bluuebunny/crossref_metadata_2025 huggingface dataset:
A stress regulatory network for co‐ordinated activation of proteasome expression mediated by yeast heat shock transcription factor
Authors: Hahn Ji‐Sook , Neef Daniel W. , Thiele Dennis J.
Published: March 2006

Heat shock transcription factor (HSF) mediates the transcriptional response of eukaryotic cells to heat, infection and inflammation, pharmacological agents, and other stresses. Although genes encoding heat shock proteins (HSPs) are the best characterized targets of HSF, recent genome‐wide localization of Saccharomyces cerevisiae HSF revealed novel HSF targets involved in a wide range of cellular functions. One such target, the RPN4 gene, encodes a transcription factor that directly activates expression of a number of genes encoding proteasome subunits. Here we demonstrate that HSF co‐ordinates a feed‐forward gene regulatory circuit for RPN4 activation. We show that HSF activates expression of PDR3, encoding a multidrug resistance (MDR) transcription factor that also directly activates RPN4 gene expression. We demonstrate that the HSF binding site (HSE) in the RPN4 promoter is primarily responsible for heat‐ or methyl methanesulphonate induction of RPN4, with a minor contribution of Pdr3 binding sites (PDREs), while a Yap1 binding site (YRE) is responsible for RPN4 induction in response to oxidative stress. Furthermore, heat‐induced expression of Rpn4 protein leads to expression of Rpn4 targets at later stages of heat stress, providing a temporal controlling mechanism for proteasome synthesis upon stress conditions that could result in irreversibly damaged proteins. In addition, the overlapping transcriptional regulatory networks involving HSF, Yap1 and Pdr3 suggest a close linkage between stress responses and pleiotropic drug resistance.
Phosphoenolpyruvate synthetase and pyruvate, phosphate dikinase of Thermoproteus tenax: key pieces in the puzzle of archaeal carbohydrate metabolism
Authors: Tjaden Britta , Plagens André , Dörr Christine , Siebers Bettina , Hensel Reinhard
Published: March 2006

The interconversion of phosphoenolpyruvate and pyruvate represents an important control point of the Embden–Meyerhof–Parnas (EMP) pathway in Bacteria and Eucarya, but little is known about this site of regulation in Archaea. Here we report on the coexistence of phosphoenolpyruvate synthetase (PEPS) and the first described archaeal pyruvate, phosphate dikinase (PPDK), which, besides pyruvate kinase (PK), are involved in the catalysis of this reaction in the hyperthermophilic crenarchaeote Thermoproteus tenax. The genes encoding T. tenax PEPS and PPDK were cloned and expressed in Escherichia coli, and the enzymic and regulatory properties of the recombinant gene products were analysed. Whereas PEPS catalyses the unidirectional conversion of pyruvate to phosphoenolpyruvate, PPDK shows a bidirectional activity with a preference for the catabolic reaction. In contrast to PK of T. tenax, which is regulated on transcript level but exhibits only limited regulatory potential on protein level, PEPS and PPDK activities are modulated by adenosine phosphates and intermediates of the carbohydrate metabolism. Additionally, expression of PEPS is regulated on transcript level in response to the offered carbon source as revealed by Northern blot analyses. The combined action of the differently regulated enzymes PEPS, PPDK and PK represents a novel way of controlling the interconversion of phosphoenolpyruvate and pyruvate in the reversible EMP pathway, allowing short‐term and long‐term adaptation to different trophic conditions. Comparative genomic analyses indicate the coexistence of PEPS, PPDK and PK in other Archaea as well, suggesting a similar regulation of the carbohydrate metabolism in these organisms.
Streptococcus gordonii utilizes several distinct gene functions to recruit Porphyromonas gingivalis into a mixed community
Authors: Kuboniwa Masae , Tribble Gena D. , James Chloe E. , Kilic Ali O. , Tao Lin , Herzberg Mark C. , Shizukuishi Satoshi , Lamont Richard J.
Published: March 2006

Dental plaque biofilm formation proceeds through a developmental pathway initiated by the attachment of pioneer organisms, such as Streptococcus gordonii, to tooth surfaces. Through a variety of synergistic interactions, pioneer organisms facilitate the colonization of later arrivals including Porphyromonas gingivalis, a potential periodontal pathogen. We have investigated genes of S. gordonii required to support a heterotypic biofilm community with P. gingivalis. By screening a plasmid integration library of S. gordonii, genes were identified that are crucial for the accumulation of planktonic P. gingivalis cells into a multispecies biofilm. These genes were further investigated by specific mutation and complementation analyses. The biofilm‐associated genes can be grouped into broad categories based on putative function as follows: (i) intercellular or intracellular signalling (cbe and spxB), (ii) cell wall integrity and maintenance of adhesive proteins (murE, msrA and atf), (iii) extracellular capsule biosynthesis (pgsA and atf), and (iv) physiology (gdhA, ccmA and ntpB). In addition, a gene for a hypothetical protein was identified. Biofilm visualization and quantification by confocal microscopy confirmed the role of these genes in the maturation of the multispecies community, including biofilm architectural development. The results suggest that S. gordonii governs the development of heterotypic oral biofilms through multiple genetic pathways.
The carboxyl‐terminal linker is important for chemoreceptor function
Authors: Li Mingshan , Hazelbauer Gerald L.
Published: March 2006

