Stick insects look just like the naturally-occurring sticks and twigs that surround them in a forest. This is an aesthetic feature that helps them evade predation more effectively than other insects.
However, a paper published in the journal Ecology this week by researchers from Kobe University highlights an unexpected irony concerning this innate camouflage capability. In particular, it underscores how stick insects may ensure their own species’ survival whether they fall victim to predation or not.
Image Credit: Kobe University
Just like anything else a bird eats, the stick insect passes through the animal’s digestive tract. But herein lies the kicker; the eggs that reside within the stick insect’s body at the time can sometimes pass entirely through the bird’s digestive tract unscathed.
When it comes time for the bird to defecate, these now undigested stick insect eggs occasionally find themselves in places where the insects never would have ventured otherwise and may even hatch, depending on several factors. That said, birds may effectively drive stick insect territory expansion by spreading their fertilized eggs into new regions.
Citing the study, in which the researchers fed three different kinds of stick insects to brown-eared bulbuls, between 5 and 20 percent of the insects’ eggs survived the birds’ digestive tracts. Furthermore, a smaller percentage of those hatched successfully despite everything they had been through.
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Notably, a wide variety of plants exploit this cycle by hosting colorful and tasty fruits that animals can’t resist. As animals snag and take off with the goods, the seeds inside them become dispersed across the landscape and enable widespread distribution for an otherwise immobile organism.
Whether this is an intentional adaptation on the stick insects’ part or an unlikely circumstance of luck, it seems that stick insects have the reproductive advantage in it all.
"Our next step is analyzing the genetic structure of stick insects," explained lead researcher Kenji Suetsugu.
"Based on this we'd like to investigate whether similar genetic structure of stick insects can be found along birds' migration flight paths and whether there are genetic similarities between stick insects and plants that rely on birds for seed distribution."
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From this, the researchers would be able to discern whether birds impact stick insect territory expansion at all. It should be exciting to learn whether the results validate these claims.