Parasite diversity within native and invasive terrapins : implications for conservation

Abstract

Terrapins are one of the most endangered vertebrate groups, with almost half of the more than 300 extant species threatened with extinction. This study was conducted to investigate parasite host-switching from the invasive American Red-eared slider, Trachemys scripta elegans, to the native Mediterranean pond terrapin, Mauremys leprosa in natural environments in southern France and Spain. The study also included a risk assessment approach that was developed to assess the viability of the native M. leprosa terrapins in a small river of southern France. The diversity of haemogregarine parasites within South African terrapins was also explored. The thesis is structured as follows: CHAPTER 1 gives a broad introduction to reptiles and chelonians as well as the importance of chelonians in ecosystems with emphasis to the threats that are driving terrapins to decline. The various terrapin species examined during this study as well as the parasite groups of interest (Monogenea and Apicomplexa) are also discussed in detail. CHAPTER 2 documents the extent of platyhelminth invasions from T. s. elegans to natural M. leprosa populations in northern Spain and southern France. From DNA barcoding analysis based on the sequencing of the Cytochrome c Oxidase I gene, the inferred Minimum Evolution tree and p-distance comparisons of closely related haplotypes revealed a greater polystome richness within M. leprosa than expected, suggesting that host switching may take place in natural environments. T. s. elegans would serve as a carrier for a variety of polystomes that usually infest American turtles in their home range. These are transmitted to M. leprosa throughout the south of France, also suggesting that turtle polystomes are not strictly host-specific. CHAPTER 3 investigates polystome egg production under changing environmental conditions. The experimental procedure that was conducted on M. leprosa showed that environmental temperature has an effect on the egg laying rhythm of its parasite, i.e., Neopolystoma sp., with a two day lag of egg production in response to environmental temperature change. Results suggest the adaptability of the parasite to the physiology of their chelonian hosts which are ecthothermic animals. They also show that eggs production may be attributable to the release of host factors like hormones that once secreted may act and stimulate parasite reproduction. CHAPTER 4 relates risk assessment for the viability of the native Mediterranean pond terrapin (M. leprosa) in a natural environment by using the Relative Risk Model (RRM) method, taking into consideration various threats and environmental conditions that may impact this species. CHAPTER 5 examines the diversity of South African terrapin haemogregarines (Protozoa: Apicomplexa: Haemogregarinidae) as well as their phylogenetic placement among haemogregarines based on molecular and morphological evidences. CHAPTER 6 summarizes all findings of the study and explores new ways of Research.