Evolution of Virulence in Nematode Parasites of Fig Wasps

Fig Wasp and Nematode Interaction:

Fig pic - from HowstuffworksThis 1993 David Herre paper discusses how increased opportunities for parasite transmission will promote the evolution of increased virulence. This is in contrast to the usual assumption that parasites and other disease-producing organisms tend to evolve benign relationships with their hosts.

The model system used to demonstrate this point is the natural history of fig-pollinating wasps and the nematodes that parasitize these wasps. This system is useful because the foundress wasps that remain within the fig fruit may be counted and their lifetime reproductive success can be measured.

In Herre’s experiments, 11 species of Panamanian fig wasps were studied. The nematode virulence of different population structures (i.e. vertical vs. horizontal transmission) were determined by comparing the relative reproductive success of infected versus uninfected single foundress wasps.  It was found that the nematode species with the greatest estimated virulence were associated with host wasp species that are characterized by population structures providing the most frequent opportunities for horizontal transmission of their parasites. This is evidence that counters the theory that parasites and other disease-producing organisms tend to evolve benign relationships with their hosts over time.

The links provided below explore the fig-wasp life cycle in more detail.

Fig Wasp Life Cycle:

http://science.howstuffworks.com/zoology/insects-arachnids/fig-wasp.htm

  • fig wasps play an essential role in the fig’s life cycle, as the plant’s only pollinator
  • fig plant provides wasp with source of food and shelter
  • the fig fruit is a syconium, and is like an inverted flower
  • fig wasp climbs to center of syconium through ostiole
  • enzyme in fig is ficin, which breaks down wasp carcass into protein
  • some vegetarians and vegans refuse to eat figs and fig products

http://www.youtube.com/watch?v=JfkiYfrStrU

  • David Attenborough video

http://www.esa.org/esablog/field/the-story-of-the-fig-and-its-wasp/

  • a fig is not actually a fruit, it is an inflorescence
  • the seeds are the ovaries of the fig
  • this tree-wasp relationship is a well-known example of coevolution
  • parthenocarpic – seedless

http://www.environmentalgraffiti.com/food-and-drink/news-fig-nursery-and-mausoleum-fig-wasp

  • there are several varieties of fig and fig wasps

References:

1. Herre, E.A., Population Structure and the Evolution of Virulence in Nematode Parasites of Fig Wasps. Science, 259, 1442-1444 (1993)

2. Image reference: http://science.howstuffworks.com/zoology/insects-arachnids/fig-wasp1.htm

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