and information to achieve specific societal goals, and (3) science policy decision-making as a process aimed at “reconciling” the dynamic relationship between “supply” and “demand.” The core of our argument is that “better” science portfolios (that is, portfolios viewed as more likely to advance desired societal outcomes, however defined) would be achieved if science policy decisions reflected knowledge about the supply of science, the demand for science, and the relationship between the two. We provide a general method for pursuing such knowledge, using the specific example of climate change science to illustrate how research on science policy could be organized to support improved decisions about the organization of science itself.     

The roles of tolerance in the evolution, maintenance and breakdown of mutualism

Tolerance strategies are cost-reduction mechanisms that enable organisms to recover some of the fitness lost to damage, but impose limited or no cost on antagonists. They are frequently invoked in studies of plant–herbivore and of host–parasite interactions, but the possible roles of tolerance in mutualism (interspecific cooperation) have yet to be thoroughly examined. This review identifies candidate roles for tolerance in the evolution, maintenance and breakdown of mutualism. Firstly, by reducing the cost of damage, tolerance provides a key pathway by which pre-mutualistic hosts can reduce the cost of association with their parasites, promoting cooperation. This holds for the evolution of ‘evolved dependency’ type mutualism, where a host requires an antagonist that does not direct any reward to their partner for some resource, and of ‘outright mutualism’, where participants directly trade benefits. Secondly, in outright mutualism, tolerance might maintain cooperation by reducing the cost of a persisting negative trait in a symbiotic partner. Finally, the evolution of tolerance might also provide a pathway out of mutualism because the host could evolve a cheaper alternative to continued cooperation with its mutualistic partner, permitting autonomy. A key consequence of tolerance is that it contrasts with partner choice mechanisms that impose large costs on cheats, and I highlight understanding any trade-off between tolerance and partner choice as an important research topic in the evolution of cooperation. I conclude by identifying tolerance as part of a more general phenomenon of co-adaptation in mutualism and parasitism that drives the evolution of the cost/benefit ratio from the interaction.     

Keeping eggs warm: thermal and developmental advantages for parasitic cuckoos of laying unusually thick-shelled eggs

Obligate brood parasites have evolved unusually thick-shelled eggs, which are hypothesized to possess a variety of functions such as resistance to puncture ejection by their hosts. In this study, we tested the hypothesis that obligate brood parasites lay unusually thick-shelled eggs to retain more heat for the developing embryo and thus contribute to early hatching of parasite eggs. By doing so, we used an infrared thermal imaging system as a non-invasive method to quantify the temperature of eggshells of common cuckoos (Cuculus canorus) and their Oriental reed warbler (Acrocephalus orientalis) hosts in an experiment that artificially altered the duration of incubation. Our results showed that cuckoo eggshells had higher temperature than host eggs during incubation, but also less fluctuations in temperature during incubation disturbance. Therefore, there was a thermal and hence a developmental advantage for brood parasitic cuckoos of laying thick-shelled eggs, providing another possible explanation for the unusually thick-shelled eggs of obligate brood parasites and earlier hatching of cuckoo eggs compared to those of the host.     

Different uses of plant semiochemicals in host location strategies of the two tachinid parasitoids

Some members of the family Tachinidae (Insecta: Diptera) deposit numerous very small eggs, termed “microtype” eggs, on the food plants of their caterpillar hosts. Parasitization is successful only when the hosts ingest these eggs. To increase the chance of hosts encountering the eggs, microtype tachinid parasitoids have to choose a suitable plant that harbors hosts and lay their eggs near the hosts. In their host location process, semiochemicals emitted by host-infested plants offer the tachinids a reliable cue. We investigated the behavioral responses of two microtype tachinid parasitoids, Pales pavida and Zenillia dolosa, to maize plants infested with their caterpillar host, Mythimna separata, in a wind tunnel. P. pavida females showed a significantly higher rate of landing on caterpillar-infested plants than on mechanically wounded or intact plants, whereas Z. dolosa landed on both the caterpillar-infested and mechanically wounded plants at significantly higher rates than on intact plants. We also examined which part of a caterpillar-infested maize leaf induces oviposition. P. pavida deposited eggs on the margin of the leaf, whereas Z. dolosa preferentially laid eggs around a caterpillar-infested area or a mechanically wounded spot. P. pavida eggs retained their parasitization ability for more than 15?days after they were deposited, whereas the eggs of Z. dolosa could not survive more than 5?days after oviposition. Our results suggest that each tachinid parasitoid employs a different host location strategy to exploit semiochemicals coming from plant–herbivore interaction as cues in order to increase their parasitization success.     

