High parasite virulence necessary for the maintenance of host outcrossing via parasite-mediated selection.

Biparental sex is widespread in nature, yet costly relative to uniparental reproduction. It is generally unclear why self-fertilizing or asexual lineages do not readily invade outcrossing populations. The Red Queen hypothesis predicts that coevolving parasites can prevent self-fertilizing or asexual lineages from invading outcrossing host populations.

Gene flow accelerates adaptation to a parasite.

Gene flow into populations can increase additive genetic variation and introduce novel beneficial alleles, thus facilitating adaptation. However, gene flow may also impede adaptation by disrupting beneficial genotypes, introducing deleterious alleles, or creating novel dominant negative interactions. While theory and fieldwork have provided insight into the effects of gene flow, direct experimental tests are rare.

Associations of Evolutionary-Concordance Diet and Lifestyle Pattern Scores with Incident, Sporadic Colorectal Adenoma in a Pooled Case-Control Study.

Differences in diet and lifestyle relative to those of our Paleolithic-era ancestors may explain current high incidences of chronic diseases, including colorectal cancer (CRC), in Westernized countries. Previously reported evolutionary-concordance diet and lifestyle pattern scores, reflecting closeness of diet and lifestyle patterns to those of Paleolithic-era humans, were associated with lower CRC incidence. Separate and joint associations of the scores with colorectal adenoma among men and women are unknown.

The evolution of parasite host range in heterogeneous host populations.

Theory on the evolution of niche width argues that resource heterogeneity selects for niche breadth. For parasites, this theory predicts that parasite populations will evolve, or maintain, broader host ranges when selected in genetically diverse host populations relative to homogeneous host populations. To test this prediction, we selected the bacterial parasite Serratia marcescens to kill Caenorhabditis elegans in populations that were genetically heterogeneous (50% mix of two experimental genotypes) or homogeneous (100% of either genotype).

Dauer life stage of Caenorhabditis elegans induces elevated levels of defense against the parasite Serratia marcescens.

Host-parasite research often focuses on a single host life stage, yet different life stages may exhibit different defenses. The nematode Caenorhabditis elegans has an alternate dispersal life stage, dauer. Despite dauer's importance in nature, we know little of how it responds to parasites.

Sex and Mitonuclear Adaptation in Experimental Populations.

To reveal phenotypic and functional genomic patterns of mitonuclear adaptation, a laboratory adaptation study with nematodes was conducted in which independently evolving lines were initiated from a low-fitness mitochondrial electron transport chain (ETC) mutant, Following 60 generations of evolution in large population sizes with competition for food resources, two distinct classes of lines representing different degrees of adaptive response emerged: a low-fitness class that exhibited minimal or no improvement compared to the mutant ancestor, and a high-fitness class containing lines that exhibited partial recovery of wild-type fitness. Many lines that achieved higher reproductive and competitive fitness levels were also noted to evolve high frequencies of males during the experiment, consistent with adaptation in these lines having been facilitated by outcrossing. Whole-genome sequencing and analysis revealed an enrichment of mutations in loci that occur in a -centric region of the interactome and could be classified into a small number of functional genomic categories.

No measurable fitness cost to experimentally evolved host defence in the Caenorhabditis elegans-Serratia marcescens host-parasite system.

Host susceptibility to parasites can vary over space and time. Costs associated with the maintenance of host defence are thought to account for a portion of this variation. Specifically, trade-offs wherein elevated defence is maintained at the cost of fitness in the absence of the parasite may cause levels of host defence to change over time and differ between populations.

Turnover in local parasite populations temporarily favors host outcrossing over self-fertilization during experimental evolution.

The ubiquity of outcrossing in plants and animals is difficult to explain given its costs relative to self-fertilization. Despite these costs, exposure to changing environmental conditions can temporarily favor outcrossing over selfing. Therefore, recurring episodes of environmental change are predicted to favor the maintenance of outcrossing.

Evolution of Caenorhabditis elegans host defense under selection by the bacterial parasite Serratia marcescens.

Parasites can impose strong selection on hosts. In response, some host populations have adapted via the evolution of defenses that prevent or impede infection by parasites. However, host populations have also evolved life history shifts that maximize host fitness despite infection.

Host mating system and coevolutionary dynamics shape the evolution of parasite avoidance in Caenorhabditis elegans host populations.

Hosts exhibit a variety of defence mechanisms against parasites, including avoidance. Both host-parasite coevolutionary dynamics and the host mating system can alter the evolutionary trajectories of populations. Does the nature of host-parasite interactions and the host mating system affect the mechanisms that evolve to confer host defence? In a previous experimental evolution study, mixed mating and obligately outcrossing Caenorhabditis elegans host populations adapted to either coevolving or static Serratia marcescens parasite populations.

Nematode-bacteria mutualism: Selection within the mutualism supersedes selection outside of the mutualism.

The coevolution of interacting species can lead to codependent mutualists. Little is known about the effect of selection on partners within verses apart from the association. Here, we determined the effect of selection on bacteria (Xenorhabdus nematophila) both within and apart from its mutualistic partner (a nematode, Steinernema carpocapsae).