Bug’s Color is Warning for One Predator, Invisible to Another

The Hibiscus Harlequin Bug (Tectocoris diophthalmus) would seem to be in a bit of a pickle. It has to avoid two different predators with two different defenses that seemingly contradict each other. But the bug has an elegant solution and makes its brilliant, beautiful shell pull double duty in a way that we can’t easily see. 

One predator the bug has to deal with is birds, which will try and eat them. But birds learn that's a bad idea pretty quickly: The harlequin bug is related to stinkbugs and is loaded with chemicals that birds seem to find disgusting once they actually get a taste. After just one or two run-ins, a bird will be conditioned to avoid the bugs. This isn’t the case for one of the harlequin’s other predators, though. Mantises seem to have no problem with the way harlequins taste, and will eat them with no second thoughts. 

To deter birds, the harlequin would do well to advertise that fact that it tastes bad with a warning signal. This is called aposematism, and often shows up in animals in the form of conspicuous colors or patterns (for example, the various bright shades of poison dart frogs). Since their flavor isn’t a turn off to mantises, the harlequin's best bet is to hide from them entirely with camouflage. There’s the rub: To stay out of both birds’ and mantids’ stomachs, the harlequin bug needs to be both aposematic and cryptic, conspicuous and inconspicuous, at the same time.  

How can it do that? Well, what’s conspicuous and what’s not is in the eye of the beholder. The same thing can help the harlequin stand out or hide, depending on the animal that’s looking at it and how that animal’s visual system works. 

For the harlequin bug, the trick lies in the color orange. The bug’s shell is pale to bright orange all over and sometimes its back is spotted with iridescent blue-green patches. To birds, with their sharp eyes and good color vision, an orange bug sitting out on a green leaf is hard to miss, and the speckles help them stand out even more. At the same time, an orange bug on a green leaf is actually hidden from mantises. This is because the mantid visual system is much different than a bird’s or a human’s. Their color vision isn’t very good and the world as they see it is pretty monochromatic. They’re sensitive to green, but orange and red don’t stand out all that well. They rely on movement and differences in brightness to differentiate objects. Thus, an orange harlequin bug not doing much else to draw attention to itself won’t stand out, to the mantid’s eye, from a leafy green background. 

By donning the right color, the harlequin bug can have it both ways and advertise its defenses to one predator while camouflaging itself from another.  

A pair of Australian biologists, Scott A. Fabricant and Marie E. Herberstein, found this out when they modeled how plain orange and spotted harlequin bugs would look to a mantis’ eye. Their model showed that orange bugs were basically indistinguishable from the background, while the speckled bugs stood out a little more. Live mantises, meanwhile,  showed that they could detect the spotted bugs from about a foot away but had to be right on top of the plain orange ones before they noticed them. In a second experiment, mantises were placed on a branch that forked and led to two leaves, one with a plain bug on it and one with a spotted bug. The mantises went after the spotted bugs more often, but when the choice was between a plain orange bug and an empty leaf, the mantises acted like there was no food at at all. 

While orange hides the harlequin bug from mantises, its shiny spots can still give it away.  The researchers think that this flaw in its camouflage explains the variation in the bug’s appearance across its range in Australia. In areas where mantises are its main predator, the bug may be under pressure to maintain a pale orange with little or no spotting, but is free to sport a brighter shell with more, larger spots in areas where birds are the bigger concern. Where the two predators overlap, a little spotting and the right shade of orange can help it both be seen and hide in plain sight. 

Andreas Trepte via Wikimedia Commons // CC BY-SA 2.5
Climate Change Has Forced Mussels to Toughen Up
Andreas Trepte via Wikimedia Commons // CC BY-SA 2.5
Andreas Trepte via Wikimedia Commons // CC BY-SA 2.5

Researchers writing in the journal Science Advances say blue mussels are rapidly evolving stronger shells to protect themselves against rising acid levels in sea water.

