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PostPosted: Sat Dec 18, 2010 4:28 pm 
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From: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1198242/

Front Zool. 2005; 2: 11.
Published online 2005 June 29. doi: 10.1186/1742-9994-2-11.

PMCID: PMC1198242
Copyright © 2005 Nolte and Sheets; licensee BioMed Central Ltd.

Shape based assignment tests suggest transgressive phenotypes in natural sculpin hybrids (Teleostei, Scorpaeniformes, Cottidae)

Arne W Noltecorresponding author1 and H David Sheets2
1Institute for Genetics, Evolutionary Genetics, Weyertal 121, 50931 Cologne, Germany
2Dept. of Physics, Canisius College, 2001 Main St., Buffalo, NY 14208, USA
corresponding authorCorresponding author.
Arne W Nolte: arne.nolte@uni-koeln.de; H David Sheets: sheets@canisius.edu
Received April 20, 2005; Accepted June 29, 2005.

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0),
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

***************************************************Abstract***************************************************

Background

Hybridization receives attention because of the potential role that it may play in generating evolutionary novelty. An explanation for the emergence
of novel phenotypes is given by transgressive segregation, which, if frequent, would imply an important evolutionary role for hybridization. This process
is still rarely studied in natural populations as samples of recent hybrids and their parental populations are needed. Further, the detection of transgressive
segregation requires phenotypes that can be easily quantified and analysed. We analyse variability in body shape of divergent populations of European
sculpins (Cottus gobio complex) as well as natural hybrids among them.

Results

A distance-based method is developed to assign unknown specimens to known groups based on morphometric data. Apparently, body shape represents
a highly informative set of characters that parallels the discriminatory power of microsatellite markers in our study system. Populations of sculpins are
distinct and "unknown" specimens can be correctly assigned to their source population based on body shape. Recent hybrids are intermediate along the axes
separating their parental groups but display additional differentiation that is unique and coupled with the hybrid genetic background.

Conclusion

There is a specific hybrid shape component in natural sculpin hybrids that can be best explained by transgressive segregation. This inference of how hybrids
differ from their ancestors provides basic information for future evolutionary studies. Furthermore, our approach may serve to assign candidate
specimens to their source populations based on morphometric data and help in the interpretation of population differentiation.


************************************************Background************************************************

Although hybridization has long been considered important in the diversification of plants zoologists often considered it detrimental and thus unimportant [1].
The debate of the relative importance of hybridization has received recent attention because the advance of molecular techniques has resulted in a surge
of data suggesting that hybridization is taking place rather frequently in the animal kingdom as well. This in turn has revived questions surrounding the
potential role that hybridization may play in the penetration of evolutionary novelty in animals [2,3]. A simple explanation for novel phenotypes of
hybrids is available through the process of transgressive segregation. Briefly, transgressive segregation is a phenomenon specific to segregating hybrid
generations and refers to individuals that exceed parental phenotypic values in any direction. This could be caused by heterosis, which is most pronounced in
first generation hybrids, or alternatively by the complementary action of parental alleles dispersed among divergent parental lineages. If this is frequent, then
an important evolutionary role for hybridization is more easily explained [4].

In fact, there is abundant evidence that transgressive segregation is common in both plants and animals and that the genetic architecture for it is rather
commonplace than exceptional [5]. Given these findings, it is astonishing, that relatively few studies have evaluated transgressive segregation in natural systems [4].
On the one hand this a results from the paucity of study systems where sufficiently large samples are readily available and from the simple fact that quantitative
genetics experiments are usually conducted in controlled environments in order to separate environmental from genetic effects. If one searches for transgressive
segregation one would ideally study traits, which are determined by several genes and that display a hidden divergence of the underlying genetic network [5].
Finally, one has to study direct hybrids and not lineages of hybrid origin because otherwise secondary evolutionary processes will have reshaped any hybrid lineage
and secondarily modified characters cannot be easily distinguished from transgressive traits. Despite these difficulties many evolutionary studies will ultimately have
to incorporate natural populations in real ecosystems if the effects and outcome of hybridization are to be analysed.

