Host manipulation by Ligula intestinalis: a cause or consequence of parasite aggregation?

Previous investigations suggest that the infection of the cyprinid roach, Rutilus rutilus, with the larval plerocercoid forms of the cestode, Ligula intestinalis, creates behavioural and morphological changes in the fish host, potentially of adaptive significance to the parasite in promoting transmission to definitive avian hosts. Here we consider whether these behavioural changes are important in shaping the distribution of parasite individuals across the fish population. An examination of field data illustrates that fish infected with a single parasite were more scarce than expected under the negative binomial distribution, and in many months were more scarce than burdens of two, three or more, leading to a bimodal distribution of worm counts (peaks at 0 and >1). This scarcity of single-larval worm infections could be accounted for a priori by a predominance of multiple infection. However, experimental infections of roach gave no evidence for the establishment of multiple worms, even when the host was challenged with multiple intermediate crustacean hosts, each multiply infected. A second hypothesis assumes that host manipulation following an initial single infection leads to an increased probability of subsequent infection (thus creating a contagious distribution). If manipulated fish are more likely to encounter infected first-intermediate hosts (through microhabitat change, increased ingestion, or both), then host manipulation could act as a powerful cause of aggregation. A number of scenarios based on contagious distribution models of aggregation are explored, contrasted with alternative compound Poisson models, and compared with the empirical data on L. intestinalis aggregation in their roach intermediate hosts. Our results indicate that parasite-induced host manipulation in this system can function simultaneously as both a consequence and a cause of parasite aggregation. This mutual interaction between host manipulation and parasite aggregation points to a set of ecological interactions that are easily missed in most experimental studies of either phenomenon.     

Host dispersal as the driver of parasite genetic structure: a paradigm lost?

Understanding traits influencing the distribution of genetic diversity has major ecological and evolutionary implications for host–parasite interactions. The genetic structure of parasites is expected to conform to that of their hosts, because host dispersal is generally assumed to drive parasite dispersal. Here, we used a meta‐analysis to test this paradigm and determine whether traits related to host dispersal correctly predict the spatial co‐distribution of host and parasite genetic variation. We compiled data from empirical work on local adaptation and host–parasite population genetic structure from a wide range of taxonomic groups. We found that genetic differentiation was significantly lower in parasites than in hosts, suggesting that dispersal may often be higher for parasites. A significant correlation in the pairwise genetic differentiation of hosts and parasites was evident, but surprisingly weak. These results were largely explained by parasite reproductive mode, the proportion of free‐living stages in the parasite life cycle and the geographical extent of the study; variables related to host dispersal were poor predictors of genetic patterns. Our results do not dispel the paradigm that parasite population genetic structure depends on host dispersal. Rather, we highlight that alternative factors are also important in driving the co‐distribution of host and parasite genetic variation.     

A field study on the influence of food and immune priming on a bumblebee–gut parasite system

Laboratory experiments are often preferred over field experiments because they allow the control of confounding factors that would otherwise influence the causal effect of a particular focal experimental factor. These confounding factors can, however, significantly alter the response of an organism confronted with a particular situation, which can have great implications. In a field experiment with a bumblebee host–parasite system, we looked at the influence of additional food supply and immune challenge on various colony fitness values and parasite traits. We could confirm the importance of food on the colony fitness, but not on parasite infection probability or parasite genetic diversity. In contrast to the findings of laboratory experiments of this system, challenge of the immune system had no significant effect on colony fitness or parasite infections. These results likely reflect an overriding effect of environmental variation without disproving the concept of a cost of defence per se. But the results also demonstrate that confounding factors purposely controlled for in the laboratory have to be weighed against their ecological relevance, and stress the need for careful analysis before any direct transfer is made of laboratory results to field situations.     

Sympatric morphotypes of the restricted-range Tashan Cave Garra: distinct species or a case of phenotypic plasticity?

Environmental Biology of Fishes - Among Tashan cave barb Garra tashanensis inhabiting a small cave in southwest Iran, two mental disc (sucking mouth disc) forms were observed. To assess their...     

Cancer research,a field on the verge of a paradigm shift?

The theoretical framework for the field of cancer research is based on two main principles. The first is that cancer advances in a stepwise manner, with each alteration driving cells further toward a malignant state. Second, to cure cancer we must target only cancer-specific properties. Here, we analyze the birth and propagation of the cancer research paradigm. We believe the current paradigm is immersed in crisis and that the field would benefit from integrating theories within and outside the normal modes of research to compile a new framework, with the hope of faster progress and significantly fewer cancer-related deaths.     

