Gradual Adaptation Toward a Range-Expansion Phenotype Initiated the Global Radiation of Toads

Abstract

Recent studies have identified range expansion as a potential driver of speciation. Yet it remains poorly understood how, under identical extrinsic settings, differential tendencies for geographic movement of taxa originate and subsequently affect diversification. We identified multiple traits that predict large distributional ranges in extant species of toads (Bufonidae) and used statistical methods to define and phylogenetically reconstruct an optimal range-expansion phenotype. Our results indicate that lineage-specific range-shifting abilities increased through an accumulation of adaptive traits that culminated in such a phenotype. This initiated the episode of global colonization and triggered the major radiation of toads. Evolution toward a range-expansion phenotype might be crucial to understanding both ancient widespread radiations and the evolutionary background of contemporary invasive species such as the cane toad.

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.…”

Evolution of adaptive phenotypic traits without positive Darwinian selection

“…Another aspect of the human alteration of the environment that addresses the issue of exaptation is that of invasive species, and a large literature has attempted to identify common traits of successful invaders (Williamson and Fitter, 1996;Sax and Moreover, several recent studies have provided evidence that successful radiations in the evolutionary past have been due to traits present in the ancestors before the radiation. For example, a phylogenetic analysis of toads (Anura: Bufonidae) identified a suite of characters correlated with range expansion that were inferred to have been present in the ancestors of the family prior to its global expansion (Van Bocxlaer et al, 2010). Similarly, rapid expansion of the avian family Zosteropidae through the Old World tropics was attributed to traits present in the family's common ancestor (Moyle et al, 2009).…”

Population Genetic Structure and Species Status of Asiatic Toads (Bufo gargarizans) in Western China

“…Frost (2015) also synonymized them with B. gargarizans. Nevertheless, these three names continue to appear in recent literature (e.g., B. andrewsi, Van Bocxlaer et al, 2010). There are several detailed genetic examinations of these populations and all of them rejected the three-species (or subspecies) division.…”