Growth and metamorphosis data from a rearing experiment on Rana ornativentris

Amphibian larvae exhibit high plasticity in response to environmental conditions such as food and temperature, determining the timing and size of metamorphosis. While extensive research has been conducted on the mechanisms governing when and at what size metamorphosis occurs, specific models indicating species-specific metamorphic points have not been established. To create such a model, we conducted a rearing experiment using Rana ornativentris larvae as an example. We reared the larvae under different feeding conditions, monitored their growth, and recorded the number of days to metamorphosis and the body size at metamorphosis.

Methods
R. ornativentris tadpoles were reared in a laboratory to obtain data on individual growth curves and consequential actual size and age at metamorphosis. Variations in aquatic growth rates were created by varying the amount of available food.

Two egg masses were collected from the field on April 9, 2017 and incubated until they hatched. When tadpoles reached Gosner’s stage 25 (Gosner 1960) on April 17, they were individually placed in a plastic container (129-mm diameter, 72-mm height) with 300 mL of aged tap water (day 0). Individuals were randomly assigned to one of the six food treatment groups (shown below) with seven individuals per group. In total, six or nine individuals that hatched from each egg mass were photographed with a scale to estimate the initial body weight using a formula for the relationship between snout-vent-length (SVL) and body weight obtained in another study (W(mg) = 206 × SVL(mm)2.85, Iwai et al. 2019). Containers were incubated (MIR-254-PJ or MIR-554-PJ, Panasonic, Japan) at a constant temperature (18 °C) and a 12:12 h light:dark cycle. 

Commercial fish food (Hikari-haiga, Kyorin, Japan) was crushed to a powder, mixed with a 1% agar solution, and placed in a Petri dish of 84 mm diameter. Food pellets were bored using straws of different diameters, and a fixed amount of food (1.6, 2.5, 3.2, 4.1, 5.0 mg/day, and ad libitum) per individual was supplied every three or four days when the water was changed and the containers cleaned. Body weight was measured once every 3−21 days. 

Metamorphosis was defined as the emergence of the first forelimb and was inspected daily.