We have compared selfed and outbred offspring from individual plants of the annual plant Nigella degenii to examine patterns of inbreeding depression in two direct components of fitness (flower number and pollen viability) and a number of morphological or phenological characters for which the optimal phenotype may be habitat specific. Selfing lowered flower number, plant height, flower size, and pollen viability and caused a shift toward later germination and flowering dates. There was no significant difference in inbreeding depression between fitness components and characters reflecting morphology or phenology regardless of how inbreeding response was estimated. Family-level analyses revealed moderately strong correlated responses involving flower number and each of the nonfitness characters, whereas pollen viability showed an independent response to inbreeding. On the basis of these observations, we hypothesize that morphology and phenology could make a significant contribution to lifetime inbreeding depression in N. degenii, that inbreeding responses in different types of characters involve loci with both general and specific effects on the phenotype, and that morphological inbreeding depression has contributed to the evolutionary reduction of floral structures so prevalent in the Nigella arvensis complex.

Understanding the genetic consequences of changes in population size is fundamental in a variety of contexts, such as adaptation and conservation biology. In the study presented here, we have performed a replicated experiment with the plant Nigella degenii to explore the quantitative genetic effects of a single-founder bottleneck. In agreement with additive theory, the bottleneck reduced the mean (co)variance within lines and caused stochastic, line-specific changes in the genetic (co)variance structure. However, a significant portion of the (co)variance structure was conserved, and 2 characters-leaf and flower (sepal) size-turned out to be positively correlated in all data sets, indicating a potential for correlated evolution in these characters, even after a severe bottleneck. The hierarchical partitioning of genetic variance for flower size was in good agreement with predictions from additive theory, whereas the remaining characters showed an excess of within-line variance and a deficiency of among-line variance. The latter discrepancies were most likely a result of selection, given the small proportion of lines (23%) that remained viable until the end of the experiment. Our results suggest that bottlenecked populations of N. degenii generally have a lower adaptive potential than the ancestral population but also highlight the idiosyncratic nature of bottleneck effects.

The structuring of quantitative genetic variation can have a significant impact on the adaptive potential and long-term viability of species in changing landscapes. The present study of the grass Briza media investigated the relationships between patterns of heritable variation in phenotypic characters and descriptors of landscape structure, landuse history and local habitat conditions in a landscape known to have undergone a progressive and massive loss of semi-natural grassland habitat over the past 300 years. Our analyses revealed significant levels of heritable variation for characters related to overall plant size and spikelet size-number ratio, with estimates of broad-sense heritability ranging between 29 and 34%. Differences between demes accounted for a minor fraction of the total variation. In contrast to previous allozyme results from the same plant material, which suggest significant impacts of both neutral and selective processes, neither the demespecific means nor the heritabilities for the phenotypic characters were consistently associated with landscape structure or land-use history. The results of the study indicate that the structuring of quantitative variation has been relatively insensitive to habitat fragmentation, at least over the time frame considered in this study system.