As an example, hybrid zones among divergent lineages are viewed as natural laboratories and offer interesting study systems [6]. In these, the fitness of hybrids
is a key component to understand the dynamics of the hybrid zone as a whole [7]. Transgressive segregation may affect hybrid fitness as it is a mechanism that
would make hybrids different and thus produces the raw material upon which selection can act.

We have recently identified hybrid zones of European sculpins belonging to the Cottus gobio complex (Scorpaeniformes, Cottidae) that fulfill the above requirements.
Sculpins are small, benthic freshwater fishes that occur in streams throughout Europe, with closely related species distributed throughout the northern hemisphere.
Previous studies have revealed a high cryptic diversity of this group across the entire distribution range [8]. Our focus area is the River Rhine System, where
divergent lineages of sculpins are known to occur in parapatry and have come into secondary contact [8,9]. Small tributaries to the Lower Rhine drainage are
inhabited by isolated populations of 'stream' sculpins, a lineage endemic to the River Rhine [8,10]. These stream populations correspond to Cottus rhenanus [11].
Intriguingly, a new 'invasive' lineage, has recently appeared within the main channels of larger rivers that where previously free of Cottus [10]. The invasive sculpins
represent a different species, Cottus perifretum [11] that differs from sculpins in streams of the Rhine area (C. rhenanus) in body shape and in that its lateral body
is largely covered by modified scales vs. an almost complete absence of such modified scales [10]. Invasive sculpins come into secondary contact with populations of
stream sculpins where small tributaries disembogue into the main channel of larger rivers. In these areas individuals belonging to both parental populations
as well as hybrids among them occur syntopically. With respect to transgressive segregation the above prerequisites are fulfilled. First, sufficiently divergent
lineages come into contact and produce recent hybrids. Secondly, these hybrids can be readily identified using genetic data. Finally, variation in body shape provides
a well-suited character complex since sophisticated methods are available to study shape [12]. Furthermore, previous studies on body shape show that this
character complex is usually determined by multiple genes [13-15]. Below we combine genetic and phenotypic approaches to study body shape in sculpin
hybrid zones and present data suggesting that transgressive body shape phenotypes occur in natural sculpin hybrids.

In order to study variation in shape, parental groups and their hybrids were classified to establish how their phenotypes and genotypes were related. Since shape
was of key interest, we relied on model based population genetic approaches [16] to independently cluster and assign specimen to their populations of origin
or to determine their hybrid status. Such model based clustering is not possible in the analysis of shape because a powerful "theory of population shape"
comparable to population genetic theory is lacking that would allow to independently infer population affinity.

However, simple assignment methods can contribute much in the sense of the first assignment approaches in genetics that were employed for much more basic
questions [17] namely the problem that distances alone are biologically and conceptually hard to interpret. As an alternative to an abstract distance one may
ask whether a given character is sufficiently informative to be diagnostic at the individual, population or at higher levels to help in assessing the significance of results.
This general problem also applies to quantitative morphometric studies, especially when multivariate analyses are used. We have developed a distance based
assignment approach with statistical tests that parallel population genetic approaches [18]. The method is not intended to give a measure of the absolute distance
among groups but may help to interpret the differences among groups. One purpose of this paper is to introduce shape based assignment as a multivariate measure
of distinctness and to employ this approach to study the relationships of genotypes and phenotypes at natural hybrid zones.


Results > http://www.ncbi.nlm.nih.gov/pmc/article ... ecid342125

Discussion > http://www.ncbi.nlm.nih.gov/pmc/article ... ecid788357


Last edited by ken kennedy on Sat Dec 18, 2010 7:34 pm, edited 1 time in total.

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PostPosted: Sat Dec 18, 2010 5:45 pm 
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Image
The left angelfish in the above photo is a still shot from a video of wild altums in nature. The angelfish on the right is?
Well the importer ordered large adult altums and he got this one above together with these below.
Image
This photo above was earlier posted in another thread for ID which location http://www.finarama.com/forum/viewtopic ... 9617#19617
and a number of members here identified the angels as upper Rio Negro or Sta Isabel to be more specific.

