Hermaphroditism & evolution

November 1, 2001
From: Katie Noonan

I am a high school science teacher in Oakland, California, USA. My students and I came upon gobs of sea hares in Lake Merritt (a tidal lagoon in the center of Oakland). Egg ribbons were dense around the shore. The odd thing is that sea hare breeding has not been noticed by our resident Lakekeeper in several years. The lagoon, which undergoes wild salinity changes over the year, is very saline at this time, at least 35 ppt.

We have an adult and some eggs in a tank in the classroom. The adult seems to be hanging on, eating algae and moving. The eggs are developing also. A species Aplysiopsis? was listed among Lake Merritt fauna, and I assume this is what we saw. It is about an inch long, brown with simple flaps over its back - no frills. I photographed it and will send a scan when it is developed.

Where can I find something about the evolutionary maintenance of hermaphroditism in these mass-breeding creatures?

Katie

ktnoon@aol.com

Noonan, K., 2001 (Nov 1) Hermaphroditism & evolution. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/5583

Dear Katie,
I look forward to seeing the photos. If you have one of the egg masses that would be interesting as well. If your animals are sea hares then they won't be Aplysiopsis. Although the name Aplysiopsis is very similar to the Sea Hare genus Aplysia it belongs to a quite distinct group off sea slugs called the sacoglossans which feed by sucking the cell contents from algae. If you look at the Species List and scroll down to the ORDER Sacoglossa, you will find many example of that group. You will find a species of the genus Aplysiopsis from Calfornia on the list, Aplysiopsis oliviae, and a Japanese species, for which we have better photos, Aplysiopsis minor.

I suspect from your dscription that you have a Sea Hare, but at 1 inch long (aprox 25mm), it is very small to be laying eggs considering that the two common Californian Sea Hares, Aplysia californica and Aplysia vaccaria grow to a very large size.

Now to your question about hermaphroditism. Natural selection and the maintenance of characters is an interestng topic but I don't know if it really applies to hermaphroditism in Sea Hares. There are some features which are set so deep in a species genetic makeup that change is very unlikely to occur. Hermaphroditism is a state acquired very far back in the evolutionary line to which all sea slugs and land snails and slugs belong. There has of course been debate on why hermaphroditism was acquired, but unfortunately it happened so long ago, we can only speculate about its origins in the pulmonates and opisthobranchs.
Best wishes,
Bill Rudman

Rudman, W.B., 2001 (Nov 1). Comment on Hermaphroditism & evolution by Katie Noonan. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/5583

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