Biomedical subjects

Craig R Johnson

Publications and source records attributed to Craig R Johnson.

8 recordsLinked to original sources

PubMed2006

Linking richness, community variability, and invasion resistance with patch size.

The influence of community dynamics on the success or failure of an invasion is of considerable interest. What has not been explored is the influence of patch size on the outcomes of invasions for communities with the same species pool. Here we use an empirically validated spatial model of a marine epibenthic community to examine the effects of patch size on community variability, species richness, invasion, and the relationships between these variables. We found that the qualitative form of the relationship between community variability and species richness is determined by the size of the model patch. In small patches, variability decreases with species richness, but beyond a critical patch size, variability increases with increasing richness. This occurs because in large patches large, long-lived colonies attain sufficient size to minimize mortality and dominate the community, leading to decreased species richness and community variability. This mechanism cannot operate on smaller patches where the size of colonies is limited by the patch size and mortality is high irrespective of species identity. Further, invasion resistance is strongly correlated with community variability. Thus, the relationship between species richness and invasion resistance is also determined by patch size. These patterns are generated largely by an inverse relationship between colony size and mortality, and they depend on the spatial nature and patch size of the community. Our results suggest that a continuum of possible relationships can exist between species richness, community variability, invasion resistance, and area. These relationships are emergent behaviors generated by the individual properties of the particular component species of a community.

Biodiversity↗

PubMed2006

Robustness of surrogates of biodiversity in marine benthic communities.

The usefulness of surrogates to estimate complex variables describing community structure, such as the various components of biodiversity, is long established. Most attention has been given to surrogates of species richness and species diversity and has focused on identifying a subset of taxa as a surrogate of total community richness or diversity. In adopting a surrogate measure, it is assumed that the relationship between the surrogate(s) and total richness or diversity is consistent in both space and time. These assumptions are rarely examined explicitly. We examined the robustness of potential surrogates of familial richness and multivariate community structure for macrofauna communities inhabiting artificial kelp holdfasts by comparing among communities of dissimilar ages and among communities established at different times of the year. This is important because most benthic "landscapes" will be a mosaic of patches reflecting different intensities, frequencies, and timing of disturbances. The total abundance of organisms and familial richness of crustaceans or polychaetes were all good predictors of total familial richness (R2 > 0.68). In contrast, while the familial richness of other groups, such as mollusks and echinoderms, were well correlated with total familial richness for communities at an early stage of development, the strength of these relationships declined with community age. For multivariate community structure, carefully selected subsets of approximately 10% of the total taxa yielded similar patterns to the total suite of taxa, irrespective of the age of the community. Thus, useful surrogates of both familial richness and multivariate community structure can be identified for this type of community. However, the choice of technique for selecting surrogate taxa largely depends on the nature of the pilot data available, and careful selection is required to ensure that surrogates perform consistently across different-aged communities. While the specific taxa selected as surrogates will vary among different communities, and possibly even among similar communities at different sites, the techniques and the concepts we address are applicable to any community type.

Animals↗

PubMed2004

Pathogenic and humoral immune responses to porcine reproductive and respiratory syndrome virus (PRRSV) are related to viral load in acute infection.

Although much research has been performed on porcine reproductive and respiratory syndrome virus (PRRSV), little quantitative information is available on the relationships between virulence and in vivo virus replication, among isolates recovered at different times in the history of PRRS, or the relative levels of virulence associated with individual virus isolates. In this study, the in vivo growth properties of virulent field isolates and attenuated PRRSV isolates were compared. The results show that virulent PRRSV isolates exhibit longer and more elevated levels of viremia, induce faster and more intense humoral immune responses, negatively affect body weight gain, induce higher death rates, and cause more severe clinical signs in a respiratory disease model. We found that the more virulent field isolates grew to significantly higher levels in pigs than did cell-culture adapted isolates. We concluded that the pathogenic consequences and immunological responses of pigs to PRRSV are directly related to viral load in acute infection as reflected in viral titers in blood.

Animals↗

PubMed2004

Oral immunization induces local and distant mucosal immunity in swine.

Transmission of porcine reproductive and respiratory syndrome virus (PRRSV) in semen and reproductive disease in pregnant swine might be reduced by vaccines that induce mucosal immunity in the reproductive tract. Cholera toxin (CT), when delivered orally, is a potent mucosal adjuvant and immunogen in swine. To determine if oral immunization additionally elicits immunity at distant mucosal surfaces, we examined antibody responses to CT-B subunit in the reproductive tract and oral cavity. Orally administered CT induced distant mucosal immunity, as measured by antibodies to CT-B subunit in saliva and vaginal secretions. Presentation of PRRSV nucleocapsid as a genetic fusion with CT resulted in local mucosal antibody production, but no response was observed in vaginal secretions. The results demonstrate the feasibility of using orally administered CT for the induction of immunity to reproductive pathogens in swine. However, effective induction of PRRSV-specific immune responses in the reproductive tract requires a better understanding of the mechanisms of antigenicity and adjuvanticity at distant mucosal sites.

