Inbreeding and inbreeding depression in the wild lupine

The loss of genetic variability and reduced viability and fecundity due to inbreeding have received considerable attention from conservation biologists. This study seeks to explicitly understand the effects of both population size and density on genetic and demographic components of reproduction in Lupinus perennis.; In Chapter 1, I examined the effects of self-pollination and resource addition on seed production and offspring performance. I demonstrated the existence of strong inbreeding depression (delta = 0.88) in L. perennis . Interestingly, resource addition to the maternal plants in the field significantly decreased proportion of seedling survival, which suggested that resource addition to maternal plants delayed the expression of inbreeding depression in their offspring.; In Chapter 2, I investigated the relationships among population size, fitness and inbreeding depression in 8 paired populations. As predicted, multiplicative performance was significantly lower in small populations compared to large populations. There was also a higher seed abortion in small populations than in large populations.; In Chapter 3, I first described a novel chromosome-walking method to isolate microsatellite loci, and then investigated relationships between population size and genetic variation. Large populations harbored significantly higher allelic diversity than small populations. Analyses indicated that although most variation was found within populations, there was significant differentiation between large and small populations.; In Chapter 4, I used microsatellite markers to genetically characterize the mating systems of 8 populations varying in size and density. I found that outcrossing rate (tm = 0.667 to 0.949 with average of 85%) was positively correlated with population size, while negatively correlated with population density. More interestingly, I demonstrated a significant positive correlation between biparental inbreeding and population density.; The existence of the lower genetic variation and higher inbreeding level in small populations is consistent with the lower reproductive success of small populations. The data will not only improve understanding of the fundamental biological principles at work in small populations, but also will be of great use in designing management strategies for the wild lupine. Results from this study should also help in management of other taxa before they reach the threshold of extinction.