Arms races between social parasites and their hosts: geographic patterns of manipulation and resistance

The evolutionary interactions between permanently social parasiticspecies and their hosts are of special interest because socialparasites are not only closely dependent on, but are also closelyrelated to, their hosts. The small European slavemaker Harpagoxenussublaevis has evolved several characters that help manipulateits host. In this study we investigated adaptations of thissocial parasite to its local hosts and the geographic patternof host resistance in two main host species from three differentpopulations. In behavioral experiments, we examined whetherhost colonies from three geographically distant Leptothoraxacervorum populations varied in their ability to defend thenest against social parasites. Naive colonies from the unparasitizedEnglish population killed attacking slavemakers more often thandid host colonies from two parasitized populations. We alsofound strong interpopulation variation in the ability of theslavemaker to manipulate host behavior. H. sublaevis uses theDufour gland secretion to induce intracolonial fights and, ingeneral, this "propaganda" substance was most effective againstlocal hosts. Our results suggest that the social parasite isleading the arms race in this aspect. Similar experiments uncovereddifferences between two populations of the second host speciesL. muscorum and could demonstrate that nest defense in bothhost species is similarly efficient. In L. acervorum, monogynouscolonies were more successful in nest defense, whereas socialstructure had no impact in L. muscorum. Colony size did notaffect the efficacy of nest defense in either host species.The caste of the slavemaker had a strong influence on the successof an attack.     

中国虫霉目真菌及其寄主昆虫名录更新

报道了中国虫霉目Entomophthorales真菌共计79种,隶属2科11属,并对其所涉及的寄主昆虫名称进行了规范与更新,且给出了各寄主的分类地位和中英文名称对照。     

Sexually transmitted diseases of insects: distribution, evolution, ecology and host behaviour

Sexually transmitted diseases (STDs) of insects are known from the mites, nematodes, fungi, protists and viruses. In total 73 species of parasite and pathogen from approximately 182 species of host have been reported. Whereas nearly all vertebrate STDs are viruses or bacteria, the majority of insect STDs are multicellular ectoparasites, protistans or fungi. Insect STDs display a range of transmission modes, with 'pure' sexual transmission only described from ectoparasites, all of which are mites, fungi or nematodes, whereas the microparasitic endo-parasites tend to show vertical as well as sexual transmission. The distribution of STDs within taxa of insect hosts appears to be related to the life histories of the hosts. In particular, STDs will not be able to persist if host adult generations do not overlap unless they are also transmitted by some alternative route. This explains the observation that the Coleoptera seem to suffer from more STDs than other insect orders, since they tend to diapause as adults and are therefore more likely to have overlapping generations of adults in temperate regions. STDs of insects are often highly pathogenic, and are frequently responsible for sterilizing their hosts, a feature which is also found in mammalian STDs. This, combined with high prevalences indicates that STDs can be important in the evolution and ecology of their hosts. Although attempts to demonstrate mate choice for uninfected partners have so far failed it is likely that STDs have other effects on host mating behaviour, and there is evidence from a few systems that they might manipulate their hosts to cause them to mate more frequently. STDs may also play a part in sexual conflict, with males in some systems possibly gaining a selective advantage from transmitting certain STDs to females. STDs may well be important factors in host population dynamics, and some have the potential to be useful biological control agents, but empirical studies on these subjects are lacking.     

Population structure and the co-evolution between social parasites and their hosts

Co-evolutionary trajectories of host-parasite interactions are strongly affected by the antagonists' evolutionary potential, which in turn depends on population sizes as well as levels of recombination, mutation, and gene flow. Under similar selection pressures, the opponent with the higher evolutionary rate is expected to lead the co-evolutionary arms race and to develop local adaptations. Here, we use mitochondrial DNA sequence data and microsatellite markers to assess the amount of genetic variability and levels of gene flow in two host-parasite systems, each consisting of an ant social parasite--the European slavemaker Harpagoxenus sublaevis and the North American slavemaker Protomognathus americanus--and its two main host species. Our population genetic analyses revealed limited gene flow between individual populations of both host and parasite species, allowing for a geographic mosaic of co-evolution. In a between-system comparison, we found less genetic variability and more pronounced structure in Europe, where previous behavioural studies demonstrated strong local adaptation. Within the European host-parasite system, the larger host species Leptothorax acervorum exhibited higher levels of both genetic variability and gene flow, and previous field data showed that it is less affected by the social parasite H. sublaevis than the smaller host Leptothorax muscorum, which has genetically depleted and isolated populations. In North America, the parasite P. americanus showed higher levels of gene flow between sites, but overall less genetic diversity than its hyper-variable main host species, Temnothorax longispinosus. Interestingly, recent ecological and chemical studies demonstrated adaptation of P. americanus to local host populations, indicating the importance of migration in co-evolutionary interactions.     

