Archive for November, 2007

Novel mutualism

An article on the ant plant Humboldtia brunonis from Western Ghats, India.

Megha Shenoy & Renee M Borges. A novel mutualism between an ant-plant and its resident pollinator. Naturwissenschaften DOI 10.1007/s00114-007-0289-0

Pollination systems in which the host plant provides breeding sites for pollinators, invariably within flowers, are usually highly specialized mutualisms. We found that the pollinating bee Braunsapis puangensis breeds within the caulinary domatia of the semi-myrmecophyte Humboldtia brunonis (Fabaceae), an unusual antplant that is polymorphic for the presence of domatia and harbours a diverse invertebrate fauna including protective and non-protective ants in its domatia. B. puangensis is the most common flower visitor that carries the highest proportion of H. brunonis pollen. This myrmecophyte is pollen limited and cross-pollinated by bees in the daytime. Hence, the symbiotic pollinator could provide a benefit to trees bearing domatia by alleviating this limitation. We therefore report for the first time an unspecialisedmutualism in which a pollinator is housed in a plant structure other than flowers. Here, the cost to the plant is lower than for conventional brood-site pollination mutualisms where the pollinator develops at the expense of plant reproductive structures. Myrmecophytes housing resident pollinators are unusual, as ants are known to be enemies of pollinators, and housing them together may decrease the benefits that these residents could individually provide to the host plant.

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An interesting report by Steiner et al on the ant Lasius austriacus where the authors show that monogynous colonies of this ant species lacks aggression between colonies. In fact workers ‘integrate’ across colonies, maintaining self-nonself discrimination. This paper argues that the lack of aggression in ant colonies (documented only in 21 species till date) could be the first stage of establishing peace and this in turn could lead to super colonies. The results shown in Figure 1 of this article, which shows genetic relatedness, aggression, discrimination and cuticular hydrocarbons variation at different geographic distances [0-100 km] is simply stunning.

Steiner FM, Schlick-Steiner BC, Moder K, Stauffer C, Arthofer W, Buschinger A, Espadaler X, Christian E, Einfinger K, Lorbeer E, Schafellner C, Ayasse M & Crozier RH. 2007. Abandoning Aggression but Maintaining Self-Nonself Discrimination as a First Stage in Ant Supercolony Formation. Current Biology 17: 1903-1907.

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Been surfing through the literature for signs of multiple recruitment mechanisms in any single ant species. I assumed there would be some work on Camponotus species as they exhibit tandem running (one-on-one & group recruitment), solitary foraging, and mass recruitment. Though there is quite a lot of work carried out on recruitment behaviour in Camponotus, they all seem to address one strategy in each species.
But, I found this interesting paper by non other than ‘the duo’, Holldobler and Wilson. Of the several interesting points in this article is that when the major workers cannot cross gaps to reach a terrain, they build bridges, to which other workers are visually attracted. However once the chains are formed, workers lay trail pheromones on this ‘bridge’ to recruit nestmates. The five different recruitment systems used by the African Weaver ant,
Oecophylla longinoda as documented in this article are:
(a) recruitment to new food sources, mediated by odor trails produced from the rectal gland, coupled with tactile stimuli during mouth-opening, antennation, and head-waggling
(b) recruitment to new terrain, mediated by odor trails produced from the rectal gland and tactile stimulation through antennation
(c) emigration to new sites
(d) short-range recruitment to territorial intruders, during which the terminal abdominal sternite is maximally exposed and dragged for short distances over the ground to release an attractant from the sternal gland
(e) long-range recruitment to intruders, mediated by odor trails from the rectal gland and by antennation and intense body jerking

There are some fantastic sketches and close up photographs of these ants in the article.

Holldobler B and Wilson EO. 1978. The multiple recruitment systems of the African Weaver Ant,
Oecophylla longinoda (Latreille) (Hymenoptera: Formicidae). Behav Ecol Socio 3: 19-60.

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