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==Taxonomy== ''Dermatemys mawii'' is the only living [[species]] in the [[Family (biology)|family]] [[Dermatemydidae]].<ref>{{cite journal |url=http://www.iucn-tftsg.org/wp-content/uploads/file/Accounts/crm_5_000_checklist_v4_2011.pdf |title=Turtles of the world, 2011 update: Annotated checklist of taxonomy, synonymy, distribution and conservation status |journal=Chelonian Research Monographs |volume=5 |date=2011-12-31 |author1=Rhodin, Anders G.J. |author2=van Dijk, Peter Paul |author3=Inverson, John B. |author4=Shaffer, H. Bradley |author5=Roger, Bour |archive-url=https://web.archive.org/web/20120131102839/http://www.iucn-tftsg.org/wp-content/uploads/file/Accounts/crm_5_000_checklist_v4_2011.pdf |archive-date=2012-01-31 |url-status=dead }}</ref> Its closest relatives are only known from [[fossil]]s with some 19 genera described from a worldwide distribution in the [[Jurassic]] and [[Cretaceous]].{{citation needed|date=November 2021}} ===Etymology=== The [[Specific name (zoology)|specific name]], ''mawii'', is in honour of the collector of the [[Holotype|type specimen]], Lieutenant Mawe of the British Navy.<ref>{{cite book |last1=Beolens |first1=Bo |last2=Watkins |first2=Michael |last3=Grayson |first3=Michael |date=2011 |title=The Eponym Dictionary of Reptiles |location=Baltimore |publisher=Johns Hopkins University Press |page=171 |isbn=978-1-4214-0135-5}}</ref> This species is usually vernacularly called ''tortuga blanca'' in Spanish, because it can be readily distinguished when prepared as food. When the meat of this turtle is cooked, it turns a white colour, unlike the more common turtle meat (''[[Trachemys scripta]]''), which colours dark.<ref name=Campbell1998>{{cite book |last=Campbell |first=Jonathan A. |date=1998 |title=Amphibians and Reptiles of Northern Guatemala, the Yucatán and Belize |url=https://books.google.com/books?id=orUl8Ezs1iQC&pg=PA111 |location=Norman, Oklahoma |publisher=University of Oklahoma Press |pages=111–113 |isbn=0806130660}}</ref> ===Genetics=== Many species sharing a similar distribution have [[Phylogeography|phylogeographic]] structure revealed in their [[genome]]s, with the population often being split into at least three subgroups representing the three main Atlantic hydrological basins of this region, the [[Papaloapan]], [[Coatzacoalcos River|Coatzacoalcos]] and [[Grijalva River|Grijalva]]-[[Usumacinta River|Usumacinta]]. A 2011 study of the [[mitochondrial DNA]] (mtDNA) of extant populations throughout the range of this species, however, revealed a less clear differentiation. Although some genetic structure was evident, most locations showed a high rate of mixing of different lineages, with two main closely related mitochondrial [[haplotype]]s dominating the population. Three divergent mitochondrial lineages were found: an extremely rare one dubbed '1D' only found in four samples from [[Sarstoon River|Sarstún]] and [[Salinas River (Mexico)|Salinas]] on the southeast edge of the Grijalva-Usumacinta basin, a second northernmost 'Papaloapan' lineage restricted to the Papaloapan basin in the state of [[Veracruz]], to the west of the [[Sierra de Santa Marta]] and the [[Isthmus of Tehuantepec]], and a third widespread 'central' lineage that was found in all studied localities. It appeared as if a formerly clear [[Phylogeography|phylogeographical pattern]] had been obscured by transport and introductions of turtle populations from one waterway to another, i.e. secondary blurring by large-scale [[gene flow]] between populations. Low haplotype diversity at some localities indicated prehistoric [[population bottleneck]]s, possibly after a drastic cull from over-harvesting, followed by population expansions. As it is almost certain the [[Ancient Maya]] were engaged in long distance trade in this turtle species and consumed large amounts, it was deemed most probable that the Maya were responsible for this (see section on interaction with humans below).<ref name=González2011>{{cite journal |last1=González Porter |first1=Gracia P. |last2=Hailer |first2=Frank |last3=Flores Villela |first3=Oscar |last4=García Anleu |first4=Rony |last5=Maldonado |first5=Jesús E. |date=17 May 2011 |title=Patterns of genetic diversity in the critically endangered Central American river turtle: human influence since the Mayan age? |journal=Conservation Genetics |volume=12 |issue=5 |pages=1229–1242 |doi=10.1007/s10592-011-0225-x|s2cid=39768099 }}</ref> Even today, turtles have been found trapped in small isolated ponds (called ''aguadas'' in Guatemala) where they would be unlikely to naturally disperse to, or in areas they do not naturally occur, likely moved there by people in order to harvest them at a later date.<ref name=vogtetal/><ref name=Campbell1998/> Although most haplotypes were relatively closely related, there was one highly divergent haplotype which only showed up in four samples from Sarstún and Salinas, divergent enough to represent a possible new hyper-critically endangered [[cryptic species]]. Hydrological reproductive barriers between populations may have led to the main lineages splitting in the [[Pliocene]] to [[Pleistocene]] (3.73–0.227 million years ago), generally enough time to accumulate the genetic divergences for [[speciation]] to occur. The sampling locations, however, also contained the common central haplotypes.