Monday, 28 September 2015

botany - Can galls be formed from mutualistic relationships?


According to Wikipedia, galls (cecidia) are formed by parasitic insects and mites like gall wasps (Neuroterus albipes). At some metamorphic stage, these organisms alter cell division processes in meristematic tissues of their host plants, which creates a tumour on (typically) the surface of leaves, branches or roots. These organisms use the galls as their habitat and/or food source (exploiting the sugars present).


However, I also know that bullhorn acacia and ants form an interspecific mutualistic relationship (with galls), so apparently galls don't need to be parasitic. Are there any other specific plant-insect pairs that have the same type of mutualistic gall relationship as the acacia-ant system?



Answer




Yes, pollinating fig wasps are gall inducing and mutualistic at the same time, and actually essential for the pollination of figs (see e.g Martinson et al., 2015). During the very intricate mutualism, fig wasps deposit eggs in some of the flowers and leave others. The flowers with eggs and later larvae will develop into galls that will produce new wasps but no seeds, while the flowers that lack wasp larvae will produce seeds. However, the hatched females that leave the figs will pick up pollen before leaving, and are essentially the only vector for cross pollinations between fig plants.


(with the aim of expanding the answer later...)


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