Integrative study of ostracods in high-altitude aquatic ecosystems, Nam Co, Tibetan Plateau: Taxonomic revisions, discovery of a new species, and ontogenetic features

This thesis focuses on the integrative taxonomy of ostracods in the high-altitude aquatic ecosystem of Nam Co, Tibetan Plateau (TP). By combining morphological, ecological, and molecular methods, this approach aims to accurately delimit species boundaries. Nam Co, due to its altitude and geographical location, is key for climate research, improving our understanding of regional and global climate patterns and the impacts of climate change in high-altitude environments. The Nam Co ecosystem, hosting endemic species adapted to extreme conditions, provides insights into species evolution and ecology. Ostracods from the high regions of the Tibetan Plateau, particularly Nam Co, are important (paleo) limnological bioindicators because of their sensitivity to temperature and salinity, but requires an accurate species identification. The study aims to: (1) Document and clarify taxonomic inconsistencies of Tonnacypris stewarti comb. nov. by detailing morphology, valve ontogeny, ecological aspects, current distribution, and reproductive strategies; (2) Describe a new Heterocypris species, distinguishing it from close congeners H. incongruens and H. salina, using reliable taxonomic characters, and employ the mitochondrial COI gene to reconstruct its phylogenetic relationship with selected Heterocypris and Cyprinotus species; (3) Record valve ontogeny and egg morphology of Heterocypris exodonta sp. nov. from the Tibetan Plateau and compare growth patterns with related species (H. incongruens, from Mexico, and H. salina, from Germany). The taxonomic clarification of Tonnacypris stewarti comb. nov. (previously Herpetocypris stewarti Daday 1908) involved resolving previously overlooked synonyms and proposing a revised nomenclature. Meticulous morphological analyses and an extensive literature review revealed that seven definitive synonyms corresponded to this single species described over 116 years ago. Additionally, a detailed examination of the ontogenetic series of T. stewarti from surface sediment samples from Nam Co revealed the presence of an adult and seven juvenile stages, though the first juvenile stage (A-8) was poorly preserved. Only female specimens were found suggesting geographic parthenogenesis within the Palearctic region, with sexual populations documented in Mang-tsa, TP, and Lake Band-e Amir, Afghanistan. This study unified the (paleo) ecological information associated with this species, recognized as an indicator of cold, oxygenated, oligotrophic, and fresh to brackish waters, improving (paleo) ecological interpretations and knowledge of ostracod diversity. This research also describes a new species, Heterocypris exodonta sp. nov. Bonilla-Flores & Karanovic from a pond in the Nam Co region, TP. The species description is based on detailed morphological analysis of valves, soft body, and mitochondrial COI gene sequence, with comparison to H. incongruens from Mexico City and H. salina from Braunschweig, Germany. Distinctive features, such as the morphology of the female genital lobes and the structure of the internal opening of the normal pores, were used as key taxonomic characteristics for the first time within this predominantly parthenogenetic genus. The phylogenetic tree based on the COI dataset supports the description of this new species, and suggest the potential presence of cryptic species within Heterocypris incongruens. The three species examined, H. exodonta (Nam Co, Tibetan Plateau), H. incongruens (Mexico City, Mexico), and H. salina exhibit an r-type ecological strategy, thriving in temporary ponds with high oxygen levels and undergoing rapid population growth. This information will allow for better identification of distribution patterns, ecological adaptations to particular environments, acknowledgment of morphological variability, and emphasis on biodiversity conservation, enabling the prioritization of conservation areas and the effective management of natural resources. Laboratory cultures and observations over approximately three months documented nine stages (eight juveniles and one adult) for the three Heterocypris species, revealing post-embryonic changes in valve morphology and growth patterns. SEM photos of their eggs highlighted two main layers: an outer rough layer and an internal embryonic cuticle, serving as protective barriers against adverse environmental conditions. Early juvenile stages (A-8 to A-2) displayed a hexagonal reticulation pattern on their valve surface, which disappeared with maturity. Valve measurements showed the mean growth ratio closely aligning with the Brooks' Rule, at 1.260 for crustaceans. In this context, the culture of organisms in a laboratory setting remains relevant as it contributes to understanding their biology and life cycles; validates their role as sensitive indicators of water quality, providing insights into their behavior and responses under controlled conditions. This thesis significantly advances our understanding of the aquatic fauna in the TP, contributing to aquatic ecology and paleolimnology. It highlights the importance of taxonomic clarity and interdisciplinary approaches in ostracod research.