The effect of the taxon and geographic range size of host eucalypt species on the species richness of gall-forming insects

Abstract This field study was designed to test whether the taxonomic group and geographic range size of a host plant species, usually found to influence insect species richness in other parts of the world, affected the number of gall species on Australian eucalypts. We assessed the local and regional species richness of gall-forming insects on five pairs of closely related eucalypt species. One pair belonged to the subgenus Corymbia, one to Monocalyptus, and three to different sections of Symphyomyrtus. Each eucalypt pair comprised a large and a small geographic range species. Species pairs were from coastal or inland regions of eastern Australia. The total number of gall species on eucalypt species with large geographic ranges was greater than on eucalypt species with small ranges, but only after the strong effect of eucalypt taxonomic grouping was taken into account. There was no relationship between the geographic range size of eucalypt species and the size of local assemblages of gall species, but the variation in insect species composition between local sites was higher on eucalypt species with large ranges than on those with small ranges. Thus the effect of host plant range size on insect species richness was due to greater differentiation between more widespread locations, rather than to greater local species richness. This study confirms the role of the geographic range size of a host plant in the determination of insect species richness and provides evidence for the importance of the taxon of a host plant.     

Age and host effects on clutch size in the Mexican fruit fly, Anastrepha ludens

We document individual and age-specific variation in reproductive output and clutch size of Anastrepha ludens Loew. (Diptera: Tephritidae). The influence of host size, color, and density on clutch size are also examined. Individual and groups of flies were offered artificial hosts composed of agar spheres wrapped in Parafilm. The gross reproduction rate of individual flies was 1000 eggs/female and 165 clutches/female with a range of 1 to 40 eggs/clutch. Mean clutch sizes for these females ranged from 4.5 to 10.6 eggs/clutch. The number of eggs/clutch laid by females held in groups was highly correlated with host size, ranging from about 4.4 eggs/clutch in 2 cm diameter hosts to 12.7 eggs/clutch in 11 cm hosts. Host color, host density, fly density, and fly age did not affect clutch size. This study suggests that variation among females and host size are the principal determinants of clutch size in A. ludens.

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Résumé L'examen a porté sur l'influence du polymorphisme et des modifications dues à l'âge des mouches sur la fécondité et la taille des pontes de A. ludens Loew (Dipt. Tephritidae). L'étude a concerné aussi l'influence de la dimension, de la couleur et de la densité des hôtes sur la taille des pontes. Des mouches isolées ou par groupes ont reçu des hôtes artificiels formés de sphères d'agar enveloppées dans du parafilm. La fécondité brute de femelles isolées a été de 1000 oeufs/femelle et de 165 pontes/femelle, avec une variation de 1 à 40 oeufs/ponte. La taille moyenne des pontes des différentes femelles isolées s'étalait de 4,5 à 10,6 oeufs/ponte. Le nombre d'oeufs/ponte des femelles groupées était fortement liée à la dimension de l'hôte, s'étalant de 4,4 oeufs/ponte pour des hôtes de 2 cm de diamètre à 12,7 oeufs/ponte pour ceux de 11 cm de diamètre. Ni la couleur et la densité des hôtes, ni la densité et l'âge des mouches n'ont influé sur la taille des pontes. Ces résultats suggèrent que les variabilités du comportement des femelles et de la dimension des hôtes déterminent par priorité la taille des pontes de A. ludens.