Sensory adaptation in bacterial chemotaxis is mediated by chemoreceptor methylation and demethylation. In Escherichia coli, methyltransferase CheR and methylesterase CheB bind both substrate sites and a carboxyl‐terminal pentapeptide sequence carried by certain receptors. Pentapeptide binding enhances enzyme action, an enhancement required for effective adaptation and chemotaxis. Pentapeptides are linked to the conserved body of chemoreceptors through a notably variable sequence of 30–35 residues. We created nested deletions from the distal end of this linker in chemoreceptor Tar. Chemotaxis was eliminated by deletion of 20–40 residues and reduced by shorter deletions. This did not reflect generalized disruption, because all but the most extremely truncated receptors activated kinase, were substrates for adaptational modification and performed transmembrane signalling. In contrast, linker truncations reduced rates of adaptational modification in parallel with chemotaxis. We concluded the linker is important for chemotaxis because of its role in adaptational modification. Effects of linker truncations on CheR binding to receptor‐borne pentapeptide implied linker (i) makes pentapeptide available to modification enzymes by separation from the helical receptor body, and (ii) is a flexible arm allowing dual binding of enzyme to pentapeptide and modification site. The data suggest linker and the helix from which it emerges are structurally dynamic.
Evidence for the involvement of Plasmodium falciparum proteins in the formation of new permeability pathways in the erythrocyte membrane
Authors: Baumeister Stefan , Winterberg Markus , Duranton Christophe , Huber Stephan M. , Lang Florian , Kirk Kiaran , Lingelbach Klaus
Published: March 2006

The intraerythrocytic developmental stages of the malaria parasite Plasmodium falciparum are responsible for the clinical symptoms associated with malaria tropica. The non‐infected human erythrocyte is a terminally differentiated cell that is unable to synthesize proteins and lipids de novo, and it is incapable of importing a number of solutes that are essential for parasite proliferation. Approximately 12–15 h after invasion the parasitized cell undergoes a marked increase in its permeability to a variety of different solutes present in the extracellular milieu. The increase is due to the induction in the erythrocyte membrane of ‘new permeability pathways’ which have been characterized in some detail in terms of their transport and electrophysiological properties, but which are yet to be defined at a molecular level. Here we show that these pathways are resistant to trypsin but are abolished by treatment of intact infected erythrocytes with chymotrypsin. On resuspension of chymotrypsinized cells in chymotrypsin‐free medium the pathways progressively reappear, a process that can be inhibited by cytotoxic agents, and by brefeldin A which inhibits protein secretion. Our results provide evidence for the involvement of parasite encoded proteins in the generation of the pathways, either as components of the pathways themselves or as auxiliary factors.
Cloning, functional expression and characterization ofMesorhizobium lotiarylamineN‐acetyltransferases: rhizobial symbiosis supplies leguminous plants with the xenobiotic N‐acetylation pathway
Authors: Rodrigues‐Lima Fernando , Dairou Julien , Diaz Clara L. , Rubio Maria C. , Sim Edith , Spaink Herman P. , Dupret Jean‐Marie
Published: March 2006

ArylamineN‐acetyltransferases (NATs) are xenobiotic‐metabolizing enzymes involved in the detoxification of numerous aromatic chemicals. The NAT‐dependent N‐acetylation pathway has not previously been detected in plants. We demonstrate here the occurrence of the NAT‐dependent pathway in leguminous plants, due to symbiosis withMesorhizobium loti. We cloned two NAT enzymes fromM. lotiand showed that these two recombinant enzymes catalysed the N‐acetylation of several known NAT substrates, including aniline‐derived pesticide residues. We also demonstrate the existence of a functional NAT‐dependent acetylation pathway in the root nodules ofLotus japonicusinoculated withM. loti.M. lotiis the first non‐eukaryotic organism shown to express two catalytically active NAT isoforms. This work also provides the first evidence for acquisition of a xenobiotic detoxification pathway by a plant through symbiosis with a soil microbe.
Yeast ribosomal P0 protein has two separate binding sites for P1/P2 proteins
Authors: Krokowski Dawid , Boguszewska Aleksandra , Abramczyk Dariusz , Liljas Anders , Tchórzewski Marek , Grankowski Nikodem
Published: March 2006

The ribosome has a distinct lateral protuberance called the stalk; in eukaryotes it is formed by the acidic ribosomal P‐proteins which are organized as a pentameric entity described as P0‐(P1‐P2)2. Bilateral interactions between P0 and P1/P2 proteins have been studied extensively, however, the region on P0 responsible for the binding of P1/P2 proteins has not been precisely defined. Here we report a study which takes the current knowledge of the P0 – P1/P2 protein interaction beyond the recently published information. Using truncated forms of P0 protein and several in vitro and in vivo approaches, we have defined the region between positions 199 and 258 as the P0 protein fragment responsible for the binding of P1/P2 proteins in the yeast Saccharomyces cerevisiae. We show two short amino acid regions of P0 protein located at positions 199–230 and 231–258, to be responsible for independent binding of two dimers, P1A‐P2B and P1B‐P2A respectively. In addition, two elements, the sequence spanning amino acids 199–230 and the P1A‐P2B dimer were found to be essential for stalk formation, indicating that this process is dependent on a balance between the P1A‐P2B dimer and the P0 protein.
Four signalling domains in the hybrid histidine protein kinase RodK of Myxococcus xanthus are required for activity
Authors: Rasmussen Anders Aa. , Wegener‐Feldbrügge Sigrun , Porter Steven L. , Armitage Judith P. , Søgaard‐Andersen Lotte
Published: March 2006

