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PubMed2005

Snail odour-clouds: spreading and contribution to the transmission success of Trichobilharzia ocellata (Trematoda, Digenea) miracidia.

Chemical communication among freshwater organisms is an adaptation to improve their coexistence. Here,we focus on the chemical cues secreted by the freshwater gastropod Lymnaea stagnalis, which are known to stimulate behavioural responses of Trichobilharzia ocellata (Plathelminthes, Digenea, Trematoda) miracidia. Such responses are commonly claimed to influence transmission positively, but in response to chemical cues miracidia randomly change their swimming direction. This kind of response does not necessarily increase transmission, because miracidia may be trapped at the periphery of very large snail odour-clouds, which may prevent them from approaching the snail. On the other hand, the odour clouds may be too small to improve host-localisation. To shed light on these scenarios, the spreading of molecules released around L. stagnalis (active space) was visualised by recording host-finding responses of T. ocellata miracidia when they approached snails. Behavioural responses of miracidia indicated the spreading of compounds forming an attractive active space only around the host-snail L. stagnalis, but not around sympatric non-host-snail species. The active space increased approximately linearly with the time the snail rested at the same spot and within 5 min it reached a volume of more than 30 times that of the snail. We also demonstrated in a large-scale experiment, that the active space of L. stagnalis significantly increases the transmission success of T. ocellata miracidia. Additionally, the microhabitat selection of T. ocellata miracidia was studied, demonstrating that peripheral locations near the water surface were preferred, which are also preferred sites of L. stagnalis. Improved chemoperception and microhabitat selection may have been a consequence of coevolution with snails and benefited miracidia, which became efficient transmissive stages.

Animals↗

PubMed2006

Phylogenetic distribution and evolution of mycorrhizas in land plants.

A survey of 659 papers mostly published since 1987 was conducted to compile a checklist of mycorrhizal occurrence among 3,617 species (263 families) of land plants. A plant phylogeny was then used to map the mycorrhizal information to examine evolutionary patterns. Several findings from this survey enhance our understanding of the roles of mycorrhizas in the origin and subsequent diversification of land plants. First, 80 and 92% of surveyed land plant species and families are mycorrhizal. Second, arbuscular mycorrhiza (AM) is the predominant and ancestral type of mycorrhiza in land plants. Its occurrence in a vast majority of land plants and early-diverging lineages of liverworts suggests that the origin of AM probably coincided with the origin of land plants. Third, ectomycorrhiza (ECM) and its derived types independently evolved from AM many times through parallel evolution. Coevolution between plant and fungal partners in ECM and its derived types has probably contributed to diversification of both plant hosts and fungal symbionts. Fourth, mycoheterotrophy and loss of the mycorrhizal condition also evolved many times independently in land plants through parallel evolution.

Biological Evolution↗

PubMed2003

Herman Jan Phaff: professor, mentor, friend and colleague.

Herman Jan Phaff, the father of yeast ecology, was born in the Netherlands in 1913. In his early years, he spent much time in his family's winery, which sparked his interest in microbes. Trained in the famous Delft tradition, Phaff discovered many unrecognized ecological niches of yeast, such as shellfish, rabbit stomach, frass of bark beetles, tree exudates, cactus roots, Capri figs, sewage, Drosophila flies and shrimp. He is also remembered for his pioneering work on the coevolution of yeasts, insects and plants as well as for his work on yeast beta-glucanase, which resulted in major advances in the understanding of the nature of the yeast cell wall. Phaff's legacy includes research on pectin degradation by fungal enzymes and the application of molecular approaches to yeast systematics. He discovered and described many yeasts, such as the yeast named in his honor, Phaffia rhodozyma, which led to the establishment of a very important industrial fermentation process yielding high concentrations of the pigment astaxanthin, used throughout the world to provide a natural source of this important carotenoid.

History, 20th Century↗

PubMed2026

Parasites and allergies: a complex bidirectional relationship from evolutionary origins to modern therapeutics.

