Cryptic Species and Their Evolutionary Significance


Cryptic species are detected at an ever‐increasing rate, mainly due to the application of molecular data. While the impact of this hidden diversity on macro‐ecology and conversation biology is widely recognized, its evolutionary significance is rarely. In recent years, it became apparent that definitions of cryptic species are too ambiguous to allow the differentiation between natural phenomena from human‐made artefacts. Hence, recently, a unifying conceptual framework has been proposed highlighting the necessity to test the degree of reduced phenotypic disparity in cryptic species. Within this reduced disparity also lies the evolutionary significance, as cryptic species can be regarded as the opposite of adaptive radiations. Specifically, studies on evolutionary stasis can substantially benefit from including these by addressing both patterns of reduced disparity and processes resulting in the lack of phenotypic evolution. In addition, this will allow connecting macro‐evolutionary and paleontological studies with micro‐evolutionary investigations of genotype‐phenotype linkage.

Key Concepts

  • Cryptic species are phenotypically highly similar species.
  • Species complexes resulting from taxonomic artefacts should not be considered as cryptic species.
  • To identify cryptic species, first one should establish species boundaries and only then study processes resulting in phenotypic similarity.
  • Cryptic species could result from recent speciation, parallelism, convergence or stasis.
  • Evolution of cryptic species through stasis holds the potential to enlighten us about deceleration of phenotypic evolution.
  • Cryptic species (shallow morphological differences, pronounced genetic divergence) could be considered as the opposite of adaptive radiation (pronounced morphological differences, shallow genetic divergence).

Keywords: taxonomy; speciation; recent divergence; parallelism; convergence; stasis; paleontology; morphology; phenotype; adaptive radiations

Figure 1. Unifying conceptual framework based on Struck et al. . The x‐axis represent time since divergence from the last common ancestor. Often genetic divergence is used as proxy for this. The y‐axis represents the degree of phenotypic disparity. The dark blue area is the area of ongoing speciation and hence no species boundaries have been established yet (white circles). The light blue area indicates evolution between pairs of species (orange circles) as it is intuitively assumed. That is phenotypic disparity more or less increases linear with time. The orange area reflects cases (yellow circles) in which phenotypic evolution occurs at a much higher rate than anticipated such as in adaptive radiations. The green area represents cases (red circles) of significantly reduced phenotypic disparity given time as it is the case in cryptic species.
Figure 2. Schematic representation of the Anopheles example for recent divergence (based on the results of Reidenbach et al., ). The left panel exemplifies the recent divergence of the two cryptic species. In the middle, the genomic inversion at chromosome 2 is shown and the right one lists the ecological differences observed between the two species.
Figure 3. Schematic representation of the Mastigias example of parallelism and convergence based on the results by Swift et al. . The phylogenetic relationship between the two morphotypes (oceanic and lake; indicated by the two icons) is shown to the left. Swift et al. regarded the origin of the two lake morphotypes within the Chinese Sea as well as two within the Pacific Islands & South Philippinean Seas as examples of parallelism as they originated from the same oceanic species. In contrast, they concluded that the other lake morphotypes to each other as well as to these previous ones evolved by convergence as they originated from different oceanic species.
Figure 4. Schematic representation of the Cavernacmella example for stasis given the results of Wada et al. . Wada et al. recognized a total five cryptic species as well as five morphologically distinct, noncryptic species within them (indicated by the different forms and colours; icons are relative in size to each other). The occurrence of these ten species is indicated as well as their life‐history and habitat (epigenean and cave‐dwelling; indicated by the two icons).
Figure 5. Schematic representation how different biological disciplines can contribute to the research of cryptic species and thereby increase our understanding of macro‐ecological, evolutionary and genomic patterns and processes.


Adams M , Raadik TA , Burridge CP and Georges A (2014) Global biodiversity assessment and hyper‐cryptic species complexes: more than one species of elephant in the room? Systematic Biology 63 (4): 518–533.

Bensch S , Pérez‐Tris J , Waldenström J and Hellgren O (2004) Linkage between nuclear and mitochondrial DNA sequences in avian malaria parasites: multiple cases of cryptic speciation? Evolution 58 (7): 1617–1621.

Bernardo J (2011) A critical appraisal of the meaning and diagnosability of cryptic evolutionary diversity, and its implications for conservation in the face of climate change. In: Hodkinson TR , Jones MB , Waldren S and Parnell JAN (eds) Climate Change, Ecology and Systematics, pp. 380–438. Cambridge, UK: Cambridge University Press.

Bickford D , Lohman DJ , Sodhi NS , et al. (2007) Cryptic species as a window on diversity and conservation. Trends in Ecology & Evolution 22 (3): 148–155.

Caputi L , Andreakis N , Mastrototaro F , et al. (2007) Cryptic speciation in a model invertebrate chordate. Proceedings of the National Academy of Sciences 104 (22): 9364–9369.

Chomicki G and Renner SS (2017) Partner abundance controls mutualism stability and the pace of morphological change over geologic time. Proceedings of the National Academy of Sciences 114 (15): 3951–3956.

