DEVELOPMENT OF GYRINOPHILUS-PORPHYRITICUS - IDENTIFICATION OF THE ANCESTRAL DEVELOPMENTAL PATTERN IN THE SALAMANDER FAMILY PLETHODONTIDAE

We describe the development, from fertilization to hatching, of the salamander Gyrinophilus porphyriticus (family Plethodontidae; tribe Hemidactyliini). G. porphyriticus has a relatively large clutch size (n = 87 eggs in the clutch examined) and egg diameter (mean = 4.0 mm, S.D. = 0.12, n = 4, range = 3.9-4.1) for a plethodontid. Early cleavage is asymmetrical and asynchronous. Gastrulation and neurulation are typical of that described for other species of plethodontids, particularly those with large, heavily yolked eggs. We present a normal table of development from tailbud to hatching divided into nine stages. Development of somites, pigmentation pattern, gills, tail fins, eyes, and limb buds is described. We use data from outgroup taxa, such as non-plethodontid salamanders and frogs, to polarize nine characters chosen to define the ancestral developmental pattern of plethodontids: 1) developmental mode (direct or larval), 2) timing of oviposition, 3) clutch size, 4) percentage of egg volume contributing to embryonic structures, 5) timing of appearance of the front limb buds relative to the hind limb buds, 6) extent of gill branching, 7) presence or absence of tail fins, 8) external eye morphology, and 9) the presence or absence of lateral-line organs. Comparisons of G. porphyriticus to nine other plethodontid species allow us to hypothesize probable evolutionary transformations for these characters. G. porphyriticus has the ancestral condition for all nine characters. The three species of Desmognathus with aquatic larvae are derived for two or three of the nine characters. They each have 1) a clutch size of less than 50 eggs, 2) a relatively low percentage of egg volume contributing to embryonic structures, and/or 3) nearly simultaneous appearance of the front and hind limb buds. Finally, we explore the evolutionary implications of retaining the ancestral developmental pattern in the plethodontid tribe Hemidactyliini and salamanders in general. We propose that the retention of the ancestral developmental pattern has permitted the evolution of a specific type of paedomorphosis, larval paedomorphosis, that correlates with a cave-dwelling existence. (C) 1994 Wiley-Liss, Inc.