Geographic and Genetic Isolation in Australian Amphibia

Abstract

The continent of Australia has a moist section along the east coast and another in the south-west corner. These two areas are separated by a broad arid zone that acts as an effective barrier for those species of amphibia that require a moist environment. Hyla aurea is found in both of the moist zones but is absent from the arid center. The two populations, which are now discontinuous, probably have not been connected in recent times. There has been almost no morphological differentiation during the period of isolation but genetic divergence has reached the point where the two populations are behaving as different species. Crosses of east Australia x south-west Australia individuals result in complete hybrid inviability. Similar experiments have been conducted with Crinia signifera, a species showing the same type of distribution, and the results are nearly the same. Crosses of east Australia x south-west Australia individuals result in considerable inviability of the progeny. On the island of Tasmania Crinia signifera and the very similar Crinia tasmaniensis occur. Crosses of east Australian signifera x Tasmania signifera gives normal progeny. Crosses of east Australia signifera x Tasmania tasmaniensis results in complete hybrid inviability. These data suggest a double invasion of Tasmania by signifera. The first group evolved into tasmaniensis but the second has not diverged from the mainland type. The south-west Australian analogue of the eastern Hyla aurea should be known as Hyla raniformis (Parker). No name is available for the southwest Australian species formerly included in Crinia signifera. A new name, Crinia insignifera, is proposed.