991 resultados para Harris, LaDonna
Resumo:
Nitric oxide regulates many important cellular processes including motility and invasion. Many of its effects are mediated through the modification of specific cysteine residues in target proteins, a process called S-nitrosylation. Here we show that S-nitrosylation of proteins occurs at the leading edge of migrating trophoblasts and can be attributed to the specific enrichment of inducible nitric oxide synthase (iNOS/NOS2) in this region. Localisation of iNOS to the leading edge is co-incidental with a site of extensive actin polymerisation and is only observed in actively migrating cells. In contrast endothelial nitric oxide synthase (eNOS/NOS3) shows distribution that is distinct and non-colocalised with iNOS, suggesting that the protein S-nitrosylation observed at the leading edge is caused only by iNOS and not eNOS. We have identified MMP-9 as a potential target for S-nitrosylation in these cells and demonstrate that it co-localises with iNOS at the leading edge of migrating cells. We further demonstrate that iNOS plays an important role in promoting trophoblast invasion, which is an essential process in the establishment of a successful pregnancy.
Resumo:
Summary Understanding the factors influencing variation in the degree of sperm competition is a key question underlying the mechanisms driving sexual conflict. Previous behavioural and comparative studies have indicated that carnivores appear to have evolved under sperm competition but an analysis of the predictors of the level of sperm competition is missing. In this study, we use phylogenetic comparative methods to investigate life-history parameters predicted to affect the degree of sperm competition in terrestrial carnivores using variation in relative testes size (RTS, after controlling for body size allometry) as a measure of the level of sperm competition. Due to a paucity of consistent data across taxa, we used three measures of RTS: testes mass (n = 40 species), testes and epididymes mass combined (n = 38), and testes volume (n = 48). We also created a derived data set (n = 79) with testes mass estimated from regression analyses on the other measures of testes size. Carnivores with shorter mating seasons had relatively larger testes, consistent with the hypothesis that sperm competition is greater when the degree of female oestrous synchrony is high. This relationship was stronger in spontaneous versus induced ovulators, suggesting higher sperm competition levels in spontaneous ovulators. This is the first comparative study to show this within mammalian taxa. Neither social mating system nor reproductive lifespan were significantly associated with variation in RTS and hence are poor predictors of sperm competition levels. None of the above relationships were found to be significant for the testes and epididymes mass combined data set, but our understanding of the role of the epididymis in sperm competition is too limited to draw any conclusions. Finally, we consistently found a significant phylogenetic signal in all analyses, indicating that phylogeny has played a significant role in the evolution of carnivore testes size and, therefore, in shaping levels of sperm competition. Our results shed new light into the factors affecting levels of sperm competition in terrestrial carnivores by showing that the degree of oestrous synchrony and ovulation type interact to predict variation in RTS.
Resumo:
Male-biased sexual size dimorphism is typical of polygynous mammals, where the degree of dimorphism in body mass is related to male intrasexual competition and the degree of polygyny. However, the importance of body mass in monogamous mammals is largely unknown. We investigated the effect of body mass on life-history parameters and territory size in the red fox (Vulpes vulpes), a socially monogamous canid with slight sexual dimorphism. Increased body size in males appeared to confer an advantage in territory acquisition and defense contests because heavier males held larger territories and exerted a greater boundary pressure on smaller neighbors. Heavier male foxes invested more effort in searching for extrapair matings by moving over a wider area and farther from their territories, leading to greater reproductive success. Males that sired cubs outside their own social group appeared to be heavier than males that only sired cubs within their social group or that were cuckolded, but our results should be treated with caution because sample sizes were small. Territory size, boundary pressure, and paternity success were not related to age of males. In comparison, body mass of females was not related to territory size, probability of breeding, litter size, or cub mass. Only age affected probability of breeding in females: younger females reproduced significantly less than did older females, although we did not measure individual nutritional status. Thus, body mass had a significant effect on life-history traits and territory size in a socially monogamous species comparable to that reported in polygynous males, even in the absence of large size dimorphism.
Resumo:
Wolbachia are bacteria present within the tissues of most filarial nematodes. Filarial nematode survival is known to be affected by immune responses generated during filarial nematode infection and immune responses to Wolbachia can be found in different species harbouring filarial nematode infections, including humans. Using the rodent filarial model Litomosoides sigmodontis, we show that pre-exposure to wolbachia surface protein in a Th1 context (but not in a Th2-context) enhances worm survival on subsequent challenge. This study suggests that despite abundant evidence that pro-inflammatory reactions to the endosymbiont have detrimental effects on the both the nematode and mammalian host, they may under some circumstances be beneficial to the nematode.
