Age Determination of the Stream Frog, Rana sakuraii, by Skeletochronology

Abstract

In long-lived species such as amphibians, age determination of individual animals is important in elucidating population dynamics and life histories. Although four methods have been used for aging amphibians, only skeletochronology and mark-recapture are reliable (see Halliday and Verrell, 1988). Markrelease-recapture potentially provides the most reliable data on age, but this method is very labor-intensive and takes a long time to yield a result. On the other hand, skeletochronology using phalanges has proved to be an excellent tool to investigate population age structure. Although this method has potential problems (such as endosteal resorption of periosteal bone which may alter the early year rings), many studies have been conducted successfully using skeletochronology in anurans (e.g., Hemelaar and van G lder, 1980; Gibbons and McCarthy, 1983; Hemelaar, 1985). In this paper, we report on the age structure, age at first reproduction, and growth rates of Rana saku aii as determined by skeletochronology. The stream frog, Rana sakuraii, is distributed in central Honshu from the Kanto to Kinki districts, Japan (Matsui and Matsui, 1990). The frogs inhabit mountain forests in summer and appear in streams in late autumn, overwintering under submerged stones. Breeding begins in February-March, and breeding activity lasts for a few weeks to a month (Kusano and Fukuyama, 1987, 1989). Specimens were collected in an upper tributary of the Bonbori River (35?42'N, 139?11'E), at 380 m, about 37 km west of the Tokyo metropolitan area. This stream is located in a mountainous region covered with planted coniferous forests of Cryptomeria japonica and Chamaecyparis obtusa and secondary deciduous forest. From 1988 to 1990, we collected breeding adults by hand during February-March. The frogs were sexed u ing secondary sexual characteristics such as thumbpad development, and snout-vent length (SVL) was measured to the nearest 0.5 mm with a slide caliper. Th fourth toe of the right or left hind leg was clipped off each frog and stored in separate vials containing 10% buffered formalin. Only the third phalanx of each toe was used for this study. Overwintering juveniles were collected from the stream during December-April. They were measured, and then some were killed in a 0.1% MS 222 solution and fixed in 10% buffered formalin to determine their