Turtle Carapace Anomalies: The Roles of Genetic Diversity and Environment

Abstract

BackgroundPhenotypic anomalies are common in wild populations and multiple genetic, biotic and abiotic factors might contribute to their formation. Turtles are excellent models for the study of developmental instability because anomalies are easily detected in the form of malformations, additions, or reductions in the number of scutes or scales.Methodology/Principal FindingsIn this study, we integrated field observations, manipulative experiments, and climatic and genetic approaches to investigate the origin of carapace scute anomalies across Iberian populations of the European pond turtle, Emys orbicularis. The proportion of anomalous individuals varied from 3% to 69% in local populations, with increasing frequency of anomalies in northern regions. We found no significant effect of climatic and soil moisture, or climatic temperature on the occurrence of anomalies. However, lower genetic diversity and inbreeding were good predictors of the prevalence of scute anomalies among populations. Both decreasing genetic diversity and increasing proportion of anomalous individuals in northern parts of the Iberian distribution may be linked to recolonization events from the Southern Pleistocene refugium.Conclusions/SignificanceOverall, our results suggest that developmental instability in turtle carapace formation might be caused, at least in part, by genetic factors, although the influence of environmental factors affecting the developmental stability of turtle carapace cannot be ruled out. Further studies of the effects of environmental factors, pollutants and heritability of anomalies would be useful to better understand the complex origin of anomalies in natural populations.

Out of Africa: did Emys orbicularis occidentalis cross the Strait of Gibraltar twice?

“…The low genetic diversity, the star-like haplotype network of most Iberian samples ( fig. 2B), and demographic results (Velo-Antón et al, 2008, 2011b suggest recent arrival from Morocco (Fritz et al, 2007;Stuckas et al, 2014) and population expansion throughout the Iberian Peninsula.…”

A Comparison of Hatchling Locomotor Performance and Scute Pattern Variation between Two Rookeries of the Flatback Turtle (Natator depressus)

“…It is likely that non-modal scute patterns do not influence survival directly, but are indications of greater internal abnormalities (Mast and Carr, 1989). Non-modal scute patterns may be caused by genetics, environmental conditions during egg incubation, or handling of eggs (Hewavisenthi and Parmenter, 2001;Tü rkozan and Yilmaz, 2007;Velo-Anton et al, 2011), and therefore have the potential to vary among different rookeries.…”

Nest environment and hatchling fitness correlates in the sea turtles Caretta caretta and Natator depressus

“…Several hypotheses have been suggested to explain non-modal scute patterns, including genetic factors, inbreeding, disturbance to eggs, pollution and incubation temperature (Mast & Carr, 1989;Hewavisenthi & Parmenter, 2001;Velo-Anton et al, 2011). In this study the Mon Repos clutches were relocated and the Bare Sand Island ones were not.…”

“…It is likely that non-modal scute patterns do not influence survival directly, but are indications of greater internal abnormalities (Mast & Carr, 1989). Non-modal scute patterns may be caused by genetics, environmental conditions during egg incubation or handling of eggs (Hewavisenthi & Parmenter, 2001;Türkozan & Yilmaz, 2007;Velo-Anton et al, 2011), and therefore have the potential to vary among different rookeries.…”

“…Finally, I predicted that the proportion of hatchlings with non-modal scute patterns would differ between the two rookeries because of genetic and environmental differences. Both of these factors have previously been proposed as causes of nonmodal scute patterns (Hewavisenthi & Parmenter, 2001;Velo-Anton et al, 2011) …”