Host recombination is dependent on the degree of parasitism

Parasites and hosts are involved in a continuous coevolutionary process leading to genetic changes in both counterparts. To understand this process, it is necessary to track host responses, one of which could be an increase in sex and recombination, such as is proposed by the Red Queen hypothesis. In this theoretical framework, the inducible recombination hypothesis states that B-chromosomes (genome parasites that prosper in natural populations of many living beings) elicit an increase in host chiasma frequency that is favoured by natural selection because it increases the proportion of recombinant progeny, some of which could be resistant to both B-chromosome effects and B-accumulation in the germline. We have found a clear parallelism between host recombination and the evolutionary status of the B-chromosome polymorphism, which provides explicit evidence for inducible recombination and strong support for the Red Queen hypothesis.     

The chemotherapeutic effect of praziquantel against Schistosoma mansoni is dependent on host antibody response

To assess the role of host humoral immune responses in the mechanism of action of praziquantel (PZQ) against Schistosoma mansoni, the efficacy of the drug was compared in infected B cell-depleted (mu-suppressed) vs immunologically intact C3H/HeN mice. We found that PZQ was on the average only 20% as effective in eliminating adult schistosomes from mu-suppressed as compared with control animals. Indeed, in three of four experiments performed, the drug failed to significantly reduce adult worm burdens in the mu-suppressed mice. These results were not due to a delay in parasite death in the infected B cell-depleted animals, because adult worms recovered from these mice as late as 7 wk after chemotherapy were indistinguishable in number and appearance from those recovered from non-drug-treated animals. The efficacy of PZQ against schistosomes in mu-suppressed mice was completely restored by passive transfer of immune serum from donor mice infected for 6 wk and partially restored with IgG purified from the same sera. Moreover, IgG as well as IgM antibodies were detected by immunofluorescence on the surface of adult worms recovered from intact mice as early as 1 hr after administration of the drug in vivo. The tubercles of the male worms appeared to be a major site for antibody binding. These results formally demonstrate that the mechanism of action of PZQ, the most important anti-schistosomal compound in current use, involves a synergy between the drug and the humoral immune response of the host, and suggest that the relevant effector antibodies act directly against parasite antigens which become exposed on the surface of the worms as a consequence of interaction with the drug.     

Inverse density dependent parasitism in a patchy environment: a laboratory system

Abstract. 1. Two species of parasitoids (Anisopteromalus calandrae (Howard) and Heterospilus prosopidis Vier) attacking the bruchid beetle, Callosobruchus chinensis (L.), show marked inverse density dependent relationships between per cent parasitism and host density per patch.
2. These patterns are well described quantitatively using data on the spatial distribution of searching time by the parasitoids and their attack rates on patches of different host density.
3. A model of optimal foraging predicts just the opposite (i.e. density dependent) patterns of parasitism.
4. Both density dependent and inversely density dependent spatial patterns of parasitism can be explained mechanistically in terms of (a) the allocation of searching time in patches of different host density and (b) the maximum attack rate per parasitoid that constrains the extent of host exploitation within a patch.     

Shiny Cowbird parasitism of a low quality host: effect of host traits on a parasite's reproductive success

ABSTRACT.   The reproductive success of parasitic cowbirds ( Molothrus spp.) varies among host species and is influenced by the degree of synchronization in timing of egg laying, the duration of parasite and host incubation periods, and the ability of hosts to incubate and rear parasite young. We studied the reproductive success of Shiny Cowbirds ( Molothrus bonariensis ) that parasitized the nests of Creamy-bellied Thrushes ( Turdus amaurochalinus ) in the Monte desert region of Argentina. Shiny Cowbirds frequently parasitized Creamy-bellied Thrush nests (60%), and most cowbirds synchronized egg laying with that of thrushes (79%). Most parasitic eggs (80%) hatched within 1 d of the hatching of the first host egg, and more than 91% of the eggs survived until the end of the incubation. However, only 60% of the cowbird eggs hatched and 52% of young survived. The proportion of Shiny Cowbirds eggs laid in Creamy-bellied Thrush nests that resulted in fledged young was 0.03, including eggs and young lost due to predation or desertion. Despite this low reproductive success, Creamy-bellied Thrushes were heavily parasitized by Shiny Cowbirds in our study area. Shiny Cowbirds may continue to parasitize these thrushes because of diffuse selection or because Shiny Cowbird chicks are more likely to fledge from Creamy-bellied Thrush nests in years or areas with greater food availability when brood reduction does not occur.     

