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Complex Life Cycles (complex + life_cycle)
Selected AbstractsChromatin-remodelling proteins of the pea aphid, Acyrthosiphon pisum (Harris)INSECT MOLECULAR BIOLOGY, Issue 2010S. D. Rider Jr Abstract Aphids display extraordinary developmental plasticity in response to environmental cues. These differential responses to environmental changes may be due in part to changes in gene expression patterns. To understand the molecular basis for aphid developmental plasticity, we attempted to identify the chromatin-remodelling machinery in the recently sequenced pea aphid genome. We find that the pea aphid possesses a complement of metazoan histone modifying enzymes with greater gene family diversity than that seen in a number of other arthropods. Several genes appear to have undergone recent duplication and divergence, potentially enabling greater combinatorial diversity among the chromatin-remodelling complexes. The abundant aphid chromatin modifying enzymes may facilitate the phenotypic plasticity necessary to maintain the complex life cycle of the aphid. [source] Expression of synapsin and co-localization with serotonin and RFamide-like immunoreactivity in the nervous system of the chordoid larva of Symbion pandora (Cycliophora)INVERTEBRATE BIOLOGY, Issue 1 2010Ricardo Cardoso Neves Abstract. Cycliophora is one of the most recently described metazoan phyla and hitherto includes only two species: Symbion pandora and Symbion americanus. With a very complex life cycle, cycliophorans are regarded as an enigmatic group with an uncertain phylogenetic position, although they are commonly considered lophotrochozoan protostomes. In order to extend the database concerning the distribution of immunoreactive substances in the free-swimming chordoid larva of S. pandora, we investigated synapsin immunoreactivity using fluorescence-coupled antibodies in combination with confocal laserscanning microscopy. Moreover, we analyzed the co-localization patterns of synapsin, serotonin, and RFamide-like immunoreactivity in the chordoid larva by 3D imaging technology based on the confocal microscopy image stacks. Synapsin is expressed in large parts of the bilobed anterior cerebral ganglion including anterior and dorsal projections. Two pairs of ventral neurites run longitudinally into the larval body of which the inner pair shows only weak, scattered synapsin immunoreactivity. In addition, a lateral synapsin immunoreactive projection emerges posteriorly from each ventral longitudinal axon. Double immunostaining shows co-localization of synapsin and serotonin in the cerebral ganglion, the outer and the inner ventral neurites, and the anterior projections. Synapsin and RFamide-like immunoreactivity co-occur in the cerebral ganglion, the outer ventral neurites, and the dorsal projections. Accordingly, the cerebral ganglion and the outer ventral neurites are the only neural structures that co-express the two neurotransmitters and synapsin. The overall neuroanatomical condition of the cycliophoran chordoid larva resembles much more the situation of adult rather than larval life cycle stages of a number of spiralian taxa. [source] Reproductive value in a complex life cycle: heat tolerance of the pitcher-plant mosquito, Wyeomyia smithiiJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 1 2005P. A. Zani Abstract Because mortality accumulates with age, Fisher proposed that the strength of selection acting on survival should increase from birth up to the age of first reproduction. Hamilton later theorized that the strength of selection acting on survival should not change from birth to age at first reproduction. As organisms in nature do not live in uniform environments but, rather, experience periodic stress, we hypothesized that resistance to environmental stress should increase (Fisher) or remain constant (Hamilton) from birth to age at first reproduction. Using the pitcher-plant mosquito, Wyeomyia smithii, we imposed heat stress by simulating the passage of a warm-weather front at different preadult and adult stages. Contrary to either Fisher or Hamilton, stress tolerance declined from embryos to larvae to pupae to adults. Consequently, reproductive value appears to have been of little consequence in the evolution of stage-specific tolerance of heat stress in W. smithii. [source] The effects of water velocity on the Ceratomyxa shasta infectious cycleJOURNAL OF FISH DISEASES, Issue 2 2009S J Bjork Abstract Ceratomyxa shasta is a myxozoan parasite identified as a contributor to salmon mortality in the Klamath River, USA. The parasite has a complex life cycle involving a freshwater polychaete, Manayunkia speciosa and a salmonid. As part of ongoing research on how environmental parameters influence parasite establishment and replication, we designed a laboratory experiment to examine the effect of water flow (velocity) on completion of the C. shasta infectious cycle. The experiment tested the effect of two water velocities, 0.05 and 0.01 m s,1, on survival and infection of M. speciosa as well as transmission to susceptible rainbow trout and comparatively resistant Klamath River Chinook salmon. The