Evaluation of a putative entomopathogenic Caenorhabditis (Nematoda: Rhabditid) and associated Serratia (Proteobacteria: Enterobacteriaceae)

A major goal of modern biology is to extend our understanding of biological systems investigated in the laboratory to their ecological and evolutionary context. With extensive understanding of the function, development and genetics of C. elegans, exploring the link between this laboratory model and the environment in which this system evolved would be very interesting because very little is known about the natural history of this premier model organism. A new strain of Caenorhabditis briggsae (SoAf) with an associated bacterium, Serratia sp. SCBI, has been isolated from South Africa using common entomopathogenic nematode trapping methods. This study taxonomically identified and evaluated entomopathogenic behavior of C. briggsae SoAf and Serratia sp. SCBI. Hemocoelic injections of Serratia sp. SCBI demonstrated pathogenicity in insect larvae, Galleria mellonella. Caenorhabditis briggsae SoAf and other Caenorhabditis, including C. elegans , were capable of infection, growth and reproduction within the insect larvae in the presence of Serratia sp. SCBI. Identification of a putative entomopathogenic C. briggsae expands on our understanding of Caenorhabditis ecology and provides a framework for further investigation of entomopathogensis in other free-living nematodes

Host Susceptibility Is Altered by Light Intensity After Exposure to Parasites

Translating research advances to natural systems using experimental laboratory studies is often difficult because of the variability between the natural environment and experimental conditions. Because environmental conditions have a large effect on an organism's physiology, responses to stressors like nutrient limitation, temperature, oxygen deprivation, predation, and parasite/pathogen infection are likely to be context dependent. Therefore, it is essential to examine the impact the study environment has on the experimental outcome. Here, we explored the effect of light exposure on susceptibility to parasite infection. The Biomphalaria glabratalSchistosoma mansoni study system is a well-established model for studying schistosomiasis. It has been general practice to maintain the vector, B. glabrata, in dark conditions after exposure to miracidia of the human pathogen S. mansoni. We evaluated susceptibility of B. glabrata to S. mansoni under 3 different light conditions during the prepatent period, light (125 lx) on a 12-12 cycle, dim light (3 lx) on a 12-12 cycle, and no light (24 hr at 0 lx). We hypothesized that stress due to photoperiod disruption (24 hr of darkness) would result in compromised immune function and lead to higher susceptibility to infection. Prevalence of infected snails differed significantly between the light conditions, and higher susceptibility was observed in the full light and complete dark conditions compared with the low light conditions. The dim conditions are representative of current methods for evaluating susceptibility in this system. Our results indicate that light exposure during the prepatent period can affect infection outcomes, and environmental conditions must therefore be considered when assessing fitness and immune response clue to interactions between host genotype and environment.Keywords: Biomphalaria Glabrata, Hemocytes, Stress, Marine, Crassostrea Gigas, Responses, Invertebrates, Immunit

Effects of Cu/Zn Superoxide Dismutase (sod1) Genotype and Genetic Background on Growth, Reproduction and Defense in Biomphalaria glabrata

Resistance of the snail Biomphalaria glabrata to the trematode Schistosoma mansoni is correlated with allelic variation at copper-zinc superoxide dismutase (sod1). We tested whether there is a fitness cost associated with carrying the most resistant allele in three outbred laboratory populations of snails. These three populations were derived from the same base population, but differed in average resistance. Under controlled laboratory conditions we found no cost of carrying the most resistant allele in terms of fecundity, and a possible advantage in terms of growth and mortality. These results suggest that it might be possible to drive resistant alleles of sod1 into natural populations of the snail vector for the purpose of controlling transmission of S. mansoni. However, we did observe a strong effect of genetic background on the association between sod1 genotype and resistance. sod1 genotype explained substantial variance in resistance among individuals in the most resistant genetic background, but had little effect in the least resistant genetic background. Thus, epistatic interactions with other loci may be as important a consideration as costs of resistance in the use of sod1 for vector manipulation

Genome-Wide Scan and Test of Candidate Genes in the Snail Biomphalaria glabrata Reveal New Locus Influencing Resistance to Schistosoma mansoni

