The impact of elevated temperature and CO2 on growth, physiological and immune responses of Polypedates cruciger (common hourglass tree frog)

Abstract

Background: Amphibians are one of the most susceptible groups to climate change as their development occurs in aquatic environments or in microhabitats with high humidity. Accordingly, our primary objective was to investigate the chronic physiological responses seen in early larval to adult stages of Polypedates cruciger (Common hourglass tree frog) to future climate change based on continuous exposure to elevated temperature and elevated CO 2 -induced low water pH. Free-swimming and free-feeding tadpoles were observed until metamorphosis under four experimental treatments; two elevated temperatures, one elevated CO 2 (reduced pH) and a control maintained at ambient temperature (29°C ± 1°C) and CO 2 (pH = 7). Elevated temperature treatments were maintained at 32°C ± 0.5°C and 34°C ± 0.5°C to represent respectively, the future climate scenarios RCP2.6 (Representative Concentration Pathway 2.6, the 'base-case' scenario) and RCP8.5 ('business-as-usual' scenario) according to the 5 th Assessment Report of the IPCC. Elevated CO 2 treatment was maintained within the pH range of 5.5-5.6 representing the range expected between RCP8.5 and RCP2.6. Results: Compared to the control, elevated CO 2 accelerated phenological progression of tadpoles through Gosner stages, thus resulting in lower body size at metamorphosis. Both elevated temperatures significantly delayed the development and reduced the growth of tadpoles. 100% mortality was observed in 34°C treatment before metamorphosis (before Gosner stage 36) while all the tadpoles died after metamorphosis (at Gosner stage 46) in 32°C treatment. Elevated CO 2 increased tadpole activity, in terms of their swimming speed, while both of the elevated temperatures reduced it compared to the control. Catalase activity increased at elevated CO 2 . Ammonia excretion by tadpoles was decreased by elevated CO 2 , but increased under temperature elevation. Both Elevated CO 2 and temperature treatments reduced the white blood cell count and its percentage of thrombocytes. Percentages of lymphocytes, monocytes and neutrophils were increased at 32°C, while lymphocyte percentage and lysozyme activity were increased at elevated CO 2 . Several deformities were observed in tadpoles at elevated temperature and CO 2 .

Heat stress and amphibian immunity in a time of climate change

“…One study simulated future climate conditions for developing Polypedates cruciger (common hourglass frog) tadpoles through increasing CO 2 and subsequently decreasing pH, which resulted in lower white blood cell counts in circulation (relative to red blood cells). However, oxygen levels were not measured in this study [ 77 ]. While amphibian larvae may have higher tolerance to hypoxia than fish, given the potential for warming and excess nutrients to increase hypoxia risk in certain ecosystems, more research is warranted here.…”

“…In addition to the study of the effects of elevated CO 2 that affects pH and white blood cell counts cited above [ 77 ], the authors examined the effects of temperatures elevated by 3 or 5°C (from 29 to 32 or 34°C) on survival and blood cell numbers in developing P. cruciger (common hourglass frog) tadpoles at the conclusion of metamorphosis. Both elevated temperatures reduced survival, and all the tadpoles at 34°C died before reaching metamorphosis.…”

Thermal Acclimation to the Highest Natural Ambient Temperature Compromises Physiological Performance in Tadpoles of a Stream-Breeding Savanna Tree Frog

“…Normally, environmental stressors such as temperature, prolonged droughts and hypoxic environments would accelerate metamorphosis by increasing the hypothalamus-pituitary-interrenal axis activity (Kikuyama et al, 1993;Owerkowicz et al, 2009;Heinrich et al, 2011;Rollins-Smith, 2017). The putatively reduced growth and the prevention of metamorphosis in tadpoles of T acc25 may indicate changes in energy allocation, with most of it being diverted to maintain a high r ṀO 2 (Ruthsatz et al, 2018;Weerathunga and Rajapaksa, 2020). Both thyroid and glucocorticoid hormones are known to trigger metamorphosis in amphibians, and elevated temperatures may activate the hypothalamus-pituitary-interrenal axis and accelerate metamorphosis (Duellman and Trueb, 1994;Crespi and Denver, 2004;Ruthsatz et al, 2018).…”

Population size and survival of the Brazilian Torrent Frog Hylodes heyeri (Anura, Hylodidae)

“…For example, severe drought decreased the survival and fecundity of Bombina variegata during ontogeny (Cayuela et al, 2016). Also, both high temperatures and drought increased mortality in Litoria aurea (Beranek et al, 2022) and Polypedates cruciger (Weerathunga & Rajapaksa, 2020). Yet, usually variation in weather is associated with variation in frog behaviour, including estivation, calling sites, reproduction and essentially all aspects that influence population dynamics (Blaustein et al, 2010; Gao et al, 2015; Lawler et al, 2006; Varjão & Ribeiro, 2018).…”