     

昆虫中分离与鉴定的caspase及其作用

天冬氨酸特异性的半胱氨酸蛋白酶(caspase)家族是执行细胞凋亡的主要酶类,对caspase结构及生物学功能的研究有助于更深入的研究细胞凋亡的分子机制。Caspase具有高度保守性,它们具有相似的氨基酸序列、结构和底物特异性。且具有QACRG的五肽活性位点,该活性位点是caspase家族的典型结构。昆虫caspase在caspase依赖型的细胞凋亡中起关键作用,文章介绍和评述昆虫中已经分离、鉴定的caspase及其功能。     

昆虫抗药性与适合度

昆虫抗药性的产生常伴有适合度劣势(即适合度代价),即抗性个体常表现出发育速率较慢、存活率和生殖力较低。文章主要阐述害虫抗药性与生物适合度和适合度代价的关系以及适合度代价产生的机制、特性及影响因素。并从生态学角度论述害虫抗药性的进化,为探索抗性发展规律及害虫抗性治理提供理论依据。     

Co-evolution between ectoparasites and their insect hosts: a simulation study of a damselfly–water mite interaction

1. A simulation model investigating the co‐evolution of water mites infesting their aquatic insect hosts during emergence is presented. The model is based on field and experimental studies of the ectoparasitic water mite Arrenurus cuspidator and the damselfly Coenagrion puella. 2. Three scenarios were studied: (1) Only the host was allowed to evolve timing of emergence, while the timing of the parasites' infestation opportunity was held constant. (2) Both host and parasite were allowed to evolve. (3) Only the parasite's timing was allowed to evolve, while the host was constrained completely. 3. In the first two scenarios, parasite abundances decreased in the course of evolution and reached values well below those found in the field, whereas in the third scenario, parasite abundances were maintained at a level close to that found in the field. In the second scenario (co‐evolution), the host seemed to be the leader in the evolutionary race. 4. It is concluded that water mite parasitism is capable of shaping emergence patterns in aquatic insects and, despite the same life‐cycle length for host and parasite, the parasite evolves fast enough to shape its hatching pattern to match the emergence pattern of its host.     

Evolutionary ecology of the relationship between oviposition preference and performance of offspring in phytophagous insects

The relationship between oviposition preference and growth, survival, and reproduction of offspring is the crux of the problem in the evolution of host associations between phytophagous insects and plants. Observed relationships between oviposition preference and performance of offspring range from good to poor. At least four hypotheses have been suggested to explain observed use of particular host plants that may not result in the fastest growth rates or greatest pupal masses: time, patch dynamics, parasite versus grazer lifestyles, and enemy-free space. Our current understanding of these relationships, however, is hampered by an almost complete lack of data on how preference and performance are related genetically. These data are needed to understand the origins of covariance between preference and performance and constraints on the evolution of host associations.     

The relationship between diet and the size of the midgut caeca in grasshoppers (Insecta: Orthoptera: Acridoidea)

A survey of the size and form of the midgut caeca in relation to diet has been carried out on 173 species from 21 families and subfamilies of Acridoidea (grasshoppers). Although differences exist in the size of the anterior caecal arms relative to body length, these differences are not related to the type of food eaten. Assuming that the anterior arms have a key role in digestive and absorptive processes, this suggests that different foods make similar demands on these processes. The posterior caecal arms are smaller in graminivorous species than in species eating other types of plants as a whole or part of their diet. This is true across all the taxa, including those families and subfamilies that are predominantly forb-feeding. It is suggested that the posterior caecal arms have a special role in the detoxification of plant secondary compounds and that the requirement for this is reduced in graminivorous species because of the lower levels of toxic secondary compounds in grasses. A specialized pocket region is present in the posterior caecal arms of some forb-feeding species. Its occurrence across the taxa is spasmodic. It may be concerned with the removal of phenolic compounds.     

