Biogeography, ecology and taxonomy of the Neotropical ostracod Cytheridella

Ostracods are common aquatic invertebrates with a ubiquitous distribution which act as popular proxies for reconstructing climate and ecosystem changes. Interrelationships between phenotypic variability, geographical distribution, environmental conditions and reproductive modes are, however, poorly understood. We propose to perform coupled morphological-ecological analyses of Neotropical Cytheridella which is a typical freshwater inhabitant occurring in a variety of habitats. The project focuses on the investigation of (1) the intraspecific morphological variability of soft and hard parts and interrelationships with ecological parameters (e.g., alkalinity, solute composition, and temperature) within and between populations through the whole geographic range from ~30N to ~30S. Quantitative information about carapace shape variability will be received by landmark based morphometric methods. (2) The compilation of an extensive ecological data set will allow us to identify species specific ecological tolerances and possible local adaptations of peripheral populations. Moreover, geochemical signatures of the ostracods` calcitic valves and host water chemistry (major and trace elements, d18O and d 13C) will enable us to determine population specific and site specific basic chemical conditions and, in particular, oxygen and carbon isotope signatures and isotopic offsets (vital effects). These data will, thus, provide essential understanding of the geochemistry of ostracod valves. (3) Resulting from this we will be able to characterise Cytheridella morphotypes, analyse their distribution and evaluate their taxonomic meaning. Finally, this actualistic approach will provide essential information which can be applied to fossil Cytheridella populations. These are, e.g., common constituents of fluvial-lacustrine deposits of a mega-wetland which developed in western Amazonia (`Lake Pebas`) at the beginning of the Miocene (~23 Ma). To date, however, nothing is known about the ecological requirements or phylogenetic relationships of these fossil taxa. Thus, the approach of the current project should offer also the opportunity to better link neontological with paleontological information in future research.

Ostracods are bivalved crustaceans which occupy marine, freshwater and even semi-terrestrial environments. They are considered to be excellent bioindicators for environmental parameters and changes and their calcitic shells provide a long history in geological times (c. 500 Million years). For their taxonomy soft and hard part characters are considered most important, however, many ostracods, in particular freshwater species, are poor in shell characters. To overcome this disadvantage we analyzed ostracod valves applying geometric morphometrics (landmarks and semilandmarks) which resulted in the discovery of a geographic differentiation within one single species but also allowed for the first time the detection of cryptic morphospecies. Our model-species for this study was the Neotropical Cytheridella ilosvayi which occurs along the entire range of the Neotropics. We studied occurrences in South Florida, Mexico (Yucatn), Panama, Columbia, and Brazil (Amazonia and South Brazil). Soft part morphology varies due to ontogenetic and sexual differences. Hard part morphology (studied via Generalized least-squares Procrustes Analysis) shows clear ontogenetic allometry, the greatest change occurs from the last juvenile (A-1) to the adult stage. Geometric morphometrics allowed also the detection of cryptic morphospecies in Yucatn. Statistical analyses including environmental parameters indicated that chloride and sulphate concentrations, related to fluctuations in precipitation, affect valve development via controlling osmoregulation and carapace calcification. These factors represent hitherto unknown drivers for ostracod ecophenotypy and emphasize that environmental predictors for morphological variability are not consistent across non-marine ostracods. The wide geographic range of this species can be explained by avian transport and its morphologically based distributional pattern matches the fly ways of water birds. Avian dispersal may also repeatedly re-introduce C. ilosvayi to Yucatnian populations possibly explaining the sympatric occurrence of two Cytheridella morphospecies.Valve chemistry is considered to provide information on environmental parameters. Our study of stable oxygen and carbon isotopes (?18O, ?13C) valve composition and physicochemical water parameters indicate a clear relationship of isotopic valve composition and climatic parameters influenced by precipitation/evaporation, input of organic and inorganic carbon and temperature. As new approach for determining the calcification period of the ostracod valves we used a time series of water data, calculated the theoretical calcite composition grown in this water and compared this data with our stable isotope data. Based on that calculation, early spring was identified as calcification period of the South Floridian C. ilosvayi.