Parasite makes ant resemble a fruit

Written by Thomas Hesselberg

Thursday, 24 April 2008

The parasite changes the appearance of the ant so it resembles a fruit. On the left is the normal ant and on the right is the infected ant. Photo by Stephen Yanoviak from Current Biology (2008) 18: R294.
The evolutionary arms race between parasites and their hosts have been ongoing, almost since the first organisms appeared on Earth. The development of hosts defences including immune, chemical and behavioural defences have forced parasites to develop more and more advanced counter-measures. Some of the most impressive outcomes include parasites, which can affect and control the behaviour and physiology of their hosts. A new addition including a parasitic nematode and an ant has recently been described by scientists from the University of Copenhagen, Denmark.

The story starts with a study of the Central American ant Cephalutus atratus, which is remarkable since its show gliding behaviour and controlled steering when falling from tall trees. However, some ants had a red abdomen instead of the usual black one and showed highly unusual behaviour. The discovery of nematodes in the abdomen of the red ants alerted the Copenhagen based research group.

They discovered that the nematodes infect ant larvae, when they ingest bird faeces. When the larvae turn into adult workers the nematodes mate in the ant abdomen and lay their eggs. However, the eggs can only mature and hatch in a bird, so the nematode has to ensure that the infected ants get eaten by a bird.

This is done in an extremely clever way. First the nematode changes the colour of the ant’s abdomen so it is red and resembles a mature fruit. Secondly it changes the behaviour of the ant so that it holds the abdomen up in the air almost constantly unlike normal ants. Thirdly it weakens the cuticle and joints of the ant, so that when a bird attacks it, the abdomen is easily split from the rest of the body, which is thorny and unpleasant for a bird.

The researchers conclude that the nematode-ant system constitute a good example of an extended phenotype. The nematode genes affect a phenotype (morphology and behaviour of the ant) outside its own body.

Source
Hughes, D. P., Kronauer, D. J. C., Boomsma, J. J. (2008). Extended phenotype: nematodes turn ants into bird-dispersed fruits. Current Biology 18: R294-R295.

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