Dauer juvenile longevity and stress tolerance in natural populations of entomopathogenic nematodes: is there a relationship?

Abstract

Qualitative and quantitative genetic analysis of life span in experimental adult animals predicts that resistance to stress and longevity are positively correlated, but such studies on field populations of animals are rare. We tested this hypothesis using dauer juveniles of 15 natural populations of the entomopathogenic nematode, Heterorhabditis bacteriophora, collected from diverse localities. Dauer juvenile longevity at 25 °C in autoclaved tap water and tolerance to major environmental stresses including heat (survival at 40 °C for 2 h), ultraviolet (UV) radiation (original virulence remaining after exposure to 302 nm UV for 5 min), hypoxia (survival at approximately 0% dissolved O 2 at 25 °C for 96 h), and desiccation (survival in 25% glycerol at 25 °C for 72 h) differed significantly among populations. Intrinsic dauer juvenile longevity, defined as the number of weeks to 90% mortality (LT 90) estimated using probit analysis of nematode survival data at 25 °C varied between 6 and 16 weeks among populations. Longevity was most strongly correlated with heat followed by UV and hypoxia tolerance, respectively, but showed no correlation with desiccation tolerance. The strong positive correlation of longevity with heat tolerance was further confirmed through principal components analysis which showed almost identical variance for heat and longevity. Among the stress factors, only UV tolerance was positively correlated with heat and hypoxia tolerance. Differences in longevity and stress tolerance in nematode populations isolated from a single 200 m 2 grassland locality further support another hypothesis that population structure of heterorhabditid nematodes is highly fragmented, thus suggesting the existence of metapopulation dynamics.