faster water velocity facilitated the greatest polychaete densities, but the lowest polychaete infection prevalence. Rainbow trout became infected in all treatments, but at the slower velocity had a shorter mean day to death, indicating a higher infectious dose. Infection was not detected in Chinook salmon even at a dose estimated to be as high as 80 000 actinospores per fish. The higher water velocity resulted in lower C. shasta infection prevalence in M. speciosa and decreased infection severity in fish. Another outcome of our experiment is the description of a system for maintaining and infecting M. speciosa in the laboratory. [source] Hepatozoon americanum: an emerging disease in the south-central/southeastern United StatesJOURNAL OF VETERINARY EMERGENCY AND CRITICAL CARE, Issue 1 2010Thomas M. Potter DVM Abstract Objective , To review the clinical epidemiologic and pathophysiologic aspects of Hepatozoon americanum infection in dogs. Data Sources , Data from veterinary literature were reviewed through Medline and CAB as well as manual search of references listed in articles pertaining to American canine hepatozoonosis. Veterinary Data Synthesis , H. americanum is an emerging disease in endemic areas of the United States. It is vital that practitioners in these areas become familiar with the clinical syndrome of hepatozoonosis and the diagnostic modalities that can be utilized to document the presence of infection. Additionally, veterinarians must understand the epidemiology of the disease in order to better prevent infections in their veterinary patients. Recent data have been published that shed new light on transmission of H. americanum to dogs; however, much remains unknown regarding patterns of infection and the natural vertebrate host source. Conclusions , While the prognosis for untreated H. americanum remains poor, for patients in which the disease is recognized and properly treated the outcome is favorable. Understanding the complex life cycle, numerous clinical symptoms, and treatment protocol will assist veterinarians who are treating patients with hepatozoonosis. [source] Two Ser/Thr protein kinases essential for efficient aggregation and spore morphogenesis in Myxococcus xanthusMOLECULAR MICROBIOLOGY, Issue 6 2006Emily A. Stein Summary Myxococcus xanthus has a complex life cycle that involves vegetative growth and development. Previously, we described the espAB locus that is involved in timing events during the initial stages of fruiting body formation. Deletion of espA caused early aggregation and sporulation, whereas deletion of espB caused delayed aggregation and sporulation resulting in reduced spore yields. In this study, we describe two genes, pktA5 and pktB8, that flank the espAB locus and encode Ser/Thr protein kinase (STPK) homologues. Cells deficient in pktA5 or pktB8 formed translucent mounds and produced low spore yields, similar in many respects to espB mutants. Double mutant analysis revealed that espA was epistatic to pktA5 and pktB8 with respect to aggregation and fruiting body morphology, but that pktA5 and pktB8 were epistatic to espA with respect to sporulation efficiency. Expression profiles of pktA5,lacZ and pktB8,lacZ fusions and Western blot analysis showed that the STPKs are expressed under vegetative and developmental conditions. In vitro kinase assays demonstrated that the RD kinase, PktA5, autophosphorylated on threonine residue(s) and phosphorylated the artificial substrate, myelin basic protein. In contrast, autophosphorylation of the non-RD kinase, PktB8, was not observed in vitro; however, the phenotype of a pktB8 kinase-dead point mutant resembled the pktB8 deletion mutant, indicating that this residue was important for function and that it likely functions as a kinase in vivo. Immunoprecipitation of Tap-tagged PktA5 and PktB8 revealed an interaction with EspA during development in M. xanthus. These results, taken together, suggest that PktA5 and PktB8 are STPKs that function during development by interacting with EspA and EspB to regulate M. xanthus development. [source] A novel bacterial signalling system with a combination of a Ser/Thr kinase cascade and a His/Asp two-component systemMOLECULAR MICROBIOLOGY, Issue 2 2005Renate Lux Summary Prokaryotes and eukaryotes have long been thought to use very different types of kinases (the His kinases of the ,bacterial' two-component systems versus the ,eukaryotic' Ser/Thr/Tyr kinases) to carry out signal transduction. This paradigm no longer holds true, because both systems are now found together in an increasing number of prokaryotic organisms and ,two-component' His kinase are present in eukaryotes. Pioneering work on bacterial protein serine threonine kinases (PSTKs) has been performed in Myxococcus xanthus, a soil bacterium with a complex life cycle that possesses orthologues of signalling-related kinases ,typical' of both the prokaryotic and the eukaryotic kingdoms. In the work reported in this volume of Molecular Microbiology, Nariya and Inouye describe a PSTK cascade that modulates the biochemical activity of MrpC, a CRP-like transcriptional regulator for essential developmental signalling pathways in