Genetic erosion, inbreeding and reduced fitness in fragmented populations of the endangered tetraploid pea Swainsona recta Original Research Article

Genetic variation and fixation coefficients were measured for 17 fragmented populations of the endangered tetraploid pea Swainsona recta ranging in size from 1 to 430 flowering plants. Allelic richness and fixation coefficient were correlated with the log population size, suggesting that reduced population size is accompanied by genetic erosion, primarily due to a loss of rare (q<0.1) alleles, and increased inbreeding. Comparative germination and growth studies of seed from five populations representing three different levels of inbreeding (low F=0.34, medium F=0.43, high F=0.57) showed a significant reduction in percentage seed germination at 2 weeks in the single high F treatment population. There were no effects on survivorship and growth beyond this up until 141 days. Results suggest that polyploidy has not prevented erosion of genetic variation at the population level, as has previously been suggested. However, the production of partial heterozygotes, e.g. AABC and AAAB, under inbreeding may be mitigating inbreeding depression assuming a partial dominance model of gene expression. Conservation effort should concentrate on populations larger than 50 sexually reproductive plants, as these appear capable of maintaining high genetic diversity and exhibit no immediate evidence of inbreeding depression, despite some elevation of the fixation coefficient.