Stable isotope analysis spills the beans about spatial variance in trophic structure in a fish host - parasite system from the Vaal River System, South Africa

A new technique to study nutrient flow in host-parasite systems by carbon stable isotope analysis of amino acids and glucose

Stable isotope analysis of individual compounds is emerging as a powerful tool to study nutrient origin and conversion in host-parasite systems. We measured the carbon isotope composition of amino acids and glucose in the cestode Schistocephalus solidus and in liver and muscle tissues of its second intermediate host, the three-spined stickleback (Gasterosteus aculeatus), over the course of 90 days in a controlled infection experiment. Similar linear regressions of δ¹³C values over time and low trophic fractionation of essential amino acids indicate that the parasite assimilates nutrients from sources closely connected to the liver metabolism of its host. Biosynthesis of glucose in the parasite might occur from the glucogenic precursors alanine, asparagine and glutamine and with an isotope fractionation of - 2 to - 3 ‰ from enzymatic reactions, while trophic fractionation of glycine, serine and threonine could be interpreted as extensive nutrient conversion to fuel parasitic growth through one-carbon metabolism. Trophic fractionation of amino acids between sticklebacks and their diets was slightly increased in infected compared to uninfected individuals, which could be caused by increased (immune-) metabolic activities due to parasitic infection. Our results show that compound-specific stable isotope analysis has unique opportunities to study host and parasite physiology.

Narrower isotopic niche size in fish infected by the intestinal parasite Pomphorhynchus sp. compared to uninfected ones

Examples of parasite-related effects on intermediate crustacean hosts are numerous but their ecological consequences on their vertebrate hosts are scarce. Here, we address the role of macroparasite infections on the trophic niche structure of definitive hosts and its potential physiological consequences using wild fish populations infected with an acantochephalan parasite Pomphorhynchus sp., a trophically transmitted intestinal worm. Infected and uninfected fish were sampled from six populations on the Marne River, France and the prevalence of intestinal parasites in the host populations ranged from 50% to 90%. Although the isotopic ratios (δ¹³ C and δ¹⁵ N) did not differ between infected and uninfected fish, we found a consistent pattern of isotopic niche size being considerably smaller in infected hosts when compared with noninfected ones. This was not explained by interindividual differences in intrinsic factors such as length/age or body condition between infected and uninfected fish. These results suggest a potential niche specialization of infected fish, which did not impair their energetic status.

Parasites as Biological Indicators: the Impact of Environmental Quality on the Infections of Lamproglena clariae (Crustacea) on Clarias gariepinus Along the Vaal River, South Africa

Anthropogenic activities influence the natural equilibrium of freshwater ecosystems resulting in negative ecological impacts. Differences in the infection variables of Lamproglena clariae in relation to variable water quality influenced by metal pollution were studied at six sites along the Vaal River, South Africa (March 2017 and October 2018). From each sampling site, in situ water quality parameters, water and sediment samples, and a minimum of 10 Clarias gariepinus were collected. Lamproglena clariae specimens collected from the gills of C. gariepinus were used to calculate the prevalence, mean intensity, and mean abundance of the parasite. Metal concentrations in water and sediment were analysed with inductively coupled plasma-optical emission spectrometry and inductively coupled plasma-mass spectrometry. Parasite intensity correlated negatively with some water quality parameters (conductivity, salinity, pH, total dissolved solids, and dissolved oxygen). Negative correlations were found between L. clariae (intensity and prevalence) and metal concentrations (Cu, Cr, Zn, Cd) in water. Parasite infections were influenced negatively at sites with high metal concentrations recorded in sediment and water and high levels of organic pollution. Sites that were found to be more polluted had lower mean intensity and mean abundance of L. clariae, indicating pollution affects the survival of this ectoparasite.