Variations in Oocyte Maturation and Lysis of the Common Toad Rhinella arenarum (Anura: Bufonidae): Is Climate Change Affecting Oocyte Functionality?

Abstract. Many recent studies have shown that amphibian populations have been affected by a variety of causes including climate change, pollution, habitat destruction, and disease. Such drivers could also influence the physiological and behavioral reproductive events of individuals. Rhinella arenarum is an amphibian species that has been extensively used as an experimental model for biological studies. This is an ecologically important species due to its abundance and wide distribution in South America. Our research on the female gonad of R. arenarum conducted in the last three decades has allowed us to observe that the competence of the ovary of this species has been slowly modified over the years, manifested by an increase in oocyte lysis during in vitro assays. To better understand the changes, a retrospective analysis of data from the last three decades was performed in order to quantify oocyte maturation and lysis in the presence of different incubation mediums. Data from three sampling years (1993, 2005, and 2018) were selected, and percentages of oocyte maturation and lysis were compared. Results show a significant decrease in oocyte maturation and an increase in oocyte lysis in the last sampling year. We also examined the climate conditions of the habitat of R. arenarum in each sampling year and their variation as a possible driver of decreased ovarian functionality. A significant increase in minimum temperatures, solar radiation, and relative humidity is reported. Alterations in the climate conditions of the natural habitat of R. arenarum might be one of many factors responsible for the decrease in ovarian functionality. Further analysis of the impact of the ongoing climate change on several aspects of amphibian phenology is needed to strengthen understanding of population declines and promote species conservation.