May 28, 2018, Kobe University
It's commonly assumed that when
insects are eaten by birds, they and their unborn young have no chance of
survival. However, a team of Japanese researchers hypothesized that the eggs
within insect bodies can pass through birds undigested. They tested this
hypothesis with stick insects, known for their hard eggs, and found that some
eggs are excreted unharmed and successfully hatch. Stick insects cannot travel
very far by themselves, so being eaten by birds could even contribute to
expanding 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 (Tokyo University of Agriculture and Technology). The findings
were published in the online edition of Ecology on May 28.
Plants cannot move around, so
they have developed various ways to distribute their seeds. The most common is seed
dispersal by animals, who eat the fruits and excrete the seeds whole. For many
birds, insects are also one of their main food sources. If insect eggs can pass
through birds unharmed, we could say that insects, just like plants, are using 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 through
digestive tracts unharmed, the insect young born from these eggs must be able to
fend for themselves, and the eggs must be viable without fertilization. Stick
insects fulfil these conditions. The insect eggs are only fertilized just
before the eggs are laid, using sperm stored within the seminal vesicle.
However, females of many stick insect species are parthenogenic, enabling them
to produce viable eggs without fertilization. In addition, like plant seeds,
stick insect eggs have a very hard shell. They lay these eggs by scattering
them on the surface of the ground, and after hatching the young locate suitable
plants for food by themselves.
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