Co-infection, kin selection, and the rate of host exploitation by a parasitic nematode

Hypothesis: Under exploitative competition, unrelated parasites should reproduce at a faster rate than related parasites. Organisms: The parasitic nematode Steinernema carpocapsae and the insect host Galleria mellonella. Methods: We created ten replicate lines each of high-migration (unrelated) and low-migration (related) nematode populations, and allowed them to evolve for 20 host passages. Results: We found no difference between treatments in the number of juvenile nematodes produced. However, juvenile nematodes began to emerge significantly sooner in the lowmigration treatment, suggesting a faster rate of host exploitation. Host mortality rate was also higher in the low-migration lines. Conclusion: The results were contrary to predictions based on exploitative competition among the nematodes.