Comment on Altaba (2015): a case of species misidentification?

Previously in this journal, Altaba (2015) presented an original hypothesis on the dispersal of small wetland snails in Central Europe after the Last Glacial Maximum, based on the discovery of rare species of the genus Vallonia at the foot of the Devín Hill (Slovakia). On the basis of the evidence available to us, it is our opinion that the existence of Vallonia declivis, Vallonia suevica, Vallonia enniensis, and Vallonia tenuilabris at Devín Gate has not been established, and that the hypothesis advanced in Altaba (2015) is therefore unsubstantiated by hard evidence.     

Host–parasite interactions and host species susceptibility of the marine oomycete parasite, Olpidiopsis sp., from Korea that infects red algae

Porphyra farms in Korea occasionally suffer from Olpidiopsis infection. As Porphyra farming proceeds from October to March, this obligatory biotrophic parasite may need an alternative host to survive during other months of the year. To find a possible alternative summer host, we collected algae from Wando, Korea, where extensive Porphyra plantations are located, and discovered an oomycete assignable to the genus Olpidiopsis from Heterosiphonia pulchra. Host susceptibility tests showed that this oomycete could also infect Heterosiphonia japonica, Dasya sp., Dasysiphonia chejuensis, and also blades of Porphyra tenera. The minimum incubation time for this Olpidiopsis sp. to infect its hosts was approximately 4 h. Zoosporangia matured in 2 days and biflagellate zoospores were released. Free zoospores remained infective in seawater for up to 7 days. The infection of Olpidiopsis sp. to H. japonica was cell-type specific and extended rhizoid-like apical cells of determinate branches were preferentially infected. FITC-conjugated lectin staining showed specific binding of concanavalin A (ConA) to extended rhizoid-like apical cells. Attachment of Olpidiopsis sp. zoospores to the host cells was inhibited by α-mannosidase. Monosaccharide inhibition experiments showed that d(+)-mannose, complementary to the lectin ConA, could also block the infection, suggesting a lectin–carbohydrate interaction during host–parasite recognition.     

Metazoan parasite species richness and genetic variation among freshwater fish species: cause or consequence?

The factors responsible for the maintenance of genetic variation among natural populations remain a mystery. Recent models of host-parasite co-evolution assume that parasites exert frequency-dependent selection on their hosts by favouring rare alleles that may confer resistance against infection. We tested this prediction in a comparative analysis that sought relationships between levels of genetic variation and the number of metazoan parasite species exploiting each host species. We used data on 40 species of North American freshwater fishes. After controlling for sampling effort and phylogenetic influences, we found no relationship between genetic polymorphism and parasite species richness among fish species. However, we found a marginal negative correlation between parasite species richness and heterozygosity. This result goes against the prediction that increased selective pressure by parasites should be associated with higher levels of genetic variation. Instead, it suggests that parasites may be colonising host species showing low levels of genetic variation with greater success than genetically more variable host species.     

Introduction of Alien Host–parasite Complexes in a Natural Environment and the Symbiota Concept

When a species is introduced in a new territory its parasites may also follow, thus forming a sort of biotic unit. We propose the term symbiota to indicate this host–parasite complex. This concept is at the basis of the present research in which 11 species of alien and native freshwater fish were collected by electrofishing in the Po river area (Northern Italy). The alien host fish Ictalurus melas and Silurus glanis were parasitized by only one monogenean species each. Lepomis gibbosus, of North American origin, hosted four monogeneans and Carassius carassius three. All these parasites should be considered as alien species, except those collected from C. carassius that should be considered in part natives and in part aliens.     

Redundant or complementary? Impact of a colonizing species on community structure and function

Recent studies suggest that species with similar functional traits will have similar effects on ecosystems, but evidence for redundancy of species impacts is limited. Here we use a long‐term experiment to gain insight into functional relationships within a desert rodent community. Experimental removal of kangaroo rats, Dipodomys spp., coupled with the recent, serendipitous colonization of a single species of large pocket mouse Chaetodipus baileyi yielded treatments that differed in the diversity of large granivorous rodents present. We evaluated functional overlap of C. baileyi and the other resident large granivores (i.e. the kangaroo rats) by comparing total energy use of granivorous rodents and total abundance and species richness of small granivores across treatments before and after the arrival of C. baileyi. We found that C. baileyi almost completely compensated for the changes in these key ecosystem‐level properties caused by kangaroo rat removal, but it differentially impacted the population dynamics of individual small granivorous rodent species. Thus, its effects were largely complementary, rather than redundant, to those of the missing kangaroo rats. Although short‐term or single‐measure analyses may suggest redundancy, our results support the longstanding dictum that niches of coexisting species are often similar but rarely, if ever, identical.     

