Species-specific model to predict amphibian metamorphosis

Abstract

Exploring the timing of life-history transitions has been a pivotal focus in the field of evolutionary ecology. Studies on amphibian metamorphosis are well suited to investigate this aspect. We propose a species-specific model to predict the optimal metamorphosis point for frog individuals with different larval growth trajectories. Because overall fitness will be determined throughout both aquatic and terrestrial stages, we included growth and survival rates of aquatic and terrestrial stages in the fitness equation. Then we conducted a rearing experiment on a brown frog, Rana ornativentris, as an example to obtain the size at metamorphosis, larval period, and larval growth trajectory. Based on these results, we determined the model's parameters to fit the actual metamorphosis patterns. Because the parameters are supposed to be evolutionarily maintained, our data-driven approach enabled obtaining fundamental ecological information (evolutionally-based life-history parameters) of the target species. Comparing the parameters among species will allow us to understand the mechanisms in determining life-history transition more deeply.

Figure 1

Behaviors of fitness elements according to larval period, $T$ (day). (a) mortality rate of aquatic and terrestrial stages; (b) survival rate on reference day; (c) size on reference day; (d) fitness equation value. The dotted line shows the value for an individual with the largest size at metamorphosis ($actS=884.7,actT=47)$, a broken line for one with median size at metamorphosis ($actS=486.5,actT=48)$, and a solid line for one with the smallest size at metamorphosis ($actS=333.0,actT=57)$. The aquatic mortality rate was identical for all the individuals (${\mu }_{\mathrm{A}}$: 0.027), thus shown as a bold line in (a).

Figure 2

Larval period and size at metamorphosis of 29 Rana ornativentris tadpoles. Left: actual data from the rearing experiment. Tadpoles were reared with different amounts of food to induce variations in growth rates. Right: estimated data using fitness equation.

Figure 3

Behavior of the value of Eq. (3) according to the size at metamorphosis ($S$). The open circle shows the observed minimum size at metamorphosis ($actS=333.0$), and the filled circle shows the observed maximum size at metamorphosis ($actS=884.7$).

Figure 4

Scheme of this study.