The southeastern United States is home to the highest amphibian species richness in North America. An often overlooked component of research on factors that drive amphibian geographic distributions is description of species range shape. Broad-scale range disjunction has implications for phylogeography, ecology, and conservation, but descriptions of fragmentation are usually based on subjective visual assessment of range maps. Here, we describe a method for objectively quantifying range fragmentation and use this method to describe the patterns of amphibian species range shapes in the Southeast. Species ranges varied widely in degree of fragmentation, from completely contiguous to highly fragmented, and degree of isolation of range fragments. Incorporating ecological niche models added information about fine-scale habitat fragmentation. Although 12 species had ranges with either high or moderate fragmentation, the only area where range fragments of more than two of the 12 species overlapped was the Appalachian Highlands, suggesting that range fragmentation in the Southeast is driven by multiple biogeographic processes.

Wallace's and Lydekker's Lines both describe important biogeographic barriers in the Indo-Australian Archipelago, with Wallace's Line demarcating the boundary of the Greater Sunda Shelf and Lydekker's Line indicating the edge of the Sahul continental shelf. Despite their similarities, Wallace's Line has been much more heavily studied than has Lydekker's Line, yet provides an interesting system for testing the source of fauna into eastern Wallacea. New collections of Northern Water Dragons, Tropicagama temporalis, from several islands in Maluku, eastern Indonesia now allow for an assessment of the phylogeography of the species and the ability to test if New Guinean or Australian populations served as the source for over-water dispersal across Lydekker's Line into Maluku. We collected specimens from remote islands in eastern Indonesia, sequenced the mitochondrial ND2 gene, and aligned the data to previously sequenced specimens on GenBank. We conducted several phylogenetic and divergence time analyses to investigate the source population and timing of dispersal. We found low genetic diversity among the islands in Maluku, and these samples showed little genetic divergence from New Guinea samples. The New Guinea and Maluku populations diverged less than 1 million years ago (Ma) and together diverged from the Australian population between 2.3 and 4.7 Ma. These results, along with patterns in other taxa, illustrated that, despite Australia's close geographic proximity to many of the islands in southeastern Indonesia, New Guinea has been the more frequent source of Wallacean fauna from Sahul.

The importance of long-distance dispersal (LDD) in shaping geographical distributions has been debated since the nineteenth century. In terrestrial vertebrates, LDD events across large water bodies are considered highly improbable, but organismal traits affecting dispersal capacity are generally not taken into account. Here, we focus on a recent lizard radiation and combine a summary-coalescent species tree based on 1225 exons with a probabilistic model that links dispersal capacity to an evolving trait, to investigate whether ecological specialization has influenced the probability of trans-oceanic dispersal. Cryptoblepharus species that occur in coastal habitats have on average dispersed 13 to 14 times more frequently than non-coastal species and coastal specialization has, therefore, led to an extraordinarily widespread distribution that includes multiple continents and distant island archipelagoes. Furthermore, their presence across the Pacific substantially predates the age of human colonization and we can explicitly reject the possibility that these patterns are solely shaped by human-mediated dispersal. Overall, by combining new analytical methods with a comprehensive phylogenomic dataset, we use a quantitative framework to show how coastal specialization can influence dispersal capacity and eventually shape geographical distributions at a macroevolutionary scale.