The location of parasites within their hosts: Site selection by Trichuris muris in the laboratory mouse

Panesar T. S. and Croll N. A. 1930. The location of parasites within their hosts: site selection by Trichuris muris in the laboratory mouse. International Journal for Parasitology10: 261–273. This paper examines those factors which determine the location of T. muris in the caecum and colon of DBA-2 male mice. In caecectomized mice, infected post-operatively, T. muris established in the ileum. Despite the very different surface architecture of the ileum T. muris thrived within the epithelium lining the villi, comparable to their cytological microhabitat in the caecum. Unembryonated eggs of T. muris collected passively in the caecum, and embryonated eggs hatched readily in vitro when placed in caecal contents. These factors, together with the transit time of eggs which reached the caecum in 1 to 6 h, probably account for this being the major location for this nematode. T. muris could be successfully transplanted from caecum to caecum at 5 and 10 days post-emergence but not afterwards. This has been interpreted to result from the inability of the older worms to re-establish the intimate intra-epithelial association and to re-excavate their characteristic tunnels. T. muris caused a significant increase in the pH of luminal environment of the caecum and the colon of infected mice. The influence of post-operative changes in the gastrointestinal tract of mice causing compensatory anatomical changes is reviewed but considered to be insignificant in the present study.     

The location of parasites within their hosts: Factors affecting longitudinal distribution of Trichinella spiralis in the small intestine of mice

Inocula of encysted larvae, excysted larvae or infected meat all resulted in aggregated distributions of adults in the anterior small intestine. However, implantation studies indicated that the larvae could establish anywhere between the duodenum and the colon. The site of larval establishment determines the subsequent location of adult T. spiralis; the site of establishment was due largely to influences such as intestinal motility, size of inoculum and the size of the vehicle of infection. Predominantly female inocula were dispersed similarly to heterosexual inocula while male populations were dispersed more widely.     

The location of parasites within their hosts: The influence of host feeding and diet on the dispersion of adults of Nippostrongylus brasiliensis in the intestine of the rat

This paper is the first in a series to experimentally examine factors which determine the location of parasites within their hosts. Nippostrongylus brasiliensis is typically found one third of the way along the small intestine of the rat between days 7 and 12 of a primary infection. When rats were fasted for 2 days, N. brasiliensis became evenly distributed along the intestine and many individuals, mostly females, entered the caecum. Upon being fed again, the parasites were at their ‘normal site’ within 24 h. Experimental diets of α-cellulose, or simple dietary compounds caused the same re-distribution as did normal food. By sectioning the rat intestine when it was full of food and relating the dispersion of worms to the presence of intestinal contents, it was confirmed that N. brasiliensis is found amongst the intestinal contents of its host. The notion of a ‘site’ is critically discussed and the merit of ‘habitat’ is argued because the ‘site’ of N. brasiliensis would appear to be less a ‘place’ but rather a combination of environmental factors.     

The location of parasites within their hosts: the behaviour of Nippostrongylus brasiliensis in the anaesthetised rat

N. brasiliensis have been observed in vivo through the exposed wall of the small intestine of anaesthetised rats. Closed circuit television has been used to record the types of movement and analyses of the images indicate that differences occur. It would appear that these differences are correlated with the feeding regime of the host and could thus lead to habitat selection. A constantly changing picture of behavioural events emerges.     

The location of parasites within their hosts: The passage of Nippostrongylus brasiliensis through the lungs of the laboratory rat

This paper examines those factors which determine the emergence of N. brasiliensis from the pulmonary circulation into the alveoli and bronchioles of the rat's lung. After injection into the superior vena cava, larvae were found to be distributed throughout the lobes of the lungs in direct relation to the mass of blood and tissue and it was concluded that this resulted from entirely random forces. Larvae which had been reversibly immobilized in piperazine were trapped in the capillaries of the lungs in the same way as untreated larvae; this accumulation was considered to be passive. Larvae could penetrate surgically collapsed lungs but did so in lower numbers than in functional lungs so host breathing movements may facilitate penetration but are not essential. Larvae could repeat their migrations in a succession of hosts, but only if removed from the lungs within 2 h, by 20 h they could not and were destroyed in the lung tissue. Larvae were passively trapped in the arterioles but can emerge only through their own behavioural efforts. Heavy larval doses (10,000) caused considerable reversible oedema and haemorrhage. This was due to the behaviour of the larvae and not the direct effect of mechanical blockage because the same was not true if 10,000 heat-killed larvae were injected. Larvae of Ancylostomatubae forme, which does not secrete enzymes, also caused haemorrhaging in rat lungs, demonstrating that larval motility alone can lead to emergence through rupturing arterioles. By 20 h larvae were active in the trachea but they showed no directional orientation and were carried passively in the mucus. At this stage they were strongly photonegative.     

