Phylogeography and speciation in the genus arthroleptella

Abstract

Moss frogs are restricted to permanently moist terrestrial habitats in the south-western Cape Fold Mountains. There is a very close association between Arthroleptella distribution and Table Mountain Sandstone. Suitable habitats are generally occupied by allopatric populations of moss frogs. Comprehensive spatial sampling of moss frogs (genus Arthroleptella) in the Cape Floristic Region biodiversity hotspot yielded 192 new distribution records; 5 842 advertisement calls from 240 individual male frogs; 31 Rag-1,76 16S, 54 12S sequences and morphological measurements of 90 specimens. There are many differences in male advertisement call and genetic sequences between populations on different mountain ranges, even over small distances. A mitochondrial and nuclear gene phylogeny of the southern African Pyxicephalidae places Natalobatrachus as the sister genus to Arthroleptella. Application of a Bayesian relaxed molecular clock model indicates that Arthroleptella arose between 20 and 39 Ma. Phylogenetic trees return two main clades within Arthroleptella: one consists of species which exhibit chirp-like calls and the second contains species with longer calls composed of a series of clicks. These two clades diverged between 19 and 22 Ma. There is a general pattern of strong phylogeographic structure with many small, isolated populations. Three species are identified within the Chirping clade and seven in the Clicking clade, including three undescribed species. This population structure is a result of the patchy distribution of suitable habitat and low vagility of the moss frogs.The distribution and speciation of moss frogs has been affected by drying and cooling climate change, changing geomorphology over the last 20 Ma and the increasing prevalence of fire over the last 5 Ma. An assessment of the threat status of each species according to IUCN criteria categorised one species as Least Concern, seven as Near Threatened, one as Vulnerable and one as Critically Endangered. The primary threats to Arthroleptella are invasive alien plants and increased fire frequencies and intensities.