M. xanthus whose transcription is under the control of a two-component system. This is the first report of both a functional PSTK cascade in bacteria and the use of both PSTK and two-component systems to control a single complex bacterial signalling event. [source] Proteome analysis of the phenotypic variation process in Photorhabdus luminescensPROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 9 2006Evelyne Turlin Dr. Abstract Photorhabdus luminescens is an insect pathogen associated with specific soil nematodes. The bacterium has a complex life cycle with a symbiotic stage in which bacteria colonize the intestinal tract of the nematodes, and a pathogenic stage against susceptible larval-stage insect. Symbiosis-"deficient" phenotypic variants (known as secondary forms) arise during prolonged incubation. Correspondence analysis of the in silico proteome translated from the genome sequence of strain TT01 identified two major biases in the amino acid composition of the proteins. We analyzed the proteome, separating three classes of extracts: cellular, extracellular, and membrane-associated proteins, resolved by 2-DE. Approximately 450 spots matching the translation products of 231 different coding DNA sequences were identified by PMF. A comparative analysis was performed to characterize the protein content of both variants. Differences were evident during stationary growth phase. Very few proteins were found in variant II supernatants, and numerous proteins were lacking in the membrane-associated fraction. Proteins up-regulated by the phenotypic variation phenomenon were involved in oxidative stress, energy metabolism, and translation. The transport and binding of iron, sugars and amino acids were also affected and molecular chaperones were strongly down-regulated. A potential role for H-NS in phenotypic variation control is discussed. [source] Study of PfMyb1 Transcription Factor Regulation Network during Plasmodium falciparum Erythrocytic CycleTHE JOURNAL OF EUKARYOTIC MICROBIOLOGY, Issue 2 2005M. GISSOT During the complex life cycle of Plasmodium falciparum, the regulation of events that occur during the erythrocytic cycle, such as proliferation and differentiation, implies a fine control of transcriptional activities governing the expression profiles of each gene. However, transcriptional regulation and notably its actors, transcription factors and regulation motifs, are poorly described in Plasmodium. In order to decipher the mechanisms implicated in transcriptional regulation, we studied a transcription factor belonging to the trytophan family and showed that the PfMyb1 protein contained in nuclear extracts has a specific DNA binding activity. We took advantage of long pfmyb1 double stranded RNA (dsRNA) to inactivate the cognate messenger and understand the role of PfMyb1 during the erythrocytic cycle. Culture treated with pfmyb1 dsRNA exhibited a 40% growth inhibition and mortality during trophozoite to schizont transition when compared to either untreated control or culture treated with unrelated long dsRNA. We have further demonstrated that pfmyb1 transcript and protein decreased up to 80% in treated trophozoite culture at the time of pfmyb1 expression peak. Thus, we investigated the effect of this partial loss of transcript and protein using a thematic DNA microarray containing PCR products, representative of P. falciparum genes involved in cell cycle and transcriptional regulation. SAM software enabled us to identify several genes over and under-expressed, potentially directly or indirectly regulated by PfMyb1. These alterations of expression were verified by qPCR and Western blotting. We are currently working on the promoters of those genes to decode determinants of gene regulation by Pfmyb1. [source] Structure of the single-stranded DNA-binding protein from Streptomyces coelicolorACTA CRYSTALLOGRAPHICA SECTION D, Issue 9 2009Zoran, tefani The crystal structure of the single-stranded DNA-binding protein (SSB) from Streptomyces coelicolor, a filamentous soil bacterium with a complex life cycle and a linear chromosome, has been solved and refined at 2.1,Å resolution. The three-dimensional structure shows a common conserved central OB-fold that is found in all structurally determined SSB proteins. However, it shows variations in quaternary structure that have previously only been found in mycobacterial SSBs. The strand involved in the clamp mechanism characteristic of this type of quaternary structure leads to higher stability of the homotetramer. To the best of our knowledge, this is the first X-ray structure of an SSB protein from a member of the genus Streptomyces and it was predicted to be the most stable of the structurally characterized bacterial or human mitochondrial SSBs. [source] Photorhabdus: a model for the analysis of pathogenicity and mutualismCELLULAR MICROBIOLOGY, Issue 11 2008David J. Clarke Summary Photorhabdus are entomopathogenic members of the family Enterobacteriaceae. In addition to killing insects Photorhabdus also have a mutualistic association with nematodes from the family Heterorhabditidiae. Therefore, the bacteria have a complex life cycle that involves temporally