The effect of host spatial distribution on patterns of parasitism by Nasonia vitripennis

Patterns of parasitism of Calliphora sp. pupae by Nasonia vitripennis (Walker) (Hymenoptera: Pteromalidae) are explored under various conditions of host aggregation. Increasing the hosts' spatial aggregation decreased the number of hosts actually parasitised but had no significant effect on the total number of hosts attacked. Increasing host aggregation also resulted in a smaller parasitoid population with a more male biased sex ratio.

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Résumé Nous avons examiné les effets de différents niveaux d'agrégation des hôtes (pupes de Calliphora) sur l'efficacité parasitaire de Nasonia vitripennis. Une augmentation de l'agrégation des pupes a diminué le nombre d'hôtes parasités bien que le nombre de pupes attaquées ait été peu modifié. Cette différence a été attribuée à un accroissement des interactions comportementales entre les parasitoïdes et à une tendance au superparasitisme plus élevée lors des distributions les plus agrégatives. Plus les hôtes étaient concentrés, moins l'effectif de parasitoïdes achevant leur développement et émergeant était important. La fréquence des males a augmenté avec la concentration des pupes. Nous avons estimé que les facteurs déterminants ont été les interactions comportementales entre femelles et leur aptitude à modifier le taux sexuel de leur descendance immédiate.Nous en avons conclu que N. vitripennis est peut-être mieux adaptée aux populations d'hôtes distribuées au hasard, type de distribution le plus vraisemblable dans les populations naturelles.

     

Cotesia plutellae parasitizing Plutella xylostella: Host-age dependent parasitism and its effect on host development and food consumption

The braconid Cotesia plutellae(Kurdjumov) (Hymenoptera: Braconidae) is amajor solitary, larval endoparasitoid of thediamondback moth, Plutella xylostella(L.) (Lepidoptera: Plutellidae). Parasitism oflarvae of different host instars and fourdevelopmental ages of the 4th instar ofthe pest was examined. The effects of hostinstar at initial parasitization on thedevelopment, survival, size and fecundity ofthe parasitoid were determined in thelaboratory at 25 °C. The effects ofparasitism on host development and foodconsumption were investigated at 28 °C.Cotesia plutellae could parasitize larvaeof all four instars of P. xylostella, butpreferred 2nd and 3rd instars. In achoice test, the relative parasitism indicesfor 2nd, 3rd and 4th instarswere 0.37, 0.39 and 0.24, respectively.Parasitism decreased sharply with increasinghost age in the 4th instar and approachedzero in host larvae that had gone beyond 37%of 4th stadium. The development time andthe final adult size of the parasitoid variedwith the host instar at initial parasitization.Parasitoids with initial parasitism in the4th instar hosts had the shortestdevelopment time, followed by those in the3rd instar, and then by those in the2nd instar. Parasitoids startingparasitism in 2nd instar hosts weresmaller in body size than those starting in the3rd or 4th instar. However, resultantfemales starting parasitism in 3rd instarhosts had the highest fecundity. Parasitizedlarvae exhibited longer development time andincreased food consumption compared withunparasitized ones. This study presents thefirst record that a solitary parasitoidregulates host behavior leading to an increasein food consumption by the host.     

The effect of egg load on readiness to accept a low-quality host plant is weak and age dependent in a geometrid moth

Abstract.  1. Most empirical and theoretical studies treat egg load as a major determinant of insect oviposition behaviour, and predict a positive link between egg load and readiness to oviposit.
2. In the present study, the correlation between egg load and readiness to lay eggs on a low-ranked host was examined in wild-caught moths, Scotopteryx chenopodiata L. (Lepidoptera: Geometridae).
3. No overall effect of egg load on oviposition could be detected. However, there was a significant interaction between egg load and wing wear: in only one wing-wear class, out of four, high egg load tended to promote oviposition, while in the three other classes the effect was insignificant.
4. The results suggest that the effect of egg load on oviposition may depend on the age of the ovipositing insect.     

