Some peculiarities of the relationships between parasitic copepods and their invertebrate hosts

According to the rule of academican E. N. Pavlovskiy, any organism of host is an environment of inhabit for a parasite (Pavlovskiy, 1934). It was analysed, which "ecological niche" or microbiotop (= microhabitat) is occupied by this or that species of symbiotic (parasitic) copepods in organisms of different groups invertebrate-hosts. The assumption lying in a basis of the given analysis means that each group of hosts may give to cohabitants only certain variants of microbiotopes independently on the general morphological structure and life mode of hosts. Five types of microbiotops offered by various groups of hosts for symbiotic copepods are designated (Ta[symbol: see text] 2). 1. The body surface of benthic invertebrates as a microbiotope is characterized by conditions being little different (concerning any kind of physical and chemical influences on copepods) from those in external environment on any other substrate. Apparently a trophical dependence plays a determining role in this case. There are certain directions in a development of adaptations, which are characteristic in some extent for all water ectoparasitic crustaceans and have one functional task--to help to an ectoparasite to keep itself on a surface of host body. In the first, the maxillules and maxillipeds significantly are developed, they get a form of large claws, with which the dopepods are strongly attached on a surface of host body and have an opportunity to move on it without a danger to be washed off. In the second, the form of the body undergoes a dorso-ventral expression and expansion of prosome, forms a cephalic shield allowing to the symbiont to press itself tightly to the host body surface and to avoid the loss of host (tab. 2). In occasions, some ectoparasites stimulate the formation of galls in skin tissues of the host, that also provides the parasite with constant conditions, without any threat to lose the host. However, this phenomenon has not a wide distribution and is observed in some groups of crustacean and echinoderm hosts. 2. The narrow tubular cavities in the organism of host either they are a part of external environment (as in channel system of spongia) or a part of internal environment of organism (as channels of blood system or thin parts of a digestive system) have always rigidly limited sizes and form. Characteristics of all parasites occupying this microbiotopes are the strong transformations. They are expressed by the reduction of legs or any other appendages (frequently in a significant degree), loss of segmentation to some extent and in eruciform (or vermiform) form of a body (tab. 2). This microbiotope is occupied by an ectoparasite in one case only (Spongicola uncifer from channel system of spongia) and by endoparasites in all other cases. 3. Large cavities connected with external environment. The formations of various genesis, such as mantle cavity of molluscs, gill cavity and marsupium of crustaceans, bursal cavity of ophiuroids and branchial cavity of ascidians, concern this type of microbiotopes. All of them are characterized by the relative difference from the external environment and rather large volume (in comparison to sizes of copepods), that provides the parasites with a sufficient protection from factors of the external environment and constant source of food such as elements of host body or food's particles brought by the water flow. Morphological changes in inhabitants of the microbiotope have two directions. They practically are absent in the overwhelming majority copepods, living in the mantle of cavity of the lamellibranches. On the other hand, the inhabitants of gill cavity and marsupium of crustaceans, bursal cavities of ophiuroids and branchial cavity of ascidians are characterized by the presence of strong transformations. Usually there are expressed in a loss of segmentation to some extent, reduction of appendages and swelling of body, as in species of the genus Sphaeronella (tab. 2). Changes are also observed in the life cycle: the tendency to reduce stages of development (development of nauplii stage, which takes place under the ovarial cover). In this case the copepodid stages hatch from the ova. 4. The internal cavity of organism of host. This type of microbiotopes in different groups of the hosts is represented in a various degree. We recognise it in a coelome of polychaetes, lacunar system of molluscs, mixocoel of crustaceans, coelome of echinoderms and cavity of body in ascidians. Two basic evolutionary directions are observed in copepods occupying this microbiotope. In the first case, the parasite is not exposed to transformations and keeps the initial plan of structure as in ancestral free-living forms. In the second case the parasites are exposed to strong transformations, they either live directly in cavity's liquid, or are surrounded by a cyst (as in Cucumaricolidae). 5. Microbiotope of the last type is most specific. The simultaneous existence in two environments--external environment (environment of the second order) and internal environment (environment of the first order) leads to the complete loss of ancestral type in a structure and level of organisation. At the same time both morphological and functional division of the parasite body into two parts produces a new formation--the ectosome and endosome. In this case we deals with the phenomenon of mesoparasitism.     