Cornils A and Held C (2014) Evidence of cryptic and pseudocryptic speciation in the Paracalanus parvus species complex (Crustacea, Copepoda, Calanoida). Frontiers in Zoology 11: 19.

Damm S , Schierwater B and Hadrys H (2010) An integrative approach to species discovery in odonates: from character‐based DNA barcoding to ecology. Molecular Ecology 19: 3881–3893.

Darwin C (1859) On the Origin of Species by Means of Natural Selection: Or the Preservation of Favoured Races in the Struggle of Life. London: John Murray.

Derycke S , De Meester N , Rigaux A et al. (2016) Coexisting cryptic species of the Litoditis marina complex (Nematoda) show differential resource use and have distinct microbiomes with high intraspecific variability. Molecular Ecology 25: 2093–2110

Diabaté A , Dabiré RK , Heidenberger K , et al. (2008) Evidence for divergent selection between the molecular forms of Anopheles gambiae: role of predation. BMC Evolutionary Biology 8 (1): 5.

Eldredge N , Thompson JN , Brakefield PM , et al. (2005) The dynamics of evolutionary stasis. Paleobiology 31 (5): 133–145.

Elgetany AH , El‐Ghobashy AE , Ghoneim AM and Struck TH (2018) Description of a new species of the genus Marphysa (Eunicidae), Marphysa aegypti sp.n., based on molecular and morphological evidence. Invertebrate Zoology 15 (1): 71–84.

Estes S and Arnold SJ (2007) Resolving the paradox of stasis: models with stabilizing selection explain evolutionary divergence on all timescales. The American Naturalist 169 (2): 227–244.

Fišer C , Robinson CT and Malard F (2018) Cryptic species as a window into the paradigm shift of the species concept. Molecular Ecology 27: 613–635.

Futuyma DJ (2010) Evolutionary constraint and ecological consequences. Evolution 64 (7): 1865–1884.

Haller BC and Hendry AP (2014) Solving the paradox of stasis: squashed stabilizing selection and the limits of detection. Evolution 68 (2): 483–500.

Hansen TF and Houle D (2004) Evolvability, stabilizing selection, and the problem of stasis. In: Pigliucci M and Preston K (eds) Phenotypic Integration: Studying the Ecology and Evolution of Complex Phenotypes, pp. 130–154. Oxford: Oxford University Press.

Hawksworth DL and Lücking R (2017) Fungal diversity revisited: 2.2 to 3.8 million species. Microbiology Spectrum 5 (4): FUNK-0052-2016.

Heethoff M (2018) Cryptic species – conceptual or terminological chaos? A response to Struck et al. Trends in Ecology & Evolution 33 (5): 310.

Knowlton N (1993) Sibling species in the sea. Annual Review of Ecology and Systematics 24 (1): 189–216.

Korshunova T , Martynov A , Bakken T and Picton B (2017) External diversity is restrained by internal conservatism: new nudibranch mollusc contributes to the cryptic species problem. Zoologica Scripta 46: 692–683.

Losos JB (2010) Adaptive radiation, ecological opportunity, and evolutionary determinism. The American Naturalist 175 (6): 623–639.

Maynard Smith J (1983) The genetics of stasis and punctuation. Annual Review of Genetics 17 (1): 11–25.

Mayr E (1963) Animal Species and Evolution. Cambridge: Belknap Press of Harvard University.

Nygren A , Parapar J , Pons J , et al. (2018) A mega‐cryptic species complex hidden among one of the most common annelids in the North East Atlantic. PLoS ONE 13 (6): e0198356.

Pante E , Puillandre N , Viricel A , et al. (2015) Species are hypotheses: avoid connectivity assessments based on pillars of sand. Molecular Ecology 24 (3): 525–544.

Perez‐Ponce de Leon G and Poulin R (2016) Taxonomic distribution of cryptic diversity among metazoans: not so homogeneous after all. Biology Letters 12: 20160371.

Pfenninger M and Schwenk K (2007) Cryptic animal species are homogeneously distributed among taxa and biogeographical regions. BMC Evolutionary Biology 7 (1): 121.

Poulin R and Pérez‐Ponce de León G (2017) Global analysis reveals that cryptic diversity is linked with habitat but not mode of life. Journal of Evolutionary Biology 30 (3): 641–649.

Rabosky DL and Adams DC (2012) Rates of morphological evolution are correlated with species richness in salamanders. Evolution 66 (6): 1807–1818.

Ramey‐Balc P , Fiege D and Struck TH (2018) Molecular phylogeny, morphology, and distribution of Polygordius (Polychaeta: Polygordiidae) in the Atlantic and Mediterranean. Molecular Phylogenetics and Evolution 127: 919–930.

Reidenbach KR , Neafsey DE , Costantini C , et al. (2012) Patterns of genomic differentiation between ecologically differentiated M and S forms of Anopheles gambiae in West and Central Africa. Genome Biology and Evolution 4 (12): 1202–1212.