The location of parasites within their hosts: The influence of surgical manipulation of the intestine and mesenteric blood supply on the dispersion of Nippostrongylus brasiliensis in the rat

In the early stages of a primary infection with N. brasiliensis in rats, adults are characteristically located about one-third of the distance anad of the pyloric sphincter. As one of a series of experimental investigations of this phenomenon, surgical manipulation of the site has been attempted. The normal site has been surgically removed, it has been reversed while keeping the blood system intact and the mesenteric arterial and venous supply has been locally restricted. In no case did surgical intervention significantly lower the number of adult parasites. In all cases there was a shift from the normal dispersion to one more orad. It has been conclusively demonstrated that there is no specific structural or physiological factor in the normal site of N. brasiliensis, which is critical for its survival. All results indicate as proposed in an earlier paper, that N. brasiliensis is a lumenal dweller and is most frequently recovered from the intestinal contents.     

Hookworm behaviour: larval movement patterns after entering hosts.

Larvae of the cat hookworm, Ancylostoma tubaeforme migrate from the skin to the lungs of both mice and cats. Experiments have examined changes in the basic movement patterns of infective larvae after as long as 5 days within host tissues. Similarly, morphological developments and changes in unbound neutral lipid were investigated. There were no changes in the larvae except for a fall in the concentrations of lipid. Furthermore, it was found that larvae which had successfully completed a migration from the skin of a mouse to its lungs could successfully complete a second migration. The evidence does not support the hypothesis that a distinct series of tissues cr physico-chemical barriers may be sequentially followed in the migration of hookworms in their hosts. The migration route is seen as a much more random, less purposeful series of events.     

Habitat selection by two Mediterranean species of Aplysia: A. fasciata poiret and a. depilans Gmelin (Mollusca : Opisthobranchia)

Factors influencing habitat selection were examined in two species of Mediterranean Aplysia. Animals and egg masses were found in four types of habitats that varied in degree of exposure to wave action. Both species were frequently found in groups. Neither species was common in areas cut off from the surge of the sea. No difference in food preference was observed. A. depilans Gmelin were primarily found in areas subject to greater wave action, while A.fasciata Poiret dominated the calmer habitats. Both species were common in intermediate environments. In late summer, when A. depilans are absent, A. fasciata penetrated some environments previously dominated by the former. Morphological and behavioural features of A. depilans and A.fasciata are consistent with adaptation to rough and calm habitats, respectively.     

Movement of a non-flagellate spermatozoon: A study of the male gamete of Nematospiroides dubius (Nematoda)

The spermatozoa of Nematospiroides dubius were studied using the scanning electron microscope and time-lapse cinematography. Spermatozoa undergo a profound change in morphology after insemination: they change from an elongate structure, 16–18 μm long, to a more rounded form about 5–10 μm in diameter. Spermatozoa from female worms stuck to, and migrated across a glass surface by the production of pseudopodia, but they adhered more readily to a glass surface coated with egg albumin. The average speed of a sample of six differentiated spermatozoa was 7·3 μm/min. Their locomotion is not considered to be amoeboid but resembles the movement of monopodial neutrophils. A hypothesis for the mechanism of movement is presented, and other possible functions of the pseudopodial region are discussed.     

The location of parasites within their hosts: the behavioural component in the larval migration of Nippostrongylus bras1l1ensis in the tissues of the rat

The role of larval behaviour in successful completion of tissue migration is briefly discussed and it is related to the passive carriage of larvae along the ‘pipes and tubes’ of the host. Larvae of N. brasiliensis were injected into selected portions of the circulatory system and following periods of 5–60 min they were recovered from the blood, liver and lungs. Larvae were also immobilised in 0·4% piperazine, a dosage which permitted recovery in about 60 min. The dispersion of treated larvae was compared with that untreated controls. It was found that larvae were carried very rapidly in the blood stream and that they became lodged in the first capillary bed that they entered. They could not pass through capillary beds without movements (and/or secretions). A decreased number of adults developed after larvae were introduced via a series of routes which required the larvae to pass through an increasing number of ‘hurdles’ to migration.     