Parasites and allergic diseases are linked by a complex, bidirectional relationship shaped by long-term host-parasite coevolution. This review discusses how different parasites may either promote or attenuate allergic responses through immunological, epithelial, and microbiome-mediated mechanisms. IgE-mediated immunity, mast cell activation, eosinophilia, and pruritus may have evolved as protective responses against helminths and blood-feeding ectoparasites. In contrast, modern allergies may partly reflect misdirected responses to harmless environmental antigens. The effects of parasites on allergy are not uniform and depend on parasite type, infection site, exposure intensity and chronicity, host immune status, and the degree of host-parasite adaptation. Protozoa such as Giardia intestinalis may contribute to food allergy-related manifestations by disrupting the intestinal barrier, altering gut microbiota composition, and modifying mucosal immune responses, particularly in atopic individuals. In contrast, selected helminths may attenuate allergic inflammation by inducing regulatory T and B cells, anti-inflammatory cytokines, antigen-presenting cell modulation, and IgG4-associated mechanisms that can limit IgE-mediated effector responses. Molecular similarities between parasite-derived antigens and environmental allergens, including conserved protein families and carbohydrate epitopes, may contribute to cross-reactive IgE responses and complicate allergy diagnostics. Therefore, current research is shifting from live helminth therapy toward defined parasite-derived molecules and immunomodulatory pathways that may inspire safer and more controlled therapeutic strategies. A clearer understanding of parasite-allergy interactions may improve diagnostic interpretation and support the development of new approaches to the management of allergic disease.

Humans↗

PubMed2005

Genetic variation in male and female reproductive characters associated with sexual conflict in Drosophila melanogaster.

Recent studies have shown that elevated mating, courtship and seminal substances affect female fitness negatively in Drosophila melanogaster. It has also been shown that males vary with respect to these characters and that male harm to females correlates positively with components of male fitness. These results suggest that there is sexual conflict over the effect of such male characters. An important component of this scenario is that females have evolved counteradaptations to male harm, but so far there is limited evidence for this. Here I define female resistance as the ability to withstand an increased exposure to males. Across 10 genetically differentiated lines of D. melanogaster, I found genetic variation among females in the reduction of lifespan that followed from exposure to males of different durations. There was also genetic variation among males with regards to the degree to which they decrease the lifespan of their mates. These results suggest that genetic variation for female ability to endure male sexually antagonistic adaptations exists and may play an important role in male-female coevolution.

Adaptation, Physiological↗

PubMed2006

Compensatory vs. pseudocompensatory evolution in molecular and developmental interactions.

The evolution of molecules, developmental circuits, and new species are all characterized by the accumulation of incompatibilities between ancestors and descendants. When specific interactions between components are necessary at any of these levels, this requires compensatory coevolution. Theoretical treatments of compensatory evolution that only consider the endpoints predict that it should be rare because intermediate states are deleterious. However, empirical data suggest that compensatory evolution is common at all levels of molecular interaction. A general solution to this paradox is provided by plausible neutral or nearly neutral intermediates that possess informational redundancy. These intermediates provide an evolutionary path between coadapted allelic combinations. Although they allow incompatible end points to evolve, at no point was a deleterious mutation ever in need of compensation. As a result, what appears to be compensatory evolution may often actually be "pseudocompensatory." Both theoretical and empirical studies indicate that pseudocompensation can speed the evolution of intergenic incompatibility, especially when driven by adaptation. However, under strong stabilizing selection the rate of pseudocompensatory evolution is still significant. Important examples of this process at work discussed here include the evolution of rRNA secondary structures, intra- and inter-protein interactions, and developmental genetic pathways. Future empirical work in this area should focus on comparing the details of intra- and intergenic interactions in closely related organisms.

Animals↗

PubMed2006

Functional and evolutionary inference in gene networks: does topology matter?

The relationship between the topology of a biological network and its functional or evolutionary properties has attracted much recent interest. It has been suggested that most, if not all, biological networks are 'scale free.' That is, their connections follow power-law distributions, such that there are very few nodes with very many connections and vice versa. The number of target genes of known transcriptional regulators in the yeast, Saccharomyces cerevisiae, appears to follow such a distribution, as do other networks, such as the yeast network of protein-protein interactions. These findings have inspired attempts to draw biological inferences from general properties associated with scale-free network topology. One often cited general property is that, when compromised, highly connected nodes will tend to have a larger effect on network function than sparsely connected nodes. For example, more highly connected proteins are more likely to be lethal when knocked out. However, the correlation between lethality and connectivity is relatively weak, and some highly connected proteins can be removed without noticeable phenotypic effect. Similarly, network topology only weakly predicts the response of gene expression to environmental perturbations. Evolutionary simulations of gene-regulatory networks, presented here, suggest that such weak or non-existent correlations are to be expected, and are likely not due to inadequacy of experimental data. We argue that 'top-down' inferences of biological properties based on simple measures of network topology are of limited utility, and we present simulation results suggesting that much more detailed information about a gene's location in a regulatory network, as well as dynamic gene-expression data, are needed to make more meaningful functional and evolutionary predictions. Specifically, we find in our simulations that: (1) the relationship between a gene's connectivity and its fitness effect upon knockout depends on its equilibrium expression level; (2) correlation between connectivity and genetic variation is virtually non-existent, yet upon independent evolution of networks with identical topologies, some nodes exhibit consistently low or high polymorphism; and (3) certain genes show low polymorphism yet high divergence among independent evolutionary runs. This latter pattern is generally taken as a signature of positive selection, but in our simulations its cause is often neutral coevolution of regulatory inputs to the same gene.

