Abstract
The Evolutionarily Significant Unit (ESU) was conceptualized in 1986 as a conservation unit below the species level, theoretically applicable to a wide range of taxa. The concept has gained support, and various definitions or criteria, some of which are inconsistent with each other, have since been proposed. Recent critiques of the ESU have pointed out the dominance of definitions biased to the identification of long-term isolation or neutral genetic variation, which has largely ignored the adaptive components. We present here the validity of such claims and show how the ESU definitions have actually been applied in research. We surveyed scientific journals for original papers supporting ESU designations and determined who among the proponents of ESU definitions have gained wider support. Our results indicate that indeed there are inconsistencies with the original concept and with the existing definitions. Although the original concept recommended both ecological and genetic data as the basis for identification of ESUs, which reflect true evolutionary variation, recent definitions have become biased to either neutral genetic variation or adaptive variation. The definition which uses genetic data to assess neutral genetic variation (long-term isolation) has gained major support, and therefore validates the earlier claims. To bridge the gap between the original concept and the practical application, we propose the use of partial ESU and full ESU designations. The application of full ESU should be limited solely to when both information about neutral genetic variation and adaptive variation are available. In other cases, in which only a part of the variation is examined, we should use the term partial ESU (e.g., molecular-based ESU) and continue to investigate focal populations from other aspects of variations to designate full ESU.
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References
Berry O, Gleeson DM (2005) Distinguishing historical fragmentation from a recent population decline—shrinking or pre-shrunk skink from New Zealand? Biol Conserv 123:197–210
Bottin L, Verhaegen D, Tassin J, Olivieri I, Vaillant A, Bouvet JM (2005) Genetic diversity and population structure of an insular tree, Santalum austrocaledonicum in New Caledonian archipelago. Mol Ecol 14:1979–1989
Bowen BW (1998) What is wrong with ESUs? The gap between evolutionary theory and conservation principles. J Shellfish Res 17:1355–1358
Bulgin NL, Gibbs HL, Vickery P, Baker AJ (2003) Ancestral polymorphisms in genetic markers obscure detection of evolutionarily distinct populations in the endangered Florida grasshopper sparrow (Ammodramus savannarum floridanus). Mol Ecol 12:831–844
Cavers S, Navarro C, Lowe AJ (2003) A combination of molecular markers identifies evolutionarily significant units in Cedrela odorata L. (Meliaceae) in Costa Rica. Conserv Genet 4:571–580
Crandall KA, Bininda-Emonds ORP, Mace GM, Wayne RK (2000) Considering evolutionary processes in conservation biology. Trends Ecol Evol 15:290–295
Davison A, Birks JD, Brookes RC, Messenger JE, Griffiths HI (2000) Mitochondrial phylogeography and population history of pine martens Martes martes compared with polecats Mustela putorius. Mol Ecol 10:2479–2488
Dizon AE, Lockyer C, Perrin WF, Demaster D, Sisson J (1992) Rethinking the stock concept: a phylogeographic approach. Conserv Biol 6:24–36
Frankham R, Ballou JD, Briscoe DA (2002) Introduction to conservation genetics. Cambridge University Press, Cambridge, UK
Fraser DJ, Bernatchez L (2001) Adaptive evolutionary conservation: towards a unified concept for defining conservation units. Mol Ecol 10:2741–2752
Goldstein PZ, DeSalle R, Amato G, Vogler AP (2000) Conservation at the species boundary. Conserv Biol 14:120–131
Green DM (2005) Designatable units for status assessment of endangered species. Conserv Biol 19:1813–1820
Grobler JP, Pretorius DM, Botha K, Kotze A, Hallerman EM, Van Vuuren BJ (2005) An exploratory analysis of geographic genetic variation in southern African nyala (Tragelaphus angasii). Mamm Bio 70:291–299
Hedrick PW (2001) Conservation genetics: where are we now? Trends Ecol Evol 16:629–636
Houlden BA, Costelo BH, Sharkey D, Fowler EV, Melzer A, Ellis W, Carrick F, Baverstock PR, Elphinstone MS (1999) Phylogeographic differentiation in the mitochondrial control region in the Koala, Phascolarctos cinereus (Goldfuss 1817). Mol Ecol 8:999–1011
Ishibashi Y, Saitoh T (2004) Phylogenetic relationships among fragmented Asian black bear (Ursus thibetanus) populations in western Japan. Conserv Genet 5:311–323
Jarne P, Lagoda P (1996) Microsatellites, from molecules to populations and back. Trends Ecol Evol 11:424–429
Karl SA, Bowen BW (1999) Evolutionary significant units versus geopolitical taxonomy: molecular systematics of an endangered sea turtle (Genus Chelonia). Conserv Biol 13:990–999
