Air temperature, water conductivity, and pH jointly determine freshwater ostracod ecological niches (Patagonia, Argentina)

Abstract

Ostracods (Crustacea) inhabiting freshwater environments are a taxonomically and ecologically diverse group of microcrustaceans that serve as valuable (paleo)environmental indicators. Yet little is known about how their distribution is jointly shaped by the combined effects of environmental factors, species traits, phylogenetic re­lations, and spatial structure. To fill this gap, we applied Joint Species Distribution Models (JSDMs) to test how these components influence species occurrence and trait-environment relationships across 163 freshwater bodies in Patagonia, Argentina. We found that ostracod distribution was mainly explained by environmental factors (30 %), including local factors such as water conductivity and pH, and climatic variables such as maximum air temperature, with the spatial random effect contributing 2.4 %. All species showed significant positive (33) or negative (35) responses to at least one environmental variable, particularly pH (10 species), air temperature (9 species), and conductivity (7 species). Species like Newnhamia patagonica and Ilyocypris bradyi/ramirezi were primarily influenced by climatic variables, whereas Limnocythere rionegroensis was mainly linked to local factors. Phylogenetic relationships played a weak role in explaining species responses to the environment. Additionally, six species traits were significantly associated with environmental variables, including local (conductivity, pH) and climatic (e.g., maximum air temperature) factors. Sexual reproduction was the most frequently associated trait, particularly with higher conductivity and pH, characteristics typical of shallow lakes of the Patagonian steppe. These findings provide a comprehensive understanding of the factors shaping the environmental niches of ostracods, enhancing their potential as bioindicators for tracking environmental change in freshwater eco­systems across Patagonia.