Growth and Development of the Green Frog, Rana clamitans, Under Natural Conditions

Compared to other vertebrates, relatively little is known concerning the rate of growth and development (other than embryonic) of amphibians in nature. In the laboratory, on the other hand, many physiological experiments, most of which concern the influence of endocrine secretions on the rate of growth and development of amphibians, have been reported. Noteworthy among these is the work of Swingle (1919, 1922) who studied the accelerating effect of thyroid extracts on metamorphosis. He found also that iodine or its inorganic compounds induced early transformation of amphibians. Many laboratory studies have been macie of the rate of growth of amphibian larvae. In general, most of these studies, especially the more critical ones, deal with salamanders. Wilder (1924) pointed out that the curve representing the larval growth of Eurycea bislinedta is sigmoid and Patch (1927) showed that two sigmoid curves are produced by Ambystoma maculatum and A. tigrinum as they increase in length, one curve being embryonic and the other larval. Later, Dempster (1930) found that the growth in weight of embryonic and larval A4. maculatum under natural conditions may be expressed as a single sigmoid curve. Among the reports dealing with the growth of frog larvae are those of Davenport (1899) and Schaper (1902). They presented rather complete data on the larval growth in weight and volume of European species of Rana resulting from the acquisition of water, organic matter and ash. More recently, Burgess (1950) made a comparative study of the increase in body dimensions of larval Scaphiopus hammondi'i, some of which were reared in tap, water and others in field-collected water. With regard to the growth of transformed amphibians, only a few cobser. vations have been made. These are limited to the frogs and toads. Some data on the growth of Rana pipiens determined by study of length-frequency curves based on large numbers of individuals taken at the same timne, have been presented by Force (1933). From recapture data obtained from 20 marked Bufo lerrestris, Hamilton (1934) concluded that young toads double their length and are sexually mature by the time they are two years of age. Raney and Ingram (1941) found considerable variation in the rate of growth of Rana catesbeiana, reporting that the average bullfrog reaches sexual maturity in about a year following transformation and attains a size near the maximum during the subsequent year. Raney and Lachner (1947) reported that adult Bufo terrestris grow slowly and probably reach their maximum letfgth in three or four years.