Leucism: the prevalent congenital malformation in the olive ridley sea turtle of northwestern Mexico.

Despite being the most abundant sea turtle in the world, the olive ridley turtle Lepidochelys olivacea is classified as Vulnerable by the IUCN. There is evidence of congenital malformations in hatchlings, and the associated causes are multifactorial, with both genetic and environmental sources. Santuario Playa Ceuta (SPC) is a sanctuary for the olive ridley, located at the northernmost region of its nesting range in the Mexican Pacific. The objective of this study was to identify and quantify the prevalence and severity of congenital malformations in olive ridley embryos/hatchlings in SPC during the 2017 nesting season. We collected 62907 eggs from 643 relocated nests that were moved to a hatchery, of which 4242 eggs with obvious development did not hatch and were analyzed for this study. Hatching success was 53.9%, with 22.5% of nests (n = 145) and 0.54% of eggs (n = 344) showing embryos or hatchlings with malformations. The nest severity index was 2.4 (range: 1-10) malformed embryos or hatchlings per nest, and the organism severity index was 1.4 (range: 1-7) malformations per malformed embryo or hatchling. Leucism was the most prevalent malformation (34.4%; 170/494 total observed), with the craniofacial region showing the greatest diversity of malformations (17/35 types). Given the geographical position of SPC, extreme environmental conditions (e.g. cold, heat, and dryness) could be one of the main causes of teratogenesis in this species. However, more studies are needed regarding the presence of contaminants, genetic factors, health assessments of nesting females, and malformation rates of nests that remain in situ versus those that are relocated.

Nesting trends of olive ridley sea turtles Lepidochelys olivacea (Testudinata: Cheloniidae) on two beaches in Northwestern Mexico after 30 and 40 years of conservation / Tendencias de anidación de la tortuga golfina Lepidochelys olivacea (Testudinata: Cheloniidae) en dos playas del noroeste de México después de 30 y 40 años de conservación

Abstract Introduction: Although olive ridley sea turtle (Lepidochelys olivacea) are the most abundant sea turtles in the world, quantitative information is scarce and unevenly distributed among regions. There are many management and conservation programs for this species, and assessments are necessary to identify nesting trends and effectively manage current conservation programs. PROTORMAR-UAS is a Research and Conservation program for the olive ridley turtle created by the Autonomous University of Sinaloa, Mexico. The program utilizes two biological stations: Santuario Playa Ceuta (SPC) and Playa Caimanero (PC). Objective: To evaluate the nesting trend of olive ridley turtles on two beaches in Northwestern Mexico and to predict prospective nesting trends for the next 30 years. Methods: Using annual nesting data collected over 40 years at SPC (1976-2016) and 30 years at PC (1986-2016), we evaluated nesting trends, hatching success, predation and poaching of olive ridley turtles on the two beaches in Northwestern Mexico. Then, prospective nesting estimates for the next 30 years were calculated predictive time series model. Results: A positive and significant correlation was identified between the number of annual nests and time for both beaches (rho = 0.850, P ≤ 0.01 for SPC; rho = 0.677, P ≤ 0.01 for PC); the average hatching success rates were 65.09 at SPC and 60.72 % at PC. The predictive time-series model indicated that the numbers of nests will continue to increase through 2045, increasing three-fold at SPC and six-fold at PC with respect to the last year of monitoring. Conclusions: There was a clear positive trend in the number of olive ridley sea turtle nests at both sites, which is consistent with trends found in other recent studies from the region. Therefore, we suggest that PC be designated a legally protected nesting area since it is located within the latitudinal limits of olive ridley nesting and given the need for resources for camp operation considering increased nesting and current problems with predation and poaching. Because in Mexico operating a nesting beach without any protection status implies not having a budget for its management.