Size-selective attack by parasitic lampreys: consideration of alternate null hypotheses

Summary The hypothesis that parasitic lampreys actively select larger host fish was tested with previously published laboratory data for Petromyzon marinus and new data for Ichthyomyzon castaneus. Whereas in previous work, expected attack frequencies were proportional to the number of potential hosts in each size group (numbers-dependent null hypothesis), the present study employed a more conservative area-dependent null hypothesis by which expected attack frequencies were adjusted to reflect the surface area of potential hosts in each size group. The balance of the data suggests that lampreys are actively size-selective. It is more difficult to demonstrate size-selectivity in the field because of sampling considerations and the need to account for size-related factors (e.g., swimming speed) that affect host availability. It is unknown if handling times are greater for larger hosts or if the quality of host blood changes with host size, and it is uncertain if lampreys achieve greater energy intake rates on larger hosts, but a larger host survives longer and assures an attacking lamprey of a longer period of feeding.     

Metabolic end-products in parasitic helminths and their intermediate hosts.

Oxidoreductases which control the metabolic end-products in helminth parasites and their intermediate hosts were reviewed, in a trial to elucidate the respiratory metabolism during host-parasite associations. Special attention was given to Schistosoma parasites and their molluscan hosts.     

Telomere dynamics in parasitic great spotted cuckoos and their magpie hosts

Although little is known on the impact of environment on telomere length dynamics, it has been suggested to be affected by stress, lifestyle and/or life‐history strategies of animals. We here compared telomere dynamics in erythrocytes of hatchlings and fledglings of the brood parasite great spotted cuckoos (Clamator glandarius) and of magpies (Pica pica), their main host in Europe. In magpie chicks, telomere length decreased from hatching to fledging, whereas no significant change in telomere length of great spotted cuckoo chicks was found. Moreover, we found interspecific differences in the association between laying date and telomere shortening. Interspecific differences in telomere shortening were interpreted as a consequence of differences in lifestyle and life‐history characteristics of magpies and great spotted cuckoos. In comparison with magpies, cuckoos experience reduced sibling competition and higher access to resources and, consequently, lower stressful environmental conditions during the nestling phase. These characteristics also explain the associations between telomere attrition and environmental conditions (i.e. laying date) for magpies and the absence of association for great spotted cuckoos. These results therefore fit expectations on telomere dynamics derived from interspecific differences in lifestyle and life history of brood parasites and their bird hosts.     

Attachment sites of parasitic lampreys: comparisons among species

Synopsis Distribution of attachment sites varies with the species of lamprey being considered. Large anadromous species (Petromyzon marinus and Lampetra tridentata) tend to attach ventrally, especially near the pectoral fins, while smaller freshwater species in shallow habitats (Ichthyomyzon castaneus and I. unicuspis) and species that feed on muscle tissue (Lampetra ayresi) tend to attach dorsally. Catostomids tend to be attacked on the head and, by the Ichthyomyzon species, on the paired fins. Distribution of attachments by P. marinus in laboratory studies may be affected by tank size. Attachments to the head and pectoral regions are probably associated with greater host mortality rates and may be underrepresented in field samples. Attachments to the pectoral region appear to combine low costs, in terms of handling time prior to feeding, with greater rates of energy intake once feeding has been initiated. Dorsal attachments by species that inhabit relatively shallow rivers and streams may be a compromise to avoid abrasion against the bottom. A consequence of dorsal attachments may be a reduced impact on host populations through prolonged attachments to individual hosts and reduced attack rates.     

The influence of parasitic water mites on the instantaneous death rate of their hosts

Summary The effect of 2 species of water mites on the instantaneous death rate of their hosts was measured on the basis of laboratory experiments. In both parasite-host association — the parasitic water mite Hydryphantes tenuabilis on the aquatic insect host Hydrometra australis and the parasitic water mite Arrenurus pseudotenuicollis on the mosquito Anopheles crucians — the effect of mite load on the instantaneous death rate of the host appeared to be linear. Also, the impact of a single parasite on the host's death rate was apparently related to the ratio of parasite to host body weight. The results of this study are in general agreement with recent theoretical investigations of the regulation of host populations by parasites.     

Lessons from parasitic flatworms about evolution and historical biogeography of their vertebrate hosts

Cophylogenetic studies investigate the evolutionary trends within host-parasite associations. Examination of the different levels of fidelity between host and parasite phylogenies provides a powerful tool to inspect patterns and processes of parasite diversification over host evolution and geological times. Within the phylum Platyhelminthes, the monogeneans are mainly fish parasites. The Polystomatidae, however, are known from the sarcopterygian Australian lungfish and tetrapods such as amphibians, freshwater turtles, and the African hippopotamus. Cophylogenetic and biogeographic vicariance analyses, supplemented by molecular calibrations, showed that the Polystomatidae may track the evolutionary history of the first aquatic tetrapods in the Palaeozoic age. Evolutionary lines of the major polystome lineages would also be intimately related to the evolution of their hosts over hundreds of millions years. Since the Mesozoic, evolution of polystomes would have been shaped mainly by plate tectonics during the break-up of Gondwanaland and subsequent dispersal of ancestral neobatrachian host lineages. Therefore the Polystomatidae could serve as a novel model to improve cophylogenetic tools and to inspect a suite of questions about the evolution of vertebrate hosts. To cite this article: O. Verneau et al., C. R. Biologies 332 (2009).     