In prokaryotes, the principal signal transduction systems operating at the level of protein phosphorylation are the two‐component systems. A number of hybrid histidine protein kinases in these systems contain several receiver domains, however, the function of these receiver domains is unknown. The RodK kinase in Myxococcus xanthus has an unconventional domain composition with a putative N‐terminal sensor domain followed by a histidine kinase domain and three receiver domains. RodK is essential for the spatial coupling of the two morphogenetic events underlying fruiting body formation in M. xanthus, aggregation of cells into nascent fruiting bodies and the subsequent sporulation of these cells. RodK kinase activity is indispensable for RodK activity. By systematically substituting the conserved, phosphorylatable aspartate residues in the three receiver domains, genetic evidence is provided that each receiver domain is important for RodK function and that each receiver domain has a distinct function, which depends on phosphorylation. Biochemical analyses provided indirect evidence for phosphotransfer from the RodK kinase domain to the third receiver domain. This is the first example of a hybrid histidine protein kinase in which four signalling domains have been shown to be required for full activity.
Regulation of protein phosphatase type 1 and cell cycle progression by PfLRR1, a novel leucine‐rich repeat protein of the human malaria parasite Plasmodium falciparum
Authors: Daher Wassim , Browaeys Edith , Pierrot Christine , Jouin Hélène , Dive Daniel , Meurice Edwige , Dissous Colette , Capron Monique , Tomavo Stanislas , Doerig Christian , Cailliau Katia , Khalife Jamal
Published: March 2006

The protein called ‘suppressor of the dis2 mutant (sds22+)’ is an essential regulator of cell division in fission and budding yeasts, where its deletion causes mitotic arrest. Its role in cell cycle control appears to be mediated through the activation of protein phosphatase type 1 (PP1) in Schizosaccharomyces pombe. We have identified the Plasmodium falciparum Sds22 orthologue, which we designated PfLRR1 as it belongs to the leucine‐rich repeat protein family. We showed by glutathione‐S‐transferase pull‐down assay that the PfLRR1 gene product interacts with PfPP1, that the PfLRR1–PfPP1 complex is present in parasite extracts and that PfLRR1 inhibits PfPP1 activity. Functional studies in Xenopus oocytes revealed that PfLRR1 interacted with endogenous PP1 and overcame the G2/M cell cycle checkpoint by promoting progression to germinal vesicle breakdown (GVBD). Confirmatory results showing the appearance of GVBD were observed when oocytes were treated with anti‐PP1 antibodies or okadaic acid. Taken together, these observations suggest that PfLRR1 can regulate the cell cycle by binding to PP1 and regulating its activity.
Two distinct regions of the large serine recombinase TnpX are required for DNA binding and biological function
Authors: Adams Vicki , Lucet Isabelle S. , Tynan Fleur E. , Chiarezza Martina , Howarth Pauline M. , Kim Jonathan , Rossjohn Jamie , Lyras Dena , Rood Julian I.
Published: March 2006

The large serine recombinase, TnpX, from the Clostridium perfringens integrative mobilizable element Tn4451, consists of three domains and has two known DNA binding regions. In this study random and site‐directed mutagenesis was used to identify other regions of TnpX that were required for biological activity. Genetic and biochemical analysis of these mutants led to the identification of important TnpX residues in the N‐terminal catalytic pocket. In addition, another region of TnpX (aa 243–261), which is conserved within large serine recombinases, was shown to be essential for both excision and insertion. Mutation of charged residues within this region led to a loss of biological activity and aberrant DNA binding. This phenotype was mediated by interaction with the distal DNA binding region (aa 598–707). In these mutants, removal of residues 598–707 resulted in loss of DNA binding, despite the presence of the primary DNA binding region (aa 533–583). Analysis of mutations within the aa 243–261 region indicated that different protein conformations were involved in the insertion and the excision reactions. In summary, we have shown that TnpX is a complex protein that has multiple intra‐ and intermolecular interaction sites, providing insight into the structural and functional complexity of this important enzyme family.
Theileria parva and the bovine CTL response: down but not out?
Authors: MCKEEVER D. J.
Published: March 2006

