Three evolutionarily significant units for conservation in the iguanid genus Brachylophus

Abstract

We examined phylogenetic relationships within the genus Brachylophus, which comprises two endangered iguana species endemic to the South Pacific islands of Fiji and Tonga. Genetic variation among Fijian Crested Iguanas B. vitiensis and Fijian and Tongan Banded Iguanas B. fasciatus was analysed using mitochondrial DNA (mtDNA) cytochrome b (cyt b) characterized from 35 individuals from island populations. Three distinct clades of Brachylophus were identified. The most divergent clade comprised B. fasciatus from Tonga, which supports the recognition of Tongan iguanas as a separate species. Molecular clock estimates suggested that the average sequence divergence (6.4%) between Tongan and Fijian B. fasciatus clades equated to 7 - 15.8 MY of separation, confirming that extant Brachylophus species have a long history of evolution in situ in the Fijian and Tongan archipelago. Phylogenetic analyses also revealed that Fijian B. fasciatus and B. vitiensis iguana populations were not reciprocally monophyletic. One clade comprised two mtDNA haplotypes from the Fijian islands of Monu, Monuriki, Devuilau, Waya and Yadua Taba. The other clade comprised B. fasciatus haplotypes from Kadavu and Gau, which was divergent from both the aforementioned Fijian clade (dA = 3.5%), and the Tongan clade (dA = 6.4%). In addition to mtDNA data, variation was assessed at microsatellite loci, and significant differentiation between iguana populations was detected. Based on both mtDNA and microsatellite analysis, the conservation priorities for these endangered lizards must be reassessed to protect iguanas as three distinct evolutionarily significant units.