Habitat selection for parasite-free space by hosts of parasitic cowbirds

Choice of breeding habitat can have a major impact on fitness. Sensitivity of habitat choice to environmental cues predicting reproductive success, such as density of harmful enemy species, should be favored by natural selection. Yet, experimental tests of this idea are in short supply. Brown-headed cowbirds Molothrus ater commonly reduce reproductive success of a wide diversity of birds by parasitizing their nests. We used song playbacks to simulate high cowbird density and tested whether cowbird hosts avoid such areas in habitat selection. Host species that made settlement decisions during manipulations were significantly less abundant in the cowbird treatment as a group. In contrast, hosts that settled before manipulations started and non-host species did not respond to treatments. These results suggest that hosts of cowbirds can use vocal cues to assess parasitism risk among potential habitat patches and avoid high risk habitats. This can affect community structure by affecting habitat choices of species with differential vulnerability.     

Use of modeling to investigate potential feeding strategies of parasitic lampreys

Synopsis A quantitative energetics model of feeding and growth by parasitic lampreys was used to assess overall rates of net energy intake under alternate feeding strategies and varying host availability. Our early attempts to predict optimal feeding behavior focused on the duration of attachment to the host, but model simulations have revealed that optima over this variable may be so flat that, as in one case, a deviation of nearly 30% from the optimal attachment time results in only a 3% decrease in the rate of net energy intake. This may contribute to the great variability that appears characteristic of feeding by parasitic lampreys. Further simulations have suggested that, because host blood is to some extent a renewable resource, lampreys should extend host survival when alternate hosts are scarce by removing blood at reduced rates. In other words, maximization of instantaneous rate of net energy intake is not equivalent to maximization of long term gain. Thus, in predicting optimal lamprey feeding behavior, it is necessary to consider simultaneously both attachment time and rate of host blood removal. Behavioral or evolutionary adjustment of these variables can have important consequences with respect to lamprey growth rates, the functional response of lampreys to changing host densities, mortality rates of host populations, and the expression of other lamprey behavioral traits.     

Oxygen and carbon isotope composition of parasitic plants and their hosts in southwestern Australia

We measured leaf dry matter ¹⁸O and ¹³C in parasitic plants and their hosts growing in southwestern Australia. Parasite/host pairs included two mistletoe species, three species of holoparasites, and five species of root hemiparasites. Among these parasite functional types, significant variation was observed in parasite/host isotopic differences for both ¹⁸O (P<0.0001, n=65) and ¹³C (P<0.0001, n=64). Mistletoes were depleted in both ¹⁸O and ¹³C compared to their hosts; parasite/host differences were –4.0 for ¹⁸O (P<0.0001) and –1.9 for ¹³C (P<0.0001). The lower ¹⁸O in mistletoe leaf dry matter compared to their hosts is consistent with the frequently observed high transpiration rates of these parasites. Root hemiparasites were also depleted in ¹⁸O and ¹³C compared to their hosts, but not to the same extent as mistletoes; parasite/host differences were –1.0 for ¹⁸O (P=0.04) and –1.2 for ¹³C (P=0.0006). In contrast to mistletoes and root hemiparasites, holoparasites were enriched in both ¹⁸O and ¹³C compared to their hosts; parasite/host differences were +3.0 for ¹⁸O (P<0.0001) and +1.5 for ¹³C (P=0.02). The enrichment in ¹⁸O for holoparasite dry matter did not result from more enriched tissue water; holoparasite tissue water ¹⁸O was less than host leaf water ¹⁸O by a difference of –3.8 when sampled at midday (P=0.0003). Enrichment of holoparasites in ¹³C compared to their hosts is consistent with a generally observed pattern of enrichment in heterotrophic plant tissues. Results provide insights into the ecology of parasitic plants in southwestern Australia; additionally, they provide a context for the formulation of specific hypotheses aimed at elucidating mechanisms underlying isotopic variations among plants.     

Cocoon silk chemistry in parasitic wasps (Hymenoptera, Ichneumonoidea) and their hosts

Bulk amino acid compositions of larval cocoon silks of 24 species of ichneumonoid parasitic wasps, representing 13 subfamilies that kill the host in a larval or prepupal stage, are compared with those of their hosts to test the hypothesis that amino acid compositions of major protein products should, in certain cases, be similar on energetic grounds. Although substantial variation in amino acid composition was found among both parasitoids and hosts, suggesting the production of different types of silks, no significant general matching was detected. However, the trend in the degree of similarity observed was in the direction predicted by a priori consideration of the nature of the parasitoid – host association. Lack of a general association may be explained by the very simple silk glands of the parasitic wasps and by the fact that, in most cases, their hosts are not completely consumed at a time when they are likely to contain any large reserves of silk proteins. The three species of Cotesia (Braconidae: Microgastrinae) investigated stood out in that their silks showed considerable interspecific variation in molar percentage amino acid composition, and this might be associated with their apparent utilization of α-helical silks rather than fibroins.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 81 , 161–170.     