Theileria parva is a tick‐borne intracellular protozoan of cattle, with obligate sequential differentiation stages in lymphocytes and erythrocytes. Immunity is mediated by cytotoxic T lymphocytes (CTL) that target and clear parasitized lymphocytes but allow persistence of infected erythrocytes, which are required for transmission to the tick. The life cycle of T. parva is haploid with the exception of a brief diploid stage in the tick vector during which sexual recombination occurs. There is evidence for antigenic diversity in field parasite populations, although broad immunity can be acquired following exposure to a limited number of strains. The CTL response in individual animals is tightly focused and its specificity is strongly influenced by major histocompatibility complex (MHC) phenotype. This review discusses the issue of how CTL immunity is likely to impact on parasite population structure in the light of available information on diversity of the parasite and its ability to recombine.
Adherence by Staphylococcus intermedius to canine corneocytes: a preliminary study comparing noninflamed and inflamed atopic canine skin
Authors: McEwan Neil A. , Mellor Dominic , Kalna Gabriel
Published: March 2006

The adherence by three strains of Staphylococcus intermedius to corneocytes collected from healthy dogs was compared to the adherence to corneocytes collected from the inflamed (erythematous) and noninflamed (normal appearing) skin of dogs suffering from atopic dermatitis. All three strains of S. intermedius adhered in greater numbers to corneocytes from both inflamed and noninflamed atopic skin than to corneocytes from healthy dogs. Adherence was greatest to corneocytes from inflamed atopic skin but one strain showed no statistical difference for adherence to inflamed and noninflamed atopic skin. These findings suggest that S. intermedius adheres extensively to both inflamed and noninflamed canine atopic skin. This may be important in the colonization of atopic skin by this microorganism. Strain variation in the ability of S. intermedius to adhere to canine atopic corneocytes is probable.
Mast cells and angiogenesis in canine melanomas: malignancy and clinicopathological factors
Authors: Mukaratirwa Sydney , Chikafa Lynne , Dliwayo Rachel , Moyo Ndumiso
Published: March 2006

The biological significance of mast cells and angiogenesis in canine melanomas is unclear. Eighty canine melanomas (56 malignant and 24 benign), investigated to determine the relationship between mast cell count (MCC), microvessel density (MVD) and clinicopathology, revealed significantly higher MCC and MVD counts in malignant melanomas. Evaluation of the prognostic significance of MCC and MVD in malignant melanomas showed a significant correlation between MCC and MVD both within and at the edges of the tumour. Multivariate analysis indicated that MCC and MVD were independent predictors of survival but the former was a significantly better prognostic marker. Greater numbers of mast cells and microvessels were found in malignant melanomas of poor prognosis. The findings demonstrate a prognostic significance of MCC and MVD in canine melanocytic tumours.
An evaluation of the clinical, cytological, infectious and histopathological features of feline acne
Authors: Jazic E. , Coyner K. S. , Loeffler D. G. , Lewis T. P.
Published: March 2006

Clinical, cytological, microbial and histopathological features of feline acne were investigated in 22 cats referred or volunteered to a veterinary dermatology practice in the south‐west region of the USA. For comparison, same parameters were evaluated in five unaffected pet cats. Additionally, all cats were evaluated by immunohistochemistry (IHC) for the presence of feline calicivirus (FCV) and feline herpes virus (FHV‐1) in acne lesions. The age of onset of acne in affected cats ranged from 6 months to 14 years with a median of 4 years. The most common dermatologic lesions were comedones (73%), alopecia (68%), crusts (55%), papules (45%) and erythema (41%). Pruritus was reported in 35% of the affected cats. Cytological evidence ofMalassezia pachydermatitiswas present on 4/22 (18%) of affected cats.Microsporum caniswas isolated from a single affected cat. Bacteria were isolated from 10 of the 22 (45%) affected cats; coagulase‐positive staphylococci and alpha‐haemolytic streptococci were most common. Histopathological features included lymphoplasmacytic periductal inflammation (86%), sebaceous gland duct dilatation (73%), follicular keratosis with plugging and dilatation (59%), epitrichial gland occlusion and dilatation (32%), folliculitis (27%), pyogranulomatous sebaceous adenitis (23%) and furunculosis (23%). In one affected cat from a household with five cats, simultaneously having feline acne, FCV antigen was detected in the biopsy of the chin by IHC. Chin tissue samples from all other affected cats, as well as the five healthy cats, were negative by IHC for FCV and FHV‐1 antigens.
Evaluation of IgG subclass responses against Dermatophagoides farinae allergens in healthy and atopic dogs
Authors: Hou Chia‐Chun , Day Michael J. , Nuttall Timothy J. , Hill Peter B.
Published: March 2006

A semiquantitative chemiluminescent Western blot analysis system was developed and validated to evaluate antigen‐specific IgG subclass responses to electrophoretically separated proteins of Dermatophagoides farinae in healthy and atopic dogs.

