Teaching at the intersection of science and society: An activity on healthcare disparities.

Understanding the relationship between science and society is an objective of science education and is included as a core competency in the AAAS Vision and Change guidelines for biology education. However, traditional undergraduate biology instruction emphasizes scientific practice and generally avoids potentially controversial issues at the intersection of biology and society. By including these topics in biology coursework, instructors can challenge damaging ideologies and systemic inequalities that have influenced science, such as biological essentialism and health disparities. Specifically, an ideologically aware curriculum highlights how ideologies and paradigms shape our biological knowledge base and the application of that knowledge. Ideologically aware lessons emphasize the relationship between science and society with an aim to create more transparent, scientifically accurate, and inclusive postsecondary biology classrooms. Here we expand upon our ideologically aware curriculum with a new activity that challenges undergraduate biology students to consider the impacts of healthcare disparities. This lesson allows instructors to directly address systemic inequalities and allows students to connect biomedical sciences to real-world issues. Implementing an ideologically aware curriculum enables students to challenge prevailing worldviews and better address societal problems that lead to exclusion and oppression.

Genome Size Changes by Duplication, Divergence, and Insertion in Caenorhabditis Worms.

Genome size has been measurable since the 1940s but we still do not understand genome size variation. Caenorhabditis nematodes show strong conservation of chromosome number but vary in genome size between closely related species. Androdioecy, where populations are composed of males and self-fertile hermaphrodites, evolved from outcrossing, female-male dioecy, three times in this group. In Caenorhabditis, androdioecious genomes are 10-30% smaller than dioecious species, but in the nematode Pristionchus, androdioecy evolved six times and does not correlate with genome size. Previous hypotheses include genome size evolution through: 1) Deletions and "genome shrinkage" in androdioecious species; 2) Transposable element (TE) expansion and DNA loss through large deletions (the "accordion model"); and 3) Differing TE dynamics in androdioecious and dioecious species. We analyzed nematode genomes and found no evidence for these hypotheses. Instead, nematode genome sizes had strong phylogenetic inertia with increases in a few dioecious species, contradicting the "genome shrinkage" hypothesis. TEs did not explain genome size variation with the exception of the DNA transposon Mutator which was twice as abundant in dioecious genomes. Across short and long evolutionary distances Caenorhabditis genomes evolved through small structural mutations including gene-associated duplications and insertions. Seventy-one protein families had significant, parallel decreases across androdioecious Caenorhabditis including genes involved in the sensory system, regulatory proteins and membrane-associated immune responses. Our results suggest that within a dynamic landscape of frequent small rearrangements in Caenorhabditis, reproductive mode mediates genome evolution by altering the precise fates of individual genes, proteins, and the phenotypes they underlie.

Slow Recovery from Inbreeding Depression Generated by the Complex Genetic Architecture of Segregating Deleterious Mutations.

The deleterious effects of inbreeding have been of extreme importance to evolutionary biology, but it has been difficult to characterize the complex interactions between genetic constraints and selection that lead to fitness loss and recovery after inbreeding. Haploid organisms and selfing organisms like the nematode Caenorhabditis elegans are capable of rapid recovery from the fixation of novel deleterious mutation; however, the potential for recovery and genomic consequences of inbreeding in diploid, outcrossing organisms are not well understood. We sought to answer two questions: 1) Can a diploid, outcrossing population recover from inbreeding via standing genetic variation and new mutation? and 2) How does allelic diversity change during recovery? We inbred C. remanei, an outcrossing relative of C. elegans, through brother-sister mating for 30 generations followed by recovery at large population size. Inbreeding reduced fitness but, surprisingly, recovery from inbreeding at large populations sizes generated only very moderate fitness recovery after 300 generations. We found that 65% of ancestral single nucleotide polymorphisms (SNPs) were fixed in the inbred population, far fewer than the theoretical expectation of ∼99%. Under recovery, 36 SNPs across 30 genes involved in alimentary, muscular, nervous, and reproductive systems changed reproducibly across replicates, indicating that strong selection for fitness recovery does exist. Our results indicate that recovery from inbreeding depression via standing genetic variation and mutation is likely to be constrained by the large number of segregating deleterious variants present in natural populations, limiting the capacity for recovery of small populations.

Model-based genotype and ancestry estimation for potential hybrids with mixed-ploidy.

Non-random mating among individuals can lead to spatial clustering of genetically similar individuals and population stratification. This deviation from panmixia is commonly observed in natural populations. Consequently, individuals can have parentage in single populations or involving hybridization between differentiated populations. Accounting for this mixture and structure is important when mapping the genetics of traits and learning about the formative evolutionary processes that shape genetic variation among individuals and populations. Stratified genetic relatedness among individuals is commonly quantified using estimates of ancestry that are derived from a statistical model. Development of these models for polyploid and mixed-ploidy individuals and populations has lagged behind those for diploids. Here, we extend and test a hierarchical Bayesian model, called entropy, which can use low-depth sequence data to estimate genotype and ancestry parameters in autopolyploid and mixed-ploidy individuals (including sex chromosomes and autosomes within individuals). Our analysis of simulated data illustrated the trade-off between sequencing depth and genome coverage and found lower error associated with low-depth sequencing across a larger fraction of the genome than with high-depth sequencing across a smaller fraction of the genome. The model has high accuracy and sensitivity as verified with simulated data and through analysis of admixture among populations of diploid and tetraploid Arabidopsis arenosa.

Genome Evolution: On the Road to Parasitism.

Roughly 1 billion people are infected with nematode parasites, but there is little understanding of the genomic changes that accompany the evolution of parasitism. A new study analyzes the genome of Caenorhabditis bovis, a nematode that may be evolving a parasitic lifestyle.

stratag: An r package for manipulating, summarizing and analysing population genetic data.

We introduce the r package stratag as a user-friendly population genetics toolkit. stratag provides easy access to a suite of standard genetic summaries as well as the ability to rapidly manipulate stratified genetic data for custom analyses. Tests of population subdivision with most common measures of population subdivision (e.g., FST , GST , ΦST , Χ2 ) can be conducted within a single function. The package also provides wrapper functions that allow users to configure and run popular external programs such as genepop, structure, and fastsimcoal from within r, and smoothly interface with popular r packages adegenet and pegas. stratag is intended to be an open-source dynamic package that will grow with future needs and user input.