Algorithms↗

PubMed2006

Evolutionary divergence of LFY function in the mustards Arabidopsis thaliana and Leavenworthia crassa.

LEAFY (LFY), a transcription factor involved in the regulation of flower development in Arabidopsis thaliana, has been identified as a candidate gene in the diversification of plant architecture in Brassicaceae. Previous research with Leavenworthia crassa, which produces solitary flowers in the axils of rosette leaves, has shown that the L. crassa LFY ortholog, LcrLFY, rescues most aspects of flower development in A. thaliana but showed two novel traits: flowers produced additional petals and inflorescences produced terminal flowers. In this paper, we explore the molecular mechanisms responsible for these novel phenotypes. We used microarray hybridizations to identify 32 genes differentially expressed between a transgenic LcrLFY line and a control transgenic LFY line. Of particular interest, TERMINAL FLOWER 1 (TFL1) transcripts were found at elevated levels in LcrLFY lines. To distinguish regulatory versus functional changes within the LcrLFY locus, reciprocal chimeric transgenes between LcrLFY and LFY were constructed. These lines implicate divergence of LcrLFY cis-regulation as the primary cause of both novel transgenic phenotypes but implicate divergence of LcrLFY protein function as the primary cause of elevated TFL1 levels. Taken together these results show that LcrLFY has diverged from A. thaliana in both the cis-regulatory and protein-coding regions and imply that molecular coevolution of LcrLFY and the L. crassa TFL1 ortholog, LcrTFL1, contributed to the evolution of rosette flowering.

Arabidopsis↗

PubMed1990

The role of helminths in the biological control of mammals.

Biological control of invertebrates has been successful while that of vertebrates has been, with the exception of myxomatosis in rabbits, unsuccessful; reasons for this are discussed. Demographic studies of small mammals suggest that population regulation occurs by several different mechanisms, more than one of which may be acting at the same time. Coevolution is an important phenomenon in host-parasite associations, nevertheless parasites may limit host population abundance. The basis of the regulatory effect on the host population is that parasite-induced host mortality or reduction in fecundity is density-dependent. Increasing evidence of the density-dependent effects of helminths on host survival and reproduction is forthcoming from laboratory studies but has not been confirmed in the field. The theory that a helminth parasite may regulate mammal population abundance has been verified recently in the laboratory. A multidisciplinary research programme aimed at understanding the mechanisms responsible for formation of house mouse (Mus domesticus) plagues and seeking strategies to reduce mouse numbers is discussed. One aspect of the work involves investigation of the potential of the nematode, Capillaria hepatica, as a biological agent in the control of wild mice in the cereal-growing regions of Australia. Biological control of mammals is viewed within the context of integrated pest management. A helminth species which reduces host survival or fecundity at an increasing rate as host abundance increases has a role in host population regulation. There is potential to capitalize on that role and apply the helminth as a biological agent in the control of mammals which have attained pest status.

Animals↗

PubMed1993

Host genes, parasites and parasitic infections.

Resistance to infection of mammalian hosts by parasites is under genetic control at many different levels: between species, between races, breeds and lines of single species and between individuals. These genetic effects have been described in many host-parasite systems. Here we review the interaction between three elements: host genes, parasites and the environment in which parasitic infections develop. Already livestock industries exploit genetic variation between breeds, particularly for the control of trypanosomiasis and tick infestation in cattle. In most populations, and to many diseases, resistance is heritable and selective breeding for resistance in commercial livestock species has been successful experimentally. Attempts at utilizing genetic variation are placed in the broad context of the coevolution of host and parasite, the limited knowledge we have of the mode of action of resistance genes and our ability to use genetic information to predict resistance to parasites.

Animals↗

PubMed1994

Evolutionary expansion of the Monogenea.

