Lamprichthys tanganicanus: a killifish
Rhadinocentrus ornatus: a Rainbowfish
If somebody sold that rainbow as a new Lamprichthys species how believable would it be?
How hard is it to believe tanganicus and this rainbow had a common ancestor?
It's a lot less changes,for example, than exiguum has to go through as derived from Raddaella.
So maybe "killifish" or "fish of the creek" isn't accurate. Maybe when the continents split rainbows headed for freshwater and we have pelagic rainbows all over australia and africa and only one left in South America and none in Asia but we have forest rainbowfish all over Africa and South America and in a few places pelagic and forest forms intermingle, that's why we'll have an aphyosemion, an epiplatys and an lampeye so often found together, each state out their part of the niche: epiplatys at the top, Aphyosemion at the bottom the pelagic ones drying in the bright sunshine. Still all the same fish though, just adaptations to their particular niche.
So I'm suggesting rainbows and killies are closer to each other than killies are the the fish that evolved (as a clade) after killies, the needlefish. Two foot long pencil thin gars are not going to be mistaken for killies anytime soon but I do find it somewhere between alarming and disconcerting that a killie and a rainbow could be this similar yet so far apart and convergent evolution only goes so far here.
So one thing that came out of Parenti (1981)* was a shift in thinking from "all killies descended from Aplocheilus" to "all killies descended from something very like Pachypanchax."
So you can go for a couple of decades looking at Pachypanchax all weird. How can they be the key to anything?
Then you find this monster, swimming around creeks of Madagascar, the land the time forgot and suddenly it's far less of a mystery.
Look at it carefully, what does it look like? Blue fish, red spots, yellow fins. Sound familiar?
So, as we ponder the diversity of color patterns killifish have evolved into perhaps we should give more consideration to the color patterns they evolved *from*. It's a lot easier to explain mimbom and schmitti knowing these things may have swum inshore in two different places in the tethys sea that would later be pushed together to for the continent of Africa. The top one, west of the Dahomey gap while the one that came up fro the "south" was all points east of the Dahomey Gap.
I think the idea any killies evolved from any other is specious, you can make any one out of any Pachypanchax easily, and in fact it may be the only way to explain killi genes. We'll see as we learn more about what they are.
The other great question is where did the ancestors of killies come from and where do they come from. Short answer: the grey mullet. Ish.
Parent 1981 where, at least in my mind, biogeography really came of age in the study of killies much in the same way chromosome and genetic analysis came about in Scheel's time. ROTOW in 1970 barely mentioned biogeography whereas in 1981 Parenti wrote at length about it.
And that's good, it does help explain a great deal.
However one thing I do not see anything written about and perhaps I just haven't looked hard enough and that's about the soil. We hear mention of leafy basement liter or a rocky or muddy or peat filled pond or stream but that's really al.
Consider killifish have been where they are for about 100 million years plus or minus 50my. In that time many changes in genes and physical appearance occurred, some to a greater extent than others and some at a faster rate than others.
And we tend to look at biogeography as the overarching physical force a work - the environment, we call it, but there are also forces at plan on the genes.
In the barbs there is a genus that has twice the chromosomes of a sister genus, and another that has four times that. In Cryptocoryne one species (COR) has a different number of sets of chromosomes whether you find it i Makaya, Thailand or Borneo. So, the number of sets of chromosomes can double.
But changes can also occur to genes from random means and radiation is the working definition of random, it's the only true source of randomness in nature. You can't generate random numbers, only pseudorandom numbers. It's an issue in mathematics.
The nature of these random mutations are mostly various forms of high energy radiation and cosmic rays are the ones that do the most damage to the DNA molecule. The amount of cosmic rays hitting the earth is limited by the earths magnetic field and that broke up about the time the last great ice age started and that's well in the rise of killies timeframe. OS there's that, one of the reasons for the increased rate of speciation in killies, cichlids and rainbows at the very least is the increase rate of random mutation from more and higher energy cosmic rays hitting earth.
Second, and this is what I find odd is I do not ever see it mentioned but the soil chemistry of the coastal rain forest varies greatly and differing percentages of minerals in different countries ay affect genes or *expression* of genes if a specific mineral is needed to form a catalytic precursor. A good example of this is selenium, found in deposits half a mile thick in Senegal as selenium phosphate, also found in Bolivia and Gabon.
It may turn out varying percentages of exotic trace minerals may alter the efficiency of certain chemical reactions this up (or down) regulating genes that control color and color pattern. It may turn out if you swapped fish from say Makokou and inland Cameroon they make "change into each other" as a reflection of the soil types. This is may be soil as well as biogeography that affects the genetic and thus phenotypic expression of color and color patterns in at least killifish.
This is one possile explanation for the Raddaella species: kunzi, batesti and splendidum is one evolved from the other. In this photos it's possible to imagine BAT over time morphing into KUZ and SPL (morederived forms in Cyprinodontidae tend to be omre spender in Aphysemion) but the reverse is not as easy to imagine.
