A plant with seeds that look and smell like antelope droppings to attract dung beetles, which then disperse and bury the seeds, is described in a paper published online this week in Nature Plants. It is suggested that since the seeds are hard and offer no reward to the dung beetles, this represents a rare example of deception in plant seed dispersal.
Examples of flowers, especially orchids, that look like other plants or insects in order to attract animals that will pollinate them are numerous, but whether mimicry is used to help disperse seeds is controversial.
The nut seeds of Ceratocaryum argenteum are larger than those of related species and give off a pungent smell reminiscent of antelope droppings. Could this be an example of deception, an aromatic disguise to trick unwitting dung beetles into dispersing the seeds? In the De Hoop Nature Reserve of the southern Cape of South Africa, Jeremy Midgley and colleagues investigated.
The size and texture of the nuts suggest that they could be collected and cached by small mammals, but no such mammals that display this ’scatterhoarding’ behaviour are known in the region and camera traps set up by the researchers showed indigenous rodents ignoring the nuts. Instead they saw dung beetles (Epirinus flagellatus) taking an interest, rolling nuts away and burying them.
The authors analysed the volatile cocktail of chemicals given off by the seeds and found that their concentration and composition were similar to those emitted from eland and bontebok dung. To a beetle, they may smell just like the antelope droppings that are vital for their reproductive process. However, the nuts are too hard for the duped beetles to eat or lay eggs in after they have been painstakingly rolled to a choice location and buried. By mimicking antelope dung, in both appearance and scent, C. argenteum may be tricking the dung beetles into dispersing the seeds of the plant without reward.
Midgeley, J, White, J, Johnson, S, & Bronner, G. (2015) Faecal mimicry by seeds ensures dispersal by dung beetles. Nature Plants, doi:10.1038/nplants.2015.141