zanthoxylum

(writing in progress)

Title: Salutary treatment for seed-dispersing animals

Subtitle: Certain plants have seeds dispersed by animals without the usual rewards of sugary fruit-pulp or oily arils. The real payment is vital although it seems intangible.

Plants attract seed-dispersing animals by offering packages of food energy, such as sugary fruit-pulp or oily arils. Such packages fuel the transportation of the seeds. Plants that achieve dispersal by means of unrewarding, but conspicuous and appealing, packaging of the seeds do so simply by means of deception. Genera such as Zanthoxylum exploit the hardwired response of animals to conspicuous objects that mimic real, edible fruits.

Surprisingly many plants achieve seed-dispersal by attracting frugivores without providing any substantial reward for the animals to swallow and disperse – whether by defecation or regurgitation – the seeds in a viable condition. Indeed, such a variety of birds and mammals disperses the seeds of widespread genera such as Zanthoxylum (initially brightly-coloured capsules which dry and split instead of ripening) that the attraction to their fruits could not be sustained were it based merely on false advertisement (i.e. deceptive mimicry).

There must be a more basic reason. A clue to the real reward is the medicinal value of plants to humans.

The genus Zanthoxylum is, for example, renowned for various medicinal effects including analgesic, anti-oxidant, anti-microbial and anti-inflammatory. Extracts of Zanthoxylum also control parasites such as protozoans (which cause leishmaniasis and trypanosomiasis) and helminth worms. This genus is also well-known for its production of various alkaloids.

One of these, sanguinarine, is used in commercial toothpastes and oral rinses because even traces of this toxin inhibit bacterial growth. Such strong and diverse medicinal properties suggest that plants such as Zanthoxylum pay birds and mammals for dispersal by supplying a dispensary of medicinal formulations from the deceptively dry and indigestible fruit-walls, capsules, and seed-coats.

Although the medicinal effects of these substances may be subtle, similar subtlety is acknowledged in plants which reward seed-dispersing animals with fruit-pulp that contains health-enhancing vitamins.

(writing in progress)

Posted on June 10, 2022 08:04 AM by milewski