title: Specialist versus generalist life histories and nucleotide diversity in Caenorhabditis nematodes.
abstract: Species with broad ecological amplitudes with respect to a key focal resource, niche generalists, should maintain larger and more connected populations than niche specialists, leading to the prediction that nucleotide diversity will be lower and more subdivided in specialists relative to their generalist relatives. This logic describes the specialist-generalist variation hypothesis (SGVH). Some outbreeding species of Caenorhabditis nematodes use a variety of invertebrate dispersal vectors and have high molecular diversity. By contrast, Caenorhabditis japonica lives in a strict association and synchronized life cycle with its dispersal host, the shield bug Parastrachia japonensis, itself a diet specialist. Here, we characterize sequence variation for 20 nuclear loci to investigate how C. japonica's life history shapes nucleotide diversity. We find that C. japonica has more than threefold lower polymorphism than other outbreeding Caenorhabditis species, but that local populations are not genetically disconnected. Coupled with its restricted range, we propose that its specialist host association contributes to a smaller effective population size and lower genetic variation than host generalist Caenorhabditis species with outbreeding reproductive modes. A literature survey of diverse organisms provides broader support for the SGVH. These findings encourage further testing of ecological and evolutionary hypotheses with comparative population genetics in Caenorhabditis and other taxa.
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Toronto, , Toronto, Ontario, Canada , M5S 3B2, Department of Applied Biological Sciences, Saga University, , Saga 840-8502, Japan.
authors.forename: Shuning
authors.initials: S
authors.lastname: Li
authors.forename: Richard
authors.initials: R
authors.lastname: Jovelin
authors.forename: Toyoshi
authors.initials: T
authors.lastname: Yoshiga
authors.forename: Ryusei
authors.initials: R
authors.lastname: Tanaka
authors.forename: Asher D
authors.initials: AD
authors.lastname: Cutter
mesh_terms: D000818:Animals; D002107:Caenorhabditis / Q000235:genetics / Q000502:physiology*; D014644:Genetic Variation; D015801:Helminth Proteins / Q000235:genetics; D020062:Heteroptera / Q000502:physiology*; D008969:Molecular Sequence Data; D019105:Random Amplified Polymorphic DNA Technique; D017422:Sequence Analysis, DNA; D013559:Symbiosis
chemical_list: D015801:Helminth Proteins
keywords: Caenorhabditis; Parastrachia; generalists; niche; phoresy; specialists