Host specificity of the Bacillus thuringiensis δ-endotoxin toward Lepidopteran species: Spodoptera littoralis Bdv. and Pieris brassicae L

Crystals from several strains of Bacillus thuringiensis among the first 10 serotypes were tested for their effectiveness (in terms of LC₅₀ or LD₅₀) in killing Spodoptera littoralis larvae. The δ-endotoxin obtained from the isolates aizawai 7–29 and entomocidus 601 was found to be the most active against S. littoralis; lethal doses were considerably lower than those obtained with the berliner 1715 strain but were nevertheless 10 times higher than that of this last strain against Pieris brassicae. Interestingly, entomocidus crystals were active toward both Lepidopteran species. Protein fractions with molecular mass ranging from 60 to 70 kDa, obtained by dissolving crystals with gut proteases from the two insect species, proved to be active when delivered by intrahemocoel injection. Based on the use of mild detergents such as Triton N-101, sodium cholate, or both, conditions for stabilizing the activity of the solubilized fractions are reported. Under these conditions only, the molecules of toxin thus obtained were as active against S. littoralis larvae as the native crystals, whatever the route of administration and whatever the enzymes used. The same fractions induced different responses in P. brassicae larvae, which manifested a much higher sensitivity to the proteolysis-activated molecules, particularly after intrahemocoel injection, thus suggesting differences between the two insect species as regards the nature of toxic effects. The results clearly illustrate two different patterns in activity spectrum among Lepidopteran species and they also indicate that structural characteristics of the protoxin are predominant factors in determining host specificity.     

Do different parasite species interact in their effects on host fitness? A case study on parasites of the amphipod Paracalliope fluviatilis

There is a gap in our understanding of the relative and interactive effects of different parasite species on the same host population. Here we examine the effects of the acanthocephalan Acanthocephalus galaxii, an unidentified cyclophyllidean cestode, and the trematodes Coitocaecum parvum and Microphallus sp. on several fitness components of the amphipod Paracalliope fluviatilis, using a combination of infection surveys and both survival and behavioural trials. In addition to significant relationships between specific parasites and measures of amphipod survival, maturity, mating success and behaviour, interactions between parasite species with respect to amphipod photophilia were also significant. While infection by either A. galaxii or C. parvum was associated with increased photophilia, such increases were negated by co-infection with Microphallus sp. We hypothesize that this is due to the more subtle manipulative effect of A. galaxii and C. parvum being impaired by Microphallus sp. We conclude that the low frequency at which such double infections occur in our sampled population means that such interactions are unlikely to be important beyond the scale of the host individual. Whether or not this is generally true, implying that parasitological models and theory based on single parasite species studies do generally hold, requires cross-species meta-analytical studies.     

Cultural evolution and the social sciences: a case of unification?

This paper addresses the question of how to understand the relationship between Cultural Evolutionary Science (CES) and the social sciences, given that they coexist and both study cultural change. I argue that CES is best understood as having a unificatory or integrative role between evolutionary biology and the social sciences, and that it is best characterized as a bridge field; I describe the concept of a bridge field and how it relates to other non-reductionist accounts of unification or integration used in the philosophy of science literature.     

Cryptic or pseudocryptic: can morphological methods inform copepod taxonomy? An analysis of publications and a case study of the Eurytemora affinis species complex