separated pathogenic and mutualistic associations with two different invertebrate hosts. This tripartite Photorhabdus,insect,nematode association provides researchers with a unique opportunity to characterize the prokaryotic contribution to two different symbioses, i.e. pathogenicity and mutualism while also studying the role of the host in determining the outcome of association with the bacteria. In this review I will outline the life cycle of Photorhabdus and describe recent important advances in our understanding of the symbiology of Photorhabdus. Finally, the contribution made by this model to our understanding of the nature of symbiotic associations will be discussed. [source] Parasites in food webs: the ultimate missing linksECOLOGY LETTERS, Issue 6 2008Kevin D. Lafferty Abstract Parasitism is the most common consumer strategy among organisms, yet only recently has there been a call for the inclusion of infectious disease agents in food webs. The value of this effort hinges on whether parasites affect food-web properties. Increasing evidence suggests that parasites have the potential to uniquely alter food-web topology in terms of chain length, connectance and robustness. In addition, parasites might affect food-web stability, interaction strength and energy flow. Food-web structure also affects infectious disease dynamics because parasites depend on the ecological networks in which they live. Empirically, incorporating parasites into food webs is straightforward. We may start with existing food webs and add parasites as nodes, or we may try to build food webs around systems for which we already have a good understanding of infectious processes. In the future, perhaps researchers will add parasites while they construct food webs. Less clear is how food-web theory can accommodate parasites. This is a deep and central problem in theoretical biology and applied mathematics. For instance, is representing parasites with complex life cycles as a single node equivalent to representing other species with ontogenetic niche shifts as a single node? Can parasitism fit into fundamental frameworks such as the niche model? Can we integrate infectious disease models into the emerging field of dynamic food-web modelling? Future progress will benefit from interdisciplinary collaborations between ecologists and infectious disease biologists. [source] ADAPTIVE MIGRATORY DIVERGENCE AMONG SYMPATIRIC BROK CHARR POPULATIONSEVOLUTION, Issue 3 2005Dylan J. Fraser Abstract Ecological processes clearly contribute to population divergence, yet how they interact over complex life cycles remains poorly understood. Notably, the evolutionary consequences of migration between breeding and nonbreeding areas have received limited attention. We provide evidence for a negative association between interpopulation differences in migration (between breeding and feeding areas, as well as within each) and the amount of gene flow (m) among three brook charr (Salvelinus fontinalis) populations inhabitingMistassini Lake, Quebec, Canada. Individuals (n=1166) captured throughout lake feeding areas over two consecutive sampling years were genotyped (10 microsatellites) and assigned to one of the three populations. Interpopulation differences in migration were compared based on spatial distribution overlap, habitat selection, migration distance within feeding areas, and morphology. We observed a temporally stable, heterogeneous spatial distribution within feeding areas among populations, with the extent of spatial segregation related to differential habitat selection (represented by littoral zone substrate). Spatial segregation was lowest and gene flow highest (m=0.015) between two populations breeding in separate lake inflows. Segregation was highest and gene flow was lowest (mean m=0.007) between inflow populations and a third population breeding in the outflow. Compared to outflow migrants, inflow migrants showed longer migration distances within feeding areas(64,70 km vs. 22 km). After entering natal rivers to breed, inflow migrants also migrated longer distances (35,75 km) and at greater elevations (50,150 m) to breeding areas than outflow migrants (0,15 km; ,10,0 m). Accordingly, inflow migrants were more streamlined with longer caudal regions, traits known to improve swimming efficiency. There was no association between the geographic distance separating population pairs and the amount of gene flow they exchanged. Collectively, our results are consistent with the hypothesis that reduced gene flow between these brook charr populations results from divergent natural selection leading to interpopulation differences in migration. They also illustrate how phenotypic and genetic differentiation may arise over complex migratory life cycles. [source] Molecular paleoecology: using gene regulatory analysis to address the origins of complex life cycles in the late PrecambrianEVOLUTION AND DEVELOPMENT, Issue 1 2007Ewan F. Dunn SUMMARY Molecular paleoecology is the application of molecular data to test hypotheses made by paleoecological scenarios. Here, we use gene regulatory analysis to test between two competing paleoecological scenarios put forth to explain