Both groups mounted similar D. farinae‐specific IgG1 and IgG4 responses to multiple antigens, but IgG2 and IgG3 responses were difficult to detect. The most commonly recognized bands in both groups were 18 and 98 kDa antigens for IgG1 and 18, 45, 66, 98, 130 and 180 kDa for IgG4. The number of bands recognized per dog did not differ significantly, but significantly more atopic dogs had an IgG1 response to a 180 kDa protein. The overall D. farinae‐specific IgG1 and IgG4 responses were slightly higher, but not significantly different, in the healthy group. The results suggest that some antigens produced by D. farinae can induce different subclass responses. However, as most of these responses are seen in both healthy and atopic dogs, they are likely to merely represent recognition of foreign proteins presented to the immune system, rather than involvement in the pathogenesis of atopic dermatitis. The role of the 180 kDa antigen warrants further study.
Postharvest chilling induces oxidative stress response in the dwarf tomato cultivar Micro‐Tom
Authors: Malacrida Cecilia , Valle Estela M. , Boggio Silvana B.
Published: March 2006

Oxidative stress is involved in the response of Lycopersicon esculentum fruits (cultivar Micro‐Tom) to chilling. Changes in activated oxygen scavenging enzymes, superoxide dismutase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.11.1.6), ascorbate peroxidase (APX, EC 1.11.1.11), and glutathione reductase (GR, EC 1.6.4.2) were examined during ripening after postharvest chilling. Also, lipid peroxidation, respiration, and pigment contents were determined. These parameters were affected by chilling, especially the lycopene content and the respiration rate that showed a high value when the fruits were transferred to higher temperatures. CAT activity increased the day after the fruits were re‐warmed, while the activity of GR was higher in the chilled than in the non‐chilled green fruits. Lipid peroxidation was more evident at the ‘pre‐chilled’ yellow and red fruits. APX and SOD were not affected by previous chilling in ripening fruits. These results indicate that oxidative stress is generated by conservation at 4°C. The antioxidant response of tomato fruit could be mediated by CAT and GR but not by SOD or APX. Moreover, CAT seemed to respond to the increase in the respiration rate.
The evolution of the phenotypic covariance matrix: evidence for selection and drift inMelanoplus
Authors: ROFF D. A. , MOUSSEAU T.
Published: March 2006

Phenotypic variation in trait means is a common observation for geographically separated populations. Such variation is typically retained under common garden conditions, indicating that there has been evolutionary change in the populations, as a result of selection and/or drift. Much less frequently studied is variation in the phenotypic covariance matrix (hereafter,Pmatrix), although this is an important component of evolutionary change. In this paper, we examine variation in the phenotypic means andPmatrices in two species of grasshopper,Melanoplus sanguinipesandM. devastator. Using thePmatrices estimated for 14 populations ofM. sanguinipesand three populations ofM. devastatorwe find that (1) significant differences between the sexes can be attributed to scaling effects; (2) there is no significant difference between the two species; (3) there are highly significant differences among populations that cannot be accounted for by scaling effects; (4) these differences are a consequence of statistically significant patterns of covariation with geographic and environmental factors, phenotypic variances and covariances increasing with increased temperature but decreasing with increased latitude and altitude. This covariation suggests that selection has been important in the evolution of thePmatrix in these populations Finally, we find a significant positive correlation between the average difference between matrices and the genetic distance between the populations, indicating that drift has caused some of the variation in thePmatrices.
Limits to adaptation in asexual populations
Authors: DE VISSER J. A. G. M. , ROZEN D. E.
Published: March 2006

In asexual populations, the rate of adaptation is basically limited by the frequency and properties of spontaneous beneficial mutations. Hence, knowledge of these mutational properties and how they are affected by particular evolutionary conditions is a precondition for understanding the process of adaptation. Here, we address how the rate of adaptation of asexual populations is limited by its population size and mutation rate, as well as by two factors affecting the fraction of mutations that confer a benefit, i.e. the initial adaptedness of the population and the variability of the environment. These factors both influence which mutations are likely to occur, as well as the probability that they will ultimately contribute to adaptation. We attempt to separate the consequences of these basic population features in terms of their effect on the rate of adaptation by using results from evolution experiments with microorganisms.
Effects of inbreeding and rate of inbreeding in Drosophila melanogaster– Hsp70 expression and fitness
Authors: PEDERSEN K. S. , KRISTENSEN T. N. , LOESCHCKE V.
Published: March 2006

Induction of heat shock proteins (Hsp) is a well‐known mechanism through which cells cope with stressful conditions. Hsp are induced by a variety of extrinsic stressors. However, recently intrinsic stressors (aging and inbreeding) have been shown to affect expression of Hsp. Increased homozygosity due to inbreeding may disrupt cellular homeostasis by causing increased expression of recessive deleterious mutations and breakdown of epistatic interactions. We investigated the effect of inbreeding and the rate of inbreeding on the expression of Hsp70, larval heat resistance and fecundity. In Drosophila melanogaster we found that inbred lines (F ≈ 0.67) had significantly up‐regulated expression of Hsp70, and reduced heat resistance and fecundity as compared with outbred control lines. A significant negative correlation was observed between Hsp70 expression and resistance to an extreme heat stress in inbred lines. We interpreted this as an increased requirement for Hsp70 in the lines suffering most from inbreeding depression. Inbreeding depression for fecundity was reduced with a slower rate of inbreeding compared with a fast rate of inbreeding. Thus, the effectiveness of purging seems to be improved with a slower rate of inbreeding.
Rapid and convergent evolution of parental care in hydrobiid gastropods from New Zealand
Authors: HAASE M.
Published: March 2006

