>On Fri, 29 Nov 1996, Harro Hieronimus wrote:
>> Well, there are several arguments why rainbowfish are a rather young
>> family.
>> 1. There relatives are also rather modern fish.
>What do you consider their closest relatives to be? I know there has
>been some recent work done on the relatedness of the various families we
>are interested in. However, I have not seen any of it. If anyone has
>any references to it I would be greatful.
I'm not quite sure what their real closest relatives are but we have
to look for them in the Telmatherinidae and their relatives.
>> 2. These fishes are still closely related to other fish which have the
>> same history, coming from seawater relatives and invading fresh water,
>> like Telmatherina and Bedotia.
>Do we really know that fish such as Bedotia and Melanotaenids originated
>from salt water? Based upon what evidence? Allen suggests melanotaenids
>are freshwater evolved since they have not crossed Webers Line. If they
>were marine they could have swum it as it is not that far apparently.
Yes, we know. Australia - together with New Guinea - has left the ancient
continent (forgot the name, the stage before Gondwana) very early. Thus
if it were primary freshwater fish they must be very very old - like lungfishes
and species like Scleropages. Sign of old species is, that they don't evolve
strongly (as the two Australian species didn't do). Rainbowfish still seem
to be in the course of evolution. According to all what we know in the
evolutionary biology that's a sign of a rather young (that's relative, also
a few million years is young) family.
>Correct me if I am wrong but Telmatherinidae are closer to Pseudomugilidae
>than Melanotaenidae?
That's true, if you don't look at some striking similarities between werneri and
T. ladigesi.
>> 3. No fossils
>Who's looked for them or looked and been able to identify them? There
>are relatively few "modern" (ie, non lungfish) freshwater fish fossils in
>Oz that have been collected, most are poorly identified or known of and no
>one is working on them.
There have been people searching, but of course they may have been
overlooked. But I don't believe you'll find very old ones!
>> 4. Strong speciation in M. trifasciata and M. splendida and others,
>> which is a sign for modern fishes.
>Why? Pupfish (Cyprinodon) as a genus have been around well in excess of
>10 million years, probably more like 30 and they are very speciose.
Are they? Or have they been? Most pupfish are at the end of their way. If you
have such an extreme isolation under extreme conditions like in pupfish
you will find speciation of extinction. I don't think they are much older than
10 million years - and thus a rather young family.
>> Rainbowfish are thaught to have an age of a few million years, maybe two or
>> three.
>Define rainbowfish. Do you mean Melanotaenidae, Melanotaenia, or
>something else? According to paleontologists the average age of a
>species in the fossil record is 6 million years. Who thinks they are 2-3
>million years old? What is your source of this information?
E.g. look into Jerry's new book.
>> Within the last few 100.000 years
>> we have had many periods when the continental shelf of Australia was
>> dry and a few 10.000 years again under water, time for species to develop.
>Yes, actually much more than the last few 100 000 years. But, why do we
>assume they only speciated after the last rise in sea level when there
>have been many early opportunities for this to happen? Now, I'm not
>saying they couldn't have done it in the last 10 000 years just that I doubt
>it strongly.
Of course not!! Speciation has begun maybe since the rainbowfish invaded
the freshwater, but for nearly sure (nearly sure, I haven't been there at
that time although I'm feeling old today - you know I'm going to move)
speciation began after the first time the sea level sank as a result of the
ice age and the ice masses on arctis and antarctis.
Personally I believe that the M. trifasciata speciation began just about
10.000 years ago and the result is that we have varieties which may
become species if the isolation persists.
>> There should have been one rainbowfish ancestor, with some species developing
>> in a first step.
>Only if the genus Melanotaenia is monophyletic. This just means they all
>came from one ancestor, vs polyphyletic, meaning that there is more than
>one ancestor to the genus. There is some evidence that the genus is not
>monophyletic as we presently recognise it. The work of folks at Qld Uni
>found that M. affinis was as distinctive as G. incisus from the
>Melanotaenia spp they examined. This suggests there is something wierd
>going on (and also that M. affinis aren't very closely related to
>goldies, herbies, or tris as Allen first proposed).
