The species that compose a cryptic species complex are no more or less important than any other species. The problem lies in our ability (or inability) to differentiate the species within a complex. If we assume that all of the individuals that “look alike” are a single species, we view it as a species that has a wide range of biological traits (whether that is range, diet, breeding habits, etc), with some demonstrating certain traits and others demonstrating different traits. It may be that that reflects a single (but variable) species. Alternatively, the different suites of traits may reflect different species, with each having a narrower range of traits. So how we classify a species influences how we interpret ecology and evolution. Perhaps cryptic species remind us that what we call a species is still a hypothesis. Testable, but still a hypothesis.

Cryptic species are actually real species. They are important for quantifying biodiversity. They derive from speciation processes like all other species. Therefore, in conservation science, they must be considered like the other species. However, I don't think they are more important than other species; maybe they are only more interesting for certain scientists, because the finding of a complex of cryptic species, for instance by means of molecular markers, is often unexpected.

Cryptic species is a difficut item within ecology, which seem to be important. Certain ecological patterns (e.g. distribution pattern of certain species across environmental variables) can be related to the fact that a cryptic species might be at work. We have done a study (Zettler et al., 2013) on this, where we discover that cryptic species can explain certain of the obserbed patterns.This make it difficult of course in interpreting certain ecological patterns or use it static concepts (e.g. indicators; see Zettler et al., 2013).

The species that compose a cryptic species complex are no more or less important than any other species. The problem lies in our ability (or inability) to differentiate the species within a complex. If we assume that all of the individuals that “look alike” are a single species, we view it as a species that has a wide range of biological traits (whether that is range, diet, breeding habits, etc), with some demonstrating certain traits and others demonstrating different traits. It may be that that reflects a single (but variable) species. Alternatively, the different suites of traits may reflect different species, with each having a narrower range of traits. So how we classify a species influences how we interpret ecology and evolution. Perhaps cryptic species remind us that what we call a species is still a hypothesis. Testable, but still a hypothesis.

In line with some of the previous answers, I don't think cryptic species are more or less important; they are just species. The interesting thing about cryptic species is that they inform us about evolutionary processes, and in particular may provide clues about processes we may have missed in delineating species only by morphology (the traditional way). For instance, many mammals use olfactory signals as sexual cues, but of course humans have lost a refined sense of smell, so our tendency would be to overloook olfaction as an important signal driving mate choice. Discovering cryptic species informs us about additional ecological and evolutionary processes at play in nature.

Cryptic species are cryptic only for us. They recognise themselves well, otherwise they will frequently hybridise and we will be unable to detect any cryptic species

It depends on context. Does it matter if you misidentify species? If so, then cryptic species matter a lot as they will make that task much harder.

Consider cases where if you don’t realize that a species you are focusing on is different to what you suppose it to be. You might easily infer the wrong behaviours, ecologies and values.

I made a brief summary about this in the context of "taxonomic accuracy" in a paper about invasive alien species (on RG at:

https://www.researchgate.net/publication/233099744_Of_Cecropias_Snarks_and_Boojums?ev=prf_pub).

Hope that helps

Douglas

Article Of Cecropias, Snarks and Boojums

Not only cryptic species matter for their ecological (they usually fill different niches) and evolutionary (the so called "speciation at work" sums it up pretty well) interest; they also have significance on apllied aspects.

Biodiversity assesment and conservation, parasite/plage-host relationships, antidotes for poisons, ecotoxicology tests... all those fields can be hindered every time two cryptic species are mistaken for a single one.

A clear example is the Eisenia fetida- Eisenia andrei species pair: these earthworms have been widely used for vermicomposting, usually mistaken for the same species. It's difficult to tell which one is more efficient at this task, as several studies could have dumped them together.