The evolutionary expansion of the monogeneans has taken place in parallel with the diversification of the fish-like vertebrates. In this article the main trends in monogenean evolution are traced from a hypothetical skin-parasitic ancestor on early vertebrates. Special consideration is given to the following topics: early divergence between skin feeders and blood feeders; diversification and specialization of the haptor for attachment to skin; transfer from host to host, viviparity and the success of the gyrodactylids; predation on skin parasites and camouflage; colonization of the buccal and branchial cavities; diversification and specialization of the haptor for attachment to the gills; phoresy in gill parasites; the development of endoparasitism and the origin of the cestodes; the success of dactylogyroidean gill parasites; the uniqueness of the polyopisthocotyleans; ovoviviparity and the colonization of the tetrapods. Host specificity has been the guiding force of coevolution between monogeneans and their vertebrate hosts, but the establishment of monogeneans on unrelated hosts sharing the same environment (host-switching) may have been underestimated. Host-switching has provided significant opportunities for evolutionary change of direction and is probably responsible for the establishment of monogeneans on cephalopod molluscs, on the hippopotamus and possibly on chelonians. There are indications that host-switching may be more common in monogeneans that spread by direct transfer of adults/juveniles from host to host. A limitation on the further expansion of monogeneans is the need for water for the dispersal of the infective larva (oncomiracidium).

Animals↗

PubMed1994

Phylogeny and classification, origins, and evolution of host associations of lice.

Lice are highly successful ectoparasites. Most species of mammals and birds are infested by at least 1 but up to 6 species of lice. Current opinion is that lice evolved from free-living Psocoptera (booklice, barklice and psocids). It is generally agreed that there are 4 main groups of lice: Anoplura, Amblycera, Ischnocera and Rhyncophthirina. In contrast, there is no agreement on the phylogenetic relationships of these groups and their classification. In particular, there is much debate over the validity of the taxon Mallophaga, which is almost certainly paraphyletic. For many years the sister-group of the Boopiidae, which almost exclusively infest Australasian marsupials, was thought to be a group of lice that now infest marsupials in South America. This, however, is almost certainly incorrect; the sister-group of the Boopiidae probably contains bird-infesting lice from the Menoponidae (Amblycera). Thus, menoponid lice transferred from birds to mammals and from these arose the Boopiidae. Transfers of lice between mammals and birds have occurred on other occasions during the evolution of the lice; 2 of the 4 main groups of lice, the Ischnocera and Amblycera, contain families that infest birds and families that infest mammals. Strict cospeciation and coevolution was thought to predominate among the lice; however, detailed studies indicate this to be incorrect. Consequently, the axiom that lice and their hosts invariably coevolve should be abandoned. Ironically, biologists may learn more about the evolutionary biology of hosts when host-switching has occurred.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1983

Feeding strategy and the mechanics of blood sucking in insects.

As a means of exploring foraging strategies of blood-feeding insects, we studied the mechanics of blood feeding. We develop a mechanistic model for the dynamics of non-Newtonian fluid flow to describe the feeding process for blood feeders. Using available feeding and morphological data, we examine the relationship of feeding time to proboscis design, and consider optimal foraging strategies for blood feeders. Because of the flow rates typical of many blood feeders, the non-Newtonian nature of blood is of little importance for flow dynamics. Observed feeding times and flow rates do not necessarily reflect the energy requirements for feeding. The radius of the food canal is the major morphological determinant of flow dynamics. Feeding time is a monotonically increasing function of blood hematocrit. There is an optimal blood hematocrit of 0.3 which maximizes the rate of total protein intake for blood feeders, regardless of the energy output or proboscis design. This hematocrit level is typical of humans with blood parasite infections. In contrast, the rate of red blood cell intake is maximized at a hematocrit of 0.4. We argue that the existence of such optima may be a general consequence of the mechanics of feeding on nutrients dissolved or suspended in a fluid medium. Results are discussed in relation to foraging strategy, proboscis design, and the coevolution among host, vector, and parasite in blood feeding insects.

Aedes↗

PubMed1989

Structural instability of models of sexual selection.

Models for sexual selection by the coevolution of female preference and a male trait have as a generic feature the existence of a neutrally stable line of equilibria up and down which the system can drift at random. However, this feature is structurally unstable since it is destroyed by introducing either mutation or weak direct selection on female preference into the model, to be replaced by a single equilibrium (or a finite set of disconnected equilibria). This process is investigated in detail under a simple but general population genetic model. It is concluded that the level of female preference is determined by mutation, selection, and genetic drift acting directly on it, and drags the male trait along with it along the line of equilibria. More attention should be paid to selective forces acting directly on female preference.

Biological Evolution↗

PubMed1983

Properties of DI particle resistant mutants of vesicular stomatitis virus isolated from persistent infections and from undiluted passages.

