Genetic bottlenecks and dysgenic gene flow into re-established populations of the grassland daisy, Rutidosis leptorrhynchoides

Abstract

Allozyme and chromosomal variation were compared between five small re-established populations of the endangered grassland daisy Rutidosis leptorrhynchoides and the two large, wild tetraploid (2n = 44) populations from which they were derived, to assess whether re-establishment has been associated with a significant genetic bottleneck. Mean allelic richness at five allozyme loci was lower in re-established populations than in their progenitors, but there were no differences in levels of heterozygosity or gene fixation. In contrast, re-established populations had a greater range of cytotypes than the wild populations, with novel cytotypes including euploids, aneuploids and chromosomal rearrangements. Some of this increased cytological diversity may be attributable to increased rates of disjunctional errors under increased inbreeding in small populations. However, the presence of 2n = 33 triploid plants in the re-established populations, along with the occurance of two allozyme alleles that are otherwise unique to a neighbouring diploid population, both suggest that immigration is also influencing the chromosomal architecture of the new populations. Although the two types of genetic diversity examined show apparently contrasting responses to re-establishment, both of the observed changes in diversity may negatively affect population viability. If losses in allozyme diversity are paralleled by a loss of mating types in this self-incompatible species there is the potential for significant effects on population demography. Increased frequencies of chromosomal abnormalities, which are often associated with lowered fertility, will also reduce mean individual fitness.