However in another thread, http://www.finarama.com/forum/viewtopic ... 1054#21054
the same angelfish was identifiesd asTapajos and that it looked more Scalare. Now there is confusion.

In this photo below, the left angelfish was identified here as true altum (but according to Heiko, in another thread,
it is not; it is a Rio Negro Scalare.) while the angelfish on the right is another one from the batch imported as altum.
Image

Clearly from the pictures presented above, especially the first/top one. The shape of the two angelfish are very much alike.
Definitely, the angels that were imported are not Orinoco Altums. However, to say they are Scalare, imo, they are not.

Morphometrics using scale and fin ray counts have been done with the different angelfish variants/localities to distinguish them from one
variant/locality to another and from one species to another. But these morphometrics though can not be easily/readily used by simple hobbyists
in identifying the wild angelfish variants that they have.

In addition to the scale and fin ray counts, can body shape be part of the morphometrics as presented in the paper above. Introducing shape based
assignment as a multivariate measure of distinctness and to employ this approach to study the relationships of genotypes and phenotypes at natural hybrid zones.
Also can size/height be part of the morphometrics. In the case with the eyes, do altums have bigger eyes in proportion to the face or caudal peduncle than scalares?

Natural hybrid zone. Is/are there angelfish hybrid zones? This needs to be determined.

To be continued


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PostPosted: Sat Dec 18, 2010 10:25 pm 
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I've asked that question before and just a few days ago I bumped that thread back to the top...I did that because it seems many more fish are being ID'd as altums nowadays than ever before...at least to me. I am by no stretch an expert or even a novice for that matter but all of this IDing as altums...well I'm not so sure that it is entirely correct.

To me I think the Orinoco fish is something wholly different than all of the rest. I also think that if the Orinoco fish have made it into other river systems they have definately mated with other angels native to those river systems giving rise to the peruvians and the negros and all of these other varieties we are seeing as of late. If this is really true then it bodes well for the lucky breeder who can keep altums alive and cross them with scalare breeder forms. That breeder will see some excellent hardy fish I bet!

I agree the taxonomy of pterophyllum has been rather weird for many many years but I still wholeheartedly believe the Orinoco fish is unique compared to all others. One can look to some of the very old literature back in the 30's when pterophyllum was first introduced to USA aquariums and in almost every article there is reference to the "rare" and "elusive" giant angelfish...although I haven't found the term altum in any of that literature.

I'm not trying to say that anyone's fish are not altums I'm just trying to say that in the last year or so I think IDing pterophyllum has become looser and faster than ever before. Let's remember prices and demand are higher than ever before for so called "true altums"...and apparently all of sudden everyone is able to keep them alive and even breed them nowadays when conventional wisdom in the past has always been they are difficult to keep alive and nearly impossible to breed. It just doesn't add up to me...even with the expansion of knowledge concerning their husbandry mainly due to the web.

This recently posted image from catfishbi is classic orinoco altum to me...look at that notch! I would argue that this fish looks ALOT different than any of the pics Ken posted above based on that very pronounced notch alone (except for the second pic which shows a fish that exhibits the pronounced notch but with this fish the bar that runs through the eye tells me it is something a little bit different)...which the "classic" altum has always been known for...

Image


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PostPosted: Sun Dec 19, 2010 12:39 am 
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Yes, but, these fish change their shape/eye bar/pre dorsal notch as they grow and mature.


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PostPosted: Sun Dec 19, 2010 8:42 am 
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Phill Austen wrote:
Yes, but, these fish change their shape/eye bar/pre dorsal notch as they grow and mature.


Have you ever seen a mature altum without a full blown predorsal notch though? Seems that would be a one good indicator to me...and on some of these other fish I just do not see that particulary pronounced notch...

Just so we don't start beating a dead horse yet again perhaps a better approach would be to say something like have you ever seen a definitve predorsal notch with mature scalare?


