From cocks and hens * to cockroaches (and elephants…)

Yasuhiro Uehara and Naoto Sugiura describe a new mutualistic relationship between a cockroach and Monotropastrum humile (Botanical Journal of the Linnean Society 185: 113–118, 2017; https://doi.org/10.1093/botlinnean/box043). [M. humile is a mycoheterotrophic herb [a plant that obtain nutrients from mycorrhizal fungi that are attached to the roots of a photosynthetic vascular plant], which is another interesting tale in its own right, but back to the main story…  Uehara and Sugiura demonstrate that forest cockroaches – Blattella nipponica – consistently visit and consume the pulp of this plant that is embedded with numerous minute seeds, and show that the ‘roaches’ excreted frass [faeces of insect larvae] contained seeds that were not only intact, but were also viable [‘capable of living‘].

Since the approx. 4,600 species of cockroaches (in the insect order Blattodea) are cosmopolitan (‘found all over the world’), the authors reasonably speculate that seed dispersal by cockroaches – blattodoendozoochory? – may be “a pervasive, but as yet undocumented, dispersal mechanism”. [Ed. – Although, since they have in fact demonstrated this phenomenon in their paper, maybe it’s more accurate to say insufficiently documented…] And if the cockroach is really one of the few animals that can survive nuclear Armageddon, then it may be down to these humble invertebrates to help plants revegetate the scarred and scorched E/earth … if the plants survive that apocalyptic event that is.

 

A mammoth discovery…

From rather small seed ‘movers and shakers‘ above to extremely large ‘sexual go-betweens’ now: Elephants. Although flying birds have potential for seed dispersal of extraordinary distances over land and sea (or just on land), terrestrial-tied animals are generally much more limited in the distances they can cover, and therefore how far they can disperse any seeds. However, Katherine Bunney et al. provide evidence that the savanna elephant [Loxodonta africana africana] of Africa is the longest distance terrestrial vertebrate seed-disperser yet investigated (Biotropica 49: 395–401, 2017; doi: 10.1111/btp.12423).

Their modelling work predicts that 50 % of seeds ingested by these plant-munching pachyderms are carried over 2.5 km from source, and distances up to 65 km are achievable (in what they euphemistically refer to as “maximum gut passage time” **). To put this achievement into context, the article by Erik Stokstad includes a nice graphic indicating seed dispersal abilities ranging from ants (1 m) to migratory birds (300 km). And, by way of underlining the importance of this elephantine discovery, Mauro Galetti (an ecologist at São Paulo State University, São Paulo, Brazil) cautions that “the extinction of elephants would have a profound effect on plant survival and gene flow”.

* see previous item…in this series; cocks are the male birds, hens are the females [see also this for various confusions that can arise with those terms…]

** Presumably constipated animals have the potential to disperse seeds further – until their condition is ‘resolved’ – and maybe even wider once the faecal blockage is finally ‘uncorked’, probably with some force.

[This is part 2 of a multi-part series of short items celebrating the creatively imaginative and enterprising ways in which plants dupe poor unsuspecting animals into doing their sexual bidding…]

Image credits: cockroach from Sripathiharsha; Elephant from Muhammad Mahdi Karim