Thanks for all these insights, it helps a lot :)

Here is an interesting news story that illustrates the issue:

http://news.sciencemag.org/signal-noise/2014/04/two-new-snapping-turtle-species-overnight

It says:

"Turns out that the largest river turtle in North America is not one but three species. Researchers from the University of Florida and the University of Vermont uncovered this unexpected species richness after sequencing DNA from alligator snapping turtles and analyzing body shapes. The findings, published this month in Zootaxa, indicate that the three species are genetically and morphologically distinct—and are more endangered than originally thought, Scientific American reports."

See the primary article here:

http://www.mapress.com/zootaxa/2014/f/z03786p165f.pdf

A cryptic species is, as the name says, cryptic. We know virtually nothing about it as long as we cannot see it, i.e. as long as we cannot identify it, i.e. as long as it is not described properly. It is very helpful if a cryptic species is ‘identified’ but it is not helpful if this is the end of the line. Taking the example of Douglas concerning Alligator Turtles, there were obviously some guys combining genetics, ecology and morphology describing two new species. This is modern taxonomy at its best. In this context we maybe should think about a phenomenon. And please correct me if I am wrong. I have the feeling that cryptic species are primarily the output of molecular based research. Morphological based research generally does not stop at the point ‘there is something interesting, but someone else should find out what it is’.

Alexandre, I know this is not exact the answer to your question. I agree with Ferruccio that a cryptic species has to be considered like all other species. But that is this also possible if it stays cryptic? See the comment of Gert.

By the way, some months ago there was a question in the sense ‘is traditional taxonomy still important?’ Dear taxonomists – how many taxonomical questions have you seen at ResearchGate last month? Is this rally the significance of taxonomy in the scientific community? Are taxonomists an endangered ‘species’?

Dear ecologists and genetists – did you realize all the questions asking for identification of something? Any idea how long someone is there to answer (properly)?

The point raised by Harald on the possibility of considering cryptic species in the same way as non-cryptic species supports the importance to make efforts in order to identify cryptic species and understand their ecological roles within ecosystems.

This whole matter gets even more complicated with asexual organism. The group I know best, the Glomeromycota (arbuscular mycorrhizal fungi) contains 'species' that I cannot separate morphologically, and yet their molecular analysis places them apart at the distance of order, not just species. Other 'species' are defined in a way that completely bewilders me as I can see no logic, except for the desire to be an author attached to a name. The nomenclatural code doesn't help much as it requires only that the rules be followed to establish a name, regardless of any biological logic (it is about nomenclature, not biology). It is a challenge even to define what a 'non-cryptic' species is for these organisms, let alone cryptic species. Culture collections would help a lot but the ones that exist are threatened by funding inadequacy and in any case contain only a small fraction of the species in the group, and even less of the diversity within a 'species'. I am a bit cynical from years of experience, but it seems to me that the fault often lies with researchers who are happy to apply a name but not so eager to accept that the name might be mis-applied. This, as pointed out by Harald, feeds into the debate about taxonomists and their perceived value in the scientific community.

The fact that cryptic species are generally morphologically similar to the known/identified species raises many interesting questions that may not otherwise be asked or explored. Most cryptic species are currently first identified using molecular methods (eg. see: Page, TJ, Choy, SC & Hughes, JM. 2005. The taxonomic feedback loop: symbiosis of morphology and molecules. Biol. Letters, 1: 139-142) so the questions: "why are they morphologically/phenotypically similar yet genetically different; is it at the early stages of speciation; what are the driving forces underpinning this; are their niche similar, if so, what is the level of competition, etc." need to be answered.

So while cryptic species may not be important on their own, they do raise some very interesting evolutionary and ecological questions which can further our understanding of the processes and forces at work.

Going a little further, cryptic species (especially species complexes of multiple look alike species) are useful because they showcase what may be a particularly successful morphology that keeps on being maintained while behavior, physiology, ecology, etc. etc. change allowing the genetics to become different (different at a population level - of course the genes that drive the behavior, physiology, ecology, etc will be different from the beginning but we usually do not catch those until the neutral signature has become different enough for us to "see" it).