Bivalves like mussels, clams, and oysters aren’t good swimmers, and they don’t have teeth. Their hard shells are often the only things standing between themselves and a sea of dangers.

But even those shells have been threatened lately, as pollution and climate change push the ocean's carbon dioxide to dangerous levels. Too much carbon dioxide interferes with a bivalve’s ability to calcify (or harden) its shell, leaving it completely vulnerable.

A team of German scientists wondered what, if anything, the bivalves were doing to cope. They studied two populations of blue mussels (Mytilus edulis): one in the Baltic Sea, and another in the brackish waters of the North Sea.

The researchers collected water samples and monitored the mussel colonies for three years. They analyzed the chemical content of the water and the mussels’ life cycles—tracking their growth, survival, and death.

The red line across this mussel larva shows the limits of its shell growth. Image credit: Thomsen et al. Sci. Adv. 2017

Analysis of all that data showed that the two groups were living very different lives. The Baltic was rapidly acidifying—but rather than rolling over and dying, Baltic mussels were armoring up. Over several generations, their shells grew harder.

Their cousins living in the relatively stable waters of the North Sea enjoyed a cushier existence. Their shells stayed pretty much the same. That may be the case for now, the researchers say, but it definitely leaves them vulnerable to higher carbon dioxide levels in the future.

Inspiring as the Baltic mussels’ defiance might be, the researchers note that it’s not a short-term solution. Tougher shells didn’t increase the mussels’ survival rate in acidified waters—at least, not yet.

"Future experiments need to be performed over multiple generations," the authors write, "to obtain a detailed understanding of the rate of adaptation and the underlying mechanisms to predict whether adaptation will enable marine organisms to overcome the constraints of ocean acidification."

University of Adelaide
Scientists Find Potential Diabetes Drug in Platypus Venom
University of Adelaide
University of Adelaide

The future of diabetes medicine may be duck-billed and web-footed. Australian researchers have found a compound in platypus venom (yes, venom) that balances blood sugar. The team published their results in the journal Scientific Reports.

So, about that venom. The platypus (Ornithorhynchus anatinus) may look placid and, frankly, kind of goofy, but come mating season, the weaponry comes out. Male platypuses competing for female attention wrestle their opponents to the ground and kick-stab them with the venom-tipped, talon-like spurs on their back legs. It’s not a pretty sight. But it is an interesting one, especially to researchers.

Animal venoms are incredible compounds with remarkable properties—and many of them make excellent medicine. Many people with diabetes are already familiar with one of them; the drug exenatide was originally found in the spit of the venomous gila monster. Exenatide works by mimicking the behavior of an insulin-producing natural compound called Glucagon-like peptide 1 (GLP-1). The fact that the lizard has both venom and insulin-making genes is not a coincidence; many animal venoms, including the gila monster’s, induce low blood sugar in their prey in order to immobilize them.

It’s a good strategy with one flaw: GLP-1 and compounds like it break down and stop working very quickly, and people who have trouble making insulin really need their drug to keep working.

With this issue in mind, Australian researchers turned their attention to our duck-billed friends. They knew that platypuses, like people, made GLP-1 in their guts, and that platypuses, like gila monsters, make venom. The real question was how these two compounds interacted within a platypus’s body.

The researchers used chemical and genetic analysis to identify the chemical compounds in the guts and spurs of platypuses and in the guts of their cousins, the echidnas.

They found something entirely new: a tougher, more resilient GLP-1, one that breaks down differently—and more slowly—than the compounds in gila monster spit. The authors say this uber-compound is the result of a "tug of war" between GLP-1’s two uses in the gut and in venom.

"This is an amazing example of how millions of years of evolution can shape molecules and optimise their function," co-lead author Frank Gutzner of the University of Adelaide said in a statement.

"These findings have the potential to inform diabetes treatment, one of our greatest health challenges, although exactly how we can convert this finding into a treatment will need to be the subject of future research."


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