CAA: Technology Transfer: Bringing the Tools of Molecular Biology to an Ecological Genetics Program

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Abstract Susan Kalisz 9707679 CAA Measuring dispersal or the rate of movement of individuals within and among populations in nature remains a challenge for ecologists and population geneticists because of the difficulty in detecting individual movements. This difficulty is exaggerated for many plant species, in which the dispersing stages are small, such as pollen or seed. However, our ability to quantify dispersal or migration within and among plant populations is central to understanding many population and regional processes. In particular, the extent to which populations or sub-populations are connected via migration of pollen or seed will determine 1) the extent to which different populations share genes in common and 2) the extent to which local extinctions are balanced by recolonization from other populations within a region, and 3) the extent to which local adaptation will occur. Emerging DNA technologies now make it possible to use genetic markers to detect migration and outcrossing events with greater accuracy. A powerful new molecular technique for ecological and population genetics, that of making and screening genomic libraries for microsatellite DNA repeats and microsatellite DNA polymorphism analysis will be learned by the PI. Microsatellites are short, tandemly repeated simple sequences, one to six base pairs in length, that are highly polymorphic for repeat number. Amplification of the microsatellite region by polymerase chain reaction (PCR) results in fully penetrant, Mendelian-inherited, codominant markers that can be precisely identified by length. Since these markers are allelic, microsatellite data are directly applicable to population genetic models and analysis. One of the greatest advantages of microsatellite DNA markers is their extreme variability (typically 10-20 alleles/locus) that can be used to characterize population structure, determine outcrossing rates and evaluate parentage by paternity exclusion. This award will facilitate al l facets of microsatellite library production, cloning, screening and scoring: in essence, the transfer of this PCR-based technology to my program. These techniques will be learned from Dr. M. Ashley who has developed microsatellite markers for several plant and animal systems in her laboratory. The analysis of microsatellite markers will enhance current research and future development in four distinct areas: 1) Environmental variance typical in natural populations causes local extinctions to occur. Such local population extinction should select for bet-hedging traits which restore populations, both demographically and genetically. With respect to local extinctions, we hypothesize that plant populations which exist within a matrix of other population of the same species should experience selection for seed dispersal. In contrast, isolated populations should experience selection for seed dormancy, since isolated population cannot receive nor cannot export successful migrants. One goal is to quantify the relationship between seed dispersal, seed dormancy and population genetic structure. Microsatellite markers would allow the assessment of the extent to which the study populations of Collinsia verna are genetically isolated entities (and express seed dormancy phenotypes) or exchange migrants via seed dispersal (and lack seed dormancy). 2) Most models of the evolution of selfing consider the negative genetic effects of inbreeding depression as the critical factors in mating system evolution. However, a new model demonstrates that environmental variance which prohibits pollinators from visiting flowers during some portion of the flowering season can be more important than inbreeding depression in driving the evolution and maintenance of self pollination mechanisms. We have demonstrated that C. verna has high levels of outcrossing and temporal separation of male and female phases but is capable of selfing. Microsatellite markers would allow us to test this model by conductin g paternity analysis and within flower outcrossing rates.