Their importance depends on what happens if we ignore them, does it change our conclusions on :

- biodiversity estimations ?: on a global scale, yes, but ... so what..., on a local scale, it depends whether cryptic species are allopatric or sympatric...

- ecosystem functioning/resilience ?: to answer this, one must know if cryptic species share the same niche or not: this obviously depends on the cases.

and so on...

I think that such species remain cryptic until we can discover any tool to discriminate among them.

To me, the importance depends on what we mean by "species" and what assumption we have implied by "species". There is an somewhat exaggerated notion that "if there are n biologists, there will be n+1 species concepts ". I agree with Stuart that species is a testable hypothesis. My understanding of “species” is a multi-dimension entity. It occupies certain space, plays specific ecological role, has specific gene pool, and/or morphology, behavior ..and other biological features. These features give rise to a specific inertia that members of same species are more similar to each other than to members belonging to other species, in one or more dimension (axis). This notion underlies all assumptions we makes for a species hypothesis. From this sense, non-cryptic species are only those we knew them in >= 1 dimensions, but there remain n-1 to be understood.

I agree with Chengmin Shi, that each species has specific gene pool, morphology, behaviour and other biological feature. I also faced a marine invertebrate species with cryptic nature while working on intertidal benthos. I don’t know more about cryptic nature of a species but some hypothesis about origin of cryptic species boggling my mind that, When a species become cryptic?, It’s an effect of various environmental or niche factors on that species?, Is there any reason in nature for origin of cryptic species?, When a species moves/migrate from one niche to another, Is it can lead to origin of cryptic species due to changes in various biological features like behaviour, interactions with other new members, different types of food availability, different environmental factors (Temp, salinity, ph…etc.)?

Well, speciation is the result of evolutionary pressure. So, for example, if a 'species' is defined from morphology, there may have been no pressure to change morphology, but there could be huge pressures that resulted in large genetic differences. Such differences might now be regarded as sufficiently great to be considered as species-level modification, even though there is no (obvious) morphological change. With modern molecular methods, it is relatively easy to find these kinds of differences. Whether they really represent 'species' may well still be a matter of opinion!

Dear Christopher, if you find a large amount of genetic divergence, you can say that you are facing different species! However, based on only molecular data, there is surely a "grey zone" in which "opinion" plays a major role...

Going back to your original Q here - If the environment change, then they may not be so cryptic anymore. Now, how will they then coop?

I came across a paper that is relevant to this discussion: http://onlinelibrary.wiley.com/doi/10.1111/mec.12808/abstract

Though so many scholars are focusing on cryptic species, according to classical genetic principles, the phenotypes of a species will be determined by its genotypes. However, in the case of cryptic species,  identical phenotypes are expressed even many species have different genotypes. Anyone could explain the phnomenon?

Lin, "cryptic" species often just refers to morphology and sometimes it varies with life stage. In the "mosquito world" where I work, although adult females are what we most easily catch (and are the important disease vectors) often the species identifying characters are in the male genitalia. So we will label species as cryptic because we cannot tell the females apart. Of course that is an "operational reality". There are species that truly look very much alike - if you read the paper that Loren sent a link to - only distinguishable by the species of symbiont they associate with. Obviously the genetic differences are having an effect - the symbiont call tell.

I couldn't view the paper in discussion!

This cryptic species issue you are asking about is a huge problem in the plant world, that Dr. Ledyard Stebbins and I  co-authored a paper on the subject, that is listed at http://www.ecoseeds.com/stebbins.html = 267. Stebbins, G. Ledyard and Craig C. Dremann. 1998. Jepson Manual chromosome numbers may indicate new "cryptic" native grass species. GRASSLANDS 8 (3): 4-5.

The problem with plant species themselves got started in 1753 when species were sorted taxonomically by physical characters, and probably 99.999% of the plant species have already been named using that system, before we knew anything about either the genetics or the breeding systems between look-alike plant that are actually different species because they cannot breed and produce viable seeds.

