An Analysis of Hybrid Zone Dynamics in Iris

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The aim of the proposed study is to determine the effect of crosses between individuals belonging to the same species and between individuals belonging to two different species on the genetic structure and evolution of hybrid populations of irises. Paternity analyses (using protein and DNA markers) will be used to discern patterns of gene exchange in a naturally occurring hybrid population and in an I. fulva population where I. hexagona individuals have been introduced. The paternity analysis will also allow an estimate of the impact of pollen versus seed movement on the genetic structure of these two populations. These analyses will be used to determine the affect of gene flow on (i) the transfer of genes between the two species, (ii) the reproductive success of individual plants and (iii) the number of plants that cross with one another in the hybrid populations. The effects of natural selection on the survival and reproduction of I. fulva, I. hexagona and their natural hybrids will be estimated by sowing seeds from each of the species and natural hybrids into I.fulva, I. hexagona and hybrid populations. Natural selection on the different species and hybrids will, thus be measured by recording germination frequencies, survival to flowering, numbers of flowers produced and the overall biomass produced. These measurements will allow the calculation of the relative fitness of I. fulva, I. hexagona and various hybrid classes in different habitat types. The estimates of fitness, measurements of dispersal and the frequencies of different genetic markers in the hybrid populations will then be used to test models that predict specific evolutionary outcomes for hybrid populations.