Resumo:
Background: The hepatitis C virus (HCV) non-structural 5A protein (NS5A) contains a highly conserved C-terminal polyproline motif with the consensus sequence Pro-X-X- Pro-X-Arg that is able to interact with the Src-homology 3 (SH3) domains of a variety of cellular proteins. Results: To understand this interaction in more detail we have expressed two N-terminally truncated forms of NS5A in E. coli and examined their interactions with the SH3 domain of the Src-family tyrosine kinase, Fyn. Surface plasmon resonance analysis revealed that NS5A binds to the Fyn SH3 domain with what can be considered a high affinity SH3 domain-ligand interaction (629 nM), and this binding did not require the presence of domain I of NS5A (amino acid residues 32-250). Mutagenic analysis of the Fyn SH3 domain demonstrated the requirement for an acidic cluster at the C-terminus of the RT-Src loop of the SH3 domain, as well as several highly conserved residues previously shown to participate in SH3 domain peptide binding. Conclusion: We conclude that the NS5A: Fyn SH3 domain interaction occurs via a canonical SH3 domain binding site and the high affinity of the interaction suggests that NS5A would be able to compete with cognate Fyn ligands within the infected cell.
Resumo:
The costs of dispersal are an important factor promoting natal philopatry, thereby encouraging the formation of social groups. The red fox, Vulpes vulpes, exhibits a highly flexible social system and one that is thought to represent a possible stage in the evolution of more complex patterns of group-living. Although the potential benefits accruing to philopatric offspring have previously been studied in this species, the potential costs of dispersal have received less attention. We contrasted survival rates, nutritional status, injuries and reproductive output of dispersing and non-dispersing male and female foxes in an urban population to assess the relative costs of dispersal versus natal philopatry. Mortality rates were not significantly higher for dispersing foxes, either in the short- or long-term. There was no evidence of increased nutritional stress in dispersing individuals. Dispersing individuals did, however, exhibit greater levels of wounding, although this did not appear to affect survival. Dispersing females were more likely to miss a breeding opportunity early in their reproductive lifespan. In contrast, both dispersing and non-dispersing males were unlikely to breed in their first year. We conclude that the major fitness component in females affected by dispersing is age at first reproduction.
Resumo:
The period following the withdrawal of parental care has been highlighted as a key developmental period for juveniles. One reason for this is that juveniles cannot forage as competently as adults, potentially placing them at greater risk from environmentally-induced changes in food availability. However, no study has examined this topic. Using a long-term dataset on red foxes (Vulpes vulpes), we examined (i) dietary changes that occurred in the one-month period following the attainment of nutritional independence, (ii) diet composition in relation to climatic variation, and (iii) the effect of climatic variation on subsequent full-grown mass. Diet at nutritional independence contained increased quantities of easy-to-catch food items (earthworms and insects) when compared with pre-independence. Interannual variation in the volume of rainfall at nutritional independence was positively correlated to the proportion of earthworms in cub diet. Pre-independence cub mass and rainfall immediately following nutritional independence explained a significant proportion of variance in full-grown mass, with environmental variation affecting full-grown mass of the entire cohorts. Thus, weather-mediated availability of easy-to-catch food items at a key developmental stage has lifelong implications for the development of juvenile foxes by affecting full-grown mass, which in turn appears to be an important component of individual reproductive potential.
Resumo:
1Urban areas are predicted to grow significantly in the foreseeable future because of increasing human population growth. Predicting the impact of urban development and expansion on mammal populations is of considerable interest due to possible effects on biodiversity and human-wildlife conflict. 2The British government has recently announced a substantial housing programme to meet the demands of its growing population and changing socio-economic profile. This is likely to result in the construction of high-density, low-cost housing with small residential gardens. To assess the potential effects of this programme, we analysed the factors affecting the current pattern of use of residential gardens by a range of mammal species using a questionnaire distributed in wildlife and gardening magazines and via The Mammal Society. 3Twenty-two species/species groups were recorded. However, the pattern of garden use by individual species was limited, with only six species/species groups (bats, red fox Vulpes vulpes, grey squirrel Sciurus carolinensis, hedgehog Erinaceus europaeus, mice, voles) recorded as frequent visitors to > 20% of gardens in the survey. 4There was a high degree of association between the variables recorded in the study, such that it was difficult to quantify the effects of individual variables. However, all species/species groups appeared to be negatively affected by the increased fragmentation and reduced proximity of natural and semi-natural habitats, decreasing garden size and garden structure, but to differing degrees. Patterns of garden use were most clearly affected by house location (city, town, village, rural), with garden use declining with increasing urbanization for the majority of species/species groups, except red foxes and grey squirrels. Increasing urbanization is likely to be related to a wide range of interrelated factors, any or all of which may affect a range of mammal species. 5Overall, the probable effects of the planned housing development programme in Britain are not likely to be beneficial to mammal populations, although the pattern of use examined in this study may represent patterns of habitat selection by species rather than differences in distribution or abundance. Consequently, additional data are required on the factors affecting the density of species within urban environments.
