Modelling temporal dynamics of genetic diversity in stage-structured plant populations with reference to demographic genetic structure

1. Predicting temporal dynamics of genetic diversity is important for assessing long-term population persistence. In stage-structured populations, especially in perennial plant species, genetic diversity is often compared among life history stages, such as seedlings, juveniles, and flowerings, using neutral genetic markers. Because individuals in mature stages will die and be replaced by those in more immature stages over the course of time, the comparison among stages (sometimes referred to as demographic genetic structure) has been regarded as a proxy of potential genetic changes that accompany the turnover of constituent individuals. However, because demographic genetic structure had not been theoretically examined, the basic property and the validity of demographic genetic structure remained unclear. 2. We developed a matrix model which was made up of difference equations of expected heterozygosity, a common proxy of genetic diversity, of each life history stage at a neutral locus in stage-structured plant populations. Based on the model, we formulated demographic genetic structure as well as the annual change rate of expected heterozygosity (denoted as η ). We obtained theoretical expectation of demographic genetic structure and η from our model and compared them with computational results of stochastic simulation for randomly generated 3,000 life histories for model validation. We then examined the relationships of demographic genetic structure with effective population size Ne , which is the determinants of diversity loss per generation time, as well as with η . 3. Theoretical expectations on η and demographic genetic structure fitted well to the results of stochastic simulation, supporting the validity of our model. Demographic genetic structure varied independently of Ne and η , while having a strong correlation with stable stage distribution: expected heterozygosity was lower in stages with fewer individuals. 4. Our results indicate that demographic genetic structure strongly reflects stable stage distribution, rather than temporal genetic dynamics, and that inferring future genetic diversity solely from demographic genetic structure would be misleading. Instead of demographic genetic structure, the newly-defined statistics η will be an useful tool to predict genetic diversity at the same time scale as population dynamics, facilitating evaluation on population viability from a genetic point of view. ### Competing Interest Statement The authors have declared no competing interest.