Sex determination of European pond turtle (Emys orbicularis L.) juveniles in protected habitats of Lithuania

Abstract

The European pond turtle (Emys orbicularis L., 1758) is a freshwater turtle species inhabiting ponds, slow-flowing rivers and swamps. The species is endangered and strictly protected in Lithuania and in most European countries. E. orbicularis is included in the International Union for Conservation of Nature (IUCN) Red List of Threatened Species and the Red Data Book of Lithuania. The objective of this study was to determine the effect of temperature in natural habitats on egg incubation and sex of E. orbicularis individuals, and to determine their sex according to the differences in plastron appearance and morphometric measurements. The research was performed during 2021−2023 years, in protected habitats of Meteliai Regional Park. The length and width of the carapace and central height of the shell were measured each year. Observations revealed that sexual dimorphism between E. orbicularis individuals exists. Also, the study confirmed that egg incubation temperature in natural habitats of the species has an impact on the sex determination of individuals. Climatic changes and complex anthropogenic factors influence the loss of suitable habitats and the decrease of E. orbicularis populations. Temperature fluctuations during the egg incubation period may result in different sex ratios within populations. In order to conduct more detailed investigations on this topic, it is important to save the natural habitats of the species and to restore or increase the size of small endangered populations of E. orbicularis.