Genome level resolution of species boundaries and phylogeny of the north american tiger salamander radiation

Tiger salamanders (the Amby stoma tigrinum complex) are one of the most widely distributed amphibian species complexes in North America (Figure IA) and lie at an important and unique position at the intersection of research in developmental and evolutionary biology. This diverse group contains the Axolotl (Ambystoma mexicanum), a taxon that expresses a non- metamorphic (paedomorphic) life history phenotype. The Axoloti has been the poster child for the study of heterochrony (Gould 1977) and has played a prominent role in developmental laboratory research for over a century (Armstrong and Malacinski 1989; Shaffer 1993). While paedomorphosis is common across salamanders, the A. tigrinum complex is unique in the variability of its expression. The Axoloti is just one of many paedomorphic taxa and populations across the geographic range of tiger salamanders exhibit a range of life histories, from obligate metamorphosis, to facultative or obligate paedomorphosis. The evolution of a paedomorphic morphology and ecology from a transforming terrestrial ancestor through shifts in developmental timing is likely an adaptive response to environmental change (Wilbur and Collins 1973) and has a strong genetic basis (Voss and Shaffer 1997; Voss et a!. 2000; Voss and Smith 2005). The evolution of an aquatic larval life history is predicted to limit dispersal and drive population differentiation at a faster rate than differentiation among metamorphic populations (Shaffer 1984), and may act to drive lineage divergence and speciation. As such, the A. tigrinum complex exhibits similarities with many classic examples of adaptive radiation (e.g. African cichlid fish and Darwin's finches) that have served as natural laboratories for the study of speciation and the buildup of biodiversity (Seehausen 2006). There is a growing need for newly developed model systems that bridge gaps in the Tree of Life (Abzhanov et al. 2008) and the A. tigrinum complex can provide an excellent model amphibian system for the comparative study of biologically important traits (e.g. metamorphosis and regeneration) and for the study of natural selection in speciation and diversification (Routman 1993).