In biology, a cryptic species complex is a group of species which satisfy the biological definition of species; that is, they are reproductively isolated from each other, but their morphology is very similar (in some cases virtually identical).

They are typically very close relatives and in many cases cannot be easily distinguished by molecular phylogenetic studies either: If lineage sorting has not yet been completed, members of a cryptic species complex widely share plesiomorphic haplotypes, while individual species might not have evolved distinctive autapomorphic mutations yet. But usually, individual species within the complex can be separated by analysing data from multiple sources, such as by comparing DNA sequence analyses, bioacoustics and thorough life history studies.

They can, but need not be, parapatric, quite often are sympatric, and sometimes allopatric. Cryptic species complexes are not the same as populations undergoing speciation, but typically represent a situation where speciation has already broken gene flow between populations, but evolution has not progressed to a point where easily-recognizable adaptations have taken place.

Cryptic species that do not form a complex may be somewhat more distantly related and simply represent lineages that have been so successful as to require little evolutionary change, possibly coupled with parallel evolution. A famous example are the Eurasian and Short-toed Treecreepers, perhaps the first cryptic species to be recognized as such (by Christian Ludwig Brehm in 1820). Other ornithologists refused to accept that more than one species was involved, until Brehm presented his bioacoustic studies which left no room for doubt. The European Treecreeper has since turned out to be a very close relative of the Himalayan Hodgson's Treecreeper, while the Short-toed Treecreeper is probably the sister species of the North American Brown Creeper.

A related concept is the superspecies. This is a clade of at least two more or less distinctive species with approximately parapatric distributions. Not all cryptic species complexes are superspecies, and vice versa, but many are.

[edit] Examples

• Algerian Barb (several species suspected)
• Audubon's Shearwater (several species suspected)
• Asian glass catfishes (several cases known, most notoriously K. minor)
• Brachionus plicatilis complex (approximately 10 species)
• Common Bush-tanager (several species suspected)
• Golden/Mangrove/Yellow Warblers (at least two species suspected)
• Grey-cheeked Thrush and Bicknell's Thrush
• Leopard frogs
• Mouse lemurs (16 species)
• "Placidochromis" (over 30 species described in 2004)
• Pogonomyrmex barbatus and P. rugosus (at least six lineages within the two morphospecies)
• Red-legged frogs
• Rhacophorus flying frogs (several cases suspected)
• Scytalopus tapaculos
• Two-barred Flasher (suspected)
• Trichoplax adhaerens (multiple species suspected)

[edit] Consequences for biological studies

It has been suggested that cryptic species complexes are very common in the marine environment^[1]. Although this suggestion predated the detailed analysis of many systems using DNA sequence data it has been proved correct^[2]. The increased use of DNA sequence in the investigation of organismal diversity (also called Phylogeography and DNA barcoding) has led to the discovery of a great many cryptic species complexes in all habitats. In the marine bryozoan Celleporella hyalina^[3] detailed morphological analyses and mating compatibility tests between the isolates identified by DNA sequence analysis were used to confirm that these groups were >10 ecologically distinct species that had been diverging for many million years.

Evidence from the identification of cryptic species has led some to conclude that current estimates of global species richness are too low. For example, research published in January 2008 based on the mitochondrial DNA sequences of giraffes suggested that there are at least 11 genetically distinct populations.^[4][5] Similar methods also found that the Amazonian frog Eleutherodactylus ockendeni is actually at least 3 different species that diverged over 5 million years ago.^[6]

[edit] See also

• Ring species
• Species problem

[edit] References

[edit] External links

• Shellee Morehead, Jon Seger, Don Feener and Brian Brown, A cryptic species complex in the ant parasitoid Apocephalus paraponerae (Diptera: Phoridae)