Scientists discover new lineages of giant sea anemones in Japan and their surprising associations with anemones

Anemones form relationships with the sea anemones in which they live, and these associations are not accidental: some species such as the yellowtail anemone (Amphiprion clarkii) are universal and can live in almost any sea anemone, others such as the tomato clownfish (Amphiprion frenatus) are specialists. , living in only one type of sea anemone, the bubble sea anemone (Entacmaea quadricolor). The reasons for these preferences are unclear because we know very little about the genetic diversity of giant sea anemones.

Researchers from the Marine Eco-Evo-Devo Unit and Marine Genomics Unit at the Okinawa Institute of Science and Technology (OIST) and Academia Sinica in Taiwan have studied the evolutionary history of giant sea anemones in Japan.

Rio Kashimoto and others published their findings in the journal Current Biology. Their study provides a detailed analysis of the genetic diversity of the giant sea anemone (Entacmaea quadricolor) found in Japan.

Scientists have found that anemones are better at distinguishing between different populations of giant sea anemones than humans.

Through one or more sense organs, these fish identify a specific species of giant sea anemone to make their home and avoid other species. Humans, on the other hand, need to obtain samples of sea anemones and do a thorough study of their molecular data to identify individual sea anemone species. That’s exactly what OIST scientists did to better understand genetic variation among these soft-bodied marine invertebrates.

Giant sea anemones have evolved into three very different genera: Entacmaea (bubble-tipped sea anemones), Stichodactyla (carpet sea anemones), and Heteractis (magnificent sea anemones). There are currently 10 known species of giant sea anemones in the world, and seven of them live in Okinawa.

The researchers collected pieces of tentacles from all seven species. A total of 55 samples were collected in Japan at study sites ranging from southern Okinawa to north of Tokyo.

All the genes in each sample were sequenced, a technique that allowed the researchers to determine the specific genetic information contained in the RNA molecules. Using this information, they were able to construct a phylogenetic tree, a diagram showing the evolutionary relationships between species and how they evolved from a series of common ancestors.

Scientists have found remarkable genetic diversity in specimens of bubble sea anemones, identifying four unique genetic lineages – a sequence of species thought to have evolved from their ancestor.

“Within the giant bubble sea anemone (Entacmaea) species, our phylogenetic tree reveals the presence of two main groups with a common ancestor in Okinawa. The first group consists of three progeny categories, A, B and C, which are related to the yellowtail anemone as the host species. The second group, category D, is associated with the tomato anemone as a host species,” explained Ryo Kashimoto, lead author of the paper.

The researchers had observed this relationship in the wild and wanted to know if the fish could also distinguish between the two groups of sea anemones in captivity. They conducted a choice experiment using a large tank at the OIST Marine Science Station, placing one group A sea anemone at one end of the tank and one group D at the other end.

They placed either a yellowtail or a tomato juvenile anemone in the middle of the tank and recorded whether the fish chose to stay in the sea anemone or not, and if so, which group of sea anemones the species chose.

The yellowtail anemone always chose group A when choosing to stay in a sea anemone, but some fish did not choose a sea anemone. Most tomato anemones selected lineage D sea anemone, very few individuals selected lineage A, and some did not select sea anemone.

“In laboratory experiments, we observed that, in most cases, each anemone species could recognize the sea anemone lineage to which it was related in the wild, despite the fact that the clades looked the same. We also observed that these lineages did not express the same genes, especially genes for toxicity and color – sea anemones use venom for prey capture, digestion and defense and probably don’t have the same smell, which may be a key part of how anemones recognize different lineages,” Prof. Laudet, head of Marine Eco-Evo-Devo Unit, stated.

“Therefore, the anemones are able to identify different lineages of sea anemones that we humans cannot tell apart. We believe that these two major groups represent two cryptic species—species that we cannot identify by looking at them, but which are genetically distinct. “

This discovery means that the bubble sea anemone may actually be two different species hiding in plain sight, and that Okinawa and Japan are home to more marine biodiversity than previously thought.