Background: New strategies to combat the global scourge of schistosomiasis may be revealed by increased understanding of the mechanisms by which the obligate snail host can resist the schistosome parasite. However, few molecular markers linked to resistance have been identified and characterized in snails. Methodology/Principal Findings: Here we test six independent genetic loci for their influence on resistance to Schistosoma mansoni strain PR1 in the 13-16-R1 strain of the snail Biomphalaria glabrata. We first identify a genomic region, RADres, showing the highest differentiation between susceptible and resistant inbred lines among 1611 informative restriction-site associated DNA (RAD) markers, and show that it significantly influences resistance in an independent set of 439 outbred snails. The additive effect of each RADres resistance allele is 2-fold, similar to that of the previously identified resistance gene sod1. The data fit a model in which both loci contribute independently and additively to resistance, such that the odds of infection in homozygotes for the resistance alleles at both loci (13% infected) is 16-fold lower than the odds of infection in snails without any resistance alleles (70% infected). Genome-wide linkage disequilibrium is high, with both sod1 and RADres residing on haplotype blocks >2Mb, and with other markers in each block also showing significant effects on resistance; thus the causal genes within these blocks remain to be demonstrated. Other candidate loci had no effect on resistance, including the Guadeloupe Resistance Complex and three genes (aif, infPhox, and prx1) with immunological roles and expression patterns tied to resistance, which must therefore be trans-regulated. Conclusions/Significance: The loci RADres and sod1 both have strong effects on resistance to S. mansoni. Future approaches to control schistosomiasis may benefit from further efforts to characterize and harness this natural genetic variation

Effects of Cu/Zn Superoxide Dismutase (sod1) Genotype and Genetic Background on Growth, Reproduction and Defense in Biomphalaria glabrata

Resistance of the snail Biomphalaria glabrata to the trematode Schistosoma mansoni is correlated with allelic variation at copper-zinc superoxide dismutase (sod1). We tested whether there is a fitness cost associated with carrying the most resistant allele in three outbred laboratory populations of snails. These three populations were derived from the same base population, but differed in average resistance. Under controlled laboratory conditions we found no cost of carrying the most resistant allele in terms of fecundity, and a possible advantage in terms of growth and mortality. These results suggest that it might be possible to drive resistant alleles of sod1 into natural populations of the snail vector for the purpose of controlling transmission of S. mansoni. However, we did observe a strong effect of genetic background on the association between sod1 genotype and resistance. sod1 genotype explained substantial variance in resistance among individuals in the most resistant genetic background, but had little effect in the least resistant genetic background. Thus, epistatic interactions with other loci may be as important a consideration as costs of resistance in the use of sod1 for vector manipulation

Genetic and phenotypic variation associated with the resistance gene SOD1 in Biomphalaria glabrata, an important intermediate host of Schistosomiasis

Schistosomiasis afflicts 200 million people and is responsible for 200,000 deaths per year. The infection is caused by a digenean trematode in the genus Schistosoma. The parasite must cycle through both a vertebrate (human) and invertebrate (snail) host to complete the life cycle. My dissertation focuses on the genetic mechanisms of resistance in the snail intermediate host Biomphalaria glabrata to the parasite Schistosoma mansoni. Understanding the underlying mechanisms controlling resistance in the intermediate host is essential for elucidating transmission dynamics and the development of appropriate biological control techniques. Much of what we know about the resistance of the intermediate host has been determined using established laboratory strains of both the snail and trematode species. The B. glabrata/S. mansoni system serves as a model system for studying schistosomiasis. Resistance to parasite infection in the snail is highly heritable. While many genes have been implicated, allelic variation correlating with resistance has only been observed at a single gene, copper-zinc superoxide dismutase (SOD1). SOD1 is functionally relevant because it catalyzes the conversion of the highly reactive superoxide into the less reactive hydrogen peroxide and water. In the snail, hydrogen peroxide is released as part of the immune response to the invading parasite. The goal of my dissertation was to further evaluate SOD1 as a resistance locus. In the second chapter I examined allelic variation at SOD1 and looked for evidence of selection on SOD1 in natural populations of B. glabrata. To determine the utility of SOD1 as a resistance locus in natural populations, we needed to first determine if there was indeed allelic variation in natural population of B. glabrata. This is important because if the alleles do not co-occur in natural populations, then the relative selective advantage of one allele over another in terms of resistance would be of little ecological relevance in natural transmission zones. Variation at SOD1 in natural populations cannot be assumed because the initial study describing the correlation between resistance to infection and allelic variation used a hybrid laboratory strain of B. glabrata (13-16-R1). Therefore, we did not know if the co-occurrence of particular alleles at SOD1 in the 13-16-R1 lab strain was a natural phenomenon or is an artifact of the breeding history of the strain. In this study we were able to identify the likely geographic origins of the alleles in the lab strain 13-16-R1 and determine that different alleles do co-occur in some natural populations. Additionally, we found heterozygote excess at SOD1 in all the populations segregating for the allele that confers highest resistance in 13-16-R1. This result raises the possibility that overdominance is acting at SOD1 or some locus closely linked to it