Resumen Introducción: A pesar de que las tortugas golfinas (Lepidochelys olivacea) son las tortugas marinas más abundantes del mundo, su información cuantitativa disponible es escasa y se encuentra distribuida de manera desigual entre regiones. Existen muchos programas de manejo y conservación para esta especie, y sus evaluaciones son necesarias para identificar tendencias de anidación y poder manejar de manera efectiva los programas de conservación actuales. PROTORMAR-UAS es un programa de Investigación y Conservación de la tortuga golfina creado por la Universidad Autónoma de Sinaloa, México. El Programa cuenta con dos estaciones biológicas: Santuario de Playa Ceuta (SPC) y Playa Caimanero (PC). Objetivo: Evaluar la tendencia de anidación de la tortuga golfina en dos playas del noroeste de México y predecir las tendencias prospectivas de anidación para los próximos 30 años. Métodos: A partir de los datos de registros anuales de anidación de 40 años para SPC (1976-2016) y 30 años para PC (1986-2016), evaluamos las tendencias de anidación, el éxito de la eclosión y los problemas de depredación y saqueo de nidos de la tortuga golfina en las dos playas del noroeste de México. Posteriormente, se calcularon las estimaciones prospectivas de anidación para los próximos 30 años usando un modelo predictivo de series de tiempo. Resultados: Se identificó una correlación positiva y significativa entre el registro anual de nidos y el tiempo de estudio para ambas playas (rho = 0.850, P ≤ 0.01 para SPC; rho = 0.677 y P ≤ 0.01 para PC); así como el éxito de eclosión promedio de 65.09 para SPC y de 60.72 % para PC. El modelo predictivo de series de tiempo indicó que las anidaciones continuarán aumentando para el 2045, tres veces para SPC y seis para PC, con respecto al último año de monitoreo. Conclusiones: Hay una clara tendencia positiva de anidación de la tortuga golfina en ambos sitios, lo cual es consistente con la tendencia observada en otros estudios recientes de la región. Por lo tanto, sugerimos incluir a PC como un área de anidación legalmente protegida, la cual se ubica en los límites latitudinales de anidación de la tortuga golfina, dada la necesidad de contar con recursos disponibles para la operación del campamento ante el aumento de anidaciones y de problemas de depredación y saqueo. Porque en México operar una playa de anidación sin ningún estatus de protección implica no tener presupuesto para su manejo.

Congenital Malformations in Sea Turtles: Puzzling Interplay between Genes and Environment.

The completion of embryonic development depends, in part, on the interplay between genetic factors and environmental conditions, and any alteration during development may affect embryonic genetic and epigenetic regulatory pathways leading to congenital malformations, which are mostly incompatible with life. Oviparous reptiles, such as sea turtles, that produce numerous eggs in a clutch that is buried on the beach provide an opportunity to study embryonic mortality associated with malformations that occur at different times during development, or that prevent the hatchling from emerging from the nest. In sea turtles, the presence of congenital malformations frequently leads to mortality. A few years ago, a detailed study was performed on external congenital malformations in three species of sea turtles from the Mexican Pacific and Caribbean coasts, the hawksbill turtle, Eretmochelys imbricata (n = 23,559 eggs), the green turtle, Chelonia mydas (n = 17,690 eggs), and the olive ridley, Lepidochelys olivacea (n = 20,257 eggs), finding 63 types of congenital malformations, of which 38 were new reports. Of the three species, the olive ridley showed a higher incidence of severe anomalies in the craniofacial region (49%), indicating alterations of early developmental pathways; however, several malformations were also observed in the body, including defects in the carapace (45%) and limbs (33%), as well as pigmentation disorders (20%), indicating that deviations occurred during the middle and later stages of development. Although intrinsic factors (i.e., genetic mutations or epigenetic modifications) are difficult to monitor in the field, some environmental factors (such as the incubation temperature, humidity, and probably the status of feeding areas) are, to some extent, less difficult to monitor and/or control. In this review, we describe the aetiology of different malformations observed in sea turtle embryos, and provide some actions that can reduce embryonic mortality.

Mercury Concentration, DNA Methylation, and Mitochondrial DNA Damage in Olive Ridley Sea Turtle Embryos With Schistosomus Reflexus Syndrome.