the evolution of complex life cycles. The first posits that early bilaterians were holobenthic, and the evolution of macrophagous grazing drove the exploitation of the pelagos by metazoan eggs and embryos, and eventually larvae. The alternative hypothesis predicts that early bilaterians were holopelagic, and new adult stages were added on when these holopelagic forms began to feed on the benthos. The former hypothesis predicts that the larvae of protostomes and deuterostomes are not homologous, with the implication that larval-specific structures, including the apical organ, are the products of convergent evolution, whereas the latter hypothesis predicts homology of larvae, specifically homology of the apical organ. We show that in the sea urchin, Strongylocentrotus purpuratus, the transcription factors NK2.1 and HNF6 are necessary for the correct spatial expression profiles of five different cilia genes. All of these genes are expressed exclusively in the apical plate after the mesenchyme-blastula stage in cells that also express NK2.1 and HNF6. In addition, abrogation of SpNK2.1 results in embryos that lack the apical tuft. However, in the red abalone, Haliotis rufescens, NK2.1 and HNF6 are not expressed in any cells that also express these same five cilia genes. Nonetheless, like the sea urchin, the gastropod expresses both NK2.1 and FoxA around the stomodeum and foregut, and FoxA around the proctodeum. As we detected no similarity in the development of the apical tuft between the sea urchin and the abalone, these molecular data are consistent with the hypothesis that the evolution of mobile, macrophagous metazoans drove the evolution of complex life cycles multiple times independently in the late Precambrian. [source] Habitat selection as a source of inter-specific differences in recruitment of two diadromous fish speciesFRESHWATER BIOLOGY, Issue 11 2008ROBIN HALE Summary 1For aquatic species with highly dispersive offspring, the addition of new individuals into an area (recruitment) is a key process in determining local population size so understanding the causes of recruitment variability is critical. While three general causative mechanisms have been identified (the supply of individuals, habitat selection and mortality), we have a limited understanding of how variation in each is generated, and the consequences this may have for the spatial and temporal distribution of recruits. 2We examined whether active habitat selection during settlement could be the cause of variability in populations of two diadromous fish species using a field survey and laboratory-based choice experiments. If larval behaviour is important, we predicted there would be inter-specific differences in abundance between sites during the survey, and that larvae would prefer water collected from sites with higher conspecific abundances during the experiments. 3During the field survey, significant differences were detected between two rivers (the Cumberland and Grey), with one species (Galaxias maculatus) found in higher abundances at one site (the Cumberland River) while comparable numbers of a closely related species (Galaxias brevipinnis) were caught at both sites. Laboratory choice experiments were conducted to determine whether larval preferences during settlement could be the cause of these differences. G. maculatus larvae showed a preference for freshwater over saltwater, indicating that the fish may be responding to reduced salinities around river mouths during settlement. The results of a second experiment were consistent with the notion that larval preferences could be the mechanism driving differences in the populations of the two rivers, with G. maculatus preferring water collected from the Cumberland River while G. brevipinnis did not prefer water from either river. 4These results demonstrate that active habitat selection may be important in establishing spatial patterns of larvae at settlement, and that multiple cues are likely to be involved. This study also demonstrates that the behaviours exhibited by individuals can strongly influence the structure and dynamics of populations of aquatic species with complex life cycles. [source] Ontogeny of escape swimming performance in the spotted salamanderFUNCTIONAL ECOLOGY, Issue 3 2010Tobias Landberg Summary 1.,The life stage suffering the highest predation rate is expected to have the highest escape performance unless developmental or functional constraints interfere. Peak aquatic escape performance in ephemeral pond-breeding amphibians is expected to develop early in the larval period, and metamorphosis is expected to reduce or completely disrupt aquatic escape performance. In anurans, exceptionally low escape performance during metamorphosis creates selection favouring rapid metamorphosis , which minimizes the time individuals spend in the vulnerable transition between tadpole and frog. 2.,We investigated the development of aquatic escape performance in the spotted salamander, Ambystoma maculatum (Shaw, 1802), from embryonic development through metamorphosis. We expected performance to peak early in the larval period as hatchlings face high rates of predation but embryos must first develop escape behaviours. We also tested whether escape performance during metamorphosis was intermediate, as predicted by tail fin resorption, or lower than larvae and adults indicating a major physiological disruption. 