Photic and non-photic regulation of growth, development, and metamorphosis in giant tree frog (Rhacophorus maximus) tadpoles

Seasonal variations in the intermediate metabolism in South American tree-frog Boana pulchella

Seasonal metabolic changes can be observed in many anurans' species. In subtropical environments with environmental temperatures variations, the temperature is a factor that can influence the extent and intensity of activity in many anuran species. Nonetheless, some species of subtropical frogs may remain active throughout the year. Boana pulchella, a subtropical species, seems to be able to survive low temperatures and remain reproductively active even in the coldest months. Therefore, we hypothesized that B. pulchella presents seasonal changes in the energy metabolism to sustain activity during all year. This study evaluated the main energy substrate levels and metabolism of B. pulchella in plasma, liver and muscle of male individuals collected in winter, spring, summer and fall in the state of Rio Grande do Sul, Brazil. Our results showed that B. pulchella has a higher glycolytic oxidation rate in liver (P = 0.0152) and muscle (P = 0.0003) and higher glycogenesis from glucose in muscle (P = 0.0002) in summer, indicating the main energy substrates in this season is glucose. The higher muscle glycogen (P = 0.0008) and lower plasma glucose in fall (P = 0.0134) may indicate an anticipatory regulation for storing to the most thermally demanding cold period: winter. These results indicated seasonal differences in the main energy substrates, and these metabolic changes among seasons can be part of a metabolic adjustment allowing maintenance of reproductive activity all year in Boana pulchella species.

Seasonality in terai tree frog (Polypedates teraiensis): Role of light and temperature in regulation of seasonal breeding

Seasonality is represented as an initiation-termination-reinitiation of any physiological processes. Photoperiod is the most predictable environmental cue which organism use to time their daily physiology and seasonal functions. In natural light environmental conditions, day and night components change in terms of duration, intensity and spectrum of light available. In many vertebrate species, daytime light intensity and spectrum of light play a critical role in gonadal recrudescence-regression cycle. In tropical conditions, many amphibian species show a clear relationship between reproduction and seasonal distribution of rainfall. In temperate conditions, reproduction is usually centered during spring and summer seasons when environmental conditions are favorable. Poikilotherms are highly sensitive to change in environmental temperature and their physiology and metabolic activities depend on environmental temperature. How environmental factors (light and temperature) influence, the reproduction of terai tree frog (Polypedates teraiensis) is not known. We hypothesized that light acts as a proximate factor but the temperature is the ultimate factor for reproduction of terai tree frog. Three experiments were performed. In experiment one, we studied the annual reproductive cycle under natural environmental conditions. Beginning from the month of March till October 2016, we procured adult frogs (male and female) in the middle of each month. Monthly observations were recorded for body weight and gonadal weight and GSI was calculated. We found the annual change in body mass, gonadal weight and GSI in both male and female with high gonadal weight and GSI values from March to June. These results suggest that terai tree frog is seasonal breeders, and their breeding corresponds with long days. In experiment two we addressed the effects of light duration, light intensity and light spectrum on gonadal growth regression cycle. We observed that long days promote gonadal growth regression cycle. However, after achieving critical daylength there is no additive effect of light duration. Further, light intensity and spectrum have limited role in gonadal growth regression cycle of this species. In experiment three we tested the role of temperature on body weight and testicular growth under stimulatory photoperiod (12 L:12D). Group one was exposed to high temperature (34 ± 2 °C), while group two was exposed to low temperature (22 ± 2 °C). We found that low temperature promotes testicular recrudescence under laboratory conditions. Altogether our study suggests both photoperiod and temperature are involved in the regulation of seasonal breeding in tree frog. Findings from the above study could be used for captive breeding of amphibians and may be helpful in amphibian conservation programmes.