Growth of host dependent Bdellovibrio in host cell free system

A particulate, subcellular fraction of Escherichia coli was shown to promote the growth of host dependent (H-D) Bdellovibrio in the absence of host cells. The growth promoting activity was enhanced by both cations and trypsin, and destroyed by pronase. During the axenic growth unipolar spheres appear in the elongating Bdellovibrio forms. Thymidine monophosphate was more readily incorporated than thymidine into the Bdellovibrio DNA during growth in the host free system.     

The influence of host's age on the selectivity of parasitism and fecundity ofTrichogramma

Laboratory studies showed that ♀♀ ofTrichogramma embryophagum (Hartig) andT. semblidis (Aurivillius) when offered an alternative of young and old eggs of the grain moth,Sitotroga cerealella Oliv., prefer ovipositing into young eggs. The fecundity of ♀♀ that are simultaneously offered both young and old eggs was lower in comparison to ♀♀ offered only young eggs (inspite of the fact that in both variants young eggs were in excess). The results suggest that old eggs can inhibit the oviposition of some species ofTrichogramma.      

The effect of host developmental stage at parasitism on sex‐related size differentiation in a larval endoparasitoid

• 1 For their larval development, parasitoids depend on the quality and quantity of resources provided by a single host. Therefore, a close relationship is predicted between the size of the host at parasitism and the size of the emerging adult wasp. This relationship is less clear for koinobiont than for idiobiont parasitoids.
• 2 As size differentiation in host species exhibiting sexual size dimorphism (SSD) is likely to occur already during larval development, in koinobiont larval endoparasitoids the size of the emerging adult may also be constrained based on the sex of the host caterpillar.
• 3 Sex‐specific growth trajectories were compared in unparasitised Plutella xylostella caterpillars and in second and fourth instar hosts that were parasitised by the solitary larval koinobiont endoparasitoid Diadegma semiclausum. Both species exhibit SSD, where females are significantly larger than males.
• 4 Healthy female P. xylostella caterpillars developed significantly faster than their male conspecifics. Host regulation induced by D. semiclausum parasitism depended on the instar attacked. Parasitism in second‐instar caterpillars reduced growth compared to healthy unparasitised caterpillars, whereas parasitism in fourth‐instar caterpillars arrested development. The reduction in growth was most pronounced in hosts producing male D. semiclausum.
• 5 Parasitism itself had the largest impact on host growth. SSD in the parasitoid is mainly the result of differences in growth rate of the parasitoid–host complex producing male and female wasps and differences in exploitation of the host resources. Female wasps converted host biomass more efficiently into adult biomass than males.

     

The curvature of dA tracts is temperature dependent

The curvature of dA tracts has been proposed to be important in the recognition, packaging, and regulation of DNA. The effects of dA tracts on the gel mobility, rate of cyclization, and other properties of DNA have been extensively studied. The consensus value for the curvature induced by a single dA tract is about 18 degrees. There are two main competing models for the origin of the curvature of dA tracts. One model assigns the central role to sequence-dependent steric clashes and the other to sequence dependent interactions with cations. The temperature dependence of the shape functions, the molecule specific part of the diffusion coefficients, of a set of six DNAs has been examined here. The set contains DNAs with dA tracts in or out of phase with respect to the helical repeat as well as those with scrambled dA-dT regions. The results show that the curvature of dA tracts is highly temperature dependent and that the curvature is largely melted out by 40 degrees C. The curvature melts out before there is significant premelting, or breathing of the dA tracts or the scrambled dA-dT regions. The curvature does not appear to reach a plateau value at low temperatures. A qualitative model for the melting of the curvature of dA tracts is proposed.     

