It is generally believed that when insects are eaten by birds, they and their unborn offspring have no chance of survival. However, a team of Japanese researchers hypothesized that the eggs in insect bodies can pass undigested through birds. They tested this hypothesis with stick insects, which are known for their hard eggs, and found that some eggs are eliminated intact and successfully hatch. Stick insects can not travel very far, so birds can be eaten and even increase their habitat.
The research team was led by Associate Professor Kenji Suetsugu (Kobe University Graduate School of Science), Associate Professor Katsuro Ito (Kochi University) and Associate Professor Takeshi Yokoyama (University of Agriculture and Technology of Tokyo). The results were published on May 28 in the online edition of Ecology .
Plants can not move and have therefore developed various ways to distribute their seeds. The most common is seed dispersal by animals that eat the fruits and excrete the seeds altogether. For many birds, insects are also one of their main food sources. If insect eggs pass undamaged through birds, we could say that insects, just like plants, use the birds as a means of long distance transport.
To achieve this, several conditions must be met: the eggs must be strong enough to pass undamaged through the digestive tract, the insects born from these eggs must be able to survive by themselves, and the eggs must be viable without fertilization. Stick insects meet these conditions. The insect eggs are fertilized only shortly before laying the eggs, using sperm stored in the seminal vesicles. However, females of many stick insect species are parthenogenous so that they can produce viable eggs without fertilization. Plant stalks also have a very hard shell. They lay these eggs by sprinkling them on the surface of the soil, and after hatching the young find suitable plants for food themselves.
The research team fed eggs from three species of stick insects to brown-eared bulbul (one of the major bird-eaters) stock insects). In all three species between 5 and 20% of the eggs were eliminated intact. They also confirmed that eggs from the bird's excrements have successfully hatched for one species. Although eaten by birds, the unborn insects survived. Adult stinging insects are often eaten by birds, and the stomachs of adult female stinging insects are always filled with eggs, so this way is a potential way to broaden the spread of hives.
Many plants have eye-catching, nutritious fruits that develop a strategy to appeal to animals, while stick insects are easy and hard to spot. But even if they do not actively feed on insects that have low mobility, such as stick insects, eating birds is a way to expand their habitat. Many relatives of stick insects have spread over islands that are not connected to the mainland. The ability of low-mobility animals to successfully travel long distances is a topic that confused Darwin.
"Our next step is to analyze the genetic structure of rod insects," commented team leader Professor Suetsugu. "Based on this, we want to investigate whether a similar genetic structure of rod insects can be found along bird flight paths and whether there are genetic similarities between rod insects and plants that depend on birds for seed distribution." These studies will show that the spread of stick insect eggs by birds can affect the distribution and gene flow of rod insects.
Materials provided by Kobe University . Note: Content can be edited for style and length.