Patterns of differential introgression in a salamander hybrid zone: inferences from genetic data and ecological niche modelling

Hybrid zones have yielded considerable insight into many evolutionary processes, including speciation and the maintenance of species boundaries. Presented here are analyses from a hybrid zone that occurs among three salamanders – Plethodon jordani , Plethodon metcalfi and Plethodon teyahalee – from the southern Appalachian Mountains. Using a novel statistical approach for analysis of non-clinal, multispecies hybrid zones, we examined spatial patterns of variation at four markers: single-nucleotide polymorphisms (SNPs) located in the mtDNA ND2 gene and the nuclear DNA ILF3 gene, and the morphological markers of red cheek pigmentation and white flecks. Concordance of the ILF3 marker and both morphological markers across four transects is observed. In three of the four transects, however, the pattern of mtDNA is discordant from all other markers, with a higher representation of P. metcalfi mtDNA in the northern and lower elevation localities than is expected given the ILF3 marker and morphology. To explore whether climate plays a role in the position of the hybrid zone, we created ecological niche models for P. jordani and P. metcalfi . Modelling results suggest that hybrid zone position is not determined by steep gradients in climatic suitability for either species. Instead, the hybrid zone lies in a climatically homogenous region that is broadly suitable for both P. jordani and P. metcalfi . We discuss various selective (natural selection associated with climate) and behavioural processes (sex-biased dispersal, asymmetric reproductive isolation) that might explain the discordance in the extent to which mtDNA and nuclear DNA and colour-pattern traits have moved across this hybrid zone.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/79135/1/j.1365-294X.2010.04796.x.pd

Evolutionary Dynamics among Salamanders in the Plethodon glutinosus Group, with an Emphasis on Three Species: P. jordani, P. metcalfi, and P. teyahalee (Caudata: Plethodontidae).

This dissertation includes three studies that focus on the evolution of salamanders in the Plethodon glutinosus group (family Plethodontidae), that are found throughout much of the eastern United States. The first study explores species delimitation in taxonomically problematic groups and then, in that context, examines the long and contentious taxonomic history of the P. glutinosus group. Four commonly encountered problems are reviewed: (1) the presence of cryptic species complexes, (2) incomplete lineage sorting, (3) introgressive hybridization, and (4) the application of different species concepts. The history of species description in the P. glutinosus group is then discussed in light of these problems. The controversial use of DNA barcoding is also discussed, as is its potential utility in the group. The second study is a spatially fine-scale analysis of a hybrid zone that occurs among three species within the P. glutinosus group – P. jordani, P. metcalfi, and P. teyahalee – in the southern Appalachian Mountains. Spatial patterns of variation along four transects are examined at four markers: single nucleotide polymorphisms located in the mtDNA ND2 gene and the nuclear DNA ILF3 gene and the morphological markers of red cheek pigmentation and white flecks. Concordance among nuclear DNA and both morphological markers across the four transects is observed. In three of the four transects, however, the pattern of mtDNA is discordant from all other markers. This finding, in addition to previous studies demonstrating mating asymmetry and differing ecological niches, suggests the hybrid zone may be moving. The third study uses ecological niche modeling to explore range dynamics of P. jordani and P. metcalfi at three time periods: (1) present-day, (2) during the last glacial maximum 21,000 years ago, and (3) in the year 2050 under a climate warming scenario. Generated models suggest the distributions of these species are influenced by precipitation and are dynamic across the time periods studied. The conservation status of P. jordani and P. metcalfi are discussed in light of anthropogenic climate change.Ph.D.Ecology and Evolutionary BiologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/63626/1/mattchat_1.pd