Rocha‐Olivares A , Fleeger JW and Foltz DW (2001) Decoupling of molecular and morphological evolution in deep lineages of a meiobenthic harpacticoid copepod. Molecular Biology and Evolution 18: 1088–1102.

Seehausen O (2006) African cichlid fish: a model system in adaptive radiation research. Proceedings of the Royal Society B: Biological Sciences 273 (1597): 1987–1998.

Sheldon PR (1996) Plus ça change—A model for stasis and evolution in different environments. Palaeogeography, Palaeoclimatology, Palaeoecology 127 (1): 209–227.

Simard F , Ayala D , Kamdem GC , et al. (2009) Ecological niche partitioning between Anopheles gambiae molecular forms in Cameroon: the ecological side of speciation. BMC Ecology 9 (1): 17.

Smith KL , Harmon LJ , Shoo LP and Melville J (2011) Evidence of constrained phenotypic evolution in a cryptic species complex of agamid lizards. Evolution 65 (4): 976–992.

Stoks R , Nystrom JL , May ML , McPeek MA and Benkman C (2005) Parallel evolution in ecological and reproductive traits to produce cryptic damselfly species across the Holarctic. Evolution 59 (9): 1976–1988.

Struck TH , Feder JL , Bendiksby M , et al. (2018a) Cryptic species – more than terminological chaos: a reply to Heethoff. Trends in Ecology & Evolution 33 (5): 310–312.

Struck TH , Feder JL , Bendiksby M , et al. (2018b) Finding evolutionary processes hidden in cryptic species. Trends in Ecology & Evolution 33 (3): 153–163.

Struck TH , Koczula J , Stateczny D , Meyer C and Purschke G (2017) Two new species in the annelid genus Stygocapitella (Orbiniida, Parergodrilidae) with comments on their biogeography. Zootaxa 4286 (3): 301–332.

Sukumaran J and Knowles LL (2017) Multispecies coalescent delimits structure, not species. Proceedings of the National Academy of Sciences 114 (7): 1607–1612.

Swift HF , Gómez Daglio L and Dawson MN (2016) Three routes to crypsis: stasis, convergence, and parallelism in the Mastigias species complex (Scyphozoa, Rhizostomeae). Molecular Phylogenetics and Evolution 99: 103–115.

Voje KL (2016) Tempo does not correlate with mode in the fossil record. Evolution 70 (12): 2678–2689.

Vrijenhoek RC (2009) Cryptic species, phenotypic plasticity, and complex life histories: assessing deep‐sea faunal diversity with molecular markers. Deep Sea Research Part II: Topical Studies in Oceanography 56 (19): 1713–1723.

Wada S , Kameda Y and Chiba S (2013) Long‐term stasis and short‐term divergence in the phenotypes of microsnails on oceanic islands. Molecular Ecology 22 (18): 4801–4810.

Westheide W (1977) The geographical distribution of interstitial polychaetes. Mikrofauna Meeresboden 61: 287–302.

Westheide W (2008) Polychaetes: Interstitial Families. Shrewsbury: Field Studies Council.

Winker K (2005) Sibling species were first recognized by William Derham (1718). The Auk 122: 706–707.

Further Reading

Appeltans W , Ahyong Shane T , Anderson G , et al. (2012) The magnitude of global marine species diversity. Current Biology 22 (23): 2189–2202.

Cerca J , Purschke G and Struck TH (2018) Marine connectivity dynamics: clarifying cosmopolitan distributions of marine interstitial invertebrates and the meiofauna paradox. Marine Biology 165: 123.

Charlesworth B , Lande R and Slatkin M (1982) A Neo‐Darwinian commentary on macroevolution. Evolution 36: 474–498.

Coyne J and Orr H (2004) Speciation. Sunderland, MA: Sinauer Associates.

Giere O (2009) Meiobenthology–The Microscopic Motile Fauna of Aquatic Sediments. Berlin Heidelberg: Springer‐Verlag.

Karanovic T , Djurakic M and Eberhard SM (2016) Cryptic species or inadequate taxonomy? Implementation of 2D geometric morphometrics based on integumental organs as landmarks for delimitation and description of copepod taxa. Systematic Biology 65 (2): 304–327.

Meleg IN , Zakšek V , Fišer C , Kelemen BS and Moldovan OT (2013) Can environment predict cryptic diversity? The case of Niphargus inhabiting western Carpathian groundwater. PLoS ONE 8 (10): e76760.

Nygren A (2013) Cryptic polychaete diversity: a review. Zoologica Scripta 43: 172–183.

Schwenk K and Wagner GP (2001) Function and the evolution of phenotypic stability: connecting pattern to process. American Zoologist 41 (3): 552–563.

Winston JE (1999) Describing Species–Practical Taxonomic Procedure for Biologists. New York: Columbia University Press.

Contact Editor close
Submit a note to the editor about this article by filling in the form below.

* Required Field

How to Cite close
Struck, Torsten H, and Cerca, José(Jan 2019) Cryptic Species and Their Evolutionary Significance. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0028292]