Although parental care occurs in most phyla encompassing a wide array of forms, little is known about its evolution in invertebrates. Two types of egg capsules have been known among ovoviviparous New Zealand hydrobiid gastropods, elastic capsules and simple membranes. Based on a phylogenetic analysis using two mtDNA sequence fragments, I asked whether the second state was derived from the first or whether brooding had multiple origins. The evolution of ovoviviparity was also investigated in the context of habitat transition between brackish and freshwater. Maximum parsimony and Markov chain models of character state transformations in a maximum likelihood framework suggested that hydrobiids have invaded freshwater three times independently. Two of these invasions were followed by the evolution of ovoviviparity, probably in adaptation to changing water levels during periods of irregular precipitation. The syntopy of two congeneric species, one oviparous and the other one brooding, indicated that the transition between reproductive modes must have occurred rapidly.
Responses to selection on male‐phase duration in Chamerion angustifolium
Authors: ROUTLEY M. B. , HUSBAND B. C.
Published: March 2006

Protandry (when male function precedes female) can enhance fitness by reducing selfing and increasing pollen export and outcrossed siring success. However, responses to selection on protandry may be constrained by genetic variation and correlations among floral traits. We examined these potential constraints in protandrous Chamerion angustifolium (Onagraceae) by estimating genetic variation in male‐phase duration and associated floral traits using a paternal half‐sib design and selection experiment. Narrow‐sense heritability of male‐phase duration was estimated as 0.23 (SE ± 0.04) and was positively correlated with floral display. The selection experiment shortened male‐phase duration 0.8 SD from the parental average of 17.0 h and lengthened it by 2.0 SD. Furthermore, fixed floral longevity caused a negative association between male‐ and female‐phase durations. These results suggest that selection on male‐phase duration is not limited by genetic variation. However, changes in male‐phase duration may influence pollinators through correlated changes in floral display and reduced opportunities for pollen receipt during female phase.
Sexual functionality of Leptopilina clavipes (Hymenoptera: Figitidae) after reversing Wolbachia‐induced parthenogenesis
Authors: PANNEBAKKER B. A. , SCHIDLO N. S. , BOSKAMP G. J. F. , DEKKER L. , VAN DOOREN T. J. M. , BEUKEBOOM L. W. , ZWAAN B. J. , BRAKEFIELD P. M. , VAN ALPHEN J. J. M.
Published: March 2006

Females infected with parthenogenesis‐inducing Wolbachia bacteria can be cured from their infection by antibiotic treatment, resulting in male production. In most cases, however, these males are either sexually not fully functional, or infected females have lost the ability to reproduce sexually. We studied the decay of sexual function in males and females of the parasitoid Leptopilina clavipes. In western Europe, infected and uninfected populations occur allopatrically, allowing for an investigation of both male and female sexual function. This was made by comparing females and males induced from different parthenogenetic populations with those from naturally occurring uninfected populations. Our results indicate that although males show a decay of sexual function, they are still able to fertilize uninfected females. Infected females, however, do not fertilize their eggs after mating with males from uninfected populations. The absence of genomic incompatibilities suggests that these effects are due to the difference in mode of reproduction.
Adaptation to environmental stress: a rare or frequent driver of speciation?
Authors: LEXER C. , FAY M. F.
Published: March 2006

Recent results of evolutionary genomics and other research programmes indicate an important role for environment‐dependent selection in speciation, but the conceptual frameworks of speciation genetics and environmental stress physiology have not been fully integrated. Only a small number of model systems have been established for cross‐disciplinary studies of this type in animals and plants. In these taxa (e.g.DrosophilaandArabidopsis/Arabis), studies of the mechanistic basis of various stress responses are increasingly combined with attempts to understand their evolutionary consequences. Our understanding of the role of environmental stress in speciation would benefit from studies of a larger variety of taxa. We pinpoint areas for future study and predict that in many taxa ‘broad’ hybrid zones maintained by ecological selection will be valuable venues for addressing the link between environmental stress, adaptation, and speciation.
Can cytoplasmic incompatibility inducingWolbachiapromote the evolution of mate preferences?
Authors: CHAMPION DE CRESPIGNY F. E. , BUTLIN R. K. , WEDELL N.
Published: March 2006

The maternally inherited bacterium,Wolbachia pipientis, manipulates host reproduction by rendering uninfected females reproductively incompatible with infected males (cytoplasmic incompatibility, CI). Hosts may evolve mechanisms, such as mate preferences, to avoid fitness costs ofWolbachiainfection. Despite the potential importance of mate choice forWolbachiapopulation dynamics, this possibility remains largely unexplored. Here we model the spread of an allele encoding female mate preference for uninfected males alongside the spread of CI inducingWolbachia. Mate preferences can evolve but the spread of the preference allele depends on factors associated with bothWolbachiainfection and the preference allele itself. Incomplete maternal transmission ofWolbachia, fitness costs and low CI, improve the spread of the preference allele and impact on the population dynamics ofWolbachia. In addition, mate preferences are found in infected individuals. These results have important consequences for the fate ofWolbachiaand studies addressing mate preferences in infected populations.
Cell‐mediated immunity predicts the probability of local recruitment in nestling blue tits
Authors: CICHOŃ M. , DUBIEC A.
Published: March 2006

