A researcher from the Kobe University Graduate of Science in Japan has found evidence of how crickets disperse seeds for the orchid Apostasia nipponica—shedding light on seed dispersal on orchids and illustrating orthopterans as dispersal agents.
Associate Professor Suetsugu Kenji noted the novel method by which crickets and camel crickets disperse the seeds of the orchid species. His findings were published in the latest edition of Evolution Letters.
A Novel Seed Dispersal Method, From Invertebrates
In the study by Kenji, he noted that this report on seed dispersal sheds light on two of its main ingredients—crickets, which are invertebrates, as dispersal agents, and the seed dispersal mechanism affecting Orchidaceae, or the orchid family. The paper argues that the most common understanding is that wind dispersal remains the dominant strategy.
To capture this unusual seed dispersal method, Kenji conducted observations of the orchid species, directly and through the use of time-lapse photography and investigated the viability of seeds that pass through the digestive tracts of the crickets—Eulandrevus ivani, and the camel cricket, or Diestrammena yakumontana.
Kenji conducted the study in the forests of Yakushima Island, Kagoshima Prefecture, in the southern part of Japan. He found out that crickets consume the fruit of the orchid and defecate a viable seed. He noted that similar results were observed over several years, implying that stability of the mutually beneficial arrangement.
In the study, the Kobe University associate professor also noted that the seeds of A. nipponica are coated with a "lignified tissue," which most likely protects the seeds from being digested while inside the crickets. Furthermore, though both species of cricket are not capable of flight, the directional transport of the seed is done through the invertebrates' remarkable leaping abilities.
Kenji noted that whether "seed dispersal by orthopteran frugivores," such as the cricket and the camel cricket, is common in Apostasioideae requires further study.
The Importance of Seed Dispersal
In plant ecology, seed dispersal is a necessary process, mainly because of its role in the evolutionary process of plants. Seed dispersal, as noted in the study, has become a coevolved mutualistic relationship. The plant embeds its seeds in an edible, nutritious fruit. This, in turn, is plucked and eaten by a dispersal agent, mostly animals like birds and mammals, with the seeds carried far from the tree.
Through this symbiotic partnership between the plant and the agent, directional and efficient seed dispersal is ensured compared to random and natural factors like wind and water. Animals that disperse seeds, however, are not limited to birds and mammals, as reptiles and fishes have also been known to consume fruits and transport seeds.
However, unlike other families of plants, the more than 25,000 species of orchids are mostly heterotrophic. In its early life, an orchid takes its nutritional requirements from fungi before it sprouts leaves that support photosynthesis. Orchid seeds, unlike those of other plants, contain minimal reserves. It makes up for it with its dust-like appearance and sheer numbers.
Wind dispersal as the primary agent is credited to the small and light structure of the orchid seeds. They also have large air spaces that make them easier to travel with the wind.