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

Abstract

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.

Pathology of Hatchling Hawksbill Sea Turtle (Eretmochelys Imbricata) Mortalities Occurring While Under Rehabilitative Care, 2015–21

“…Dysmelias were the next most common malformations both in the study by Bárcenas-Ibarra et al (2015) and our study. The pathogenesis of dysmelias and other observed malformations is unknown in hawksbills, but probably involves genetic and environmental factors (Martin Del Campo et al 2021). The possibility that certain malformations result in embryonal mortality or inability to hatch or emerge from the nests (Kaska and Downie 1999; Bárcenas-Ibarra et al 2015) underscores the need for further research to determine the prevalence of malformations in hawksbills in the Wider Caribbean and their associated effects on hatch and emergence success and hatchling health.…”

Finding of a two-headed green turtle embryo during nest monitoring in Baa Atoll, Maldives

“…Additionally, various components such as polycyclic aromatic hydrocarbons or mercury have been identified as possible agents changing deoxyribonucleic acid (DNA) methylation patterns and thus triggering abnormal development (Bárcenas-Ibarra et al 2015 ; see Martín-del-Campo, Sifuentes-Romero & Garcías-Gasca 2019 ; Martín-del-Campo et al 2021 for a summary). The prevalence of such components in sea turtle eggs in the Maldives is currently unknown.…”