This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Well before I start collecting coats, keys or shoes, my dog always knows when we're about to leave. By picking up on subtle cues, he anticipates our next movements, reminding me he's smarter than he often shows.
But anticipation isn't always about brains. Our new research reveals that even an animal with no brain at all can anticipate what's coming next. Sea sponges are among our most distant animal relatives, lacking all the familiar sensory apparatus.
They have no brain, no nerves and no neurons. Being little more than well-organized collections of specialized cells, they're pretty much as simple as animal life gets. And yet, sea sponges carry out a wildly complicated process much like a backward version of a caterpillar's transformation, from squishy grub to free-flying bug.
Starting out as free-swimming larvae, about half the size of a chia seed, they transform themselves into shapeless, spongy lumps cemented in place. My colleagues and I have researched this miraculous metamorphosis for years. We have discovered that environmental cues play a very important role.
For instance, swimming larvae are all looking for a suitable alga—the perfect spot to settle and make their forever home. But in 2020, our group found that if we prevented larvae from experiencing sunset, they never settled, even if they were near five-star algae. How could missing sunset disrupt such an important event in a young sea sponge's life?
In a new study published in eLife, our team shows that sunset is a critical signal that preemptively tells sea sponge larvae to "get set." While the larvae are still freely swimming, long before settlement is imminent, sunset triggers modifications to parts of their DNA. Sponge larvae anticipate their big moment by preorganizing parts of their DNA to be primed and ready for "go" time. By measuring changes in the animals' DNA (which carries their genetic material) and RNA (which shows which genes are switched on), our team captured genetic freeze-frames from before and during the transformation.
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