Then in the plant world (and perhaps also in the animal world with the issue of subspecies), the whole ecotype issue is still unresolved, when plants through isolation, form genetically fixed ecotypes, then through time and isolation are they becoming separate species?  And with the ecotypes of an individual species are we seeing evolution in situ over time?  

I wrote an article on the subject of ecotypes that has an illustration of a local native grass species, Bromus carinatus, and shows where I saw evolution in situ starting to bud off separate species via its ecotypes at http://www.ecoseeds.com/juicy.gossip.three.html.  

The article also has a ecotype-article bibliography in chronological order from 1880-1996, with special attention to Dr. Greene's work in 1905 on the California poppy is very interesting, and of course the "father" of ecotypes, Dr. Turesson's work 1919-1931 then picked up by Dr. Clements and also Drs.Claussen, Keck and Hiesey at the Carnegie Institute at Stanford in the late 1930s-1950s with their common garden studies.

So getting back to the cryptic species in plants, then when researchers like Stebbins in the 1940s started counting grass chromosome numbers.  That was the first indication that relying on physical characters to solely define an individual "species" was flawed, because whenever multiple chromosome occured within an individual "species" that automatically means that you have more than one species hidden as a single taxonomic species. 

Our article was extremely controversial in 1998, because what our conclusion was, that out of the 300 California native grass species that had been named solely using physical characters, the chromosome counts were indicating that out of those 300, at least another 100 new species would have to be teased out and described taxonomically, and with grasses that would be very difficult.  

A whole new taxonomic science and set of physical characters would need to be invented to sort out the look-alikes to jive with their chomosome numbers.

We were proposing a new taxonomic nightmare for the next 100 years, to start the process of melding genetics with taxonomy when naming species, and the sorting out of look-alike species of grasses based on the fact that they cannot breed, so are true separate species at the end of the day.  

If I was making that huge earth-shaking scientific proposal alone in 1998, the paper would have never been published, but since the science was correct, and Dr. Stebbins as a co-author, how could the editor of that small publication of the California Native Grass Association at Davis, refuse Stebbins?  

So the bottom line is the cryptic species will always be hidden, until species and taxonomy recognize that they exist, and go through the species and start sorting them out if the look-alikes cannot breed with each other, and officially name the new species, so they are no longer cryptic. 

There are also valuable protective measures in place.If the production of pyrrolizidine compounds to prevent herbivory is metabolically taxing and a plant can mimic morphology instead, this is a very elegant solution.

This occurs with butterflies and a host of other animal species. Are there survival strategies also in place?

There are two kinds of cryptic species. (1) Molecular races. These track isolation internal to a species and signal a kind of pre-speciation. They are not hidden species, they are hidden pre-species. (2) Molecularly based "species". These are molecular races for which researchers search for morphological traits that match the OTUs. This leads to multiple test problems because morphological traits must be evaluated in toto, not just cherry-picked to provide "support."

Attached find the full paper on cryptic species, the subject matter under discussion

Please take a look at the following links.

http://macroecointern.dk/pdf-reprints/Struck_TEE_2018(2).pdf

https://www.nature.com/articles/s41598-017-02938-z.pdf

I agree with Dr. @Stuart and Dr Dina Madeira Fonseca , but I would like to add what I think regarding this. Due to our limitations in finding out the ecological significance of cryptic species. For the time being, it is better to call them ecologically 'null' since mathematically null is anything tending to zero or zero. For the 'importance' part, yes, they are hiding intricacies of evolution within them, as most of them are clustering at the base of any group (in my case its fungi). For the ecological importance they are not less or more than other taxa in any group, depending upon their habitat they perform the required task. So it is important to know the origin of these cryptic species to trace down the exact function of them. Most of the time they are just eDNA sequences, which cluster with/within some groups, in this case morphological data is very important. But at the same time we should also know the parent group as well, whether they have any 'cryptic' lifestyle or not, which allow them to make some polymorphic changes in the sequence and let them stay in a 'null' ecological state. This is just my opinion on this. Thank you and all the very best.

what an awesome conversation...thank you all for the knowledge I have learned from you all.