A comparative study of the relationship between host size and brood size in Apanteles spp. (Hymenoptera: Braconidae)

ABSTRACT. 1. Current models of insect oviposition predict that clutch size in parasitoids should correlate with host size, with a continuum from solitary species at one end to large gregarious broods at the other. This prediction is tested for the genus Apanteles (sensu lato).
2. The distribution of brood sizes in Apanteles is bimodal, with peaks at one (solitary species) and at about twenty (gregarious species).
3. Brood size of gregarious species correlates with host size, but when a measure of the total volume of a parasitoid brood is plotted against host size, solitary species do not lie on the same regression slope as gregarious species.
4. There is a relative shortage of gregarious species on small hosts, and a relative excess of solitary species on large hosts. Solitary species on large hosts do not fully consume the host resource.
5. The possible role of evolutionary constraints to adaptive progeny allocation in Apanteles is discussed.     

Interactions between the egg and larval parasitoids of a gall-forming midge and their impact on the host

1. The gall‐forming midge Rhopalomyia californica was exposed experimentally to parasitism and predation during only the egg stage, during only the larval stage, during neither stage, or during both stages. 2. The combined action of natural enemies that attack during both the egg stage and the larval stage led to the lowest number of midges and total insects (midges + parasitoids) in the next generation, and the highest percentage parasitism. 3. The larval parasitoid killed a large fraction of hosts without producing new parasitoid offspring, while there is some indication that the egg parasitoid on its own tended to produce the most parasitoid offspring. The contrasting implications of host mortality versus parasitoid production for biological control are discussed. 4. Exposure to larval parasitoids resulted in a reduction in the number of egg parasitoid offspring produced, but exposure to the egg parasitoid did not affect the number of larval parasitoid offspring produced significantly.     

The relationship between host selection behaviour and offspring fitness in a koinobiont parasitoid

1. When host quality varies, optimal foraging theory assumes that parasitic wasps select hosts in a manner that increases their individual fitness. In koinobiont parasitoids, where the hosts continue developing for a certain period of time after parasitisation, host selection may not reflect current host quality but may be based on an assessment of future growth rates and resources available for the developing larvae. 2. When presented with hosts of uniform quality, the koinobiont parasitoid Leptomastix dactylopii exhibits a characteristic host‐selection behaviour: some hosts are accepted for oviposition on first encounter, while others are rejected several times before an egg is laid in them, a behaviour that is commonly associated with a changing host acceptance threshold during the course of a foraging bout. 3. The fitness of the offspring that emerged from hosts accepted immediately upon encounter was compared with the fitness of offspring emerged from hosts rejected several times before being accepted for oviposition. 4. The pattern of host acceptance and rejection was not related to any of the measured fitness parameters of the offspring emerging from these hosts (development time, size at emergence, sex ratio at emergence, and female offspring egg load). 5. While complex post facto adaptive explanations can be devised to explain the nature of such a time and energy consuming host selection process, it is suggested that physiological constraints on egg production or oviposition may provide an alternative, purely mechanistic, explanation for the results obtained.     

The relationship between body size and population size in bromeliad tank faunas

Relationships between body size and abundance in collections of animals from the tanks of 73 bromeliads belonging to five species were analysed. Unlike data in previously published studies on this relationship, these collections of species are not taxonomically restricted and represent complete communities over the macroscopic range of organisms. There is no overall tendency for there to be a positive or negative relationship between population abundance and body size of morphospecies. We can find no evidence that body size-abundance patterns are triangular in complete communities. However, there is weak evidence that the relationship in the aquatic subsets of those communities may have some underlying triangularity, with medium-sized species having the largest populations.     

The relationship between cabbage root fly (Delia radicum) larval feeding and the freeze-dried matter and sugar content of Brassica roots

Five genotypes of swede (Brassica napus var. napobrassica), two genotypes of kale (B. oleracea var. acephala), and two genotypes of rape (B. napus var. napus) were each inoculated at the 8–10 true leaf stage with five cabbage root fly (Delia radicum) eggs. The percentage pupation after larval feeding on individual plant genotypes ranged from 45 to 78%, and the mean pupal weight from 6.5 to 13.0 mg. After 5 weeks, larval feeding damage had reduced root weight by up to 47%, compared with uninoculated plants. The dry matter content of undamaged roots was higher in the kales and rapes than in the swedes. Whilst the dry matter content of the rapes and swedes were not changed by D. radicum damage, that of the kales was elevated. The ethanol-soluble sugar content of the root was reduced in all cases by D. radicum larval damage. However, the effect of D. radicum damage on the concentrations of individual sugars (glucose, fructose and sucrose) was crop- and genotype-dependent. In the roots of kales and rapes, the glucose and fructose concentrations were either very low or unaffected by D. radicum damage, whilst both glucose and fructose were generally reduced in swede roots by D. radicum damage. The root sucrose concentration was either reduced or not significantly affected by D. radicum damage in all of the crop types tested. The percentage pupation and the mean pupal weight of D. radicum were inversely correlated to root freeze-dried matter content. D. radicum pupal weight was positively correlated with root fructose, glucose and ethanol-soluble sugar contents.     