Climate change effects on migration phenology may mismatch brood parasitic cuckoos and their hosts

Phenological responses to climate change vary among taxa and across trophic levels. This can lead to a mismatch between the life cycles of ecologically interrelated populations (e.g. predators and prey), with negative consequences for population dynamics of some of the interacting species. Here we provide, to our knowledge, the first evidence that climate change might disrupt the association between the life cycles of the common cuckoo (Cuculus canorus), a migratory brood parasitic bird, and its hosts. We investigated changes in timing of spring arrival of the cuckoo and its hosts throughout Europe over six decades, and found that short-distance, but not long-distance, migratory hosts have advanced their arrival more than the cuckoo. Hence, cuckoos may keep track of phenological changes of long-distance, but not short-distance migrant hosts, with potential consequences for breeding of both cuckoo and hosts. The mismatch to some of the important hosts may contribute to the decline of cuckoo populations and explain some of the observed local changes in parasitism rates of migratory hosts.     

New Spiroplasma in parasitic Leptus mites and their Agathemera walking stick hosts from Argentina

Here we report the presence of Spiroplasma 16S rRNA in populations of two parasitic Leptus mites (Leptus sayi; Leptus lomani) and their Agathemera walking stick hosts. In walking sticks Spiroplasmas were detected in the gut, as well as muscle-tissues, but not in eggs. Throughout Argentina 15.4% of L. sayi populations and 14.3% of L. lomani populations surveyed screened positive for Spiroplasma. Phylogenetic analyses (ML, BCMC) place all sequences within the Ixodetis group. Most sequences form a well-supported sister subclade to the rest of Ixodetis. We briefly discuss the role of Leptus mites in the natural transmission of Spiroplasma.     

Rodent Plasmodium-infected red blood cells: Imaging their fates and interactions within their hosts

Malaria, a disease caused by the Plasmodium parasite, remains one of the most deadly infectious diseases known to mankind. The parasite has a complex life cycle, of which only the erythrocytic stage is responsible for the diverse pathologies induced during infection. To date, the disease mechanisms that underlie these pathologies are still poorly understood. In the case of infections caused by Plasmodium falciparum, the species responsible for most malaria related deaths, pathogenesis is thought to be due to the sequestration of infected red blood cells (IRBCs) in deep tissues. Other human and rodent malaria parasite species are also known to exhibit sequestration. Here, we review the different techniques that allow researchers to study how rodent malaria parasites modify their host cells, the distribution of IRBCs in vivo as well as the interactions between IRBCs and host tissues.     

Interface between haustoria of parasitic members of the Scrophulariaceae and their hosts: A histochemical and immunocytochemical approach

Summary The haustorial structure of three African parasitic members of the family Scrophulariaceae (Buchnera hispida, Rhamphicarpa fistulosa, andStriga hermonthica) has been studied with regard to the interface between haustoria and the invaded host roots. Immunocytochemical observations at the light and electron microscopical level were carried out with monoclonal antibodies against pectin. JIM5, JIM7, and hydroxyproline-rich glycoprotein (HRGP), LM1. Lignins have been visualized by phloroglucinolhydrochloric acid staining. At the margin of the lateral interface (contact area of host root cortex and parasite cells), JIM5- and JIM7-labelled substances accumulate between parasite papillae and the host root surface indicating that pectins are implicated in sealing the parasite to the attacked host organ. The lateral interface is characterized by the presence of compressed, necrotic host cells, whereas the central interface (contact area between host stele and parasite cells) is generally devoid of host cell remnants. Phenolic substances and/or lignins can be found at the site of penetration of the haustorium into the host root. These observations and the fact that HRGPs accumulate at the host side of the interface support the view of, at least, a partial defense reaction in the invaded host root tissues. Within haustoria, HRGPs were restricted to differentiating xylem elements, implying a spatio-temporal regulation of HRGPs in developmental processes.Abbreviations BSA bovine serum albumin - FITC fluorescein isothiocyanate - HRGP hydroxyproline-rich glycoprotein - LM light microscopy - MAb monoclonal antibody - TBSB Tris-buffered saline with bovine serum albumin - TBSB-T Tris-buffered saline with bovine serum albumin and Tween 20 - TEM transmission electron microscopy     

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.