Plant Cuttings

Feeding relationships in nature (Hilary Costa et al.; Felix Bärlocher & Heinz Rennenberg]) are what make the world go round. Or, at least help energy to flow (Hilary Costa et al.; Dafeng Hui), nutrients to cycle (Hilary Costa et al.; Felix Bärlocher & Heinz Rennenberg), thereby fuelling and maintaining the great circle of life (Victoria James). It’s therefore always of interest whenever a feeding behaviour is discovered that challenges our assumptions about what should eat what. Appropriately, this post provides news of an animal whose dietary habits go against all that we’ve been told to expect.

A young specimen of Myloplus sauron (image borrowed from the article by Valéria N Machado et al. (2024).

There are few certainties in this life. But one that you could ‘set your watch by’ is that piranhas (Freya Knibb) – freshwater fish of South American rivers such as the Amazon – are carnivorous (Kim Rutledge et al.)*. Not only that, but a shoal of these devilishly-dentally-decorated piscatorial predators will strip a carcass to the bones in seconds. Or so Hollywood movies (Helen Thompson) and US President Theodore Roosevelt (Julia Layton; Helen Thompson) would have us believe.

Although there are well-documented incidents of piranhas taking bites out of humans (e.g. Jan Mol, 2006; Zoe Mintz; Lamiat Sabin), they’re probably not quite as ferocious as they’re made out to be (they have “a somewhat exaggerated reputation for ferocity”). But, they do eat flesh/meat/animals (Engrid Barnett; Lydia Smith; Kawkab Nadim), so are presumably carnivores. It is therefore not a great leap of logic to infer that a piranha-like fish will be true to its piranha cousins’ dietary preferences and also be carnivorous. Well, guess what? Yes, we now have news of a piranha-like fish that is vegetarian(!)*

Valéria N. Machado et al. (2024) describe a new species of ‘pacu’ (Desiree Bowie; Bec Crew; Eleanor Higgs) – a piranha-like fish – endemic to the Xingu River Basin (Fernanda Wenzel), a Brazilian tributary of the Amazon.

Formally named Myloplus sauron, the specific epithet of the fish’s scientific name relates to its appearance. Specifically, its “elliptical body … marked with a vertical, black bar tapering toward both ends, resembles the famous vertical-pupilled eye [the Eye of Sauron (Leon Miller), a structure belonging to the character Sauron], from the novel The Lord of the Rings by JRR Tolkien [(David Doughan; John Garth; Emily Martin)]” (Machado et al., 2024). The common – English – name of this fish is presumably therefore, Sauron. The imagination of scientists in creating scientific names for new species is a constant source of amusement and amazement (e.g. posts by Stephen Heard here, here, and here), and on this occasion seems to prove the adage that ‘beauty is in the eye [Mr P Cuttings’ emphasis] of the beholder’.

News of a human-friendly piranha-like fish** is clearly good news for humans. But, it’s also good news for plants. Why? In eating plants it is likely that Sauron may help to disperse viable plant fragments, or their reproductive structures (seeds in particular), that could establish new plants and colonies some distance from the parent population. Use of fish to disperse plant diaspores (the technical name for plant parts – such as seeds (Hans Lambers) or fruits*** that can produce a new individual) – is a well-known phenomenon and is called icthyochory (Jill Anderson et al., 2011) or piscichory (slides 7 and 8 here, and here). More specifically this is endopiscichory if the seed is ingested by the fish and subsequently ‘voided in the faeces’ – as for a pacu species that feeds on “submerged and floating fruits and disperse the seeds when they defecate”.

Given that some Amazonian fish can travel considerable distances, there is potential for dispersing offspring far and wide from the parent plant (Michael Horn et al., 2011; Matt Kaplan; Bianca Weiss et al., 2020). And, “It is thought that at least one plant species (the palm Bactris glaucescens) relies exclusively on pacu for seed dispersal” (quote from here) (Mauro Galetti et al., 2008).

