A Sea Slug Mating Ball in The Philippines - Observation of the Week, 8/20/19

Our Observation of the Week is this group of Hypseldoris iba nudibranchs, seen in The Philippines by @notdunroamin!

“In 2013, my husband and I decided to sell everything and travel,” explains Danila Mansfield, who goes by notdunroamin on iNaturalist. “We joined a number of citizen science projects, in Belize, South Africa and Timor-Leste, and very much enjoyed observing and assisting in conservation efforts.”

While she was always interested in nature, Danila says “my husband Chris, with his much deeper interest, really sparked more in me. We've taken several holidays focussed on nature and wildlife in a variety of places, and since we started scuba diving in 1996, our nature interests have become very marine focussed.” She recently took part in an underwater photography class in The Philippines, which is where she came across the nudibranchs you see above. But it didn’t start out that way.

“On one of my early dives during the course, I was observing and photographing a single Hypseldoris...adjusting my position and my strobe, and then I became aware that a second Hypseldoris was trundling along towards number 1,” recalls Danila.

When number 2 joined number 1, I took a few shots, then spotted number 3 beginning to gain ground. 1 and 2 were on a rock a few inches higher, and 3 had to climb up the rock face to join them. Then I literally fell about laughing, as I spotted number 4 gathering speed behind 3, and 4 actually barged past 3 and climbed up the rock to join 1 and 2, before 3 had made it! Finally 3 joined in, and there's the nudi party! By this point 2 or 3 other divers had joined me to see what I was so closely watching, so we shameless voyeurs continued to watch and enjoy the party! [See video slideshow here]

As I started looking into the natural history of this slug, I found out that it was described just last year by the California Academy of Science’s (CAS) own @tgosliner and @rebeccafay (among others). I reached out to Dr. Gosliner about the observation and this genus and, after adding his ID to the observation ("[H. iba] have a higher body profile and a more rounded hind end of the body than in H. variobranchia.”), he told me

The Hypselodoris group has a remarkable diversity of species and we have found that closely related species have similar but distinct color patterns. These are often cases of Mullerian mimicry where distasteful species often adopt a similar color pattern…

Often times mating individuals exude chemicals (pheromones) that attract other individuals and you will often see a mating aggregation like this. It is thought that if conditions are favorable for two individuals to decide to mate that it will be good for others in the area to also begin mating.

And according to CAS’s press release, two different looking individuals of this particular species were observed mating, and were originally thought to have been different species before genetic work was used to determine they were in fact, of the same species.

<img src="https://static.inaturalist.org/wiki_page_attachments/1323-original.jpg"/ style="width: 100%"

“I've only just become aware of iNaturalist, through a friend in a Marine Creatures group on Facebook,” says Danila (above). “I'm looking forward to checking out the observations, and trying to ID my own underwater photos.”

• by Tony Iwane
  

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  - Danila and her husband blog about their travels, check it out!
• Here’s a video of @tgosliner talking to an audience of visitors at CAS, and a short video about his passion for sea slugs.
• @rebeccafay also talked with Academy visitors about the Farallone Islands, and she doles out sage tidepooling advice here with @kestrel.

Posted on 21 de agosto de 2019, 04:08 AM by tiwane