Morphology and size of blood cells of Rhinella arenarum (Hensel, 1867) as environmental health assessment in disturbed aquatic ecosystem from central Argentina

Blood parameters of adult marsh frogs Pelophylax ridibundus (Amphibia: Ranidae) in rice paddies subjected to intense agrochemical use

We present the results of an in situ study of a set of blood parameters in adult marsh frogs (Pelophylax ridibundus (Pallas 1771) from populations inhabiting the largest system of rice fields in Bulgaria, the Tsalapitsa rice fields (TRF), under chronic stress conditions. This study was conducted in spring 2022 to assess the health status of TRF frogs compared to that of frogs occupying a reference site (RS). Furthermore, this study also compared the results obtained for the TRF population with those obtained in a study conducted at the exact same location with P. ridibundus individuals in 2013 (Zhelev et al. 2018). This comparison highlights the potential effects of persistent use of agrochemicals (pesticides and fertilizers) on the marsh frogs of later generations. Our results suggest that the general health of marsh frogs in the polluted site (PS) in southern Bulgaria has severely deteriorated. Frogs of both sexes were anemic with weakened immune systems compared to those living in the RS. The long-term use of agrochemicals in the PS affected males to a greater extent than it did females. Statistically significant hypochromia was observed in males, combined with general leukopenia, neutrophilia, lymphopenia, monocytosis, eosinophilia, and higher neutrophil/lymphocyte (N/L) ratios.

Contributions of water-borne corticosterone as one non-invasive biomarker in assessing nitrate pollution stress in tadpoles of Rana temporaria

Among a multitude of stressors to which wildlife is exposed, environmental pollution is a pervasive one that poses a serious threat. The permeable skin of amphibians is likely to increase direct contact of the body with pollutants, making them a group worth studying to access environmental quality. Consequently, finding reliable and complementary biomarkers that will present detectable and predictable changes in response to pollutants is essential to identify pollution sublethal effects on amphibians and to investigate whether these are in part responsible for population declines. The glucocorticoid hormone corticosterone (CORT), involved in many metabolic functions, is often used to measure the physiological stress response to environmental stressors in amphibians. In this study, we evaluated whether water-borne CORT can serve as a non-invasive biomarker for nitrate pollution stress in the European common frog (Rana temporaria) by comparing the effect of nitrate exposure on hormone release rates and on other physiological downstream biomarkers, i.e., ultimate physiological effects of the stressor. Specifically, we investigated the effect of different nitrate concentrations (0, 10, 50, and 100 mg/L) on water-borne CORT release rates, age, size, and body condition. Exposure to nitrate pollution significantly increased age at metamorphosis and water-borne CORT release rates, and led to reduced mass and body condition, but only at higher nitrate concentrations (i.e., 50 and 100 mg/L). Considering this similar sensitivity to other acknowledged biomarkers, water-borne CORT was a reliable biomarker of physiological stress in R. temporaria exposed to nitrate pollution stress in a controlled single-stressor laboratory approach. Thus, water-borne CORT is a promising method to be included in more holistic approaches. We recommend that such approaches keep testing multiple biomarker combinations, as species are exposed to several stressors likely to interact and produce varied outcomes in different biomarkers in their natural habitats.

Effect of parasitism of Lernaea cyprinacea on tadpoles of the invasive species Lithobates catesbeianus

The introduction of invasive species is one of the greatest threats currently faced by natural ecosystems, causing ecological imbalances between native populations and transmission of a variety of diseases. We reported the interaction between two exotic species given by the parasitic infestation of the copepod Lernaea cyprinacea in the early stages of the development of the American bullfrog Lithobates catesbeianus in the central area of Argentina. In this paper we analysed the leukocyte profile of parasitized and non-parasitized tadpoles of L. catesbeianus with L. cyprinacea and their body condition (BC) as biomarkers of the health status of organisms. A total of 27 tadpoles of L. catesbeianus were analysed (12 non-parasitized and 15 parasitized). The lower BC recorded in parasitized organisms show a lower health status in these tadpoles, which could be affecting the metamorphosis and therefore impact at the population level. Leukocyte response of L. catesbeianus tadpoles to the parasitism of L. cyprinacea was found. Mature and immature lymphocyte frequencies and hematocrit were higher in parasitized compared to non-parasitized tadpoles, which is a typical response to the presence of parasites. However, eosinophils and monocytes were recorded at high frequencies in not parasitized tadpoles, which could be due to the important role played by these leucocytes in the metamorphosis of frogs. The results of this study constitute a first antecedent on leukocyte profile in aquatic stages of anurans during an ectoparasitosis and its possible implications for environmental health. The parasitism of L. cyprinacea influences the biology of the American bullfrog at both the individual and population levels. Parasitized individuals are not killed directly by the parasite, but they can create conditions for secondary infections, growth retardation, behavioral changes and, ultimately, reduce populations.

Health status of Pelophylax ridibundus (Amphibia: Ranidae) in a rice paddy ecosystem in Southern Bulgaria and its importance in assessing environmental state: haematological parameters

Pollution effects on haematological parameters in Pelophylax ridibundus individuals were investigated; animals were collected from two sites in Southern Bulgaria: the Tsalapitsa rice fields (RF) and the Vacha river (reference site, RS). Blood analysis showed significant differences between the haematological parameters of RBC, WBC, Hb, packed cell volume (PCV) and frogs' leucogram from RF and those from RS. These findings provide information on long-term background pollution of the habitat (RF) under investigation. In our view, the erythropenia, leucopenia, hypоchromia, lower values of PCV, St-neutrophilia, Sg-neutropenia, basopenia, eosinophilia, monocytosis and lymphopenia that were found in Pelophylax ridibundus individuals inhabiting the Tsalapitsa rice fields were probably caused by the pesticides and fertilizers that enter the paddy cages during the rice production process. The present study proves the practical usefulness of haematological parameters of Pelophylax ridibundus individuals in bioindication analyses for environmental assessment of agroecosystems.