Resumo:
Traffic collisions can be a major source of mortality in wild populations, and animals may be expected to exhibit behavioral mechanisms that reduce the risk associated with crossing roads. Animals living in urban areas in particular have to negotiate very dense road networks, often with high levels of traffic flow. We examined traffic-related mortality of red foxes (Vulpes vulpes) in the city of Bristol, UK, and the extent to which roads affected fox activity by comparing real and randomly generated patterns of movement. There were significant seasonal differences in the number of traffic-related fox deaths for different age and sex classes; peaks were associated with periods when individuals were likely to be moving through unfamiliar terrain and would have had to cross major roads. Mortality rates per unit road length increased with road magnitude. The number of roads crossed by foxes and the rate at which roads were crossed per hour of activity increased after midnight when traffic flow was lower. Adults and juveniles crossed 17% and 30% fewer roads, respectively, than expected from randomly generated movement. This highly mobile species appeared to reduce the mortality risk of minor category roads by changing its activity patterns, but it remained vulnerable to the effects of larger roads with higher traffic flows during periods associated with extraterritorial movements.
Resumo:
Oxidised low density lipoprotein (LDL) may be involved in the pathogenesis of atherosclerosis. We have therefore investigated the mechanisms underlying the antioxidant/pro-oxidant behavior of dehydroascorbate, the oxidation product of ascorbic acid, toward LDL incubated With Cu2+ ions. By monitoring lipid peroxidation through the formation of conjugated dienes and lipid hydroperoxides, we show that the pro-oxidant activity of dehydroascorbate is critically dependent on the presence of lipid hydroperoxides, which accumulate during the early stages of oxidation. Using electron paramagnetic resonance spectroscopy, we show that dehydroascorbate amplifies the generation of alkoxyl radicals during the interaction of copper ions with the model alkyl hydroperoxide, tert-butylhydroperoxide. Under continuous-flow conditions, a prominent doublet signal was detected, which we attribute to both the erythroascorbate and ascorbate free radicals. On this basis, we propose that the pro-oxidant activity of dehydroascorbate toward LDL is due to its known spontaneous interconversion to erythroascorbate and ascorbate, which reduce Cu2+ to Cu+ and thereby promote the decomposition of lipid hydroperoxides. Various mechanisms, including copper chelation and Cu+ oxidation, are suggested to underlie the antioxidant behavior of dehydroascorbate in LDL that is essentially free of lipid hydroperoxides. (C) 2007 Elsevier Inc. All rights reserved.
Resumo:
The pea aphid, Acyrthosiphon pisum Harris (Hemiptera: Aphididae) is found in red and green color morphs. Previous work has suggested that the aphidiine parasitoid Aphidius ervi Haliday preferentially attacks green pea aphids in the field. It is not clear whether these results reflect a real preference, or some unknown clonal difference, such as in immunity, between the aphids used in the previous studies. We used three susceptibility-matched pairs of red and green morph pea aphid clones to test for preferences. In a no-choice situation, the parasitoids attacked equal proportions of each color morph. When provided with a choice, A. ervi was significantly more likely to oviposit into colonies formed from green morphs when the neighboring colony was formed from red morph aphids. In contrast, red morphs were less likely to be attacked when their neighboring colony was of the green morph. By preferentially attacking green colonies, A. ervi may reduce the likelihood of intraguild predation, as it is suggested that visually foraging predators preferentially attack red aphid colonies. Furthermore, if this host choice behavior is replicated in the field, we speculate that color morphs of the pea aphid may interact indirectly through their shared natural enemies, leading to intraspecific apparent competition.
