Molecular and morphological analysis of the critically endangered Fijian iguanas reveals cryptic diversity and a complex biogeographic history

Abstract

The Pacific iguanas of the Fijian and Tongan archipelagos are a biogeographic enigma in that their closest relatives are found only in the New World. They currently comprise two genera and four species of extinct and extant taxa. The two extant species, Brachylophus fasciatus from Fiji, Tonga, and Vanuatu and Brachylophus vitiensis from western Fiji, are of considerable conservation concern with B. vitiensis listed as critically endangered. A recent molecular study has shown that Brachylophus comprised three evolutionarily significant units. To test these conclusions and to reevaluate the phylogenetic and biogeographic relationships within Brachylophus, we generated an mtDNA dataset consisting of 1462 base pairs for 61 individuals from 13 islands, representing both Brachylophus species. Unweighted parsimony analyses and Bayesian analyses produced a well-resolved phylogenetic hypothesis supported by high bootstrap values and posterior probabilities within Brachylophus. Our data reject the monophyly of specimens previously believed to comprise B. fasciatus. Instead, our data demonstrate that living Brachylophus comprise three robust and well-supported clades that do not correspond to current taxonomy. One of these clades comprises B. fasciatus from the Lau group of Fiji and Tonga (type locality for B. fasciatus), while a second comprises putative B. fasciatus from the central regions of Fiji, which we refer to here as B. n. sp. Animals in this clade form the sister group to B. vitiensis rather than other B. fasciatus. We herein describe this clade as a new species of Brachylophus based on molecular and morphological data. With only one exception, every island is home to one or more unique haplotypes. We discuss alternative biogeographic hypotheses to explain their distribution in the Pacific and the difficulties of distinguishing these. Together, our molecular and taxonomic results have important implications for future conservation initiatives for the Pacific iguanas.

Intercontinental dispersal by a microendemic burrowing reptile (Dibamidae)

“…For example, the Fijian iguanas (Brachylophus) almost certainly originated via trans-Pacific rafting from the New World, where all their closest relatives (both extant and fossil) are found [25]. Although the dispersal was in the opposite direction, this might seem to provide a precedent for dibamids.…”

“…Because all extant dibamids are found in tropical (Southeast Asia) or subtropical (eastern Mexico) climates, it seems likely that ancestral taxa would share similar requirements, thus limiting the possibility of dispersal to the warmer Eocene interval at 55 -35 Myr ago. Alternatively, convincing examples of trans-Pacific overseas dispersal do exist [25,26]. Although no absolute upper time limit exists for an oceanic rafting event, support for this route would be bolstered if shallow trans-Pacific genetic divergences make Beringian dispersal untenable.…”

Out of the Neotropics: Late Cretaceous colonization of Australasia by American arthropods

“…These include the kagu of New Caledonia (Rhynochetos jubatus) and its putative sister lineage, the Neotropical sunbittern Eurypyga helias [15]. The charismatic Fijian and Tongan iguanas (Brachylophus [16]) are postulated to have colonized Melanesia by transoceanic rafting from the Neotropics, but neither the mechanism nor the timing of the colonization is well understood. Similarly, the fossorial lizard family Dibamidae is represented by 22 species in southeast Asia and a single species that is endemic to Mexico, likely the result of transoceanic or overland dispersal across Beringia in the Eocene [17].…”

A new species of iguana Brachylophus Cuvier 1829 (Sauria: Iguania: Iguanidae) from Gau Island, Fiji Islands

“…The genus Brachylophus currently consists of three living (B. bulabula, B. fasciatus, and B. vitiensis) and one extinct (B. gibbonsi) species of iguanas from Fiji and Tonga in the South Pacific (Pregill & Steadman 2004;Keogh et al 2008). Additionally the extinct monotypic iguana genus Lapitiguana was also known only from Fiji and was twice the length of the largest living Brachylophus (Pregill & Worthy 2003).…”

“…These iguanas have possibly been present there for 40 million years and their closest relatives occur in the New World in the North American southwest deserts (Townsend et al 2011). Keogh et al (2008) recently reviewed Brachylophus using the available genetic and morphological data, resulting in the author's description of the new species Brachylophus bulabula. All three living species were restricted taxonomically to only the islands where either of these data sets was available in that study.…”