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PostPosted: Sun Dec 19, 2010 1:00 pm 
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Have you ever seen a mature altum without a full blown predorsal notch though?

have you ever seen a definitve predorsal notch with mature scalare?[/quote]
Edward,
I have seen fish that I believe to be Altum which were exported from Bogota with varying degrees of "notch", the "notched Scalare types that I have seen, had less deep notches than the fish that I believe to be Altum, along with a different bar pattern, larger scales, a lighter brown colour on their dorsal contour and a smaller mouth at a slightly different angle.
I think that we are inevitably beating a dead horse with this, because, as yet we do not have the information (but I am sure it is coming). The photos from Dale Jordan were, for me, the first verified immage of an extremely altumish fish from the Rio Negro drainage. For my money, all the talk of hybrid fish is too premature. I am sure that the identities of these fish will be established, but thus far, the answers (such as they are) tend to raise more questions


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PostPosted: Sun Dec 19, 2010 2:52 pm 
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Rio Negro fish with Altum type "notch"
http://www.segelflosser.de/forum/viewto ... =37&t=2820


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PostPosted: Sun Dec 26, 2010 7:15 pm 
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Phill Austen wrote:
Quote:
Have you ever seen a mature altum without a full blown predorsal notch though?

have you ever seen a definitve predorsal notch with mature scalare?

Edward,
I have seen fish that I believe to be Altum which were exported from Bogota with varying degrees of "notch", the "notched Scalare types that I have seen, had less deep notches than the fish that I believe to be Altum, along with a different bar pattern, larger scales, a lighter brown colour on their dorsal contour and a smaller mouth at a slightly different angle.
I think that we are inevitably beating a dead horse with this, because, as yet we do not have the information (but I am sure it is coming). The photos from Dale Jordan were, for me, the first verified immage of an extremely altumish fish from the Rio Negro drainage. For my money, all the talk of hybrid fish is too premature. I am sure that the identities of these fish will be established, but thus far, the answers (such as they are) tend to raise more questions


The presence or lack of the pre-dorsal notch is a quantitative trait and may vary depending on the angelfish population.

The talk of hybridization, imo, is not premature. There is a lot of confusion regarding the rio negro angels and discussing the hybrid possibility may give an alternative
explanation why the URN angels have similar or intermediate features to altums and scalares.

There is no DNA evidence that shows that the upper Rio Negro angels are hybrids but neither is there proof that they are pure Scalare. It has been shown though,
through morphometrics that there is a cline in the Rio Negro. A phenotypic cline may be evidence of a hybrid zone. The possibility of hybrids can not be dispelled.

Quote:
From the Sculpin study

In order to study variation in shape, parental groups and their hybrids were classified to establish how their phenotypes and genotypes were related. Since shape
was of key interest
, we relied on model based population genetic approaches [16] to independently cluster and assign specimen to their populations of origin
or to determine their hybrid status.


Although animals recognize their conspecifics and will not normally mate with a different species or even variant, interbreeding may still occur...

Wolves and Coyotes are enemies as seen in these two videos

http://www.youtube.com/watch?v=fAoszVLRP6U

http://www.youtube.com/watch?v=nx8DJiliIoc

and yet

http://rsbl.royalsocietypublishing.org/ ... 2e9591ada9
Rapid adaptive evolution of northeastern coyotes via hybridization with wolves


http://www.plosone.org/article/info:doi ... ne.0003333
Hybridization among Three Native North American Canis Species in a Region of Natural Sympatry


Amazon Cichlid Hybrid
http://www.funpecrp.com.br/gmr/year2005 ... l_text.htm
Evidence for a natural hybrid of peacock bass (Cichla monoculus vs Cichla temensis)

Discus ancestors hybridized
http://www.labmeeting.com/paper/2888944 ... ertebrates

Quote:
...This observation is unusual and we propose that the origin of meiotic multiples in males and females is based on a series of translocations that involved heterochromatic regions after hybridization of ancestor wild Discus species.


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PostPosted: Fri Dec 31, 2010 10:45 pm 
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Phil, The more i look at the Rio Negro fish with Altum notch on segelflosser the more it looks Photoshopped. The fish itself is a near perfect profile even though it's in a net. The fish's "texture" looks different than anything in the surrounding photo, almost like a drawing superimposed into a photo. Also, just to the right of the fish, the net is double thickness, whereas the fish is enclosed in single netting, and the netting is not "malformed" in correlation to the contour of the fish.

