Unreliable colour patterns in seaslugs

MSU's blog | Created 2 years ago

As part of the Net Conservation Benefits Fund project, we have discovered 18 new species of Chromodoris nudibranch sea slugs. In our paper (Flexible colour patterns obscure identification and mimicry in Indo-Pacific Chromodoris nudibranchs; Mol. Phylo. Evol. 124, 27-36) we show that many of these new species have very similar colour patterns to already described species, which can be confusing when trying to identify species. This finding suggests that these colour patterns are not very reliable. However we now have a much better idea of where many of the described species occur in the Indo-Pacific. We also found that some ‘Pacific’ species occur in the Indian Ocean in Western Australia. This group of nudibranchs was also thought to occur only in shallow water (less than 30 metres), but we found them at depths of up to 100 metres on mesophotic (low light) reefs.

Another important finding from our work was that two species appear to be mimicking the colour patterns of other locally abundant species. We found that the colour patterns of these mimic species vary dramatically across their range in the Indo-Pacific (see figure below which shows geographic colour variation in C. colemani). Mimicry has been found in another group of chromodorid nudibranchs (Felimida), but this is the first time it’s been documented in Chromodoris. Chromodoris nudibranchs are also really interesting because they feed on sponges and are able to store the toxic chemicals from sponges into specialized glands, making them toxic. In the future it would be interesting to determine how mimicry and toxicity are related in these nudibranchs.

There is still a lot more to be done to better understand the evolutionary relationships in Chromodoris, so we are continuing this work by using large amounts of data from across the genome to determine how different species of Chromodoris are related to one another. Watch this space!

- Kara Layton


graphical abstract

Map showing distributions of different colour morphs.
Image copyright WA Museum