Lake Malawi hybridization

[GTR73]

Found this article on another website discussing hybridization at Thumbi West Island, where two different variations of C. afra have occured (northern vs soutthern population). Very interesting reading:

Hybridization at Thumbi West Island

[Ged]

An excellent article.

To what extent hybridization has occurred and the reason for it taking is very interesting. Has hybridization occurred because of environmental influences i.e. the trade winds making the water cloudy or is the abundance and size of M. zebra males a factor. It does not help explain why the northern population where hybridization is the lowest that blue barring is found in more individuals. Streelman et al. suggests that this is a re-expression of a phenotype that was absent in the translocated stock. Is this an example of peripatric speciation or the founder effect.

You may also be interested in having a look at the following.

http://www.evolutionsbiologie.uni-konstanz...l.Ecol.2002.pdf

[GTR73]

Wow. So rising and lowering water levels over the years have also played a part.

For me, these research exercises really demonstrate what all African cichlid owners should know: how easily they crossbreed. And adds weight to the determination that they all evolved from the one fish thousands of years ago.

Getting back to the C.afra - be interesting to speculate what specimens may have been imported into Oz - I wonder if any have ever come from Thumbi Island? Are there any other species this has happened to in the Rift Lakes? Most likely. So therefore even our prized imports could be mongrels!

The other interesting thing is the mention of a Lake Malawi fish exporter depositing the C.afra there in the first place back in 1963 (gee, I wonder who it was). Given that the originating locations for C.afra were miles and miles from Thumbi Island, you could assume this exporter most likely wasn't bothered in boating all the way back to the origin and just dumped the fish at Thumbi Island out of convenience.

So it can all happen way too easily!

[Lee Miller]

Hi GTR73,

I can’t remember the name of the person who had the fish collecting/exporting operation at Otter Point but I think it was a French name. The story I was told was that this person had his ‘permission to operate’ revoked by the Malawi Government and was given little or no time to get out of the country. This all happened quite a few years ago but the buildings are still there.

Before this person left the country (so the story goes) he released all of his stock – from all over the lake – at Otter Point, which explains the variety of fish we saw there.

Otter Point is very close to Thumbi Island and if we were to point the finger at anyone it would most probably be this ex-exporter.

Cheers,

Lee.

[Ged]

I have discussed this issue with both Ad Konings and Michael Oliver.

In the early 1960’s T. E. "Peter" Davies and his wife Henny operated a lucrative cichlid export business out of Cape Maclear in southern Lake Malawi, just opposite Thumbi West Island. Ad in talked to Peter Davies on his return to the U.K. and was informed of the circumstances of the establishment of C. afra on the island.

After operating for several years at Cape Maclear Peter Davies received a letter from the government that he had 48 hours to pack up his belongings and to leave the country as the Malawi government was going to take over his property. He didn't want to kill the fish (that he had in the holding tanks) so he just released them into the lake in front of his house. This is a sandy beach and most of the fish released were rock-dwelling mbuna. The southern part of Thumbi West (Mitande Point) is the nearest rocky habitat of that release site and some fish made it to those rocks and established themselves. Ad Konings also said that this one-time release scenario is also confirmed by David Eccles, who was fisheries officer at the time.

[Bijengum]

Interesting article but its beyond me how someone could write an article on that subject and not use any pics.

Found this article on another website discussing hybridization at Thumbi West Island, where two different variations of C. afra have occured (northern vs soutthern population). Very interesting reading:

Hybridization at Thumbi West Island

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[Lee Miller]

Hi Ged,

Something smells fishy here

With all due respect to Ad Konings, the nearest and/or most accessible, rocky habitat to the premises pointed out to us as being those of Peter Davies (see – I told you it was a French name ) is Otter Point. To the best of my recollection (it has been 5 years since we were there) Thumbi West would have to be at least a kilometre from the beach at the Davies’ site, and it’s mostly deep, open water.

Common sense and logic would seem to suggest that a species such as C. afra would stay close to shore if looking for cover/habitat rather than head into deep water. A left turn from the Davies’ site takes you to Otter Point and a right turn takes you down the beach, past Chembe Village, to Domwe Island (in my opinion also a more likely destination for free-swimming released fish).

The ‘Hybridization’ article states:

In the 1960s, an aquarium fish exporter based at Cape Maclear introduced roughly 20 cichlid species from northern Lake Malawi to a single site (Mitande Point: Fig. 1, site 1) at Thumbi West Island, presently located in Lake Malawi National Park…

Unfortunately, the article doesn’t state how these fish were introduced, nor does it give any information on how the other 19 species fared, but I can’t see someone with 48 hours to get out of the country taking fish across the lake to release them (and that doesn’t fit with Ad’s or the locals’ versions of events).

So, is it suggested that 20 species of fish were released at the Davies’ site and swam across a kilometre of deep, open water to find sanctuary? And sufficient numbers made it to establish breeding populations? I don’t think so! If that were likely how could the lake maintain such a diversity of geographically unique populations? It’s the tyranny of distance that ensures that hybridization, due to natural causes, is kept to an absolute minimum.

It’s a mystery isn’t it? Just how did those little afras get to Thumbi West? Was someone deliberately trying to establish a population? We’ll probably never know!

Cheers,

[GTR73]

So does anyone think the C.afra"Thumbi Island West" would have been, or potentially be, exported to Australia?

[Ged]

I agree that we will never know how they arrived at Thumbi West Island. I know I wouldn't admit that I had deliberately introduced one species let alone 20 species to an island and have been the cause of hybridization in the wild.

It is quite possible that the the Davies' property was at Otter Point as you stated. When I discussed the issue I asked Ad whether it was Peter Davies that operated out of Cape Maclear and when I was not corrected I presumed that was the exact location.

I have read a few other studies of translocated species in Lake Malawi and I think a couple of them were at Thumbi West. I will check and see if I still have copies of them.

Does anyone have a copy of Ribbink et al. (1983) A preliminary survey of the cichlid fishes of rocky habitats in Lake Malawi. South African Journal of Zoology 18: 149-310. I have read a cople of extracts from the text but I am keen to get a full copy.

I can't be sure but I doubt any C afra have been collected at Thumbi West and imported in Australia.

[Lee Miller]

Hi Ged,

Part of the confusion may relate to where 'Cape Maclear' is, or what it is.

If you look at this map; http://www.cichlidpress.com/safari/malawi/...malawi-cape.htm

you'll see that Cape Maclear is actually at the tip of Domwe Island, but locally the whole area from Domwe Island to Otter Point is known as Cape Maclear. So Peter Davies' operation was technically close to Otter Point, in the Cape Maclear area. Ad would have been spot-on if he had confirmed that Peter Davies operated out of Cape Maclear.

Cheers,

Lee.