I realize this has nothing to do with the topic of this thread but this photo has appeared elsewhere, and question its authenticity.

Steve


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PostPosted: Sat Jan 01, 2011 12:53 am 
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That's interesting Steve, I did ask the contributor for more information on the thread, but received no reply. there is a high level of scepticiscism in many of the posts in that forum with regard to Altum identity and provenance.


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PostPosted: Sat Jan 01, 2011 2:50 am 
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Happy New Year everone, and I would like to say a few words about this topic as well.

Morphometric measurements are crucial for taxonomy of any species, regardless of what it is, plant, fish etc. Without measurements we cannot described a species, we have to show that it differs from other species and that there still are significant differences even with its closest relatives making it unique and warranting separate species status. However, at the same time we also know that variations can exist in morphometric measurements within a species. When a new species is to be described its morphometric measurements must be different beyond the range of variation within the most closely related species.

Let us look at the scalare versus altum situation in this context. P scalare has been described over a large range in the Amazon and shows considerable variation in all sorts of morphological characters. This is the result of extensive field collections that have been made over the past 130 odd years (correct me if I am wrong here, I mean in terms of years). Initially, when there were much fewer collections more than one species was described within scalare as we now refer to it, and by this I mean P. eimekei. The most likely reason why it was described was because it was different in morphometrics to P scalare as it was described then. Through many more field collections the variation within P scalare was recognized and it was therefore discovered that P eimekei was nothing else than a P scalare variant, and this was therefore the reason why P eimekei was lumped into P scalare (the term "lumped" is a scientific term which is used when scientists decide to combine one species with another, and then the older name is maintained and the later one is rejected and thereafter not used any longer). Taken together, all of the morphometric measurements which define a scalare angel are then referred to as the "species concept" of scalare.

P altum was orginally described from the Orinoco and some morphological/morphometric variation has certainly also been documented within that species. Now we have more and more reports of the Rio Negro paradox fishes and we have this hypothesis that they are hybrids between P altum and P scalare. This hybrid hypothesis has been developed because the morphometric measurements on these hybrids appear to be be intermediate between those of P scalare and P altum. This hypothesis is strengthened by firstly the fact that the Orinoco and the Amazon are linked via the Casiquiare canal, making the movement of fishes possible. As the direction of movement of fishes is thought to be from the Orinoco into the Amazon and not in the opposite direction, there is the idea that this hybridization involves introgression (literally meaning P altum creeping into P scalare) which progressively gets less as the distance from the Orinoco increases. These morphological measurements included the famous notch on the head and various other morphological characters such as concave versus convex tail fin as well as other more subtle things which apparently only the specialist can identify. This means that we now have a situation where different persons have different opinions about what a true altum should actually look like. Some persons are conservative and say all the characters have to look exactly like what they perceive to be an altum, others have a less strict definition. This sort of situation only fuels controversy which I do not think is very constructive. The question therefore actually is, how far are we prepared to "stretch" our measurements of altum to still allow fishes into the so-called "species concept" of altum.

On top of this we do not have accurate measurements of what true altum x scalare actually look like and what their morphometric measurements would be. The question is whether they would be perfectly "half way" in these measurements or whether they would tend towards altum or scalare. If it could be assumed that they would be half way, then the argument would be simple, because any fishes that we would find in nature could then be placed on a scale from scalare to altum. However, the genes that control morphology are not likely to behave like this, some would be dominant and others would be recessive so first generation hybrids may look much more like altum or scalare, but we simply do not know.

On top of all this, how do we know that there are really two different species, scalare and altum and whether what we are seeing is not a very wide variety of variation within one species? Or did these two species separate from a common ancestor long ago and are now combining as hybrids again. Again, we simply do not know.

How can we perhaps start understanding all this? Well we need to study the sequences of the DNA of nuclear and mitochondrial genes in order to get an accurate indication. Why I say this is because this evidence is not influenced by dominant and recessive genes, you measure the sequences accurately and you can determine original species and possible hybrids. At the same time as saying this, I want to state that my opinion is not that DNA sequences can replace morphological assessments, both are definitely required in order to make sense of all this. However, without the DNA studies this will continue to remain a debate. It is my considered opinion that morphometric measurements alone cannot give us the answers for the reasons that I have given above.

