Mating behaviour

February 25, 2003
From: Hans Tibboel

Dear Sir,
On a recent dive cruise in Myanmar I came across two different species of nudibranchs mating with each other. As I've never witnessed this before I was wondering if anybody else has ever noticed this same behaviour and if it will result in actual egglaying and offspring of the participating nudi's.
Hans Tibboel

Dear Hans,
I guess you are not talking about the spotted and unspotted forms of Chromodoris annulata you mentioned in your last message. This question has been raised recently on the Forum when I posted Phil Slosberg's photo showing typical H. bullocki and H. apolegma mating.

In general, matings between different species are very rare, and if they occur, the eggs are either in infertile, or if offspring do occur, the offspring are infertile. There are some strange exceptions amongst the plants but on the whole, mating is considered a good indication that the partners are the same species. I realise that this argument becomes a bit circular, but organisms have usually developed good morphological and behavioural mechanisms to prevent cross-species matings.

The first question I would ask is are you sure that the two animals were actually mating, and if so, how do you know they were different species?
Best wishes,
Bill Rudman

Rudman, W.B., 2003 (Feb 25). Comment on Mating behaviour by Hans Tibboel. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

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