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Abstract

Australian populations of the primitive podonomine genus Archaeochlus have a restricted distribution associated with seepage areas on granite outcrops in south-western and central Australia. These granite outcrops are disjunct and the intervening land offers no apparent suitable habitat for Archaeochlus. This paper uses the DNA sequence of the mitochondrial Cytb gene to assess the phylogenetic relationships between populations of three species, and to examine the hypothesis that these populations achieved their present distribution via ancient river systems that existed up until about 65 million years ago. The phylogeny supports the existence of the three species, but also raises the possibility that a population of A. brundini from Baladjie Rock may be specifically distinct. The phylogenetic relationships do not discriminate between the ancient river hypothesis and alternative explanations. However, estimation of the times of separation of the various populations within species indicates that these populations are too recent to have spread via the river systems. The results show that for each species the most northerly populations are the oldest and that there has been a southward spread of the populations. It is postulated that the southward spread may be a consequence of the increasing aridity of the northern parts of their range since the end of the tertiary.