3.,Escape performance shows a complex ontogeny that is first positively influenced by embryonic and early larval development and then negatively correlated with tail resorption and body size. Escape distance was the only performance metric not affected by life stage. In contrast, both escape velocity and duration showed ontogenetic peaks early in the larval period with the lowest performance found in early embryos and adults and intermediate performance during metamorphosis. 4.,This pattern suggests that metamorphosis does not impose a major physiological disruption on escape performance. Because spotted salamanders do not pass through a frog-like ,ontogenetic performance valley' during metamorphosis, they may be less subject than anurans to selection favouring rapid metamorphosis. 5.,Functional implications of phenotypic variation should be considered in an ontogenetic framework because the relationship between body size and escape performance can be reversed on either side of an ontogenetic performance peak. The assumption that metamorphosis radically disrupts basic functions such as predator evasion does not seem universally warranted and suggests examination of ontogenetic performance trajectories in a diversity of animals with complex life cycles. [source] Dynamic models allowing for flexibility in complex life histories accurately predict timing of metamorphosis and antipredator strategies of preyFUNCTIONAL ECOLOGY, Issue 6 2009Andrew D. Higginson Summary 1.,The development of antipredator defences in the larval stage of animals with complex life cycles is likely to be affected by costs associated with creating and maintaining such defences because of their impact on the timing of maturation or metamorphosis. 2.,Various theoretical treatments have suggested that investment in defence should both increase or decrease with increasing resource availability, but a recent model predicts investment in defences should be highest at intermediate resource level and predator density. 3.,Previous models of investment in defence and timing of metamorphosis provide a poor match to empirical data. Here we develop a dynamic state-dependent model of investment in behavioural and morphological defences that enables us to allow flexibility in investment in defences over development, the timing of metamorphosis and the size of the organism at metamorphosis that were absent from previous theory. 4.,We show that the inclusion of this flexibility results in different predictions to those of the fixed investment approach used previously, especially when we allow metamorphosis to occur at the optimal time and state for the organism. 5.,Under these more flexible conditions, we predict that morphological defences should be insensitive to resource level whilst behavioural defences should either increase or decrease with increasing resources depending on the predation risk and the magnitude of the fitness benefits of large size at metamorphosis. 6.,Our work provides a formal framework in which we might progress in the study of how the use of antipredator defences is affected by their costs. Most of the predictions of our model in are in good accord with empirical results, and can be understood in terms of the underlying biological assumptions. The reasons why simpler models failed to match empirical observations can be explained, and our predictions that are a poor match help to target the circumstances which warrant future study. [source] Predators and cannibals modulate sex-specific plasticity in life-history and immune traitsFUNCTIONAL ECOLOGY, Issue 1 2008D. J. Mikolajewski Summary 1In organisms with complex life cycles, optimality models predict age and size at transition to translate larval condition into adult fitness. Recent studies, however, revealed that only a proportion of fitness is explained by age and size at transition. Moreover, sexes differ in the linkage of larval condition and adult fitness. 2In this study, we tested the hypothesis that immune traits may be partly decoupled from age and size at habitat transition and therefore contribute to the sex-specific linkage of larval condition and adult fitness. 3We reared larvae of the damselfly Coenagrion puella under the threat of predators and cannibals. We then examined sex-specific patterns in two life-history traits as well as two immune traits and tested for independency of the plastic responses among life-history and immune traits. 