A behavioral study of the beetle Tenebrio molitor infected with cysticercoids of the rat tapeworm Hymenolepis diminuta

The host–parasite relationship, Tenebrio molitor–Hymenolepis diminuta, was analyzed. The learning behavior of infected and uninfected (control) beetles in a T-maze was compared. The infected beetles moved much slower in the T-maze than the controls. The infected beetles reached the same level of learning as the controls. However, they needed more trials than the controls. The effect of the infection was already distinct after the first week and even higher after the second week. This indicates that the initial phase of infection caused stress in the beetles. Longer infection did not worsen their ability to learn. Thus, the parasites clearly changed the behavior of their intermediate host and probably made them more susceptible to their final host, the rat.     

Small bite,large impact–saliva and salivary molecules in the medicinal leech, <Emphasis Type="Italic">Hirudo medicinalis</Emphasis>

Blood-sucking leeches have been used for medical purposes in humans for hundreds of years. Accordingly, one of the most prominent species has been named Hirudo medicinalis by Carl Linne in 1758. Feeding on vertebrate blood poses some serious problems to blood-sucking ectoparasites, as they have to penetrate the body surface of the host and to suppress the normal reactions of the host to such injuries (swelling, pain, inflammation) to remain undetected during the feeding period. Furthermore, the parasites have to take measures to inhibit the normal reactions in host tissues to blood vessel damage, namely hemostasis and blood coagulation (platelet aggregation and activation, activation of thrombin and formation of fibrin clots). During evolution, leeches have acquired the ability to control these processes in their hosts by transferring various bioactive substances to the host. These substances are supposedly produced in unicellular salivary gland cells and injected into the wound at the feeding site through tiny salivary ductule openings in the jaws that the leech uses to slice open the host body surface and to cut blood vessels in the depth of the wound. This review summarizes current knowledge about the salivary gland cells and the biological effects of individual saliva components as well as hints to the potential usefulness of some of these compounds for medical purposes.     

Social Hackers: Integration in the Host Chemical Recognition System by a Paper Wasp Social Parasite

 Obligate social parasites in the social insects have lost the worker caste and the ability to establish nests. As a result, parasites must usurp a host nest, overcome the host recognition system, and depend on the host workers to rear their offspring. We analysed cuticular hydrocarbon profiles of live parasite females of the paper wasp social parasite Polistes sulcifer before and after usurpation of host nests, using the non-destructive technique of solid-phase micro-extraction. Our results reveal that hydrocarbon profiles of parasites change after usurpation of host nests to match the cuticular profile of the host species. Chemical evidence further shows that the parasite queen changes the odour of the nest by the addition of a parasite-specific hydrocarbon. We discuss the possible role of this in the recognition and acceptance of the parasite and its offspring in the host colony. Received: 18 November 1999 / Accepted in revised form: 22 December 1999     

The parasite connection in ecosystems and macroevolution

In addition to their obvious negative effects (“pathogens”), endoparasites of various kinds play an important role in shaping and maintaining modern animal communities. In the long-term, parasites including pathogens are indispensable entities of any ecosystem. To understand this, it is essential that one changes the viewpoint from the host’s interests to that of the parasite. Together with geographic isolation, trophic arms race, symbiosis, and niche partitioning, all parasites (including balance strategists, i.e. seemingly non-pathogenic ones) modulate their hosts’ population densities. In addition, heteroxenic parasites control the balance between predator and prey species, particularly if final and intermediate hosts are vertebrates. Thereby, such parasites enhance the bonds in ecosystems and help maintain the status quo. As the links between eukaryotic parasites and their hosts are less flexible than trophic connections, parasite networks probably contributed to the observed stasis and incumbency of ecosystems over geologic time, in spite of continuous Darwinian innovation. Because heteroxenic parasites target taxonomic levels above that of the species (e.g. families), these taxa may have also become units of selection in global catastrophies. Macroevolutionary extrapolations, however, are difficult to verify because endoparasites cannot fossilize.     

Genetic structure of Mediterranean chukar (Alectoris chukar, Galliformes) populations: conservation and management implications

The chukar (Alectoris chukar, Galliformes) is a species hunted throughout its native range from the East Mediterranean to Manchuria and in the USA, which hosts the world’s largest introduced population. This study aims to investigate the genetic structure of Mediterranean chukar populations to aid management decisions. We genotyped 143 specimens at two regions of the mitochondrial DNA (mtDNA: cytochrome b, control region) and eight loci of the microsatellite DNA. Samples were collected in northern (Limnos, Lesvos, Chios) and southern (Crete) Aegean islands (Greece) and Cyprus. We also carried out mtDNA-based comparison with chukars (n?=?124) from Asia (16 countries) and the USA (five states). We propose six management units for Mediterranean populations. Given their genetic integrity, Limnos and Cyprus, which host different subspecies, proved to be of primary conservation interest. We found exotic A. chukar mtDNA lineages in Lesvos, Chios and Crete and produced definitive genetic evidence for the Asian origin of the US chukars.