I still believe Melanotaeniidae are monophyletic. What work?
And most of all, what method? Do you remember my critics
on some of the "modern" methods which create results they want to have?
>> The history tells us that M. trifasciata and M. herbertaxelrodi have been
>> isolated for a very long time. While M. trifasciata developed a great lot
>> of varieties M. herbertaxelrodi did not - because there may have been no
>> isolation in the Lake Tebera area..
>That was certainly not one of my arguements. You wouldn't expect to see
>differentiation when you only have one population, ie Lake Tebra.
Wrong, see Lake Malawi and Lake Tanganjica and, as far as we know today,
M. boesemani and M. ajamaruensis as well as C. fasciata and C. sentaniensis.
>> In a family were species tend do develop varieties very quickly (and the
>> tri's varieties had only about 10.000 years)
>Sure, rainbows tend to develop _colour_ varieties "relatively" quickly.
>So what? Why did the tris have only about 10 000 years to do this? This
>may be true to a degree _if_ they occupied the lake that once existed in
>the Gulf of Carpentaria. However, I don't think that is the reason you
>are suggesting. You are presumably saying they only invaded Australian
>waters 10 000 years ago? Why couldn't they have done it earlier though?
I'm quite sure that a common ancestor of all tri's we know lived in the waters
which are now partially filled with the Gulf of Carpentaria. I don't know if
there already were varieties (I haven't been there, see above) but there was
even theoretically a gene flow between all of the varieties living today in
rivers ending in the Gulf. The M. trifasciata ancestor has surely been older,
but I think that the varieties are really young, about after last ice age.
One sign (no proof) is that you can't find two rivers which aren't connected
having the same variety.
>> Tri's are rather deepbodied at least when they become old. Herb's are
>> never as deepbodied. And this is (!) astonishing as a lake dwelling species
>> which would just be a variety of a stream dwelling should be much more
>> deepbodied!
>Perhaps tris were once a lake adapted fish, thus the reason for their
>deep, rather than slender bodies. It's interesting to note that those on
>the eastern side of Cape York tend to be more slender. It gets more
>interesting when you consider that around 10000 years ago there was a
>massive freshwater lake in the Gulf of Carpentaria (three times bigger
>than Lake Bonneville which once covered ~1/5 to 1/4 of Utah!) to which
>many of the rivers presently containing tris would have drained into.
10.000 years are long enough to loose a deep body. However, it's still
a hypothesis.
>> Of course there may be great colour similarities between a certain
>> tri-population and herbs. However, my explanation: by chance!
>Gotto agree with you there! :-)
Thanks. Evolution isn't directed in a certain direction. Many things in
evolution happened just by chance.
>Further food for thought on rainbowfish ages. M. exquisita primarily
>(only??) exist above waterfalls in the Katherine and Alligator Rivers
>(and maybe elsewhere in that vicinity). How old are these waterfalls? I
>would argue that exquisita were present before the waterfalls. At a
>later point, a splendida invaded the area and exquisita disappeared either
>through competition or hybridization below these waterfalls. It is
>notable that the Qld Uni folks found that M.s. australis from the NT had
>mtDNA's very similar to exquisita which they felt was was likely to
>introgression (hybridisation) between them. And some folks firmly
>believe rainbows don't hybridise in the wild. :-) Although, you should
>note, this probably happened a long time ago.
You're surely right with your idea on the distribution of the species.
However, we also find this in other fish and I'm quite sure the waterfalls
aren't very old. The are in the tropics, were landscape changes very quickly.
However, we have to know more about the geology to be sure.
>I'm sure everything I've just said is a load of goat's milk too. But at
>least it's start...... :-)
I think that the RML should not only consist of SPAM ;-) but also
some more sophisticated items :->> Let's work for a good mix.
Harro