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 sa lamander Gyrinophilus porphyriticus (family Plethodontidae; tribe Hemi dactyliini). 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 typica l of that described for other species of plethodontids, particularly t hose with large, heavily yolked eggs. We present a normal table of dev elopment from tailbud to hatching divided into nine stages. Developmen t of somites, pigmentation pattern, gills, tail fins, eyes, and limb b uds is described. We use data from outgroup taxa, such as non-plethodo ntid salamanders and frogs, to polarize nine characters chosen to defi ne the ancestral developmental pattern of plethodontids: 1) developmen tal 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 latera l-line organs. Comparisons of G. porphyriticus to nine other plethodon tid species allow us to hypothesize probable evolutionary transformati ons for these characters. G. porphyriticus has the ancestral condition for all nine characters. The three species of Desmognathus with aquat ic larvae are derived for two or three of the nine characters. They ea ch have 1) a clutch size of less than 50 eggs, 2) a relatively low per centage of egg volume contributing to embryonic structures, and/or 3) nearly simultaneous appearance of the front and hind limb buds. Finall y, we explore the evolutionary implications of retaining the ancestral developmental pattern in the plethodontid tribe Hemidactyliini and sa lamanders in general. We propose that the retention of the ancestral d evelopmental pattern has permitted the evolution of a specific type of paedomorphosis, larval paedomorphosis, that correlates with a cave-dw elling existence. (C) 1994 Wiley-Liss, Inc.