The point this raises is if this is true then what is te explanation for the vat difference in color patterns within Raddaella: it's easy to explain them away by assuming they evolved from each other but what if they were reacting to local environmental conditions viz a viz the soil. The common ancestor to killies and rainbows is Anthias it might be possible for genes that are only expresses in marine biota may be repressed in freshwater and in areas of unusual mineral contents perhaps that resembles the trace element profile of the sea then perhaps these unregulated minerals not normally found in all areas (and Selenium ie one such exampe, it's high in areas of coastal Gabon and Senegal only along the coast) cause the genes that express colors to up-regulate foooling them into as it were, into turning on marine color pattern genes, long since inactive since the Anthias days. This idea is supported by the rather tenuous idea that L. tanganicus may have a higher degree of color compared to a lot of lampeyes owing to the mineral content of the water by this same mechanism.
We can tell how far evlved or as we say "derived" killies are with conventional physical metrics, bones and dna. There's a great variance in Aphyosemion for example with Radaella having an absurdly small number of chromosomes and Diapteron having the most,it's something on the order of 8 to 40. Now, chromosomes can be reduced in number from environmental stress but as things become more derived the tendency is to increase the number of chromosomes and this is always going on. A lot of killie species have two or more populations with different numbers of chromosomes even today - the process never stops.
n=18 and 2n=36 - Scheel's fish India n = 19 and 2n = 38 chromosomes." [1978 Khuda-Bukhsh] Vietnam 2n=40 [1992 Magtoon]
so that's one way. Also as killies adapt, the requirement for evolution their jaws change to reflect feeding habits in their new habitat and this should be comparatively quick as their ancestors were pelagic marine fish but as "fish of the creek" they now live in tiny amounts of water and feeding will be specialized compared to a pelagic existence thus structural changes in the jaw occur. From this we can tell more and less derived forms.
Parenti did a thorough examination of the jaw bones of all killifish genera. Not species, genera. The potential gotcha is if we've defined genera improperly this would not be representative of all genera if not all species were examined. The converse though, new general may rise out of this, and they did: Fundulopanchax was raised from a subgenus of Aphyosemion to a full genus. Aphyosemion and Fundulopanchax had different ancestors.
In a nutshell the slender bodied Aphyosemion and the more stout bodied Fundulopanchax are thought now to have evolved from different lines.
Right. So, ever see a picture of what that common ancestor was? The idea it may be some long extinct fossil relic is an obvious conclusion to which I saw: coelacanth.
Parenti states flat out you can't have any assumptions going on and the idea Aplocheilus was the ancestor to all killies was based on metrics. Parenti's work with jawbones of all killies was monumental and gave new insight and showed aplocheilus was a derived form from something pachypanchax-ish.
So, what I'm suggesting here is there were provably at least four species in two clades in the right part of the Tethys sea at the right time such that it's not impossible that killifish could have come from what is now pachypanchax but also from the other fish there at the time. This hypothesis would explain the differences between aphyosemion, a stout fish, blue with red dots and yellow fins and a stout pachypanchax like this still exists today. And in fact a lot, quite a lot of color patterns of west african killies show up in extant Pachpanchax but a lot also show up in the other clade that we now call rainbows but they're having trouble over in rainbow land because the ones in madagascar and one part of AU aren't the same as the rest in the same way it's not obvious to see how lampeyes fit in with the rest of them.
So, what I'm suggesting in response to Parenti saying, roughly "killies come from Pachpanchax" them I'm merely adding: 1) And that thing may have been a collection of things: what if that hypothetical ancestor came in 5 different color morphs. This if we look for the origin of color patterns in killifish there's no real reason to think we'd actually find them, they have have inherited them.
2) One common ancestor is to my mind a flaw in thinking. What it it wasn't one grey fish tat turned into all killies what if it was 6 color forms of the same fish? What if it were two closely related species instead?
Both killies and rainbows have a number of species that just don't fit in anywhere else and there me a whole species grouping between the killas and the rainbows we missed that includes the rainbows that don't fit in, the pseudomugil rainbows, the diopters of rainbowland and the madagascar rainbows. Tanganicus may belong here and that, that opened up a can of worms.
Of course this is highly speculative and not based on any hard evidence and I'm really just thinking out loud. But, at some point Jouke van Der Zee will be finished with his review of lampeyes and we'll know a bit more and have some more pieces to the puzzle.
So the best I can say for this idea is it's self-consistent.
I think it's actually easier to imagine some killies have come from Bedotia and not Pachypanchax, there are a number of species of Bedotia and some of them are turning into bivs you'd think by looking at tem plus they're the only source of an trilobate tail and the walkeri orange/fallax tail. I think it's worth looking at. ymmv.
In trying to analyze evolutionary trends within killifish we mst distinguish between what is possible and what is not possible. First, these are forest fishes for the most part and could not exist until not just forrests but biodverse forests with bugs falling off trees all the time. Another curious coincidence is how the evolution of the human genome in Africa might hpothetically mimic the radiative adaption of killifish throughout Africa the premise being that man, before he was man, was a forest dweller with a need for clean fresh water. Where you find man, you'll also find killifish, we all love the shoreline.