Many closely related cichlid species pairs from Lake Malawi will show high levels of morph/behavioral divergence but low levels of genetic/genomic divergence. This will likely be true for many recent adaptive radiations. DNA barcoding is not likely to be useful in these instances.

The increased calcium concentrations associated with the

addition of gypsum to ponds may cause a gradual, but substantial,

decline in total alkalinity.The increased concentration of calcium associated with the addition of gypsum has been shown to reduce total alkalinity

through the precipitation of calcium carbonate. The use of

gypsum may therefore reduce the productivity of acidic ponds.

It may be necessary to correct total alkalinity with lime and

increase phosphorus levels with fertilization if treatment with

gypsum causes these parameters to fall below acceptable levels.

The calcium ions supplied by gypsum act as electrolytes in

the flocculation of colloidal particles. For example, gypsum

applied at rates of 100-500 mg/liter substantially reduced

turbidity in one study. However, similar reductions in turbidity

were achieved using 20-25 mg/liter of alum, which is a more

cost effective treatment

Thymallus nigrescens and Thymallus baicalensis

The first a pelagic lake-dweller, the second a river form; species status questionable due to genetic data

Contact Steven Weiss and Igor Knizhin

Clemens

The following references do not focus on species pairs, but they do indicate that phylogenetic relationships based on morphology are often not supported by genomic comparisons.

Toews, DPL and A Brelsford. 2012. The biogeography of mitochondrial and nuclear discordance in animals. Molecular Ecology 21: 3907-3930.

Chow, S and H Kishino. 1995. Phylogenetic relationships between tuna species of the genus Thunnus (Scombridae: Teleostei): Inconsistent implications from morphology, nuclear and mitochondrial genomes. Journal of Molecular Evolution 41: 741-748.

Perhaps the river and estuarine lampreys (Lampetra sp.) will be of interest to you?

This first paper my deals with sympatric speciation and with colour polypolymorphism as a proxy for possible divergence. you can kind of look at colour and morphology in a similar light. The problem with speciation, is that while some researchers may consider a population of individuals a new species based upon one of the many species concepts, others my disagree. for example in your question: are there any examples of species pairs with divergent  morphology but no DNA differences.

Now firstly at what level of genetic divergence between fish do you consider "different genetically". A very basic example of what I assume you are wanting is found in husbandry (farming) where organisims of the same "species" are artificially selected for a different morphological trait but retain a high proportion of there ancestors genetic make up and are still see as the same "species".  I hope I have helped the second paper goes into the nitty gritty of the problems faced in fish taxonomy and is definantly worth a read if you are working in this field. 

Regards, 

Hi Sergei,

a bit on the lines of Alexander's reply, in the case of sympatric speciation, especially during the early phases, you expect that only part of the genome is divergent while the rest is homogenized by gene flow.

For instance, we work on Nicaraguan crater lake cichlids and these fish have recently diverged in sympatry in benthic and limnetic forms.

We (see publications) recently for two of these species (Amphilophus astorquii and Amphilophus zaliosus) we have shown that the differences in external body morphology observed in nature have, in fact, genetic bases (and we mapped QTL). However, if you look at divergence at neutral loci (such as mitochondrial control region), Fst is pretty low (due to gene flow)...

I hope this helps!

Best,

Carmelo

Article Genomic architecture of ecologically divergent body shape in...

Hi Sergei,

Perhaps the following references will be of interest to you!

- Lamya Chaoui, M. Hichem Kara, Jean Pierre Quignard, Eric Faure, François Bonhomme, 2009. Strong genetic differentiation of the gilthead sea bream Sparus aurata (L., 1758) between the two western banks of the Mediterranean. Comptes Rendus Biologies. 332 (4), 329–335.

- Lamya Chaoui, Pierre-Alexandre Gagnaire, Bruno Guinand, Jean-Pierre Quignard, Costas Tsigenopoulos, M. Hichem Kara and François Bonhomme, 2012. Microsatellite length variation in candidate genes correlates with habitat in the gilthead sea bream Sparus aurata. Molecular Ecology 21, 5497–5511.

Some species of flatfishes eg. Bothus myriaster and Crossorhombus azureus show differences in sexes

Withing genus Salvelinus, species are morphologically distinct but genetically close (interspecies hybrids may survive and even be fertile). It is well studied group and literature is huge. Look through Reist, J.D. and C.D. Sawatzky. 2010. Diversity and Distribution of Chars, Genus Salvelinus, in Northwestern North America in the Context of Northern Dolly Varden (Salvelinus malma malma (Walbaum 1792)). DFO Can. Sci. Advis. Sec. Res. Doc. 2010/014. vi + 18 p. 

Thank you all!

Finally, my case.

In my study on DNA barcoding one can  find results on variation analysis of the gene COI in Stichaeus grigorjewi and S. nozawae. Their values have low variation and overlap. But they are really different species with distinct features on morphology, behaviour , feeding, etc. However, they are found in the area of sympatry and have a narrow area, and as well are considered the most primitive members of the family Stichaeidae.

Sergei, DNA barcoding can be an useful tool but it is by no means (at least in my opinion) the "be all, end all" of deciding when two species are different species or not. Maybe, if you would test other molecular markers, such as mitochondrial control region, microsatellites or SNPs throughout the genome, you would find a certain level of differentiation...

Best,

Carmelo

Many closely related cichlid species pairs from Lake Malawi will show high levels of morph/behavioral divergence but low levels of genetic/genomic divergence. This will likely be true for many recent adaptive radiations. DNA barcoding is not likely to be useful in these instances.

Dear Sergei

You can consider some species of Poecilids such as guppies or swordtails. Also, there is some model fish that show sex differences in morphological traits, such as convict cichlid, Siamese fighting fish, and Astatotilapia burtoni. You can try.

Bests

Depends on your definition of "species". Traditional taxonomy taught that the "species" involved both the morphology and the "work" (behaviour)  and was categorical in nature. Others today treat the "species" as an evolving population in an evolutionary sense. So, for example, an otherwise identical  species that was awake during the day and a species that was awake at night (sympatric species) would be different based on a category approach. A geneticist would dispute that, simply looking at the genetic data (and usually not looking at the whole genome).  Neither approach is "truth", they are just different concepts.

Coulson et al 2011 (DNA barcoding of Canada’s skates, Molecular Ecology Resources (2011) 11, 968–978) noted that here was a lack of genetic differences between Amblyraja hyperborea and Amblyraja jenseni. However, while very similar in appearance, morphology and most meristics, upper jaw tooth count is different between these "sibling" species. They also appear to have different growth and maturity and I am presently examining that aspect. They are largely geographically separate and what we may be observing is a recent separation. I agree that DNA bar coding is a useful tool but is not in itself definitive in defining species.