Hello Atena; Can you tell your readers what organism you are studying? What were the outcomes in other studies involving other members of this group? There must be some common practice among the authors you have read. Following the practice of those authors would be a start.

Best regards, Jim Des Lauriers

@James Des Lauriers

This organism is belonging to the flowering plants, dicots.

Who will identify your species based on molecular studies? Better not to have "sleepless nights" and merge them.

@Tepas Chakrabarty

So many thanks for your answer. Your statement clearly consistent with our opinion.

However, this is a disaster regarding plant taxonomy that there is not a single rule in these cases. One scientist (well-known one), only rely on molecular results, besides distinct morphological differences, synonymized genetically closed species. While remaining authors have the contrasting idea.

@Athena Eslami,

Molecular studies are okay but when you are going for species delimitation, the results of such molecular studies should be supported by sharp external morphological differences.

@Tepas Chakrabarty

What will be better to do if genetically closed species (only 4 bases dissimilarity) do not show sharp morphological differences?

Differences are only relating to only the size of one or two characters.

A paper was published in Taxon sometimes back: Sleepless nights - please do not describe your species based on molecular differences.

I hope this helps.

@Tepas Chakrabarty

It will be surely useful. So many thanks

Hello Atena; Tapas has an appropriately cautious approach. Among many ant genera there are plenty of examples of “cryptic” taxa. They are often given informal designations such as Strumigenys ca-01. Given such a designation the “taxon” can be unambiguously identified in the literature without risking cluttering the nomenclature with invalid names. The discussion can continue in the literature in a way that resolves the uncertainties. Your examples are likely similar to this one.

Best regards, Jim Des Lauriers

Exact title

Sleepless nights: When you can't find anything to use but molecules to describe new taxa

Thank you very much @Subir Bandyopadhyay

Thank you very much @James Des Lauriers

@ Atena Eslami. What you might have encountered are sibling or cryptic species. If there is some molecular evidence that they are different, such evidence often manifests itself in one or more minute phenotypic differences. If you cannot notice these differences then don't describe your species. Morphologically similar species can be synonymized but don't use molecular data for this purpose.

@Ahmed Thandar

So many thanks for your answer.

Such situations have always been problematic. One way is to look into allied disciplines such as anatomy and physiology to observe the differences between otherwise morphologically similar species. Cryptic species are morphologically similar but genetically wide apart. We have not understood so far as why this happens in nature. But we have accepted and recognised such lines. Only a few base pair differences should not constitute a new species according to me but it does not have enough characters to be reflected in morphology. When wide range of specimens belonging to the same taxon from varying ecological niches are examined such minute differences (as you are talking about) should be commonly seen. There is no solid definition of species.

• Shahid Nawaz. I understand your problems and agree with you on all counts. In the lack of a universally accepted species definition and the presence of cryptic species one will have to resort to integrative taxonomy where one takes into account morphological, molecular, physiological, ethological, biogeographic, and other characters into account. There are many papers dealing with separation of cryptic species, but most of these require special techniques. However, one is often limited by the size of the samples, lack of data from other researchers or our own personal limitations. I must, therefore, ask you to make a decision based on the information you have in front of you and don't be afraid to stick your neck out.

Shahid Nawaz Ahmed Thandar

Dear Professors, So many thanks for your answers.

Best Regards

Just fours nucleotide changes is certainly not a criteria for separating the organisms. Variability among the same species can have far more differences than that. I would say that you have no evidence from molecular to separate them. And yet this also is not sufficient evidence to "synonymies" them. Try getting more data or a different sort of data.