The depressive effect of Pi on the force-pCa relationship in skinned single muscle fibers is temperature dependent

Increases in P_i combined with decreases in myoplasmic Ca²⁺ are believed to cause a significant portion of the decrease in muscular force during fatigue. To investigate this further, we determined the effect of 30 mM P_i on the force-Ca²⁺ relationship of chemically skinned single muscle fibers at near-physiological temperature (30°C). Fibers isolated from rat soleus (slow) and gastrocnemius (fast) muscle were subjected to a series of solutions with an increasing free Ca²⁺ concentration in the presence and absence of 30 mM P_i at both low (15°C) and high (30°C) temperature. In slow fibers, 30 mM P_i significantly increased the Ca²⁺ required to elicit measurable force, referred to as the activation threshold at both low and high temperatures; however, the effect was twofold greater at the higher temperature. In fast fibers, the activation threshold was unaffected by elevating P_i at 15°C but was significantly increased at 30°C. At both low and high temperatures, 30 mM P_i increased the Ca²⁺ required to elicit half-maximal force (pCa₅₀) in both slow and fast fibers, with the effect of P_i twofold greater at the higher temperature. These data suggest that during fatigue, reductions in the myoplasmic Ca²⁺ and increases in P_i act synergistically to reduce muscular force. Consequently, the combined changes in these ions likely account for a greater portion of fatigue than previously predicted based on studies at lower temperatures or high temperatures at saturating Ca²⁺ levels. force-pCa relationship; phosphate; fatigue     

The effect of alcohol consumption on the circadian control of human core body temperature is time dependent

The few controlled studies dealing with the action of alcohol on core body temperature in humans have focused on the effect of a single dose of ethanol and reported that it has a hypothermic effect. No studies report the effects of repeated ethanol intake over a 24-h period, a pattern of consumption much closer to the clinical condition of chronic alcoholism. We therefore designed a trial in which alcohol was repeatedly and regularly administered, with a total dose of 256 g. Nine healthy male volunteers (mean age 23.3 +/- 2.9 yr; range 21-30) each served as his own control. The circadian temperature rhythm was studied by a single-blind, randomized, crossover study that compared a 26-h alcohol session to a 26-h placebo session. The trial controlled for so-called masking effects known to affect temperature. The volunteers were in bed; the ambient temperature was maintained between 20 and 22 degrees C. Meals were standardized. And light was controlled during the night. All sessions took place between November and April. The two sessions were separated by 2 to 5 wk. Rectal temperature was monitored every 20 min throughout the trial. We found the standard hypothermic effect of alcohol in the early hours of the trial, during the daytime, but our principal result is that alcohol consumption induced a very significant hyperthermic effect (+0.36 degrees C) during the night and thereby reduced the circadian amplitude of core body temperature by 43%. The dramatic decrease of the amplitude of circadian temperature rhythm that we observed may explain, at least in part, some clinical signs observed in alcoholic patients, including sleep and mood disorders. We suggest that jet lag, shift work, and aging, which are known to alter body temperature, are aggravated by alcohol consumption.     

The effect of Jacobin Cuckoo Clamator jacobinus parasitism on the body mass and survival of young in a new host species

The southern African subspecies of Jacobin Cuckoo Clamator jacobinus serratus is a brood parasite of a range of host species. While Jacobin Cuckoos do not evict host young, previous research has found that host young rarely survive the nestling period. Here we provide the first records of Jacobin Cuckoo parasitism of a new host species, the Southern Pied Babbler Turdoides bicolor. We investigate rates of brood parasitism and the survival of host young. The Southern Pied Babbler is one of the largest recorded hosts for Jacobin Cuckoos and, unusually, we find that host young tend to survive the nestling period and maintain similar body mass to host young in unparasitized broods. However, host young were less likely to survive to independence than young raised in unparasitized nests, suggesting a post‐fledging reproductive cost to hosts.     

Mycorrhizal colonization in cowpea is host dependent and heritable

Cowpea genotypes (101) of diverse origin were evaluated for their endomycorrhizal colonization under natural field conditions in an alfisol soil. There was considerable variation in colonization ranging from 0 to 28.6%. The genetic coefficient of variability was high (55.9), heritability moderate (46.2) with high genetic advance (78.3) revealing that mycorrhizal colonization is not only host dependent but heritable.     