Vinit Kumar , you might be interested in this recent publication by McPeek and Siepielski regarding different ways species can be more or less ecologically equivalent: Article Disentangling Ecologically Equivalent from Neutral Species: ...

I also feel like I should note that cryptic species can have very different ecological roles (as is the case for some parasitic or parasitoid animals that look very similar but have different hosts), and ecologically equivalent species might not be cryptic, as is likely the case for some land snail and damselfly species that are easy for (some) humans to tell apart because of their different markings, but have pretty much the same habitat requirements, predators, and prey. "Cryptic," often simply means difficult for humans to distinguish, which may or may not correlate with ecological similarity.

Here are three good and recent theoretical articles that deal with cryptic species and their formation processes and how to recognize them, as well as their applicability in conservation and ecological studies.

Article Finding Evolutionary Processes Hidden in Cryptic Species

Article Cryptic Species - Conceptual or Terminological Chaos? A Resp...

Article Cryptic Species – More Than Terminological Chaos: A Reply to Heethoff

By becoming aware of cryptic species, you can watch evolution in real time. For example 30 years ago I started cultivating a native grass Hierochloe odorata, and native grasses commonly multiply their chromosomes, so essentially they are evolving into new species--even though taxonomically they look identical. In California 100 of our 300 native grasses have increased their chromosome numbers.

So about 15 years into the cultivation of the Hierochloe grass, found a faster growing polyploid and separated it out from the rest. Now, another 15 years later, about 3% of that polyploid has been increasing its chromosome numbers, so I now have a grass so big that it no longer fits in the shipping boxes.

It is like catching a fish that is too big, so I toss them into a special place for them to grow, and see if they continue to gigantisize in the future. I never thought that evolution could happen in only a few decades, but if we keep an eye on the native grasses and their chromosome numbers, we can be the real-time observers of evolution taking place during our lifetimes.

From the perspective as I know, of course Yes, the importance of the cryptic species increase the gene amounts directly due to the relationship with Diversity, particularly Genetic Diversity.

According to the traditional morphological and behavior characteristic, the state of these speices are regarded as the same species ,actually cryptically, i.e. a complex. However, the potential functions is unknown in detail.

As the component of the ecosystem, existence is reasonable.

Sometimes cryptic species are justified by molecularly paraphyletic species, that is, those species with exemplars distant on a cladogram using DNA. My recent studies indicate that progenitor species are common, and these have multiple molecular races. In the groups I have studied, the distance between two exemplars of one paraphyletic species on a molecular cladogram averages 9 nodes, i.e., 9 minimally linked shared phylogenetic ancestors. The dispersion of molecular races from a progenitor (paraphyletic) species at 3 sigma (3 standard deviations) is 13 minimally linked shared ancestors on a cladogram. This means that two exemplars of the same species must be at least 13 nodes distant on a molecular cladogram before they should even be considered as possible cryptic species rather than simply different molecular races of one species.

Hi Richard Zander

can you be more precise? If I look at a tree of alleles of a rapidly evolving gene (for instance mitochondrial COI in animals), when there are 50 alleles, it does not mean that there are 50 cladogeneses... Thank you in advance. How do,you define a node (do you apply a threshold on the ratio Pi-within/Pi-between to delimite your "nodes" ? An average of 9 such nodes does not seem, to me, the general rule in animals at least (though I admit there are cases when cryptic species are not sister species).

I'm defining molecular races for situations in a molecular cladogram when multiple lines extend to three or more exemplars of the same species. If the three lines are multifurcation, we do not know if the DNA is different among the tree or not. But if there is one node among them, we know that two lines share a trait the other does not have, thus there are two races implies It helps if the races are in different parts of the world, because they may be just different occasional mutations. Naturally to detect races of species, a great deal of sampling must be done among individual species.