We investigated whether the variation in T‐cell‐mediated immune function of blue tit nestlings affected their fledgling success and the probability of local survival. We studied the relationship between immune function and survival under two rearing conditions: control, unmanipulated, and experimentally enlarged broods. Brood enlargement had negative effects on nestling immune response. Immune response was positively related to fledgling success and it predicted the probability of local recruitment. However, the relationship between immune response and the probability of recruitment was significantly positive only among control broods and nonsignificant among enlarged broods. The effect of immune response on the recruitment probability was not affected by variation in body mass. Our study suggests that selection for immune responsiveness seems to be weak or even absent under unfavourable rearing conditions as simulated by brood size enlargement. Therefore, year‐to‐year environmental variation and environmental heterogeneity may constrain evolution towards higher immune responsiveness.
One tool, many uses: precopulatory sexual selection on genital morphology inAquarius remigis
Authors: BERTIN A. , FAIRBAIRN D. J.
Published: March 2006

While congruent evidence indicates that sexual selection is the most likely selective force explaining the rapid divergence of male genital morphology in insects, the mechanisms involved in this process remain unclear. In particular, little attention has been paid to precopulatory sexual selection. We examine sexual selection for mating success on male genital components in six populations ofAquarius remigis, a water strider characterized by unique genital morphology. Multivariate selection analysis confirms previous findings that precopulatory sexual selection favours longer external genitalia, and provides new evidence that this selection acts independently on external genital components. In contrast, the size of the major internal genital sclerite is not correlated with mating success. Thus, precopulatory sexual selection acts strongly on the size of the external genitalia, but not on the intromittent organ itself. These results highlight the multiple functions of genital organs and the importance of both precopulatory and post‐copulatory sexual selection in shaping the remarkable diversity of male genitalia in insects.
Sex, mutation and fitness: asymmetric costs and routes to recovery through compensatory evolution
Authors: PISCHEDDA A. , CHIPPINDALE A.
Published: March 2006

A wild‐type population of Drosophila melanogaster was used to assess the impact of a known deleterious mutation, nub1, when it had (1) evolved for up to 180 generations with the mutation or (2) recently had the same mutant allele introgressed into it. Relative to this benchmark, we observed much stronger initial fitness depression in males (−74%) than in females (−38%) and also relatively greater fitness recovery by evolved males (+55%) than females (+17%). Experimental assays revealed amelioration in both juvenile and adult fitness and suggested that the greater relative recovery of male fitness was from gains through sexual selection. These evolutionary changes in male fertility depended on pairing with their coevolved mates for both mate choice and post‐copulatory components of sexual selection. Without replication at the population level, these results are used to motivate a general hypothesis rather than definitively test it: Differences in reproductive optima may generally skew mutational effects towards the more strongly sexually‐selected sex due to genic capture and condition dependence.
Phenotypic plasticity of host–parasite interactions in response to the route of infection
Authors: VIZOSO D. B. , EBERT D.
Published: March 2006

The microsporidium Octosporea bayeri can infect its host, the planktonic crustacean Daphnia magna, vertically and horizontally. The two routes differ greatly in the way the parasite leaves the harbouring host (transmission) and in the way it enters a new, susceptible host (infection). Infections resulting from each route may thus vary in the way they affect host and parasite life‐histories and, subsequently, host and parasite fitness. We conducted a life‐table experiment to compare D. magna infected with O. bayeri either horizontally or vertically, using three different parasite isolates. Both the infection route and the parasite isolate had significant effects on host life‐history. Hosts matured at different ages depending on the parasite isolate, and at a size that varied with infection route. The frequency of host sterility and the host's life‐time reproductive success were affected by both the infection route and the parasite isolate. The infection route also affected parasite life‐history. The production of parasite spores was much higher in vertically than in horizontally infected hosts. We found a trade‐off between the production of spores (the parasite's horizontal fitness component) and the production of infected host offspring (the parasite's vertical fitness component). This study shows that hosts and parasites can react plastically to different routes of infection, suggesting that ecological factors that may influence the relative importance of horizontal and vertical transmission can shape the evolution of host and parasite life histories, and, consequently, the evolution of virulence.
The biological limitations of transcriptomics in elucidating stress and stress responses
Authors: FEDER M. E. , WALSER J.‐C.
Published: March 2006

Global analysis of mRNA abundance via genomic arrays (i.e. transcriptomics or transcriptional profiling) is one approach to finding the genes that matter to organisms undergoing environmental stress. In evolutionary analyses of stress, mRNA abundance is often invoked as a proxy for the protein activity that may underlie variation in fitness. To provoke discussion of the utility and sensible application of this valuable approach, this manuscript examines the adequacy of mRNA abundance as a proxy for protein activity, fitness and stress. Published work to date suggests that mRNA abundance typically provides little information on protein activity and fitness and cannot substitute for detailed functional and ecological analyses of candidate genes. While the transcriptional profile can be an exquisitely sensitive indicator of stress, simpler indicators will often suffice. In view of this outcome, transcriptomics should undergo careful cost‐benefit analysis before investigators deploy it in studies of stress responses and their evolution.
Correlated responses to selection for stress resistance and longevity in a laboratory population of Drosophila melanogaster
Authors: BUBLIY O. A. , LOESCHCKE V.
Published: March 2006

