**Acknowledgements**

*Natural History and Ecology of Mexico and Central America*

values for certain taxonomic groups.

control region in leatherback turtles [57].

criteria for use as a barcode sequence [50, 57].

be recovered from samples after long storage periods.

high level of barcode variation between specimens, which helps in the identification of cryptic species and thus its use in species identification, biodiversity and conservation studies. The barcode can also be used to facilitate species identification when this is difficult due to the organism ontogeny or due to only receiving an individual's remains. However, disadvantages exist when using this marker, such as the lack of clarity between the genetic separation values between intra- and interspecific divergence in the selected marker. The discovery of new species cannot be confined solely to a universal barcode, since this marker has errors in the genetic separation

Another commonly used marker is the control region in mDNA, which contains a displacement loop, known as the "D-loop", believed to be the most rapidly evolving region of the mitochondrial genome in most vertebrates. This structure contains most of the regulatory elements for the mitochondrial genome expression and is used to study intraspecific population structures. It has proven useful in the study of sea turtles, with molecular markers derived from the control region used to identify sea turtle natal origins and in the case of the loggerhead turtle (*Caretta caretta*) used to demonstrate their transpacific migration. In 1994, another study designed primers from the control region and amplified a 496 bp fragment for this

The control region is a ubiquitous characteristic of vertebrate mitochondrial genomes, its name is due to its structure that consists of a triple chain of ~0.8-1 kb and is located between the genes that encode tRNAPro on the light strand (L -strand) and tRNAPhe on the heavy strand (H-strand). This morphology is created by the displacement of the parental H-strand by a DNA of 0.6–0.8 kb complementary to the L-strand. The control region measures between 880 and 1400 bp, and in some species, it can be greatly extended due to its repeated sequences. However, its reduced size and the increased understanding of its replication and transcription mechanisms, its sequence availability in many species, this region represents a good marker to analyse the non-coding regulatory genome to the evolution in the time of the establishment of mammals about 150 million years. In the late 1990s, Dutton et al. described the control region's use, in conjunction with recapture information, to test the philopatry hypothesis. Naro-Maciel et al. conducted a study using the control region as a marker for the DNA barcode, highlighting that although this region is useful in numerous species conservation studies, it does not meet all the

One advantage of this genetic marker in sea turtle molecular studies is its high degree of variability. It is the most variable region of the mitochondrial and nuclear genome, evolving ten times faster than nDNA and can be used for species identification, even reaching the sub-species level. It degrades slower than nDNA and can

This chapter showed different stages of sea turtles, one in particular Kemp's ridley. Since that sea turtle has as a unique site to nest, it is important to understand what the real situation about the cycle of life, anthropogenic threats, genetic diversity, and pollution. Not only, for the turtles but for human beings. To see that, previous studies in sea turtles were describe in tissue samples such as carapace, kidney, liver, heart, etc. Another kind of used sample was blood. Blood as test tissue allows information on recent exposure to anthropogenic pollutants, it is inexpensive and easy to acquire. Also, it represents a relationship between the concentrations of heavy metals with other tissues, since the blood transports them through the

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**5. Conclusion**

This research was supported by SIP-20110067, 20161179, 20171851, 20196213, 20200840 and 20211061 projects from the Instituto Politécnico Nacional (IPN). The Apoyos económicos of Comisión de Operación y Fomento de Actividades Académicas (COFAA), Estímulos al Desempeño de los Investigadores (EDI), and Beca de estímulo institucional de formación de investigadores (BEIFI) from the IPN; and the National System of Researchers (SNI); the National Council of Science and Technology (CONACYT) provided fellowships and scholarships for MARL, CPLQ, FYCS, KAZF, VLS, and AAZN. Investigacion, Capacitacion y Soluciones Ambientales y Sociales A.C., Grupo tortuguero de las Californias A. C. We thank the entire community and Juan Martínez Ortíz of Rancho Nuevo, Aldama, Tamaulipas. Special thanks to Martha López Hernández, CONANP, Tamaulipas and Blanca Mónica Zapata Nájera, CONANP., and H. Hugo Acosta Sánchez-United Nations Development Programme-Comisión Nacional de Áreas Naturales Protegidas, Ciudad Victoria, Tamaulipas, Mexico