Context‐dependent effects of mycorrhizae on herbivore density and parasitism in a tritrophic coastal study system

1. Stressful abiotic conditions and mycorrhizal fungi have both been shown to influence plant quality significantly, yet the interactive effects of these factors on relationships among plants, herbivores, and natural enemies remain unclear. 2. In this study, the results of a factorial field experiment are reported in which the effects of plant stress and mycorrhizae on density and parasitism of three herbivores of Baccharis halimifolia L. were examined. 3. Plant stress was increased by adding salt to the soil, and association with mycorrhizal fungi was increased by inoculating plant roots. 4. Inoculation with mycorrhizal fungi resulted in increased density of all three herbivore species, but the effects of mycorrhizae on parasitism varied by species and with soil salinity levels. For the gall maker Neolasioptera lathami Gagne, mycorrhizae decreased parasitism regardless of soil salinity levels. For the leaf miners Amauromyza maculosa Malloch and Liriomyza trifolii Burgess, mycorrhizae effectively negated the decrease in parasitism resulting from increased salinity. 5. The results of this study show that the effects of mycorrhizae on parasitism may be context dependent, and can be positive or negative depending upon species and environmental conditions.     

Human cytomegalovirus-induced host cell enlargement is iron dependent

A hallmark of human cytomegalovirus (HCMV) infection is the characteristic enlargement of the host cells (i.e., cytomegaly). Because iron (Fe) is required for cell growth and Fe chelators inhibit viral replication, we investigated the effects of HCMV infection on Fe homeostasis in MRC-5 fibroblasts. Using the metallosensitive fluorophore calcein and the Fe chelator salicylaldehyde isonicotinoyl hydrazone (SIH), the labile iron pool (LIP) in mock-infected cells was determined to be 1.04 ± 0.05 µM. Twenty-four hours postinfection (hpi), the size of the LIP had nearly doubled. Because cytomegaly occurs between 24 and 96 hpi, access to this larger LIP could be expected to facilitate enlargement to 375% of the initial cell size. The ability of Fe chelation by 100 µM SIH to limit enlargement to 180% confirms that the LIP plays a major role in cytomegaly. The effect of SIH chelation on the mitochondrial membrane potential (_M) and morphology was studied using the mitochondrial voltage-sensitive dye JC-1. The mitochondria in mock-infected cells were heterogeneous with a broad distribution of _M and were threadlike. In contrast, the mitochondria of HCMV-infected cells had a more depolarized _M distributed over a narrow range and were grainlike in appearance. However, the HCMV-induced alteration in _M was not affected by SIH chelation. We conclude that the development of cytomegaly is inhibited by Fe chelation and may be facilitated by an HCMV-induced increase in the LIP. cell size; mitochondria     

Brood parasitism selects for no defence in a cuckoo host

In coevolutionary arms races, like between cuckoos and their hosts, it is easy to understand why the host is under selection favouring anti-parasitism behaviour, such as egg rejection, which can lead to parasites evolving remarkable adaptations to ‘trick’ their host, such as mimetic eggs. But what about cases where the cuckoo egg is not mimetic and where the host does not act against it? Classically, such apparently non-adaptive behaviour is put down to evolutionary lag: given enough time, egg mimicry and parasite avoidance strategies will evolve. An alternative is that absence of egg mimicry and of anti-parasite behaviour is stable. Such stability is at first sight highly paradoxical. I show, using both field and experimental data to parametrize a simulation model, that the absence of defence behaviour by Cape bulbuls (Pycnonotus capensis) against parasitic eggs of the Jacobin cuckoo (Clamator jacobinus) is optimal behaviour. The cuckoo has evolved massive eggs (double the size of bulbul eggs) with thick shells, making it very hard or impossible for the host to eject the cuckoo egg. The host could still avoid brood parasitism by nest desertion. However, higher predation and parasitism risks later in the season makes desertion more costly than accepting the cuckoo egg, a strategy aided by the fact that many cuckoo eggs are incorrectly timed, so do not hatch in time and hence do not reduce host fitness to zero. Selection will therefore prevent the continuation of any coevolutionary arms race. Non-mimetic eggs and absence of defence strategies against cuckoo eggs will be the stable, if at first sight paradoxical, result.