4Results revealed immune traits to be partly decoupled from life-history traits. Moreover, the sexes differed in the plasticity of life-history as well as immune traits. Our results give strong evidence that sex-specific translation of larval condition into adult fitness may be linked to immune traits as well as age and size at transition. [source] Food web topology and parasites in the pelagic zone of a subarctic lakeJOURNAL OF ANIMAL ECOLOGY, Issue 3 2009Per-Arne Amundsen Summary 1Parasites permeate trophic webs with their often complex life cycles, but few studies have included parasitism in food web analyses. Here we provide a highly resolved food web from the pelagic zone of a subarctic lake and explore how the incorporation of parasites alters the topology of the web. 2Parasites used hosts at all trophic levels and increased both food-chain lengths and the total number of trophic levels. Their inclusion in the network analyses more than doubled the number of links and resulted in an increase in important food-web characteristics such as linkage density and connectance. 3More than half of the parasite taxa were trophically transmitted, exploiting hosts at multiple trophic levels and thus increasing the degree of omnivory in the trophic web. 4For trophically transmitted parasites, the number of parasite,host links exhibited a positive correlation with the linkage density of the host species, whereas no such relationship was seen for nontrophically transmitted parasites. Our findings suggest that the linkage density of free-living species affects their exposure to trophically transmitted parasites, which may be more likely to adopt highly connected species as hosts during the evolution of complex life cycles. 5The study supports a prominent role for parasites in ecological networks and demonstrates that their incorporation may substantially alter considerations of food-web structure and functioning. [source] Alternative parasite development in transmission strategies: how time flies!JOURNAL OF EVOLUTIONARY BIOLOGY, Issue 10 2010M. BADETS Abstract Among parasitic platyhelminths with complex life cycles, it has been well documented that transmission opportunities are the main forces shaping the diversity of life-history traits and parasite developmental strategies. While deviations in the development pathway usually involve shortening of life cycles, their extension may also occur following perception of remaining time by parasites. Polystoma gallieni, the monogenean parasite of Hyla meridionalis, is able to trigger two alternative developmental strategies depending on the physiological stage of the tadpoles upon which larvae attach. The distribution and reproductive outputs of both resulting phenotypes were surveyed to address questions about the dynamics of transmission in natural environments. Because modifications in the completion of life cycles can have drawbacks which may perturb the dynamic equilibrium of the resulting host,parasite systems, experimental infestations were also performed to assess parasite,parasite interactions. Our results suggest that the bladder adult phenotype, which involves transmission between frogs and tadpoles, is supplied secondarily by the branchial phenotype which involves transmission between tadpoles and metamorphs. They also support the occurrence of finely tuned trade-offs between hosts and parasites and highlight positive trends behind the extension of direct life cycles, in which host-derived signals account for the remaining time to achieve parasitic transmission. [source] DNA BARCODING OF CHLORARACHNIOPHYTES USING NUCLEOMORPH ITS SEQUENCES,JOURNAL OF PHYCOLOGY, Issue 4 2010Gillian H. Gile Chlorarachniophytes are a small group of marine photosynthetic protists. They are best known as examples of an intermediate stage of secondary endosymbiosis: their plastids are derived from green algae and retain a highly reduced nucleus, called a nucleomorph, between the inner and outer pairs of membranes. Chlorarachniophytes can be challenging to identify to the species level, due to their small size, complex life cycles, and the fact that even genus-level diagnostic morphological characters are observable only by EM. Few species have been formally described, and many available culture collection strains remain unnamed. To alleviate this difficulty, we have developed a barcoding system for rapid and accurate identification of chlorarachniophyte species in culture, based on the internal transcribed spacer (ITS) region of the nucleomorph rRNA cistron. Although this is a multicopy locus, encoded in both subtelomeric regions of each chromosome, interlocus variability is low due to gene conversion by homologous recombination in this region. Here, we present barcode sequences for 39 cultured strains of chlorarachniophytes (>80% of currently available strains). Based on barcode data, other published molecular data, and information from culture records, we were able to recommend names for 21 out of the 24 unidentified, partially identified, or misidentified chlorarachniophyte strains in culture. Most strains could be assigned to previously described species, but at least two to as many as five new species may be present among cultured strains. [source] DNA barcodes to identify species and explore diversity in the Adelgidae (Insecta: Hemiptera: Aphidoidea)MOLECULAR ECOLOGY RESOURCES, Issue 2009R. G. FOOTTIT Abstract The Adelgidae are relatively small, cryptic insects, exhibiting complex life cycles with parthenogenetic reproduction. Due to these characteristics, the taxonomy of the group is problematic. Here, we test the effectiveness of the standard 658-bp barcode fragment from the 