Laboratory studies on Drosophila have revealed that resistance to one environmental stress often correlates with resistance to other stresses. There is also evidence on genetic correlations between stress resistance, longevity and other fitness‐related traits. The present work investigates these associations using artificial selection in Drosophila melanogaster. Adult flies were selected for increased survival after severe cold, heat, desiccation and starvation stresses as well as increased heat‐knockdown time and lifespan (CS, HS, DS, SS, KS and LS line sets, respectively). The number of selection generations was 11 for LS, 27 for SS and 21 for other lines, with selection intensity being around 0.80. For each set of lines, the five stress‐resistance parameters mentioned above as well as longevity (in a nonstressful environment) were estimated. In addition, preadult developmental time, early age productivity and thorax length were examined in all lines reared under nonstressful conditions. Comparing the selection lines with unselected control revealed clear‐cut direct selection responses for the stress‐resistance traits. Starvation resistance increased as correlated response in all sets of selection lines, with the exception of HS. Positive correlated responses were also found for survival after cold shock (HS and DS) and heat shock (KS and DS). With regard to values of resistance across different stress assays, the HS and KS lines were most similar. The resistance values of the SS lines were close to those of the LS lines and tended to be the lowest among all selection lines. Developmental time was extended in the SS and KS lines, whereas the LS lines showed a reduction in thorax length. The results indicate a possibility of different multiple‐stress‐resistance mechanisms for the examined traits and fitness costs associated with stress resistance and longevity.
Habitat dependent associations between parasitism and fluctuating asymmetry among endemic stickleback populations
Authors: BERGSTROM C. A. , REIMCHEN T. E.
Published: March 2006

Inconsistencies in the relationship between fluctuating asymmetry (FA) and fitness may be due to selection acting on the degree of trait asymmetry that differs among populations or among traits. We assessed relationships between parasite susceptibility and fluctuating asymmetry in the number of bony lateral plates among 83 populations of freshwaterGasterosteus aculeatus(three spined stickleback) and among lateral plate positions that vary in the selection they experience for symmetry. The correlation between FA and parasite infection was highly variable among samples. Excess of infected asymmetricG. aculeatusincreased significantly as the robustness of structural predator defences decreased. This effect was found for one parasite species only (Eustrongylidessp.) and was slightly stronger in females. In addition, there was a trend for there to be an excess of infected females asymmetric in those lateral plates positions that did not experience selection for their symmetry, although the trend only approached significance. These results suggest that selection for trait symmetry can obscure relationships between fitness and individual‐wide developmental stability, providing one possible explanation for some of the heterogeneity in FA/fitness relationships seen in the literature. These results are also consistent with previous reports showing that ecological segregation between symmetric and asymmetricG. aculeatusand between sexes can alter the FA/fitness relationship.
Spatial scale of local adaptation in a plant‐pathogen metapopulation
Authors: LAINE A.‐L.
Published: March 2006

The rate and scale of gene flow can strongly affect patterns of local adaptation in host–parasite interactions. I used data on regional pathogen occurrence to infer the scale of pathogen dispersal and to identify pathogen metapopulations in the interaction betweenPlantago lanceolataand its specialist phytopathogen,Podosphaera plantaginis. Frequent extinctions and colonizations were recorded in the metapopulations, suggesting substantial gene flow at this spatial scale. The level of pathogen local adaptation was assessed in a laboratory inoculation experiment at three different scales: in sympatric host populations, in sympatric host metapopulations and in allopatric host metapopulations. I found evidence for adaptation to sympatric host populations, as well as evidence indicating that local adaptation may extend to the scale of the sympatric host metapopulation. There was also variation among the metapopulations in the degree of pathogen local adaptation. This may be explained by regional differences in the rate of migration.
Introduced birds in urban remnant vegetation: Does remnant size really matter?
Authors: ANTOS MARK J. , FITZSIMONS JAMES A. , PALMER GRANT C. , WHITE JOHN G.
Published: March 2006

Abstract  Introduced birds are a pervasive and dominant element of urban ecosystems. We examined the richness and relative abundance of introduced bird species in small (1–5 ha) medium (6–15 ha) and large (>15 ha) remnants of native vegetation within an urban matrix. Transects were surveyed during breeding and non‐breeding seasons. There was a significant relationship between introduced species richness and remnant size with larger remnants supporting more introduced species. There was no significant difference in relative abundance of introduced species in remnants of different sizes. Introduced species, as a proportion of the relative abundance of the total avifauna (native and introduced species), did not vary significantly between remnants of differing sizes. There were significant differences in the composition of introduced bird species between the different remnant sizes, with large remnants supporting significantly different assemblages than medium and small remnants. Other variables also have substantial effects on the abundance of introduced bird species. The lack of significant differences in abundance between remnant sizes suggests they were all equally susceptible to invasion. No patches in the urban matrix are likely to be unaffected by introduced species. The effective long‐term control of introduced bird species is difficult and resources may be better spent managing habitat in a way which renders it less suitable for introduced species (e.g. reducing areas of disturbed ground and weed dominated areas).