Decreased aggression in captive bred fish.
- Thread starter Cherrybomb
- Start date
Matching male and female of the same species is a challenge to fish collectors in Lake Victoria because all females look alike. I was told by Dr Loiselle that common DNA analysis of Victorians didn't work out and the only sure way fish collector did was to capture holding females and grow out the fry. I guess with today technology, one can employ genome-wide comparative analysis including mitochondria DNA analysis to differentiate species. But these research level analyses are too costly to worth the effort.Ah, yes...the proverbial "magic wang"...
No, DNA cannot distinguish between closely related species...but it can, by definition, clarify which are more closely or less closely related to one another, which share common ancestors and how far back the divergence occurred. It still requires interpretation by scientists...and there is never complete agreement among them regarding how to interpret this data. Again, the picture being drawn by DNA analysis is a complex tree showing relationships...but the lines that divide one subspecies, species or genus from the next are still drawn on that diagram, quite arbitrarily, by the hands of scientists who can and do have varying motivations and preconceptions.
Can you cite a source for the comment about no detectable differences between various Malawi cichlids? That sounds frankly unbelievable. DNA testing has been used to determine which portion of a particular species' range a particular specimen originated from. It's used by Fish and Game departments to investigate poached trophies.
Recently-diverged species such as Malawi cichlids, Galapagos finches and tortoises, and many others would certainly show very few and/or small differences, but the difference must exist for them to be distinct...not necessarily distinct species, but distinct from one another. Otherwise, every spawn would produce the makings of a mixed Malawi community tank. If the DNA analysis is not carried to a fine enough degree and these differences are not seen...that does not mean that they do not exist. A case could be made...probably has been made... that all those multicoloured Malawis are simply subspecies of one varied species. BUT...that is, once more, merely semantics. Whether some/most/all/none of today's researchers believe one notion or the other, it changes...absolutely nothing. And when the pendulum swings back toward the "splitters", all that nomenclature will change yet again...but it will be just nomenclature. The fish remain...the fish.
As for assigning closeness of different species in CA or African based on DNA analyses, it is not black and white requiring subjective assessment. Speciation of these fish radiated rapidly from a common lineage over a short geological time, so dating and placing them in the tree of life is subjective. The controversy of recent grouping of Melanurus and Synspillum as the same species based on identical DNA was met with opposition from fish importers and hobbyists who have intimate knowledge of their fish.
The fact that the degree of sophistication required in a DNA analysis to differentiate these closely-related species is expensive and/or impractical...does not change the fact that differentiation exists in a very real sense. Not so long ago, literally any type of DNA analysis, of any living organism, was a scientific pipe dream. Today it's very much a reality, and tomorrow it will be better, more precise, faster and cheaper...like any technology as it matures.
And I agree that the observations of amateur scientists like hobbyists are every bit as useful as analysis by professionals, and that their opinions bear weight...but we return once again to the problem of subjectivism in determining where to draw the line between subspecies, species and genera. The typical definition of species, once considered inviolate; is: a group of organisms that can reproduce naturally with one another and create fertile offspring.
It's that "reproduce naturally" bit that causes all kinds of grief. If you combine two groups of fish of two different species, but find that crossbreeds occur without any coercion on your part...is that natural? The conditions in captivity are never completely natural, so does that make these two groups different species? How about a natural body of water into which we introduce a group of fish never found there before, and then crossbreeding occurs? Surely that can't be natural, since in nature they would never have encountered one another...so can it be used as a criterion to determine their relationship...species, subspecies...? Different experts answer these and similar questions in different ways, depending in part upon their general tendencies regarding "splitting" versus "lumping".
Science is full of examples of changing scientific names, re-grouping of species and genera, re-assignment to or creation of new groups...and reading about these changes usually carries provisos about this scientists who "subscribes" to this particular theory, where as that one does not, and this third one is postulating a completely different idea of his own.
The gray area is getting wider and longer and deeper all the time; there is literally no point in arguing about which particular species an organism or a population of organisms belongs to until there is agreement upon the definition of species and subspecies and genera, and what criteria will be used to make these decisions...and this sort of concensus appears to be less likely today than ever.
Same goes for the recent "synonymization" of siquia and nigrofasciata, I speak for the melanura situation when I say that even thought they may be identical genetically, I would argue they are at least distinct enough to be considered subspecies. And then obviously convicts will have more names to hand out, with all the drainage/lake specific variants across their range.
While I am all for the convict grouping, as I like I mentioned before I believe the phylogenetic testing provides the truth in regards to taxonomy, I did find a video of one locality in costa rica known to contain what was formerly known as siquia, living alongside what was known as "true" nigrofasciata. I am not sure if said nigrofasciata were just introduced and happened to be there, but they did look like some of the more pure strains I've seen (wild nigrofasciata seem to have a very bold and distinct breeding dress where the stripes fuse near the abdomen in females, resulting in a half black archocentrus-like breeding dress). This in my eyes raises questions as to whether our definition of a species is really applicable to all situations. But that's for another time.
The hybrid definition of species was passed on since Darwin time. Darwin and contemporaries didnt know there are hundreds endemic species of fish in Lake Malawi and Victoria, all can hybridize and produce fertile youngs. They also didn’t know about the microcosm where bacteria, archea and many Protozoa reproduce asexually so the hybrid definition doesn’t apply, yet mutation by horizontal gene transfer and speciation by natural selection do occur.
Or, in other words...they knew less than we do today, and therefore our interpretations of what we see in nature are different than theirs were, and are constantly changing. And all I am saying is that this increased knowledge base continues to grow at an exponentially increasing rate...and that therefore ideas will continue to change regarding not only speciation, but the actual idea that such even exists. It is primitive terminology based in primitive science and trying to force new information to fit the picture it paints is not the way forward.
Nobody is correct...nobody is incorrect...and constantly pointing to this or that blip of new information and saying "See! See! This proves that I am right and you are wrong!" is a complete waste of time, since the people who believe otherwise can always find supporting evidence for their stance.
I am not saying that your ideas are wrong. I am saying that your belief that you are correct and no alternative ideas or explanations can have any merit...is wrong. But you have definitely outlasted me; enjoy the perfectly clear world you seem to see!
