There have been so many points in the last emails regarding the
discussion of differences between M. herbertaxelrodi and certain
strains of M. trifasciata that I want to try to bring a little bit of
clearness into it.
Age of rainbowfish as a family
Well, there are several arguments why rainbowfish are a rather young
family.
1. There relatives are also rather modern fish.
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.
3. No fossils
4. Strong speciation in M. trifasciata and M. splendida and others,
which is a sign for modern fishes.
Speciation
Rainbowfish are thaught to have an age of a few million years, maybe two or
three. Now, what are the factors of speciation? One important one (maybe
the most important one) is isolation. 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.
There should have been one rainbowfish ancestor, with some species developing
in a first step. These have been the ancestors of M. nigrans, M. trifasciata, M.
maccullochi and others. Isolation and other - e.g. limiting - factors have
produced the specific mix we see today.
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..
There were 10.000s of years these species have been separated.
In a family were species tend do develop varieties very quickly (and the
tri's varieties had only about 10.000 years), there was no need for M.
herbertaxelrodi to develop even genetic barriers. It may be possible
that, connected again, herb's and tri's may hybridize and mix again.
But that's not really possible in the next few 1.000s of years.
There has been a common ancestor of both of the species. However,
time brought specific differences which are not seen in the morpho-
logical dates exclusively as these are quite similar.
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!
Of course there may be great colour similarities between a certain
tri-population and herbs. However, my explanation: by chance! The
isolation of tris and herbs is much longer than the tris have been
isolated themselves.
Speciation against Specialisation
Of course there is no need for speciation. However, old species like
Neoceratodus fosteri don't vary very much, the large number of
varieties shows that bows are a young family. However, there is a
need for specialisation and that's one of the major reasons for
speciation and species forming. Why do three bow species live
together without hybridization? The answer is specialisation.
And this is still going as we see.
Tris and herbs are separate species, otherways you have to reduce
the number of bows to fifteen or ten. If you just look at one special
variety and compare it to an isolated species, you might come to another
result. However, this is IMO not the right way.
Harro