Genetics and ecology of Drosophila melanogaster larval foraging and pupation behaviour

In this paper we show that, (1) Drosophila melanogaster larvae utilize a variety of pupal microhabitats in an orchard, (2) variation in larval foraging path length, pupation distance from the food and pupal microhabitat preference (on or off the fruit) is genetically based and, (3) variation in these behaviours can be maintained in a spatially heterogenous environment since there is a reversal in pupation site suitability in wet and dry pupal microhabitats. Differences in path length in both laboratory and natural populations can be attributed to genes on the second pair of chromosomes and is under simple genetic control, whereas differences in pupal height are polygenically inherited (the second pair of chromosomes influences pupal height three times more than the third pair). Pupae collected from on-fruit sites had shorter foraging path lengths and lower pupal heights than off-fruit populations. Populations from the orchard maintained their field pupal microhabitat preferences even after 1 year of rearing them in the laboratory. Larvae with the sitter larval phenotype (short path lengths and low pupal heights tended to pupate more on-fruit than those with the rover phenotype (long path lengths and high pupal heights). To determined if these genetically based differences in microhabitat preference contributed to fitness, larval pupation behaviour was studied in a “field assay” (dish with fruit on soil) with soil water content varied. At low soil water contents, pupal survivorship was significantly better on the fruit whereas, at high soil water contents, survivorship was better in the soil. There was a reversal in which microhabitat (dry or wet) was a better site for pupation. In the field environment where soil water content fluctuates in space and time, such a reversal would explain the maintenance of genetic variation for these larval behaviours. Another selective agent acting on D. melanogaster larvae in our orchard is parasitization by Asobara tabida. This parasitoid parasitizes larvae with high locomotory scores (e.g. rovers) significantly more than those with low scores (sitters). This study relates laboratory phenotypes to field phenotypes thereby linking the ecological, behavioural and genetic components of larval habitat selection in D. melanogaster.     

The ciliate epibiont Epistylis pygmaeum: selection for zooplankton hosts, reproduction and effect on two rotifers

1. A clonal culture of the peritrich Epistylis pygmaeum was used for all observations and experiments. Motile cells preferentially attached to the eggs of three species of Brachionus but also attached to the body of adult B. angularis. Zooids on the transitory egg substratum developed only short stalks, while those on the body often developed long stalks and branched colonies. Selection for the eggs positions the ciliate near the cloaca, and thus high concentrations of fine particulate material excreted by the host. Settlement on eggs occurred equally well in the light and dark, and on moving and stationary eggs. 2. Motile Epistylis cells attached to a wide variety of rotifer and crustacean zooplankton, but exhibited some pronounced selectivity. They readily settled on the eggs of other rotifers (Epiphanes, Polyarthra), on the carapace of several cladocerans (Ceriodaphnia, Daphnia, Diaphanosoma), and on the egg sacs of a copepod (Tropocyclops). They settled less readily on the bodies of the rotifers Asplanchna and Synchaeta, and rarely or never settled on the rotifer Keratella, the cladocerans Bosmina and Scapholeberis, and the body of the copepod. 3. Epistylis populations initiated with a single zooid on Brachionus increased exponentially and often contained several hundred attached zooids and motile cells after 3 days at 20 °C. Observations of a culture initiated from a single telotroch provided new information about peritrich life cycles: (1) motile cells reproduced themselves at a rapid rate (λ = 4.26 day^?1); (2) telotrochs produced or transformed into swimming zooids and vice versa. Functions of the two types of motile cells remain to be clarified. Telotrochs likely are specialised for finding and attaching to hosts. Swimming zooids can feed and reproduce, producing both their own cell type and telotrochs. Together, they should enhance dispersal and population growth, especially when hosts are rare. 4. Life‐table experiments with two species of Brachionus showed that colonisation by Epistylis had no effect on adult survival but significantly decreased fecundity, by 29% in both cases. Zooids attached to eggs could be a weight burden, increase drag, and possibly inhibit egg development. Those on the body of B. angularis also could interfere with coronal cilia, inhibiting feeding and further slowing locomotion. The ability of E. pygmaeum to select and then interfere with its hosts indicates that this epibiont has the potential to influence the species structure of zooplankton communities.     

Effect of temperature on hatching and nest site selection in the Green lynx spider, Peucetia viridans (Araneae:Oxyopidae)

1.

Thirty-seven Peucetia viridans egg sacs were incubated at 15, 17.5, 20, 25, 30, 32.5 or 35 °C. Hatching time was inversely proportional to temperature, and no hatching occurred at the extremes (15, 17.5 and 35 °C).     

Modelling the maintenance of egg polymorphism in avian brood parasites and their hosts

In avian brood parasitism, egg phenotype plays a key role for both host and parasite reproduction. Several parrotbill species of the genus Paradoxornis are parasitized by the common cuckoo Cuculus canorus, and clear polymorphism in egg phenotype is observed. In this article, we develop a population genetics model in order to identify the key parameters that control the maintenance of egg polymorphism. The model analyses show that egg polymorphism can be maintained either statically as an equilibrium or dynamically with frequency oscillations depending on the sensitivity of the host against unlike eggs and how the parasite targets host nests with specific egg phenotypes. On the basis of the model, we discuss egg polymorphism observed in parrotbills and other host species parasitized by the cuckoo. We suggest the possibility that frequencies of egg phenotypes oscillate and we appeal for monitoring of cuckoo-host interactions over a large spatiotemporal scale.     