Bringing Research Data to the Ecology Classroom through a QUBES Faculty Mentoring Network

The field of ecological research is in the midst of a data revolution. Best practices in the curation, archiving, and dissemination of data have received much attention over the past decade (e.g., Reichman et al. 2011, Whitlock 2011, Hampton et al. 2013). One result of these efforts has been a dramatic increase in open access data. Primary data associated with published manuscripts are increasingly accessible through supplementary materials, university repositories, journal-specific archives (e.g., ESA Data Registry), or public repositories (e.g., Dryad Digital Repository). Large-scale monitoring data from sensor arrays, field stations, state or federal governmental databases, and citizen science projects can be accessed on the web. Other important data streams include the digitization of biodiversity data from museum and university collections (Page et al. 2015, Holmes et al. 2016)

Effect of genetic background and <i>sod1</i> genotype on life-history traits.

<p>(A) Average size by genotypic class within each lineage at 12 weeks after egg masses were deposited. The points represent the averages of the mean size of individuals of each genotype within each of 3–4 cups (containing 13–17 F2 snails per cup). Error bars represent 1±SE (background 1: n = 45 (<i>BB</i> = 16, <i>BC</i> = 20, <i>CC</i> = 9), background 2: n = 57 (<i>BB</i> = 16, <i>BC</i> = 28, <i>CC</i> = 13) background 3: n = 58 (<i>BB</i> = 16, <i>BC</i> = 28, <i>CC</i> = 14)). Snails with the <i>CC</i> genotype grew significantly more slowly than those with <i>BC</i> and <i>BB</i> genotypes. (B) Average size at 32 weeks of each genotypic class within each lineage. Means are the average of all snails within the genotypic class, and error bars represent 1±SE (background 1: n = 27 (<i>BB</i> = 9, <i>BC</i> = 10, <i>CC</i> = 8), background 2: n = 27 (<i>BB</i> = 9, <i>BC</i> = 10, <i>CC</i> = 8), background 3: n = 30 (<i>BB</i> = 10, <i>BC</i> = 10, <i>CC</i> = 10)). Again, snails with the <i>CC</i> genotype grew significantly more slowly than those with <i>BC</i> and <i>BB</i> genotypes. (C) Average total egg production for five weeks per snail (each raised individually) by genotypic class within each lineage. Means are the average of all snails within the genotypic class, and error bars represent 1±SE (background 1: n = 25 (<i>BB</i> = 9, <i>BC</i> = 9,<i>CC</i> = 7), background 2: n = 27 (<i>BB</i> = 9, <i>BC</i> = 10, <i>CC</i> = 8), background 3: n = 30 (<i>BB</i> = 10, <i>BC</i> = 10,<i>CC</i> = 10)). (D) Mortality at 8-month census of each genotypic class within each lineage. Data points are estimates of the percent mortality in each genotypic class and error bars represent 1±SE on the proportion (for all backgrounds n = 30 (<i>BB</i> = 10, <i>BC</i> = 10, <i>CC</i> = 10)). Snails with the <i>CC</i> genotype exhibited significantly greater mortality than those with the <i>BB</i> or <i>BC</i> genotype. (E) Mortality at 12-month census of each genotypic class within each lineage. Data points are estimates of percent mortality in each genotypic class and error bars represent 1±SE on the proportion (for all backgrounds n = 30 (<i>BB</i> = 10, <i>BC</i> = 10, <i>CC</i> = 10)).</p

Resistance of genetic background as a function of average resistance of grandparental inbred lines.

<p>Mid-grandparent resistance was estimated by averaging the resistance of the four inbred, grandparental lines (determined previously). The resistance of each genetic background (Grand-offspring resistance) was estimated by parasite challenges done in triplicate (n = 24×3) for each background (• genetic background 1, ▴ genetic background 2, and ▪ genetic background 3).</p