Having had preconceptions challenged, and myths busted above, with omnivorous piranhas* and vegetarian pacu, maybe the next item will be more straightforward. Surely, everyone knows that leopards – like lions and other members of the cat family – are not only carnivores (Kenneth Carpenter et al.), but are obligate carnivores (Margaret Gates; Jim Scott). Think so? Are you sure? Hmmm, read the next post, ‘Unlikely vegetarian vertebrates Part 2’…

* Although this blog post showcases this newly-described pacu species, the scicomm item relating to its discovery does point out that ‘pacu’ is “the common name usually used for the piranha’s vegetarian relatives”. In other words, news of a vegetarian piranha-like fish isn’t completely new news. It’s just news that’s new to Mr P Cuttings – and maybe several of this blog’s readers(?) Equally new to Mr Cuttings was the fact that piranhas are considered to be omnivores (Kim Rutledge et al.) – rather than strictly carnivores – because they will eat plant material in addition to meat (Engrid Barnett; Lydia Smith; Kawkab Nadim). And I’ve even discovered that there’s an entry in Encyclopedia Britannica entitled ‘Vegetarian Piranhas’ (Sy Montgomery).

** Arguably, it’s nice to know that all fish that look like piranhas are not in fact piranhas. But, reading that “Amazonian piranhas and their relatives … are renowned for being difficult to tell apart as they change appearance throughout their lifetime”, one does wonder if Sauron – the fish – might actually be a shape-shifting [like its Lord of the Rings’ namesake, Sauron ‘the not very nice’ (Leon Miller)], diet-fluid creature that does also eat meat. Maybe Myloplus sauron is in fact a ‘wolf in sheep‘s clothing’. It’s also worth adding that the paper by Valéria N. Machado et al. (2024) deals purely with matters of a taxonomic nature, the only evidence for the new species’ herbivorous nature is their statement that, “The species feeds most [NB, not solely] on plant material being categorized as herbivore (Andrade et al., 2019)”.

All of which underlines my view that I’m not sure I’d like ‘sauron’ to be added to the flock of fishy feet-feeders in the local fish pedicure business. But, considering all the warnings about this treatment (e.g. here, Michelle Reynolds, and Grace Gallagher), one probably shouldn’t be using a fish pedicure anyway.

*** Although a diaspore (or ‘disseminule’) can be defined as ‘a reproductive plant part, such as a seed, fruit, or spore, that is modified for dispersal’ (Hans Lambers), the definition is usually broadened to include any plant part that could result in the dispersal of a plant and establishment of a new individual (Scott Zona & Cody Coyotee Howard, 2022).

REFERENCES

[In an attempt to improve narrative flow, fuller citations for scientific articles have been removed to this new section [thank you, Chris!] – do let me know if this move helps readability.]

Jill Anderson et al., Proc. R. Soc. B 278: 3329–3335, 2011; http://doi.org/10.1098/rspb.2011.0155

Andrade et al., Neotropical Ichthyology 17(4): e190026, 2019; doi: 10.1590/1982-0224-20190026

Mauro Galetti et al., BIOTROPICA 40(3): 386–389, 2008; 10.1111/j.1744-7429.2007.00378.x

Michael Horn et al., Acta Oecologica 37(6): 561-577, 2011; https://doi.org/10.1016/j.actao.2011.06.004 [https://www.sciencedirect.com/science/article/pii/S1146609X11001044]

Valéria N Machado et al., Neotropical Ichthyology. 2024; 22(1):e230095; https://doi.org/10.1590/1982-0224-2023-0095

Jan Mol, Studies on Neotropical Fauna and Environment 41(3): 189–195, 2006; https://doi.org/10.1080/01650520600630683

Bianca Weiss et al., Tropical Conservation Science 9(4), (1 January 2020); https://doi.org/10.1177/1940082916676129

Scott Zona & Cody Coyotee Howard, Flora 287, 2022, 151989; https://doi.org/10.1016/j.flora.2021.151989