Interest in cryptic species has increased significantly with current progress in genetic methods. The large number of cryptic species suggests that the resolution of traditional morphological techniques may be insufficient for taxonomical research. However, some species now considered to be cryptic may, in fact, be designated pseudocryptic after close morphological examination. Thus the “cryptic or pseudocryptic” dilemma speaks to the resolution of morphological analysis and its utility for identifying species. We address this dilemma first by systematically reviewing data published from 1980 to 2013 on cryptic species of Copepoda and then by performing an in‐depth morphological study of the former Eurytemora affinis complex of cryptic species. Analyzing the published data showed that, in 5 of 24 revisions eligible for systematic review, cryptic species assignment was based solely on the genetic variation of forms without detailed morphological analysis to confirm the assignment. Therefore, some newly described cryptic species might be designated pseudocryptic under more detailed morphological analysis as happened with Eurytemora affinis complex. Recent genetic analyses of the complex found high levels of heterogeneity without morphological differences; it is argued to be cryptic. However, next detailed morphological analyses allowed to describe a number of valid species. Our study, using deep statistical analyses usually not applied for new species describing, of this species complex confirmed considerable differences between former cryptic species. In particular, fluctuating asymmetry (FA), the random variation of left and right structures, was significantly different between forms and provided independent information about their status. Our work showed that multivariate statistical approaches, such as principal component analysis, can be powerful techniques for the morphological discrimination of cryptic taxons. Despite increasing cryptic species designations, morphological techniques have great potential in determining copepod taxonomy.     

Conservation implications of the refugee species concept and the European bison: king of the forest or refugee in a marginal habitat?

The concept of refugee species provides a theoretical framework towards increasing the predictive power of the ‘declining population paradigm’ through identifying species which are expected to suffer from a declining population syndrome. Using a simple habitat model as a framework, refugee species are defined as those that can no longer access optimal habitat, but are confined to suboptimal habitats, with consequences of decreased fitness and density, and attendant conservation risks. Refugee species may be difficult to detect in the absence of information on prior habitat use and fitness and their observed ecology will be constrained by the habitat limits forced on them. Identification of refugee species, characterisation of pre‐refugee ecology and the restoration of such species to optimal habitat is critical to their successful conservation. The concept is showcased by addressing the conundrum of a large grazing bovid, the European bison Bison bonasus, being managed as a forest specialist, despite its evolutionary background, dental morphology, neonatal behaviour, diet and microhabitat selection being characteristic of a grazing species inhabiting open, grass‐rich habitats. It is hypothesized that a combination of increasing replacement of open steppe by forest cover after the last postglacial period and increasing human pressure forced bison into forests as a refuge habitat. This process was then reinforced through active management of bison in forests as managers committed themselves to the ‘bison as forest species’ paradigm. A research agenda to test this hypothesis using an experimental approach in the conservation management of European bison by introducing populations into diverse habitat types is suggested.     

Echinococcus multilocularis in germany: increased awareness or spreading of a parasite?

The 'small fox tapeworm' Echinococcus multilocularis has recently become a matter of intense interest in Germany. A long-term increase of its prevalence in foxes has been noted in the well-known endemic areas in Southern Germany, and reports on the occurrence of the parasite in other parts of the country suggest that the parasite is actually much more widespread than previously thought. As nearly all of the relevant studies are published in the German language in a veterinary journal and in the hunting press, accessibility to the information is limited. Richard Lucius and Brigit Bilger here describe the situation, and discuss the possible reasons and consequences.     

Mixed messages from multiple information sources on invasive species: a case of too much of a good thing?

Aim The increasing number and availability of online databases of alien species beg a question of their comparability given most do not adopt standard criteria in the definition of species status or taxonomic treatment and vary in their comprehensiveness. In this study, we compare the consistency of two major European databases for the regions they have in common. We assess whether they use consistent terminology to classify species status, provide similar taxonomic classification and coverage, deliver comparable estimates of alien richness per country and identify comparable correlates of alien richness. Location Northern Europe. Methods Data on the total number of alien species as well as the number of established alien species were extracted from the online databases DAISIE and NOBANIS for 13 European countries and classified into comparable taxonomic groups. Analyses across countries examined trends in alien species richness, correlations among taxonomic groups and the explanatory power of population density, country area and per capita GDP on alien species richness. Results Alien species richness, intertaxon correlations and the significance of individual drivers of invasion were all strongly database dependent. Differences were more marked for total numbers of aliens than established aliens. Over all taxonomic groups, DAISIE had lower species richness and fewer significant intertaxon correlations but presented a greater number of significant explanatory models of alien species richness. Trends in species richness were not generally correlated between the two databases with human population density being a more important driver in DAISIE while country area had greater explanatory power in NOBANIS. Main conclusions Considerable caution should be applied when collating data from different databases because often their underlying structure and content may differ markedly. For Europe, the analysis indicates that having two contrasting databases is not an ideal basis for implementing invasive species policy and moves should be made soon to establish a central pan‐European database.