I want to post recent evidence on the African elephant which is highly pertinent to this question. Thanks to DNA evidence, the African elephant is now clearly recognized as being two species that separated a long time ago, but in spite of this they still have hybridized regularly over time.

Kind regards,

Dirk

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PostPosted: Sat Jan 01, 2011 7:46 am 
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Dirk Bellstedt wrote:
Happy New Year everone, and I would like to say a few words about this topic as well.
Hi Dirk, and Happy New Year.
I'd like to add some of my thoughts, one at a time. See if you think I've identified a problem in my understanding.

Quote:
Morphometric measurements are crucial for taxonomy of any species, regardless of what it is, plant, fish etc. Without measurements we cannot described a species, we have to show that it differs from other species and that there still are significant differences even with its closest relatives making it unique and warranting separate species status. However, at the same time we also know that variations can exist in morphometric measurements within a species. When a new species is to be described its morphometric measurements must be different beyond the range of variation within the most closely related species.
Dirk,
As you say, variations can exist within a species.

However, the next statement, that a "new species must be different beyond the range of variation WITHIN the closest species", opens up a question.

suppose I have species "A" which has big variation within. I then find a group of critters resembling some members or groups within species "A", at the extreme of the variance in features.

This new group I found, has ACTUAL physical measurements out of the range of any "A" member. It has one or two more scales, and one more fin ray, and a number of them have a very slightly, but measurably steeper notch than any individual we examined from "A".

So the group's actual features are measured as outside the averages, even outside the actual extreme end range of any individuals in "A"
However, this group has little variance within-group.


Under this question, rechecking your statement, it would appear that ACTUAL measurements from the new group are being compared to Variance within the species, rather than with the limits measured for the species.



d


Last edited by rag on Sat Jan 01, 2011 9:09 am, edited 2 times in total.

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PostPosted: Sat Jan 01, 2011 8:30 am 
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The above question aside, and going into the subject a bit more >


Purely from an uninformed but speculative position, I'd say that finding that a new population or group has "more extreme measurements than any of the individuals of the species thus found", is not a good sole measure of a new species - neither is finding a group that has more variance within-group, than the species shows between groups. It happens all the time. It happens with scalare.

So it's not all that clear what is being compared to what - and why.

In the latest scientific effort, we see that they

Quote:
...to trace the genetic and phylogeographic existing species in the genus it is necessary to delimit taxonomically the individuals collected.

To this end, Specimens were identified based on taxonomic description (Discussed in section I, general introduction of 5) of the known species of the genus Pterophyllum, according to Kullander (1986, 2003)


Step 1; Do it by measurements. They used Kullander to categorize, or "bin" their specimens. Let's see what that means.



The author states
Quote:

Lowe-McConnell in 1969 (a) quoted problems on the validation of genus and ****the existence of overlap of meristic characters****


and [quote]Besides the existence of morphological variation and overlap of character meristic, as the number of scales, may represent different mortipos [ suggestion: “morphotypesâ€


Last edited by rag on Sat Jan 01, 2011 11:46 am, edited 2 times in total.

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PostPosted: Sat Jan 01, 2011 10:39 am 
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Hi Dave,

And a Happy New Year to you as well. Whilst writing my reply, I was very careful in expressing myself to be within "rag" bounds as I knew that you would be scrutinizing my comments very carefully! Thanks for keeping a wakeful eye on the scientists that tend to make absolute and not entirely supported statements!

I have tried to keep my arguments simple, but they are obviously oversimplified and your comments and questions are completely valid and correct. When describing a species, scientists use this "species concept" idea to define something new. This is like packing cards that conform to certain descriptions into boxes, but all of a sudden you find that this card actually should not be packed into this box because it does not conform to what you have decided needs to go into any of the boxes. Experienced biologists actually know what is different, before they do the actual measurements. Sure they will do the measurements because they know that these are required, but if you are a biologist that know the group that you work on well, you develop a feel for something that is different and actually can "feel" that something is different before doing the measurements, but the measurements are essential and all biologists know this and do them before describing a new species. This may sound very unscientific, but you have also looked at an angelfish in a shop and said to yourself, "but this is different" and have the same "feel" .

