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Jarrett Johnson
Degrees:1999 B.S. University of Illinois – Urbana/Champaign2005 Ph.D. University of Missouri – Columbia Selected Recent Publications:Johnson, J. R., K. M. Faries, J. J. Rabenold, J. Briggler, J. Koppelman, and L. S. Eggert. In press. Polymorphic di- and tetranucleotide microsatellite loci for studies of the hellbender (Cryptobranchus alleganiensis bishopi). Conservation Genetics. Fitzpatrick, B. M., J. R. Johnson, D. K. Kump, H. B. Shaffer, J. J. Smith, and S. R. Voss. 2009. Rapid fixation of non-native alleles revealed by genome-wide SNP analysis of hybrid tiger salamanders. BMC Evolutionary Biology 9:176. Ryan, M. E., J. R. Johnson, and B. M. Fitzpatrick. 2009. Ecological consequences of introduced genes: Invasive tiger salamander genotypes impact native amphibians. Proceedings of the National Academy of Sciences 106:11166-11171. Johnson, J. R., R. D. Mahan, and R. D. Semlitsch. 2008. Terrestrial microhabitat use by gray treefrogs (Hyla versicolor) in oak-hickory forests. Herpetologica 64:259-269. Johnson, J. R. J. H. Knouft, and R. D. Semlitsch. 2007. Sex and seasonal differences in terrestrial distributions and core habitat estimates for populations of the gray treefrog (Hyla versicolor). Biological Conservation 140:250-258. Mahan, R. D. and J. R. Johnson. 2007. Diet of the gray treefrog ( Hyla versicolor ) in relation to foraging site location. Journal of Herpetology 41:16-23. Johnson, J. R. and R. D. Semlitsch. 2003. Defining core habitat of local populations of the gray treefrog ( Hyla versicolor ) based on choice of oviposition site. Oecologia 137:205-210. |
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Research:I am interested in the evolutionary ecology, and conservation of amphibians. My dissertation research focused on patterns of migration, dispersal, and gene flow of gray treefrogs (Hyla versicolor) and spotted salamanders (Ambystoma maculatum) in Missouri. Specifically, I have used both direct and indirect methods to investigate (a) the spatial scale of migratory movements, the location of overwintering locations, and the biotic and abiotic factors determining microhabitat use (b) the effects of matrix composition on the frequency of inter-pond movements and patterns of gene flow. Data regarding the spatial patterns of terrestrial habitat use by amphibian populations are of critical importance for the development of habitat protection criteria that incorporate non-breeding season aspects of pond-breeding amphibian life-histories.The results of my previous work indicate that migration through terrestrial habitat adjacent to breeding sites is extensive and significantly different for males and females. Furthermore, dispersal success is affected by matrix composition and inter-pond distance, but juvenile and adult movements are differently inhibited. Lastly, the type of regional dynamics exhibited by associations of populations depends upon the degree of geographic isolation and the presence of barriers to movement. Currently, I am studying the dynamics of a tiger salamander hybrid zone in central California. Over the past 5 decades the endangered California tiger salamander (A. californiense) has been in contact with the introduced barred tiger salamander (A. tigrinum mavortium) as a result of introductions by bait dealers. Previous work has demonstrated that hybridization is widespread in central valley of California, and that patterns of genetic admixture and introgression vary among regions of the genome and among aquatic habitat types (e.g., seasonal vernal pools, perennial cattle ponds). Our current work uses diagnostic single nucleotide polymorphism (SNP) markers to investigate how the outcome of hybridization differs across the genome, and test some of the causes and consequences of environment-dependent invasion success. Specifically our work has three objectives: #1: Perform large-scale scan of the genome for variation in patterns of admixture and introgression to (a) identify the proportions of the genome affected by hybrid dysfunction, hybrid vigor, and directional selection, (b) quantify variation across the genome in pattern and rate of introgression, and magnitude of environment-dependent invasion success. #2 Use F1 and backcross progeny to examine the genetics of hybrid fitness by comparing hatchling, larval, and metamorphic fitness components between pure parentals and early-stage hybrid genotypes to investigate (a) the strength of initial barriers to gene flow, (b) the proportion of the variation identified in the field that can be accounted for by simple viability selection, and (c) the relative strength of mean fitness in contemporary hybrid populations versus early generations of admixture. #3 Explore environment-dependent invasion success using line-crosses reared in aquatic enclosures placed in alternative aquatic habitats to test the hypotheses that (a) there is a tradeoff between the ability to delay metamorphosis in perennial ponds (an A. t mavortium feature) and the ability to metamorphose soon enough to escape from drying seasonal ponds, and (b) variation in metamorphic timing is associated with regions of the genome that show especially strong allele frequency differences between perennial and seasonal habitats. Other projects include the development of microsatellite genetic markers for the threatened Ozark Hellbender (Cryprobranchus alleganiensis bishopi). These highly variable molecular markers will assist efforts to increase population sizes and genetic diversity through captive breeding, and identify patterns of gene flow among extant populations. |
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