Schistosomus reflexus syndrome (SR) is a rare and lethal congenital malformation that has been reported in the olive ridley sea turtle (Lepidochelys olivacea) in Mexico. Although the etiology remains unclear, it is presumed to be genetic. Since embryonic development in sea turtles largely depends on environmental conditions, we investigated whether sea turtle total mercury content participates in the etiology of SR. Given that several toxins are known to affect both DNA methylation and/or mitochondrial DNA (mtDNA) copy number, we also probed for associations of these parameters to SR and mercury exposure. We measured the levels of each variable in malformed olive ridley sea turtle embryos (either with SR or other non-SR malformations) and embryos without malformations. Malformed embryos (with or without SR) showed higher mercury concentrations compared to normal embryos, while only embryos with SR showed higher levels of methylation compared to embryos without malformations and those with other malformations. Furthermore, we uncovered a positive correlation between mercury concentrations and DNA methylation in SR embryos. With respect to mtDNA copy number, no differences were detected across experimental groups. Because of sample size limitations, this study is an initial attempt to understand the association of environmental toxins (such as mercury) and epigenetic alterations (DNA methylation) in the etiology of SR in sea turtles.

Hox Genes in Reptile Development, Epigenetic Regulation, and Teratogenesis.

Reptiles are ancestral organisms presenting a variety of shapes, from the elongated vertebral column of the snake to the turtle dorsalized ribs or retractile neck. Body plans are specified by a conserved group of homeobox-containing genes (Hox genes), which encode transcription factors important in cell fate and vertebral architecture along the anteroposterior axis during embryonic development; thus, dysregulation of these genes may cause congenital malformations, from mild-sublethal to embryonic-lethal. The genetic pool, maternal transfer, and environmental conditions during egg incubation affect development; environmental factors such as temperature, moisture, oxygen, and pollution may alter gene expression by epigenetic mechanisms. Thus, in this review, we present information regarding Hox genes and development in reptiles, including sex determination and teratogenesis. We also present some evidence of epigenetic regulation of Hox genes and the role of the environment in epigenetic modulation of gene expression. So far, the evidence suggests that the molecular instructions encoded by Hox genes to build a snake, a lizard, or a turtle represent the interplay between genome and epigenome after years of evolution, with occasional environmentally induced molecular mistakes leading to abnormal body shapes.

Methylation status of the putative Pax6 promoter in olive ridley sea turtle embryos with eye defects: An initial approach.

Normal development involves the interplay of genetic and epigenetic regulatory mechanisms. Pax6 is an eye-selector factor responsible for initiating the regulatory cascade for the development of the eyes. For the olive ridley sea turtle (Lepidochelys olivacea), a threatened species, eye malformations have been reported. In order to study the DNA methylation status of the putative promoter of the Pax6 gene in embryos with ocular malformations, an exploratory study was carried out in which DNA was isolated from embryos with anophthalmia, microphthalmia, and cyclopia, as well as from their normal counterparts. The 5'-flanking region from the Pax6 gene was isolated, showing two CpG islands (CGIs). The methylation status of CGIs in malformed embryos was compared with that of normal embryos by bisulfite sequencing. Putative transcription factor binding sites and regulatory features were identified. Methylation patterns were observed in both CpG and non-CpG contexts, and were unique for each malformed embryo; in the CpG context, an embryo with cyclopia showed a methylated cytosine upstream the CGI-1 not present in other embryos, an embryo with left anophthalmia presented two methylated cytosines in the CGI-1, whereas an embryo with left anophthalmia and right microphthalmia showed two methylated cytosines in the CGI-2. Normal embryos did not show methylated cytosines in the CGI-1, but one of them showed one methylcytosine in the CGI-2. Methylated transcription factor-binding sites may affect Pax6 expression associated to the cellular response to environmental compounds and hypoxia, signal transduction, cell cycle, lens physiology and development, as well as the transcription rate. Although preliminary, these results suggest that embryos with ocular malformations present unique DNA methylation patterns in the putative promoter of the Pax6 gene in L. olivacea, and probably those subtle, random changes in the methylation status can cause (at least in part) the aberrant phenotypes observed in these embryos.