Resumo:
1. Disease epizootics can significantly influence host population dynamics and the structure and functioning of ecological communities. Sarcoptic mange Sarcoptes scabiei has dramatically reduced red fox populations Vulpes vulpes in several countries, including Britain, although impacts on demographic processes are poorly understood. We review the literature on the impact of mange on red fox populations, assess its current distribution in Britain through a questionnaire survey and present new data on resultant demographic changes in foxes in Bristol, UK. 2. A mange epizootic in Sweden spread across the entire country in < 10 years resulting in a decline in fox density of up to 95%; density remained lowered for 15–20 years. In Spain, mange has been enzootic for > 75 years and is widely distributed; mange presence was negatively correlated with habitat quality. 3. Localized outbreaks have occurred sporadically in Britain during the last 100 years. The most recent large-scale outbreak arose in the 1990s, although mange has been present in south London and surrounding environs since the 1940s. The questionnaire survey indicated that mange was broadly distributed across Britain, but areas of perceived high prevalence (> 50% affected) were mainly in central and southern England. Habitat type did not significantly affect the presence/absence of mange or perceived prevalence rates. Subjective assessments suggested that populations take 15–20 years to recover. 4. Mange appeared in Bristol's foxes in 1994. During the epizootic phase (1994–95), mange spread through the city at a rate of 0.6–0.9 km/month, with a rise in infection in domestic dogs Canis familiaris c. 1–2 months later. Juvenile and adult fox mortality increased and the proportion of females that reproduced declined but litter size was unaffected. Population density declined by > 95%. 5. In the enzootic phase (1996–present), mange was the most significant mortality factor. Juvenile mortality was significantly higher than in the pre-mange period, and the number of juveniles classified as dispersers declined. Mange infection reduced the reproductive potential of males and females: females with advanced mange did not breed; severely infected males failed to undergo spermatogenesis. In 2004, Bristol fox population density was only 15% of that in 1994.
Resumo:
Environmental conditions during the early life stages of birds can have significant effects on the quality of sexual signals in adulthood, especially song, and these ultimately have consequences for breeding success and fitness. This has wide-ranging implications for the rehabilitation protocols undertaken in wildlife hospitals which aim to return captive-reared animals to their natural habitat. Here we review the current literature on bird song development and learning in order to determine the potential impact that the rearing of juvenile songbirds in captivity can have on rehabilitation success. We quantify the effects of reduced learning on song structure and relate this to the possible effects on an individual's ability to defend a territory or attract a mate. We show the importance of providing a conspecific auditory model for birds to learn from in the early stages post-fledging, either via live- or tape-tutoring and provide suggestions for tutoring regimes. We also highlight the historical focus on learning in a few model species that has left an information gap in our knowledge for most species reared at wildlife hospitals.
Ascorbate does not protect macrophages against apoptosis induced by oxidised low density lipoprotein
Resumo:
Apoptosis of macrophages and smooth muscle cells is observed in atherosclerotic lesions and may play an important role in the disease progression. Oxidised low density lipoprotein (LDL) is cytotoxic and induces apoptosis in a variety of cell types. We reported previously that ascorbate protects arterial smooth muscle cells from apoptosis induced by oxidised LDL containing the peak levels of lipid hydroperoxides. We now demonstrate that macrophages undergo apoptosis when treated with this species of oxidised LDL, as detected by increased annexin V binding and DNA fragmentation. Ascorbate treatment of macrophages did not protect against the cytotoxicity of oxidised LDL, and modestly increased the levels of annexin V binding and DNA fragmentation. Oxidised LDL treatment also increased the expression of the antioxidant stress protein heme oxygenase-1 in macrophages; however, this increase was markedly attenuated by ascorbate pretreatment. Although apoptosis induced by oxidised LDL was modestly promoted by ascorbate, ascorbate apparently decreased the levels of oxidative stress in macrophages, suggesting that this pro-apoptotic effect was not mediated by a pro-oxidant mechanism, but may instead have been due to intracellular protection of the apoptotic machinery by ascorbate. (c) 2006 Elsevier Inc. All rights reserved.
Resumo:
1. The presence of an across-species trade-off between dispersal ability and competitive ability has been proposed as a mechanism that facilitates coexistence. It is not clear if a similar trade-off exists within species. Such a trade-off would constrain the evolution of either trait and, given appropriate selection pressures, promote local adaptation in these traits. 2. This study found substantial levels of heritable variation in competitive ability of the pea aphid, Acyrthosiphon pisum Harris (Homoptera: Aphididae), measured in terms of relative survival when reared with a single clone of the vetch aphid, Megoura viciae Buckton (Homoptera: Aphididae). 3. Pea aphids can move to new patches by either flying (longer distance dispersal) or walking (local dispersal) from plant to plant. There was considerable clonal variation in dispersal ability, measured in terms of the proportion of winged offspring produced, and ability to survive away from their host plant. 4. Winged individuals showed longer off-plant survival times than wingless forms of the same pea aphid clone. 5. There was no evidence of a relationship between clonal competitive ability and either measure of dispersal ability, although the power of the test is limited by the number of pea aphid clones used in the trial. 6. However, there was a positive correlation between clonal fecundity and the proportion of winged offspring produced. Although speculative, it is suggested that clones that are more likely to either overwhelm their host plant or attract higher numbers of natural enemies as a result of having higher fecundity are more likely to produce winged morphs.