Kelt DA, Brown JH (2000) Species as units of analysis in ecology and biogeography: are the blind leading the blind? Global Ecol Biogr 9:213–217
Legge JT, Roush R, DeSalle R, Vogler AP, May B (1996) Genetic criteria for establishing evolutionary significant units in Cryan’s Buckmoth. Conserv Biol 10:85–98
Luikart G, England P (1999) Statistical analysis of microsatellite DNA data. Trends Ecol Evol 14:253–256
Mace GM (2004) The role of taxonomy in species conservation. Philos Trans R Soc Lond B 359:711–719
Machordom A, Araujo R, Erpenbeck D, Ramos M (2003) Phylogeography and conservation genetics of endangered Margaritiferidae (Bivalvia: Unionidea). Biol J Linn Soc 78:235–252
Manceau V, Crampe J, Boursot P, Taberlet P (1999) Identification of evolutionary significant units in the Spanish wild goat, Capra pyrenaica (Mammalia, Artiodactyla). Anim Conserv 2:33–39
Matthee CA, Robinson TJ (1999) Mitochondrial DNA population structure of roan and sable antelope: implications for the translocations and conservation of the species. Mol Ecol 8:227–238
Miller MP, Haig SM, Wagner RS (2005) Conflicting patterns of genetic structure produced by nuclear and mitochondrial markers in the Oregon slender salamander (Batrachoseps wrighti): implications for conservation efforts and species management. Conserv Genet 6:275–287
Moritz C (1994a) Defining evolutionarily significant units for conservation. Trends Ecol Evol 9:373–375
Moritz C (1994b) Applications of mitochondrial DNA analysis in conservation: a critical review. Mol Ecol 3:401–411
Moritz C (1995) Uses of molecular phylogenies for conservation. Philos Trans R Soc Lond B 349:113–118
Moritz C (1999) Conservation units and translocations: strategies for conserving evolutionary processes. Hereditas 130:217–228
Moritz C (2002) Strategies to protect biological diversity and the evolutionary processes that sustain it. Syst Biol 51:238–254
Paetkau D (1999) Using genetics to identify intraspecific conservation units: a critique of current methods. Conserv Biol 13:1507–1509
Pennock DS, Dimmick WW (1997) Critique of the evolutionarily significant unit as a definition for distinct population segments under the US endangered species act. Conserv Biol 11:611–619
Rader RB, Belk MC, Shiozawa DK, Crandall KA (2005) Empirical tests for ecological exchangeability. Anim Conserv 8:239–247
Riddle BR, Hafner DJ (1999) Species as units of analysis in ecology and biogeography: time to take the blinders off. Global Ecol Biogeogr 8:433–441
Rojas M (1992) The species problem and conservation: what are we protecting? Conserv Biol 6:170–178
Ryder OA (1986) Species conservation and systematics: the dilemma of the subspecies. Trends Ecol Evol 1:9–10
Sandoval-Castillo J, Rocha Olivares A, Villavicencio-Garayzer C, Balaert E (2004) Cryptic isolation of Gulf of California shovelnose guitarfish evidenced by mitochondrial DNA. Mar Biol 145:883–988
Stockwell CA, Mulvey M, Jones AG (1998) Genetic evidence for two evolutionarily significant units of White Sands pupfish. Anim Conserv 1:213–225
Stokstad E (2004) Global survey documents puzzling decline of amphibians. Science 306:391
Sunnucks P (2000) Efficient genetic markers for population biology. Trends Ecol Evol 15:199–203
Swei A, Brylski PV, Spencer WD, Dodd SC, Patton JL (2003) Hierarchical genetic structure in fragmented populations of the little pocket mouse (Perognathus longimembris) in Southern California. Conserv Genet 4:501–514
van Tienderen PH, de Haan AA, van der Linden CG, Vosman B (2002) Biodiversity assessment using markers for ecologically important traits. Trends Ecol Evol 17:577–582
Vogler AP, DeSalle R (1994) Diagnosing units of conservation management. Conserv Biol 8:354–363
Waples RS (1991) Pacific salmon, Oncoryhnchus spp., and the definition of species under the Endangered Species Act. Mar Fish Rev 53:11–22
Waples RS (1998) Evolutionary significant units, distinct population segments and the endangered species act: reply to Pennock and Dimmick. Conserv Biol 12:718–721
Zink RM, Barrowclough GF, Atwood JL, Blackwell-Rago RC (2000) Genetics, taxonomy, and conservation of the threatened California Gnatcatcher. Conserv Biol 14:1394–1405
Acknowledgments
We are indebted to Y. Ishibashi and two anonymous reviewers for their helpful comments and suggestions on our draft. This study was partly supported by the Grant-in-Aid from the Ministry of Education, Science and Culture of Japanese Government (No. 16657006/No. 17370006).
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de Guia, A.P.O., Saitoh, T. The gap between the concept and definitions in the Evolutionarily Significant Unit: the need to integrate neutral genetic variation and adaptive variation. Ecol Res 22, 604–612 (2007). https://doi.org/10.1007/s11284-006-0059-z
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DOI: https://doi.org/10.1007/s11284-006-0059-z