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Evolution of parasitism-related traits in nematodes.

Chieh-Hsiang Tan1, Hillel T Schwartz1,2, Nathan Y Rodak1,3

  • 1Div. Biology and Biol. Engineering, California Institute of Technology, Pasadena, CA, 91125, USA.

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Entomopathogenic nematodes, Steinernema and Heterorhabditis, evolved to parasitize insects. Surprisingly, they can develop independently of their symbiotic bacteria, feeding on insect hemolymph and explaining their evolutionary origins.

Keywords:
HeterorhabditisL1 arrestParasitismSteinernemaaxenic cultureconvergent evolutionentomopathogenicforagingmodes of feedingsymbiosis

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Area of Science:

  • * Entomology
  • * Evolutionary Biology
  • * Nematology

Background:

  • * Parasitism drives metabolic and developmental divergence between parasitic and free-living animals.
  • * Entomopathogenic nematodes (EPNs) independently evolved an insect-parasitizing lifestyle, relying on symbiotic bacteria.
  • * The evolutionary adaptations and symbiotic relationships of EPNs remain largely unknown.

Purpose of the Study:

  • * To investigate the evolutionary adaptations of entomopathogenic nematodes (EPNs) to a parasitic lifestyle.
  • * To understand the symbiotic relationships underpinning entomopathogenicity.
  • * To explore the nutritional and developmental independence of EPNs from their symbiotic bacteria.

Main Methods:

  • * Development of an axenic culture medium for robust growth of *Steinernema hermaphroditum*.
  • * Assessment of hatchling survival in nutrient-poor environments.
  • * Evaluation of foraging abilities in *S. hermaphroditum* and *Heterorhabditis bacteriophora*.
  • * Testing the ability of EPNs to develop and reproduce within insect hosts independently of symbiotic bacteria.

Main Results:

  • * *S. hermaphroditum* hatchlings cannot survive in nutrient-poor conditions; *H. bacteriophora* hatchlings show impaired survival.
  • * Foraging ability is lost in *H. bacteriophora* and severely compromised in *S. hermaphroditum* hatchlings.
  • * Both *Steinernema* and *Heterorhabditis* nematodes can invade, develop, and reproduce in insect hosts without symbiotic bacteria, feeding on hemolymph.

Conclusions:

  • * Loss of foraging and nutrient-poor survival traits in EPNs is linked to their obligate parasitic lifestyle.
  • * EPNs can utilize insect hemolymph as a nutrient source, independent of their symbiotic bacteria.
  • * These findings offer insights into the evolutionary origins of entomopathogenic nematodes.