Top Story: March 7, 2014

Happy Oysters, Tricky Butterflies

butterflies, mimicry, mimics, swallowtail, heliconius, durrell kapan, oysters, farming, sensors, genes, genetics, supergene, doublesex

By Molly Michelson

Happy Oysters
Sensors the size of credit cards will allow farmers in Tasmania to know whether their oysters “feel like a room without a roof,” terrible, or just so-so, according to a recent article in New Scientist. The small monitors, created by Sense-T, an Aussie-government funded organization, keep track of an oyster’s heartbeat, shell opening and closing, and its depth. The sensor also observes the marine habitat the oyster occupies—measuring the salinity, temperature, oxygen levels, and pollutants in the water.

According to information on Sense-T’s website, “The real-time data about the environment and how oysters react to changes can be used to optimize production.” And New Scientist describes how the sensor can monitor the bivalve’s growth, “Farmers must periodically take oysters out of their baskets to see how much they have grown. This process is time-consuming and disruptive. The hope is that a handful of strategically placed sensors could do the job instead.” The group is also building sensors for abalone.

Tricky, Mimicky Butterflies
We’ve reported on mimicry in butterflies before (here and here), and this week brought another publication on the genes that allow this amazing phenomenon. While the previous studies looked at Heliconius butterflies, the current study looks at Papilio, or swallowtails. Both genera use mimicry in their wing colors and patterns to ward off their avian predators.

While Heliconius are Mullerian mimics, meaning they are all toxic and simply find safety in numbers, Papilio are trickier, Batesian mimics. They actually have no toxicity and are just pretending in order to keep the birds away. Both use supergenes for this mimicry in coloration and pattern—a group of neighboring genes is selected to create the wing display.

Surprisingly, however, the researchers studying the Papilio butterflies discovered that one gene controls this mimicry supergene, basically turning it on or off. The gene is called doublesex, and true to its name, it determines the gender of species in insects and other organisms. Since only select females in Papilio are mimics, this makes sense, if only partially.

“Conventional wisdom says that it should be multiple genes working together to control the whole wing pattern of a butterfly, but in this case, it’s just this one,” says Marcus Kronforst, of the University of Chicago and senior author of the study. “This single gene that controls sexual differentiation has been co-opted to do a totally new job.” The great writer Ed Yong describes it this way, “It’s like finding that the light in your bedroom also starts your car.”

We asked the Academy’s Heliconius researcher, Durrell Kapan, about the findings. “In Batesian mimicry, the butterflies are true free-loaders, and benefit from stealing the warning-signal of a well-defended toxic model species.  Their safety is lost if they are too numerous, so one of outcomes for Batesian mimetic species can be thought of as a ‘trick to hide in different coats.’  In this case, natural selection has found a balance, with over half of the butterflies are non-mimetic, all of the males and some of the females, the remaining females wear the color-pattern of distantly related toxic swallowtails species.”

Like the discoveries in the Heliconius butterflies, this genetic research could shed light on other organisms. “Across animal species, we find examples where polymorphisms occur in one sex or the other,” says lead author Krushnamegh Kunte, of the National Center for Biological Sciences in Bengaluru, India. “We’re studying it in the context of mimicry, but it’s possible that this sex differentiation pathway that we found in butterflies could be a pathway that’s more broadly important for sex-limited polymorphism.”

Image: Wei Zhang

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