Phylogenetics and evolution of bell frogs (Litoria aurea species-group, Anura: Hylidae) based on mitochondrial ND4 sequences

Membership of the Litoria aurea species-group (commonly known as the bell frogs) and relationships within this group are poorly understood. Courtice and Grigg (1975) described a bell frog species-group consisting of five species on the basis of morphology and a lack of hybridisation in areas of sympatry. This group comprised: (i) Litoria aurea (Lesson, 1829) and Litoria raniformis (Keferstein, 1867) from south-eastern New South Wales (NSW); (ii) Litoria flavipunctata (previously recognised as a geographically isolated population of Litoria aurea raniformis in the New England Tablelands of north-eastern NSW, reviewed in Courtice and Grigg, 1975); and psssss(iii) two western Australian species, Litoria cyclorhyncha (Boulenger, 1882) and Litoria moorei (Copland, 1957). Although the recognition of L. flavipunctata has not been challenged, the nomenclature is problematic. Cogger et al. (1983) synonymised L. flavipunctata and Hyla castanea (Steindachner, 1867) under Litoria castanea (Steindachner, 1867). This concept was later supported by Thomson et al. (1996) and is currently widely accepted. On the basis of morphology and behavioural analysis, Tyler and Davies (1978) included two additional species in the bell frog group, Litoria alboguttata (Gunther, 1867) and L. dahlii (Boulenger, 1896). Interestingly, both these species were originally placed within the genus Cyclorana (Cogger et al., 1983; Straughan, 1969; Tyler, 1973; Tyler et al., 1978). L. alboguttata is distributed in central and coastal Queensland, the coastal margin of the Northern Territory, and the western slopes and central plains of northern NSW (Cogger, 2000). L. dahlii is tropical, being distributed from Cape York Peninsula to the north-western Northern Territory (Cogger, 2000; Fig. 1). The inclusion of L. dahlii in the species-group was later supported by morphology, osteology, and karyotype analysis (Tyler et al., 1978), however, the inclusion of L. alboguttata was disputed on the basis of MC′F results, which suggested that this species was more closely related to species of Cyclorana than to Litoria (Maxson et al., 1982). Therefore, the bell frog group is currently thought to contain six species: L. aurea, L. cyclorhyncha, L. castanea, L. dahlii, L. moorei, and L. raniformis (also reviewed in NSW NPWS, 2002). L. castanea is thought to be extinct, however (R. Wellington pers. comm.). Within the bell frog group two species-pairs have been recognised based on external morphology, male call structure, and MC′F comparisons of serum albumin (Lee, 1967; Littlejohn, 1961, 1967; Main, 1957, 1968; Roberts and Maxson, 1985): the south-eastern bell frogs (L. aurea and L. raniformis), and the south-western bell frogs (L. cyclorhyncha and L. moorei). To date, no general consensus has emerged on the evolutionary history of the bell frogs or Australian hylids more generally and an explicit phylogeny based on a comprehensive sample of constituent taxa is lacking. This study aimed: (i) to estimate a bell frog phylogeny using mitochondrial ND4 gene sequences; (ii) to use this phylogeny to test existing hypotheses of membership of the group and relationships among the extant species; (iii) to identify the sister taxon of L. aurea; and (iv) to estimate divergence dates in the group. © 2005 Elsevier Inc. All rights reserved.