<ref name=González2011/> The existence of such divergent genes led Vogt ''et al''. to recommended splitting up the taxon into three [[evolutionary significant unit]]s, corresponding to the Sarstun, Salinas, and Papaloapan populations, and something called a 'management unit'{{efn|unexplained, but most likely ''sensu'' Moritz C (1999) ''Conservation units and translocations: strategies for conserving evolutionary processes''. Hereditas 30: 217–228. ''fide'' González (2013).<ref name=González2013/>}} for the locations where all of the 238 turtles tested in 2011 had the more common central mitochondria, for conservation purposes.<ref name=vogtetal/> Although mtDNA can reveal deep genetic structure in populations, as it is only inherited via the mother, it does not show insofar different subpopulations are independently evolving units, because different populations may interbreed without this showing in the mtDNA of individuals. A subsequent 2013 study of eight [[Locus (genetics)|loci]] of the [[nuclear DNA]] aimed to resolve this.<ref name=González2013>{{cite journal |last1=González Porter |first1=Gracia P. |last2=Maldonado |first2=Jesús E. |last3=Flores Villela |first3=Oscar |last4=Vogt |first4=Richard C. |author-link4=Richard Vogt (herpetologist) |last5=Janke |first5=Axel |last6=Fleischer |first6=Robert C. |last7=Hailer |first7=Frank |date=25 September 2013 |title=Cryptic Population Structuring and the Role of the Isthmus of Tehuantepec as a Gene Flow Barrier in the Critically Endangered Central American River Turtle |journal=PLOS ONE |volume=8 |issue=9 |pages=e71668 |pmid=24086253 |doi=10.1371/journal.pone.0071668|pmc=3783458|bibcode=2013PLoSO...871668G |doi-access=free }}</ref> This 2013 study found no sign of a recent bottleneck in the fifteen locations sampled, indicating that harvesting going for the past half century had not yet had an effect on genomic diversity, possibly a long generation time and delayed sexual maturity of ''D. mawii'' buffering against loss of genetic diversity despite population size reduction. The Sarstún and Salinas populations in general were not strongly differentiated from the neighbouring populations, but the four individuals from Sarstún and Salinas with divergent mitochondria did have divergent [[microsatellite]] loci sequences in varying amounts according to the individual, with three rare alleles only found in this [[subpopulation]] of four. The samples from Papaloapan locations were highly differentiated compared to almost all other populations, and also were rich in unique alleles. However, individuals carrying Papaloapan-type mtDNA haplotypes did not appear differentiated from the central type individuals, and these individuals occurred at relatively low frequencies amongst the central type haplotypes shared with adjacent populations to the east of the isthmus, indicating significant gene flow of mitochondrial lineages westwards across the isthmus. At the same time nuclear microsatellites appear to show gene flow in the other direction. Such conflicting signals could be caused by different episodes, or be due to a sex bias in dispersal. Also the populations from [[Sibun River]], [[Lake Salpetén]] and [[Cultural Triangle Yaxha-Nakum-Naranjo National Park|Laguna Sacnab]], all near the eastern edge of the distribution, were relatively well-differentiated from the remaining populations. This was thought to be due to losses of genetic variability from recent [[genetic drift]] and/or demographic isolation. All the other populations had high levels of gene flow, even between areas separated by geographic distances of more than 300 km. The study found that this suggests likely thousands of years of human-mediated trade, but that it might also just mean that this species is capable of moving great distances during its life. Besides microsatellite regions another part of the nuclear DNA was looked at, a 779 [[base pair|bp]] fragment of first [[intron]] of the [[RNA]] [[protein]] R35, with four haplotypes found. This revealed no phylogeographic structure: the main haplotype was common across the distribution, and the four individuals from Sarstún and Salinas all had this haplotype.<ref name=González2013/> The overall pattern is completely different in the alligator snapping turtle (''[[Macrochelys temminckii]]''), which is also often caught, but in which gene flow between populations is very low, but the mixed lineages are somewhat similar to the diamondback terrapin (''[[Malaclemys terrapin]]''), with translocations during the early twentieth century, or the radiated tortoise (''[[Geochelone radiata]]'') and gopher tortoises (''[[Gopherus polyphemus]]''), which show contemporary population structuring influenced by recent releases.<ref name=González2013/> The 2013 study concluded that as there was evidence of substantial genetic mingling the species was best regarded as a single cohesive 'management unit' for conservation purposes,<ref name=González2013/> as opposed to Vogt ''et al''. in 2011.<ref name=vogtetal/> The sample size of the individuals with the 1D mitochondria was too small to calculate insofar they represent a taxonomically relevant cryptic species.<ref name=González2013/>
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