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''Testudo'' is a genus of tortoises found in North Africa, western Asia, and Europe. Several species are under threat in the wild, mainly from habitat destruction. They are small tortoises, ranging in length from 7.0 to 35 cm and in weight from 0.7 to 7.0 kg, although the extinct ''T. atlas'' reached 2.5 m. Like most tortoises, they are herbivorous. ==Systematics== The systematics and taxonomy of ''Testudo'' is notoriously problematic. Highfield and Martin commented: Synonymies on ''Testudo'' are notoriously difficult to compile with any degree of accuracy. The status of species referred have undergone a great many changes, each change introducing an additional level of complexity and making bibliographic research on the taxa extremely difficult. Most early and not a few later checklists contain a very high proportion of entirely spurious entries, and a considerable number of described species are now considered invalid – either because they are homonyms, non-binomial or for some other reason.〔Highfield, A.C. & Martin, J. (1989): A revision of the Testudines of North Africa, Asia and Europe. Genus: ''Testudo''. ''Journal of Chelonian Herpetology'' 1(1): 1–12. (HTML fulltext ) Since then, DNA sequence data have increasingly been used in systematics, but in Testudines (turtles and tortoises), its usefulness is limited: In some of these, at least mtDNA is known to evolve more slowly in these than in most other animals.〔Avise, John C.; Bowen, Brian W.; Lamb, Trip; Meylan, Anne B. & Bermingham, Eldredge (1992): Mitochondrial DNA evolution at a turtle's pace: evidence for low genetic variability and reduced microevolutionary rate in the Testudines. ''Mol. Biol. Evol.'' 9(3): 457-473. (PDF fulltext )〕 Paleobiogeographical considerations suggest the rate of evolution of the mitochondrial 12S rRNA gene is 1.0-1.6% per million years for the last dozen million years or so in the present genus〔van der Kuyl, Antoinette C.; Ballasina, Donato L. Ph.; Dekker, John T.; Maas, Jolanda; Willemsen, Ronald E. & Goudsmit, Jaap (2002): Phylogenetic Relationships among the Species of the Genus ''Testudo'' (Testudines: Testudinidae) Inferred from Mitochondrial 12S rRNA Gene Sequences. ''Mol. Phylogenet. Evol.'' 22(2): 174–183. PMID 11820839 (HTML abstract) 〕 and ntDNA evolution rate has been shown to vary strongly even between different population of ''T. hermanni'';〔Fritz, Uwe; Auer, Markus; Bertolero, Albert; Cheylan, Marc; Fattizzo, Tiziano; Hundsdörfer, Anna K.; Sampayo, Marcos Martín; Pretus, Joan L.; Široký, Pavel & Wink, Michael (2006): A rangewide phylogeography of Hermann's tortoise, ''Testudo hermanni'' (Reptilia: Testudines: Testudinidae): implications for taxonomy. ''Zool. Scripta'' 35(5): 531-548. (PDF fulltext )〕 this restricts sequence choice for molecular systematics and makes the use of molecular clocks questionable. Conventionally, five species are placed here: * Russian tortoise or Horsfield's tortoise, ''T. horsfieldii'' * Hermann's tortoise, ''T. hermanni'' * Spur-thighed tortoise or Greek tortoise, ''T. graeca'' * * "Maghreb tortoise", ''T. (graeca) graeca'' * * Greek tortoise, ''Testudo (graeca) ibera'' * * "Persian tortoise", ''T. (graeca) zarudnyi'' * Kleinmann's tortoise or Egyptian tortoise, ''T. kleinmanni'' *Negev tortoise or Werner's tortoise, ''T.werneri'' * Marginated tortoise, ''T. marginata'' The first two are more distinct and ancient lineages than the closely related latter three species. Arguably, ''T. horsfieldii'' belongs in a new genus (''Agrionemys'') on the basis of the shape of its carapace and plastron,〔Khozatsky, L.I. & Mlynarski, M. (1966): ''Agrionemys'' - nouveau genre de tortues terrestres (Testudinidae) (- a new genus of tortoises" ). (in French ) ''Bulletin de l'Académie Polonaise des Sciences II - Série des Sciences Biologiques'' 2: 123-125. 〕 and its distinctness is supported by DNA sequence analysis.〔Fritz, Uwe; Kiroký, Pavel; Kami, Hajigholi & Wink, Michael (2005): Environmentally caused dwarfism or a valid species - Is ''Testudo weissingeri'' Bour, 1996 a distinct evolutionary lineage? New evidence from mitochondrial and nuclear genomic markers. ''Mol. Phylogenet. Evol.'' 37(2): 389–401. (PDF fulltext ) 〕 Likewise, a separate genus ''Eurotestudo'' has recently been proposed for ''T. hermanni''; these three lineages were distinct by the Late Miocene as evidenced by the fossil record.〔de Lapparent de Broin, France; Bour, Roger; Parham, James F. & Perälä, Jarmo (2006): ''Eurotestudo'', a new genus for the species ''Testudo hermanni'' Gmelin, 1789 (Chelonii, Testudinidae). (with French abstract ) ''C. R. Palevol'' 5(6): 803-811. (PDF fulltext ) 〕 Whether these splits will eventually be accepted remains to be seen. The genus ''Chersus'' has been proposed to unite the Egyptian and marginated tortoises which have certain DNA sequence similarities,〔 but their ranges are (and apparently always were) separated by their closest relative ''T. graeca'' and the open sea and thus, chance convergent haplotype sorting would better explain the biogeographical discrepancy. Conversely, the Greek tortoise is widespread and highly diverse. In this and other species, a high number of subspecies has been described, but not all generally accepted, and several (such as the "Negev tortoise" and the "dwarf marginated tortoise") are now considered to be local morphs. Some, such as the Tunisian spur-thighed tortoise, have even been separated as a separate genus ''Furculachelys'', but this is not supported by more recent studies.〔van der Kuyl, Antoinette C.; Ballasina, Donato L. Ph. & Zorgdrager, Fokla (2005): Mitochondrial haplotype diversity in the tortoise species ''Testudo graeca'' from North Africa and the Middle East. ''BMC Evol. Biol.'' 5: 29. (HTML/PDF fulltext + supplementary material)〕 However, the "Greek" tortoise likely will be split into two or more species in the near future. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Testudo (turtle)」の詳細全文を読む スポンサード リンク
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