Balamuthia mandrillaris: The multiple nuclei of Balamuthia amebas; their location, activity, and site of development

Multiple nuclei were first noted in the pseudopodia of Balamuthia mandrillaris amebas feeding on mammalian cells. Phase microscope observations of live amebas in vitro reveal that while many amebas have a single nucleus, others have multiple nuclear-like structures, now confirmed as nuclei with hematoxylin and Feulgen stains. In the live cultures, two nuclei located near the tip of an extended pseudopodium were seen to fuse resulting in one larger morphologic unit. Such merging of nuclei has not been previously reported. Other nuclei were located at positions that subsequently became the site for the outgrowth of an additional pseudopod branch. A newly discovered large structure, a polyploid nucleus, was located in the mid-part of the ameba. Nucleoli of uniform size were seen to develop from the central mass of chromatin and each became surrounded by a vesicular component as they moved into the protoplasm as morphologically complete nuclei.     

Habitat selection within species ofDrosophila: a review of experimental findings

Summary Habitat selection whereby individuals within a population have different microhabitat preferences is possibly important for genetic diversity and stability. It has received a good deal of attention, especially forDrosophila populations. The literature is summarized and an attempt is made to reconcile what appear to be contradictory findings. Some generalizations are drawn: (1) individualDrosophila choose habitats in consistent and characteristic ways; (2) some microhabitat differences are more important to flies than others; (3) genetic factors influence habitat preferences; (4) experiential factors influence habitat preferences; (5) differences in processing ability moderate the influence of experience on habitat choice. It is argued that the traditional analysis of variance models are frequently not very helpful for visualizing the process, and a computational model is suggested instead.     

Habitat selection in a large orb‐weaving spider: vegetational complexity determines site selection and distribution

1. The distribution of the large orb‐weaving spider Argiope trifasciata in old field habitats of North America and the habitat selection process this species used was studied for 2 years. 2. Because web spiders have limited dispersal abilities and an energetically costly prey capture device, they do not have the ability to sample potential foraging sites. Structural complexity of the vegetation to which the web must be attached is relatively easy to assess. The hypothesis that the structural complexity is a primary factor in determining initial web site selection was tested both by relating the natural distribution of the spiders across habitats to vegetational complexity and by manipulating the complexity of the habitats in a series of experiments. 3. Argiope trifasciata was not distributed evenly among three old field vegetation types. Habitat complexity was related to spider density in both years although no measure of insect activity, prey capture, or prey consumption was correlated with spider distribution. 4. Three experimental manipulations were conducted to test the impact of habitat structure on spider establishment: (1) the amount of natural vegetation was reduced, (2) structures were added to a simple habitat, and (3) the complexity of the structures added was varied. In each case, spiders were introduced and establishment of webs was monitored. In all manipulations, spider establishment was related to the complexity of the substrate available. 5. These results are important for understanding the cues that influence foraging site selection and therefore provide insight into the distribution of species with limited dispersal abilities and high site investment requirements.     

Extending the diffuse layer model of surface acidity behaviour: III. Estimating bound site activity coefficients

Abstract

Although detailed thermodynamic analyses of the 2-pK diffuse layer surface complexation model generally specify bound site activity coefficients for the purpose of accounting for those non-ideal excess free energies contributing to bound site electrochemical potentials, in application these terms are ignored based on one or more of the following assumptions: (1) bound site activity coefficients cancel out in the mass action quotients; (2) bound sites display ideal behaviour; and/or (3) these energies are already included in the exponential Boltzmann terms. In this work it is demonstrated that the bound site charging energy terms discussed in the two previous papers in this series have both conceptual and computational analogies to the charging energy contribution to the activity coefficients obtained from the Debye–Huckel Limiting Law. On high charge density colloidal particles at constant counterion condensation (τ), these charging energies can be related to the surface potential (ψ) by: ΔG_charging = (1 – τ)Fψ (where F is the Faraday constant). If one assumes a maximum practical accuracy of ± 10% in experimental estimates of ψ, then it is suggested that charging energies are likely to be experimentally indiscernible under conditions where τ > 0.9. These findings support the historical practice of ignoring bound site activity coefficients with the 2-pK diffuse layer surface complexation model in the following situations: for spherical particles with a radius ≥ 0.1 μm at ionic strengths ≥ 0.001 M (1 : 1), and for spherical particles with a radius >0.01 μm at an ionic strength >0.1 M (1 : 1). In contrast, charging energies (and non-ideal behaviour) are predicted to be significant at all charge densities and ionic strengths for spherical particles with a radius of 0.001 μm.