Sea slugs don’t shy away from the fish, crabs, sea turtles, or even other sea slugs that might want to take a bite out of them. Instead, the brightest and most patterned sea slugs are more active during the day. The sun’s rays are critical in enhancing the slug’s ability to ward off predators with its flamboyant appearance. The findings are detailed in a study published April 15 in the Journal of Animal Ecology.
A team from the University of Queensland in Australia analyzed sea slug coloration across 45 eastern Australian species. Poisonous animals like some nudibranchs–aka sea slugs–and poisonous dart frogs have evolved very vivid hues.
“Sea slugs use bright, contrasting colour patterns to send messages to potential predators like ‘Don’t eat me, I’m poisonous,’” study co-author and visual ecologist Cedric van den Berg said in a statement.
The team used special cameras and software to simulate what the sea slugs would look like to a potential predator. They focused on finding any shared properties in color patterns among sea slug species, which directly correlate with daytime activity. The researchers then used sophisticated statistical methods to combine close to 160 different varieties of color patterns into one single fingerprint. This fingerprint captured the difference in appearance of species more active during the day or night.
They found that sea slugs use bold visual signals like brightly colored spots, thick stripes, or enhanced body outlines to advertise that they are equipped with stinging cells, chemicals, or other defenses. And daylight is linked to making those signals stronger.
“These tactics are strongly linked to being active during daytime when there’s enough light for these signals to function,” van den Berg said. “It makes sense for these species to avoid the risky and potentially costly experience of being nibbled on or even ingested by a predator whether they are toxic or not. Their bold appearance also educates predators by being distinct from other animals while also increasing the chances of being remembered.”
According to the team, the more nocturnal sea slug species don’t need to evolve bright colors and patterns aimed at signaling to potential predators. Nocturnal sea slug predators are less likely to use their vision to hunt overnight, when the senses of touch and smell are more important.
The team hopes that this new research will lead to more work on understanding how defensive coloration evolved in marine species.
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