Here is the photo of the new population of N. rachovii (Lower Shire River MZMW 09-4) that I wrote about earlier in the African Annuals section (under N. rachovii Beira '98).

N. rachovii Lower Shire River MZMW 09-4. Photo by Brian R. Watters, Copyright 2009.

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Hi Brian,

That N. rachovii Lower Shire River MZMW 09-4 is a very attractive blue form. I liked the markings. I have been keeping my eyes open for a nice blue form and I think you just made my choice for me whenever they become available.

Bob Morenski

I'm a bit surprised that the Lower Shire R. form of N. rachovii is so similar to those from the lower Zambezi. It will be of great interest to see if it is chromosomally divergent from those, and interfertile with them.

In any event, my congratulations again for finding this form. Are you going to try to mkuziensis again?

Bruce,

The overall coloration of the Lower Shire N. rachovii is similar to the typical Lower Pungwe and Lower Zambezi "blue" forms but the color pattern on the unpaired fins, the anal and caudal in particular, is closer to that found on the "intermediate" color form (such as the Dondo population, in the Lower Pungwe area). I will prepare a photo of the latter and post it to these forums in a few days time so that you can see what I mean. Those fins have a spotted pattern rather than the coarse, broken banding of the blue form.

Specimens will, in due course, be subjected to mtDNA analysis and that will probably help us to determine its affiliation.

Another field investigation of the Pongola-Mkuze area, with a view to trying to find N. mkuziensis, is still on my list of things to do. However, at the moment I am not sure when that might be. I am not optimistic that N. mkuziensis will ever be found again, and it is quite possible that it no longer exists due to habitat disturbance (i.e. farming) as suggested many years ago by Jubb.

I have looked for it fairly thoroughly on a number of occasions and, over the years, the KwaZulu-Natal parks board people have conducted various ichthyological surveys but it has never turned up. By contrast, N. orthonotus has been found at many different places on the floodplains of both river systems. That does not necessarily mean that it is still not around but, as always when collecting Nothos, it is a matter of being at the right place at the right time.

Incidentally, I did not collect the Lower Shire population - it was collected by some friends of mine from South Africa. They had planned a trip to Malawi via Mozambique and visited the Lower Shire area on my advice, specifically to look for this fish which, on the evidence from a single preserved specimen (collected in the 70s) I felt sure must be a form of N. rachovii. You can imagine my delight when I learned that they had found it. Live wild specimens were brought to Canada for me by my good friend Otto Schmidt who was the banquet speaker at the Portland convention.

Brian

Brian,
I know you've mentioned in brief that you're familiar with Dr. Collier's not-yet-published work with nothos. I know it's not your work and don't expect you to divulge any huge amount of info, but are any of the rachovii in the hobby very different at the genetic level? Yes or no answer is good enough.

I'll agree, that is a very nice blue form.

Nick,

The answer is, Yes.

A paper is in preparation.

Brian

Thanks Brian. I can't wait to read it, though I'm sure it will be awhile yet.

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Dr. Turner, I think you are asking the correct question.

Given the biology of these fish and how vicariant their populations are one would expect to see massive genetic differences using genetic markers and DNA sequences which would make it very difficult to separate out real biological entities based on DNA work alone.

It has been rumored that the N. furzeri from the Save River/Gorongoza will soon be described as a new species. I hope their is a lot more than DNA sequences involved. I admire the quality of the work which has (been rumored to have) gone into researching the relationships of N. sp. Caprivi to kafuensis and the black rachovii with the red using mate choice and hybridization experiments.(I look forward to the rachovii paper hinted at in the Notho JAKA issue.) I hope to see such mate choice work done for the Save furzeri in addition to morphological work though this would be problematic. We thought we noticed, in mixed phenotype populations of the red and yellow fruzeri from the MZM collection, that certain females chose to mate with certain coloured males while other females had no preference at all. Sadly, Dario and I never had time or space to really investigate this and stupidly I never made any records of this and must now rely in my increasingly spotty memory.

In situ hybridization on the chromosomes would be a much better way to get a clear idea of just how evolutionary divergent the various populations/species are.

I did not mean to imply that chromosomal divergence was more important than other kinds of genetic differences, including mtDNA sequences. Merely that chromosome differentiation comes quickly to mind when one thinks of rivuline killifishes in general. N. rachovii from Beira has a very low chromosome number, and I was interested in knowing if the Shire R. form was different in any way. Classically, chromosomal divergence is supposed to lead to postmating isolating mechanisms, and has been treated by several authorities (most notably MJD White) as a "magic bullet" of speciation. In recent times, the strength of this relationship has been questioned, and it appears to be less straightforward than initially thought.

However, I certainly agree that the geographical isolation of many Notho habitats means that it is hard to interpret their divergences in terms of the classical species
category. I would take this one step further: It is difficult to apply the biological species concept meaningfully to allopatric populations in general. So, for comparisons of geographic isolates, I am comfortable with a phylogenetic species concept. However, I would argue that the argument that isolated populations are different species gets better as the number of divergent features gets larger.

For geographically contiguous or sympatric populations, however, I think that some of your reservations hold. There is a growing list of cases, for example, in which individuals that are members of the same gene pool can have highly divergent mtDNA matrilines (due, perhaps, to a past fusion of differentiated populations, or to ancient hybridization).

In these situations, geography and sampling are everything: If a form is (more or less) continuously distributed, and populations from different extremes of the distribution have different mtDNA matrilines, it is not a good idea to regard them as distinct species until one has examined some "in between" populations. The SE Brazil populations of Kryptolebias marmoratus (sensu lato) are a good example of this problem. We know that they are divergent from Caribbean populations in color pattern, and that they are sharply different in some mtDNA sequences as well. Based on the former, my colleague Wilson Costa has treated the SE Brazil populations as a separate species, K. ocellatus. The molecular data are consistent with this. However, there is a long stretch of the South American coast that has not been sampled (roughly from Recife to Rio) and there is plenty of potential for intermediate populations to exist, perhaps some with both matrilines.

Hello,

It is a very nice picture Brian. Thank you!
I am also interested to know if this form also has only 8 chromosomes as the Beira type.
You have made me very curious to know if they (you) have found other nothobranchius species?
It was mentioned in one of many conversations with Ruud on the KFN convention. He was doing a study on the rachovii types. Is he aware of this form?
I also received some eggs of N. Rachovii MZCS 49/09, i am curious to see any differences in the Beira type.

Kind Regards,
Tom