To get to the last point that you raise, you may have variance within a species that you know and then you identify something new. Again if you establish the limits for the new species, you should not have an overlap between the old and the new species, this is quite correct. However, you can have overlapping measurements for one character and then for another the measurements you do not have an overlap. Now you as a scientist decide that this is enough to constitute a new species. This is an opinion, and it is not based on scientific fact. What is uncanny though is that an experienced biologist can tell you that a group of fishes is say different or not. Very often their notion is eventually supported by DNA evidence and they are shown to be correct. The question is therefore: "Can you view someone to be a sufficient authority on a group to be able to rely on their gut feel that something is new or not". Again this is subjective and not objective. This is basically the question that has been posed at the beginning of this thread. As a molecular systematist, I hope that DNA sequence determinations will reduce this mystical subjectiveness.

Your thoughts?

Kind regards,

Dirk

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PostPosted: Sat Jan 01, 2011 11:04 am 
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Dirk Bellstedt wrote:
Hi Dave,

And a Happy New Year to you as well. Whilst writing my reply, I was very careful in expressing myself to be within "rag" bounds as I knew that you would be scrutinizing my comments very carefully! Thanks for keeping a wakeful eye on the scientists that tend to make absolute and not entirely supported statements!

I have tried to keep my arguments simple, but they are obviously oversimplified and your comments and questions are completely valid and correct. When describing a species, scientists use this "species concept" idea to define something new. This is like packing cards that conform to certain descriptions into boxes, but all of a sudden you find that this card actually should not be packed into this box because it does not conform to what you have decided needs to go into any of the boxes. Experienced biologists actually know what is different, before they do the actual measurements. Sure they will do the measurements because they know that these are required, but if you are a biologist that know the group that you work on well, you develop a feel for something that is different and actually can "feel" that something is different before doing the measurements, but the measurements are essential and all biologists know this and do them before describing a new species. This may sound very unscientific, but you have also looked at an angelfish in a shop and said to yourself, "but this is different" and have the same "feel" .

To get to the last point that you raise, you may have variance within a species that you know and then you identify something new. Again if you establish the limits for the new species, you should not have an overlap between the old and the new species, this is quite correct. However, you can have overlapping measurements for one character and then for another the measurements you do not have an overlap. Now you as a scientist decide that this is enough to constitute a new species. This is an opinion, and it is not based on scientific fact. What is uncanny though is that an experienced biologist can tell you that a group of fishes is say different or not. Very often their notion is eventually supported by DNA evidence and they are shown to be correct. The question is therefore: "Can you view someone to be a sufficient authority on a group to be able to rely on their gut feel that something is new or not". Again this is subjective and not objective. This is basically the question that has been posed at the beginning of this thread. As a molecular systematist, I hope that DNA sequence determinations will reduce this mystical subjectiveness.

Your thoughts?

Kind regards,

Dirk
Dirk, yes, there is some element of corroboratory correspondence between common knowedge within a hobby or trade, and Science.

Especially in a trade, though, the rigors might be might more than in academe. Often what passes muster in academia would be laughed out of the room in commercial settings where real jobs and big money depend on good results that can be replicated.

Nobody wants to hear from an academic who "thinks so", that the bridge will stand, or the plane will fly.

We want engineers who guarantee it.

An example of breeder knowledge corroborating or being corroborated by the science, is the recent information coming out on dogs and the hobbyists' or farmers' categorization of breeds into groups, such as "sight hounds" - categorizations which have proven to correspond to genetic investigations of relatedness between the breeds, no matter about physical appearance.


How common is it for the specialists in techniques, to have their own intimate knowledge of the critters themselves, though ?

and if it all boils down to gut feelings and subjective "feelings", we'd be better off just taking polls.


Last edited by rag on Sat Jan 01, 2011 11:31 am, edited 6 times in total.

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