Around the world in 10 million years: biogeography of the nearly cosmopolitan true toads (Anura: Bufonidae)

Abstract

Aim The species-rich family of true toads (Anura: Bufonidae) has been the focus of several earlier studies investigating the biogeography of geographically widespread taxa. Herein, we employ newly developed Bayesian divergence estimate methods to investigate the biogeographical history of this group. Resulting age estimates are used to test several key temporal hypotheses including that the origin of the bufonid clade pre-dates Gondwanan vicariance (~105 million years ago, Ma). Area cladograms are also invoked to investigate the geographical origin of the family.Location Worldwide, except the Australia-New Guinea plate, Madagascar and the Antarctic.Methods A phylogenetic hypothesis of the relationships among true toads was derived from analysis of 2521 bp of DNA data including fragments from three mitochondrial ( 12S , tRNA val , 16S ) and two nuclear ( RAG-1 , CXCR-4 ) genes. Analysis of multiple, unlinked loci with a Bayesian method for estimating divergence times allowed us to address the timing and biogeographical history of Bufonidae. Resulting divergence estimates permitted the investigation of alternative vicariance/dispersal scenarios that have been proposed for true toads. ResultsOur area cladogram resulting from phylogenetic analysis of DNA data supports a South American origin for Bufonidae. Divergence estimates indicate that the family originated earlier than had been suggested previously (78-99 Ma). The age of the enigmatic Caribbean clade was dated to the late Palaeocene-early Eocene. A return of bufonids to the New World in the Eocene was followed by rapid diversification and secondary expansion into South America by the early Oligocene (Rupelian). Main conclusionsThe South American origin of Bufonidae in the Upper Cretaceous was followed by relatively rapid expansion and radiation around the globe, ending with a return to the Americas via a Eurasian/North American land bridge in the Eocene. Though the exact route of this dispersal (Beringia or North Atlantic) remains unclear, an argument is made for the less frequently invoked North Atlantic connection. The origin of the enigmatic Caribbean lineage was found to be consistent with colonization following the bolide impact at the K/T boundary. These findings provide the first, firm foundation for understanding true toad divergence times and their truly remarkable and global radiation.

Explaining Darwin’s Corollary to Haldane’s Rule: The Role of Mitonuclear Interactions in Asymmetric Postzygotic Isolation Among Toads

“…Both mitochondrial and nuclear analyses recovered four main clades consistent with broad biogeographic regions and previous analyses of bufonids (Pauly et al 2004;Pramuk et al 2008;Van Bocxlaer et al 2010;Pyron and Wiens 2011). These clades include the Nearctic Anaxyrus, the Middle American Incilius, the South American Rhinella, and a fourth Old World clade that includes the African Amietophrynus and the Asian Duttaphrynus (we use these names as unranked clade names within the genus Bufo).…”

“…Bufo (Rhaebo) haematiticus was specified as the outgroup. All recent studies of bufonids have identified our ingroup as monophyletic with respect to B. haematiticus (Pauly et al 2004;Frost et al 2006;Pramuk et al 2008;Van Bocxlaer et al 2010;Pyron and Wiens 2011). The 35 ingroup species were selected because crossing data were available and either existing sequences or tissue samples could be obtained to construct a multilocus dataset.…”

Jurassic primates, immobile ducks and other oddities: a reply to Heads’ review of The Monkey’s Voyage

“…Furthermore, it is worth noting that the amphibian timetree as a whole indicates, as one would expect from the dispersal abilities of these animals, that the large-scale, continental distribution of amphibians is mostly well explained by the breakup of Laurasia and Gondwana (Bossuyt et al 2006;Pramuk et al 2008;Zhang and Wake 2009;Pyron 2014). In other words, the various over-water dispersal events are inferred within a time frame that generally supports a plausible history of vicariance, in line with much geological evidence.…”

Out of Asia: Natricine snakes support the Cenozoic Beringian Dispersal Hypothesis

“…Certainly, bidirectional dispersal across the Holarctic is possible for ectotherms, as seen in toads, ranid and hylid frogs, which crossed the between the OW and NW several times (Smith et al, 2005;Wiens et al, 2006Wiens et al, , 2009Pramuk et al, 2008). One possibility for the squamates is that return colonization from the NW was simply not possible due to degrading habitat at the end of Miocene in Beringia, an expectation of the CBDH.…”