Physiological features of embryonic development in terrestrially-breeding plethodontid salamanders

Abstract

Terrestrial breeding in plethodontid salamanders, in comparison to aquatic breeding in amphibians in general, is associated with long incubation time, large ovum and hatchling size, and high degree of development at hatching. These features are interrelated with each other and two presently described features. (1) The rate of embryonic development in terrestrially-breeding plethodontids is slow. The time to develop to the end of neurulation at 14–15°C is 18.6, 26.6, 30.4, and 40.2 d in Desmognathus ochrophaeus, Aneides ferreus, A. flavipunctatus, and Ensatina eschscholtzii, respectively. (2) The time an embryo spends developing beyond neurulation, relative to the time spent previously (= ‘relative incubation time’, RIT), is large. RIT in D. ochrophaeus and E. eschscholtzii averages 28% longer than that of non-plethodontid salamanders. Data for oxygen consumption during embryonic development of E. eschscholtzii indicates that the large ovum size is probably due mostly to selection for large hatchling size, rather than the need for energy during the protracted development. Large ovum size is associated with a slow rate of embryonic development which, together with the long RIT, accounts for the long incubation time.