Challagundla, Lavanya , Wallace, Lisa .
Patterns of genetic divergence across geographically variable populations of Xanthisma gracile (Asteraceae).
Numerous biotic (e.g., grazing pressure, breeding system) and abiotic factors (e.g., soil chemistry, water availability, light conditions, temperature differences) can contribute to local adaptation in plants. This often leads to geographic structure and genetic divergence between populations, and with continued isolation, new evolutionary lineages can arise.The southwestern U.S. contains many distinctive plant communities, ranging from woodlands to desert scrub, that are shaped by species adapting to environmental variation in elevation, precipitation, seasonality, and soils. Given this environmental variation, we expect that species that have achieved wide distributions will exhibit evidence of local adaptation to different microhabitats. Here, we test whether there is significant genetic divergence within Xanthisma gracile (Asteraceae) across Arizona. This species ranges from southern Colorado south to Mexico and west to southern California and occurs in a variety of habitats, including desert grasslands at low altitudes to open pine forests at intermediate altitudes. Xanthisma gracile is a chromosomally polymorphic species, with 2n numbers of 4, 5, and 6. Additionally, morphological variation in plant height, leaf shape and pubescence, and floral traits has been found across populations, resulting in the naming of races, varieties and even distinct species by some authors. Populations in Arizona were studied because they exhibit notable variation in cytology and morphology. We sampled 17 populations across Arizona and used Amplified Fragment Length Polymorphism (AFLP) to test whether there is genetic structure and whether this structure corresponds to trends in phenotypic and environmental variation noted in previous studies. Analysis of Molecular Variation revealed that most of the variation resides within populations (85%), with 10% among populations within regions, and 5% among south, central, and north regions. A comparison of pairwise genetic distances among these three regions further suggests that populations from desert habitat in central Arizona are more genetically distant than populations in areas of northern and southern Arizona, which experience higher precipitation levels. This study will help to understand in greater detail whether the differences among populations indicate locally adapted races evolving in isolation from each other and warrant recognition as separate species.
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1 - Mississippi State University, PO Box GY, Mississippi State, MS, 39762, USA
Presentation Type: Oral Paper:Papers for Topics
Location: Delaware B/Hyatt
Date: Tuesday, July 10th, 2012
Time: 8:45 AM