We describe an assay procedure to quantitate relative DI resistance of a variety of DI particle resistant (Sdi-) mutants of vesicular stomatitis virus (VSV). We show that numerous diverse Sdi- mutants of VSV are selected continuously in a stepwise manner during persistent infections, and also during serial undiluted lytic passages initiated with cloned virus. Concurrently with the successive appearance and disappearance of different Sdi- mutants of infectious VSV, new DI particle types with altered interference properties also appear and disappear, resulting in rapid "coevolution" of virus and DI particle populations. Complementation tests with Sdi- mutants indicate that mutations in at least two different virus factors (presumably associated with replication-encapsidation) can give rise to Sdi- mutants. Interference studies with chimeric DI particles indicate that DI particle template RNA rather than DI particle protein determines the interference properties of DI particles interacting with Sdi- and Sdi+ mutants of helper virus.

Defective Viruses↗

PubMed1989

Determinants of target gene specificity for steroid/thyroid hormone receptors.

The molecular specificity of the receptors for steroid and thyroid hormones is achieved by their selective interaction with DNA binding sites referred to as hormone response elements (HREs). HREs can differ in primary nucleotide sequence as well as in the spacing of their dyadic half-sites. The target gene specificity of the glucocorticoid receptor can be converted to that of the estrogen receptor by changing three amino acids clustered in the first zinc finger. Remarkably, a single Gly to Glu change in this region produces a receptor that recognizes both glucocorticoid and estrogen response elements. Further replacement of five amino acids in the stem of the second zinc finger transforms the specificity to that of the thyroid hormone receptor. These findings localize structural determinants required for discrimination of HRE sequence and half-site spacing, respectively, and suggest a simple pathway for the coevolution of receptor DNA binding domains and hormone-responsive gene networks.

Amino Acid Sequence↗

PubMed1995

Differences in DNA sequence recognition by the heat-shock factors of Drosophila melanogaster and the parasitic helminth Schistosoma mansoni.

It was recently shown that schistosome extracts contain heat-shock factor (HSF) activity that correlates with the pattern of hsp70 mRNA levels at different developmental stages of the parasite (Levy-Holtzman and Schechter (1994) Parasitology 108, 35-42). To extend our understanding of the HSF activity revealed in extracts of Schistosoma mansoni (Sm), it was further analyzed by competition experiments and compared with the well characterized HSF of Drosophila melanogaster (Dm). The interactions of HSF in Sm extracts (SmHSF) and HSF of Dm (DmHSF) with 32P-labeled heat shock element (HSE) probes, with and without unlabeled competitor DNA probes (HSE-related oligos), were analyzed by gel retardation assay. The binding and inhibition studies demonstrated that SmHSF and DmHSF differ in HSE sequence recognition: an array of three nGAAn inverted repeats according to the ideal consensus sequence (nGAAnnTTCnnGAAn) is recognized by DmHSF, but not by SmHSF. In the schistosome, binding is attained only when the third pentamer is a variant, composed of nGTAn instead of nGAAn. The presence of this variant in the promoter of the hsp70 gene of the parasite suggests coevolution of the variant sequence together with the SmHSF which interacts efficiently with the variant, but not with the ideal HSE sequence. Further inhibition studies revealed additional differences between SmHSF and DmHSF in recognition of the first and second nGAAn pentamers of HSE. In analogy to other systems of ligand-protein interactions, we propose that the complementarity between the HSE ligand and the HSF protein is higher in SmHSF, as compared to DmHSF.

Animals↗

PubMed1991

Changes in cell gene expression in human leukemic cells persistently infected with vaccinia virus.

Persistent viral infections in vitro are useful systems to study the coevolution of virus and cell populations. Persistent infection of mouse Friend erythroleukemic cells (FEL) with vaccinia virus results in profound changes of the virus as well as of the cells. To investigate phenotypic changes of other cell types, we have established a persistent infection with vaccinia virus in a human leukemic cell line (K562). This cell line can be induced to differentiate along the erythroid pathway synthesizing embryonic and fetal globins, thus providing a system in which specific genes can be stimulated. After serial passage, the persistently infected cells (K562vac) became spontaneously differentiated, as shown by the increase in the number of cells producing hemoglobin (benzidine positive cells), and resistant to superinfection. These phenotypic changes of the cells were not accompanied by changes in the viral population. Hybridization of cellular RNA with cloned embryonic and fetal globin genes indicated that uninduced K562 cells do not express these genes, whereas cells induced by hemin or butyrate express G gamma (fetal globin) epsilon and zeta (embryonic globins) genes. By contrast vaccinia infected cells spontaneously express the G gamma gene. These results demonstrate that persistent infection with vaccinia virus elicited phenotypic changes in the infected cell population; in this case the constitutive expression of fetal hemoglobin.

Cell Line↗