Administration, Oral↗

PubMed2004

Validation of a blocking enzyme-linked immunosorbent assay for detection of antibodies against porcine reproductive and respiratory syndrome virus.

Porcine reproductive and respiratory syndrome (PRRS) continues to be one of the most significant diseases of swine. IDEXX HerdChek PRRS, a commercially available enzyme-linked immunosorbent assay (ELISA), has become the industry standard for the detection of antibodies against PRRS virus (PRRSV). The need to accurately determine the PRRSV serostatus of herds and individual animals has prompted the development of several follow-up assay methods. A highly specific and repeatable blocking ELISA (bELISA) was developed on the basis of the use of an expressed PRRSV nucleocapsid (N) protein as the antigen and a biotinylated monoclonal antibody. Validation of the bELISA used sera from 316 animals experimentally and naturally infected with North American PRRSV and sera from 370 uninfected animals. Receiver operating characteristic analysis of the data calculated a diagnostic sensitivity of 97.8% and a diagnostic specificity of 100%. The between-run coefficient of variation of an internal quality control serum was 4.24%. The bELISA was able to detect seroconversion as well as the IDEXX ELISA and the indirect fluorescent antibody (IFA) assay; kappa values were 0.94 and 0.96, respectively. A collection of 133 serum samples with unexpected positive IDEXX ELISA results was obtained from 4,038 diagnostic samples submitted from farms from which PRRS-negative results were expected. The bELISA identified 97% of the samples as PRRS seronegative, while the IFA identified 100% as seronegative. The anticipated use of the bELISA is as a follow-up test to the IDEXX ELISA for determining the PRRSV serostatus of individual animals with unexpected positive test results from swine herds from which negative results are expected.

Analysis of Variance↗

PubMed2004

Cancer research training for high school and college students at a comprehensive cancer center.

BACKGROUND: The number of American students pursuing advanced science degree continues to wane. Summer research experience programs are ideal mechanisms to introduce high school and college students to scientific lifestyles. METHODS: A follow-up of participants from 1995-2003 was conducted to gauge student perception of the program and to measure outcomes. RESULTS: Data are presented from the responses of 287 (81%) participants. The Program was successful in recruiting female (67%) and underrepresented (>35%) students. Very high percentages of trainees reported pursuing advanced scientific study (>85% of high school and >92% college students). CONCLUSIONS: Summer research experiential programs can be successful in initiating or maintaining a student's interest in science careers.

Career Choice↗

PubMed2003

Invasion rates increase with species richness in a marine epibenthic community by two mechanisms.

It is widely believed that, when extrinsic conditions are similar, the likelihood of species invading established assemblages decreases with increasing species richness of the recipient community. Here we show that, for a sessile marine invertebrate community, invasion of patches increases with richness of the patch. We show that invasions can increase with local species richness by two distinct mechanisms. In the first, opportunistic colonisers with traits typical of invasive species colonise species-rich patches at higher rates because speciose patches are dominated by small colonies and mortality rates of small colonies are greater than that of large ones. Thus, mortality provides bare space for opportunists to colonise more frequently in species-rich patches. In the second, some species avoid colonising open areas of free space but preferentially associate with established colonies of particular other species, and a given preferred associate is more likely to occur in species-rich than in species-poor patches. These patterns are the result of particular properties of individual species and local species dynamics, and show that reduced risk of invasion is not necessarily an intrinsic property of species-rich communities. We conclude that resistance to invasion will be determined by the properties of the particular component species and emergent dynamics of the recipient community, and not by an aggregate community property such as richness.

Animals↗

PubMed2002

Selection for restraint in competitive ability in spatial competition systems.

The absence of 'super competitors' in nature is usually attributed to organisms facing trade-offs in resource allocation. Here we identify another mechanism, dependent on indirect interactions among species and non-random spatial organization, in which selection favours restraint in competitive ability. In simple spatial models of a three-species intransitive network, indirect interactions favour slower growth and selection limits the difference in growth rate among species. The mechanism involves a trade-off between selection at the individual level, which selects for increased growth rate, and at the community level, which acts to limit growth rate to less than the maximum possible. If the difference in growth rates among species becomes too large, then the community becomes unstable and collapses to a monoculture of the slowest growing species. The mechanism requires both the intransitive network structure and self-organized spatial structure in the system. Similar behaviours arise in more complex systems of more than three species, and where there are reversals in interaction outcomes between species pairs. The work suggests that spatial self-structuring, indirect interactions and selection acting on community properties can be important in evolution. It provides a partial explanation of the high level of species coexistence and apparent restraint in interspecific interactions evident in some assemblages of sessile marine colonial organisms.

Animals↗