Found the Smallest Animal that Transports Seeds... with its Poop
Endozoocory, the dispersal of seeds through the digestive tract of animals, is a fundamental process for plant reproduction. Although it has been widely studied in vertebrates, many scientists have hypothesized that invertebrates may also play a significant role in this process, especially for plants with very small seeds. Heterotrophic plants, which depend on fungi or other plants for at least part of their development, often produce dust-like seeds, lacking endosperm and with minimal energy reserves. An example is the genus Monotropastrum, and in particular Monotropastrum humile, which is widespread throughout East Asia, from the Himalayas to Japan.
In the past, it was believed that the cockroach Blattella nipponica was the main seed disperser for M. humile, thanks to inconspicuous fruits that discourage vertebrates, fruits that mature together with the emergence of cockroaches, and small, resilient seeds. However, the geographical distribution of B. nipponica does not completely coincide with that of M. humile, suggesting that other invertebrates might be involved.
But how to discover who the true seed disperser was? During the fruiting season of M. humile, a group of researchers conducted field studies in Sapporo, in a temperate forest in northern Japan. They placed digital cameras near the plants close to the fruits, recording who was consuming them. After identifying the potential frugivores, they captured some specimens and fed them a mixture of M. humile fruits and seeds. Then, the researchers observed the fecal pellets of each animal to see if the seeds remained intact. Why? An intact seed means they had found a potential seed transporter.
The results revealed that Porcellio scaber, the common rough woodlouse, only 8-11 mm long, can ingest and disperse the seeds of M. humile, setting a new record as the smallest internal seed dispersal agent in the world. Despite its small size, P. scaber proved to be an efficient seed disperser, challenging traditional ideas about dispersal mechanisms.
This discovery highlights the importance of various seed dispersal agents. Among other species related to M. humile, camel crickets, earwigs, and lice were found. The seeds of M. humile are small enough to be ingested by a variety of invertebrates, which seem to play a crucial role in the seed dispersal of this plant. Similar mechanisms have been observed in other plants with small seeds, suggesting that seed dispersal by invertebrates may be more common than previously hypothesized. These results invite us to reconsider the importance of all creatures, regardless of their size, in the health and sustainability of ecosystems.