5,-end of the mitochondrial cytochrome c oxidase 1 gene (COI) in differentiating among 17 species of Adelgidae, in associating life-cycle stages, and in assessing patterns of geographical variation in selected species. Species of Adelgidae are well-differentiated by DNA barcodes, enabling the identification of different morphological forms, immature stages and individuals on different hosts and at different periods of the life cycle. DNA barcodes have uncovered cryptic diversity within taxa and, in other cases, a lack of sequence divergence in species pairs previously separated by life-cycle characteristics, indicating a need for further taxonomic analysis. [source] Species identification of aphids (Insecta: Hemiptera: Aphididae) through DNA barcodesMOLECULAR ECOLOGY RESOURCES, Issue 6 2008R. G. FOOTTIT Abstract A 658-bp fragment of mitochondrial DNA from the 5, region of the mitochondrial cytochrome c oxidase 1 (COI) gene has been adopted as the standard DNA barcode region for animal life. In this study, we test its effectiveness in the discrimination of over 300 species of aphids from more than 130 genera. Most (96%) species were well differentiated, and sequence variation within species was low, averaging just 0.2%. Despite the complex life cycles and parthenogenetic reproduction of aphids, DNA barcodes are an effective tool for identification. [source] Single- or multistage regulation in complex life cycles: does it make a difference?OIKOS, Issue 2 2000Barbara Hellriegel Data on the different stages of complex life cycles are often rather unbalanced, especially those concerning the effects of density. How does this affect our understanding of a species' population dynamics? Two discrete three-stage models with overlapping generations and delayed maturation are constructed to address this question. They assume that survival or emigration in any life stage and/or reproduction can be density dependent. A typical pond-breeding amphibian species with a well-studied larval stage serves as an example. Numerical results show that the population dynamics resulting from density dependence at a single (e.g. the larval) stage can be decisively and unpredictably modified by density dependence in additional stages. Superposition of density-dependent processes could thus be one reason for the difficulties in identifying density dependence in the field. Moreover, in a simulated source-refuge system with habitat-specific density-dependent dispersal of juveniles density dependence in multiple stages can stabilize or destabilize the dynamics and produce misleading age structures. From an applied perspective this model shows that excluding multistage regulation prematurely clearly affects our ability to predict consequences of human impacts. [source] Stress response pathways in protozoan parasitesCELLULAR MICROBIOLOGY, Issue 12 2008Nathalie Vonlaufen Summary Diseases caused by protozoan parasites have a dramatic impact on world health. Emerging drug resistance and a general lack of experimental understanding has created a void in the medicine cabinet used to treat these widespread infections. A novel therapeutic idea that is receiving more attention is centred on targeting the microbe's response to the multitude of environmental stresses it encounters. Protozoan pathogens have complex life cycles, often having to transition from one host to another, or survive in a cyst form in the environment until a new host arrives. The need to respond to environmental cues and stress, and endure in less than optimal conditions, is paramount to their viability and successful progression through their life cycle. This review summarizes the research on parasitic stress responses for Apicomplexa, kinetoplastids and anaerobic protozoa, with an eye towards how these processes may be exploited therapeutically. [source] Histones and histone modifications in protozoan parasitesCELLULAR MICROBIOLOGY, Issue 12 2006William J. Sullivan Jr Summary Protozoan parasites are early branching eukaryotes causing significant morbidity and mortality in humans and livestock. Single-celled parasites have evolved complex life cycles, which may involve multiple host organisms, and strategies to evade host immune responses. Consequently, two key aspects of virulence that underlie pathogenesis are parasite differentiation and antigenic variation, both of which require changes in the expressed genome. Complicating these requisite alterations in the parasite transcriptome is chromatin, which serves as a formidable barrier to DNA processes including transcription, repair, replication and recombination. Considerable progress has been made in the study of chromatin dynamics in other eukaryotes, and there is much to be gained in extending these analyses to protozoan parasites. Much of the work completed to date has focused on histone acetylation and methylation in the apicomplexans and trypanosomatids. As we describe in this review, such studies provide a unique vantage point of the evolutionary picture of eukaryotic cell development, and reveal unique phenomena that could be exploited pharmacologically to treat protozoal diseases. [source] | |||||||||||||||||||||||||||||||