Colour forms of Hypselodoris maculosa

May 18, 2007
From: Colin Ogden

Hi Bill,
I know this discussion dates back to 1999, but I would like to add one more query to the discussion. When different colour forms of a species exist in the same place, will the different colour forms mate with each other or will they mate only with the same colour form. We have both colour forms of the Hypselodoris maculosa here, the typical form is more abundant (upper photo). We occasionally find the colour form as in the lower photo. This photo shows 3 of the unusual form together. It appears that the 2 nudis in the growth are just about to, or have just completed their mating, while the third nudi is arriving on the scene. Also the unusual colour form appears to normally be about 5 to 10 mm bigger than the normal one.

Locality: Sodwana Bay, 22 matres, South Africa, Indian, 18 February 2007, reef. Length: 30mm. Photographer: Colin Ogden.

Regards
Colin

scubao@iafrica.com

Ogden C. M., 2007 (May 18) Colour forms of Hypselodoris maculosa. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/19512

Dear Colin,
I am happy to keep any discussion going as long as it takes. Colour in animals is a very interesting and complex topic. To keep this discussion concise, there are two major types of colour variation we can find in a species. The first is a gradual change from one colour pattern to another which is what we see in most chromodorids. Its also the sort of thing we see when people of two racial groups marry - their children show traits from both their mother and their father. The other main type of colour differentiation we find within species is called polymorphism and is where there are two or more quite distinctly different colour patterns or morphs within a species. The colour of the offspring of matings between animals from different morphs is determined by quite precise genetic rules, but whatever the colour is it will be one of the distinct morphs and not a mixture of the parent's colour patterns. Many butterflies are polymorphic like this, but I am not convinced there are any polymorphic nudibranchs.

Noumea haliclona from southeastern Australia almost fits the bill, but in this case the different morphs seemed to be geographically separate, which brings up the question of whether we should consider them subspecies rather than colour morphs.

None of this really answers your question about these colour 'forms' of Hypselodoris maculosa. The biggest problem is that we really don't know enough about them to be sure they are the same species. Often the anatomical differences are quite small and very few species have been studied in any detail. That is one reason I keep asking for photos of them 'doing things' because a different egg ribbon, or egg size, or food choice, might be a clue to differences we do not even suspect.

Best wishes,
Bill Rudman

Rudman, W.B., 2007 (May 18). Comment on Colour forms of Hypselodoris maculosa by Colin Ogden. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/19512

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