The interaction between mobile DNAs and their hosts in a fluctuating environment

The interaction between mobile DNA sequences and their hosts raises important questions in the context of hosts which reproduce clonally with only rare horizontal transmission between clones. The activity of some mobile DNAs as reversible mutators of genes raises the possibility that, in a fluctuating environment, cells may gain an advantage if they have mobile DNAs which mutate genes whose inactivation is favoured in one of the environments that the population encounters. Here we analyse a model of this process and ask what would be the optimal rate of transposition in a population whose elements are maintained by this mechanism. We also examine the impact of horizontal transfer on such a population. With movement of elements between cells, we can imagine elements with differing rates of transposition and host cells with differing rates of transposition. We find that evolution in the population of elements favours a rapid rate of transposition, and evolution of the host cells favours cells in which this rapid rate of element-dependent transposition results in an optimal rate of transposition per cell. However, when horizontal transfer rates are high, some unexpected features of the model are observed. In particular, a polymorphism between cell types (some with an optimal rate of transposition and some with no transposition at all from endogenous elements) can be stably maintained. We consider the possible biological predictions of this analysis.     

The phenology and intrinsic quality of wild crucifers that determine the community structure of their herbivorous insects

This report examines the plant traits that effect the community structure of herbivorous insects on wild crucifers. Wild crucifers were classified into 4 types (A, B, C, D) according to their phenology. Type A and B plants had a pausing phenology, disappearing in the middle of the insects' active season, while type C and D plants had a continual phenology, existing all year long. The intrinsic quality of the plants as food, which was assessed by measuring the performance of herbivores, was superior in type A, B and D plants, while it was inferior in type C. The phenology and intrinsic quality were the alternative means of direct defense mechanisms against herbivorous insects: The plants with a pausing phenology were intrinsically superior (A, B), while the plants with a continual phenology were intrinsically inferior (C). However, there were a few plants with continual phenology and superior intrinsic quality (D, the type B plants that remained in the summer). Within the community of the herbivorous insects on the plants with direct defense mechanisms, the number of species and individuals was small and most of the community members were specialists of the plants. On the other hand, within the community on plants without direct defense mechanisms, the number of species was large and the proportion of generalists was high. In addition, the number of individuals was very large on the remaining type B plants, but it was small on type D plants, which were inferred to have indirect defense mechanisms.     

The non-linear relationship between body size and function in parrotfishes

Parrotfishes are a group of herbivores that play an important functional role in structuring benthic communities on coral reefs. Increasingly, these fish are being targeted by fishermen, and resultant declines in biomass and abundance may have severe consequences for the dynamics and regeneration of coral reefs. However, the impact of overfishing extends beyond declining fish stocks. It can also lead to demographic changes within species populations where mean body size is reduced. The effect of reduced mean body size on population dynamics is well described in literature but virtually no information exists on how this may influence important ecological functions. The study investigated how one important function, scraping (i.e., the capacity to remove algae and open up bare substratum for coral larval settlement), by three common species of parrotfishes (Scarus niger, Chlorurus sordidus, and Chlorurus strongylocephalus) on coral reefs at Zanzibar (Tanzania) was influenced by the size of individual fishes. There was a non-linear relationship between body size and scraping function for all species examined, and impact through scraping was also found to increase markedly when fish reached a size of 15–20 cm. Thus, coral reefs which have a high abundance and biomass of parrotfish may nonetheless be functionally impaired if dominated by small-sized individuals. Reductions in mean body size within parrotfish populations could, therefore, have functional impacts on coral reefs that previously have been overlooked.