Specialist versus generalist life histories and nucleotide diversity inCaenorhabditisnematodes

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.

Convergent evolution of sperm gigantism and the developmental origins of sperm size variability inCaenorhabditisnematodes

“…; Li et al. ). The two other species with gigantic sperm ( C. macrosperma and C. plicata ) also potentially represent “specialists” given that C. macrosperma displays a very localized geographic distribution (Felix et al.…”

Divergent mitochondrial lineages arose within a large, panmictic population of the Savannah sparrow (Passerculus sandwichensis)

“…Low return rates were not unique to Savannah sparrows in this region and the authors argued that high interannual variation in resource availability selects for an opportunistic and flexible breeding life history (Jones et al, ). Second, the specialist–generalist variation hypothesis posits that more specialized species will exhibit greater population structure, lower levels of gene flow and lower genetic diversity relative to generalist species (Li, Jovelin, Yoshiga, Tanaka, & Cutter, ). Although this hypothesis has received mixed support (e.g., Hung, Drovetski, & Zink, ; Matthee, Engelbrecht, & Matthee, ; Titus & Daly, ), a generalist ecology likely contributes to the lack of population genetic structure and large effective population sizes observed within nominate Savannah sparrows.…”

Crayfish populations genetically fragmented in streams impounded for 36–104 years

“…those with relatively large impoundments built before 1980) may be genetically isolated to some extent. Presumably, ecologically specialised species and those with small N e , low genetic variation, and high sensitivity to stochastic environmental events (Franzén & Nilsson, ; Li, Jovelin, Yoshiga, Tanaka, & Cutter, ) may suffer more severe effects of stream fragmentation by impoundments. Second, crayfish populations upstream of impoundments are at risk of local extinction due to the lack of detectable upstream dispersal and gene flow in most impounded streams.…”