Sea Slug Egg dilemma

We recently did a survey of a variety of dorid sea slug eggs to emphasize their extremes in color and shape. This collection of photos shows that shape and color vary markedly, but it did not get into an interesting phenomenon documented by Marcel. That is - what causes the eggs of a single species to vary between on another.

Many times, we have discussed how the color of a slug's egg mass is heavily depended upon the food it eats, but what about a single species producing different colored eggs?

In Marcel's photo of a pair of Doto ussi, above, we see what appears to be two recently laid egg coils, typical of this species, but of different colors - white and yellow. These two were obviously laid by the two slugs, but why the different colors? We normally think of the color of D. ussi eggs as yellow.

Thinking back to the explanation that egg colors are dependent on the foods the slug eats, may give the answer. Looking closely at the pair of slugs I noticed that they too are slightly different shades of grey, one being lighter than the other. Might they have been foraging on hydroids of different colors? If so, it is not out of the question that they could provide different color pigments to their respective egg masses.

I think so, and one more hint might be that the lighter individual is crawling on the white eggs, while the darker is crawling on the yellow eggs. Crawling over newly laid eggs is a process thought to help secure the eggs to the substrate.

It's a wild guess I know, but it sure is suggestive that the lighter animal, for whatever reason, has laid the white eggs, while the darker is parent to the yellow mass. Another twist to the old egg game.

Marcel Tanke presently again lives in his native country, the Netherlands. He started diving during the 14 years that they lived in China and Korea. Marcel has BSAC Instructor diving level. Diving took him pretty much all over Asia and many other places. Nudibranchs became his main interest after several trips to the Philippines and Indonesia. Marcel is still using a "point and click" camera, currently Olympus TG-6.

Send Marcel email at marceltanke52@gmail.com