Consequences of prairie fragmentation on the progeny sex ratio of a gynodioecious species, Lobelia spicata (Campanulaceae)

Abstract

Habitat fragmentation of prairie ecosystems has resulted in increased isolation and decreased size of plant populations. In large populations, frequency-dependent selection is expected to maintain genetic diversity of sex determining factors associated with gynodioecy, that is, nuclear restorer genes that reverse cytoplasmic male sterility (nucleocytoplasmic gynodioecy). However, genetic drift will have a greater influence on small isolated populations that result from habitat fragmentation. The genetic model for nucleocytoplasmic gynodioecy implies that the proportion of female progeny produced by hermaphroditic and female plants will show more extreme differences in populations with reduced allelic diversity, and that restoration of male function will increase with inbreeding. We investigated potential impacts of effects resulting from reduced population sizes by comparison of progeny sex ratios produced by female and hermaphroditic plants in small and large populations of the gynodioecious prairie species, Lobelia spicata. A four-way contingency analysis of the impact of population size, population sex ratio, and maternal gender on progeny sex ratios showed that progeny sex ratios of hermaphroditic plants were strongly influenced by population size, whereas progeny sex ratios of female plants were strongly influenced by population sex ratio. Further, analysis of variation in progeny-type distribution indicated decreased restoration and increased loss of male function in smaller and isolated populations. These results are consistent with reduced allelic diversity or low allelic frequency at restorer loci in small and isolated populations. The consequent decrease in male function has the potential to impede seed production in these fragmented prairies. Heredity (2005) 95, 69-75.

The Effect of Pollen Versus Seed Flow on the Maintenance of Nuclear-Cytoplasmic Gynodioecy

“…This result can be attributed to both the effect of drift, as discussed above, as well as to the asynchronous nature of frequency oscillations among demes. Our explanation is consistent with that given by previous authors (e.g., Frank 1989;Gouyon et al 1991) who invoked frequency oscillations driven by selection to explain the common observation in gynodioecious species of between-population variation in the frequency of females (i.e., Kawakubo 1994;Koelewijn and Van Damme et al 1996;Barr 2004;Murayama et al 2004;Byers et al 2005;Cuevas et al 2006;Nilsson and Agren 2006;Caruso and Case 2007;Dufay et al 2009).…”

“…Because many plant populations can be small, we might expect drift to influence genotype frequencies and the related proportion of females in the case of gynodioecious species, e.g., through the fixation or loss of either a sterility or a restorer mutation (Byers et al 2005; Nilsson and Agren 2006; Caruso and Case 2007). Drift is likely to be particularly important in species with subdivided populations, where different genes can be fixed in different demes.…”

Inter simple sequence repeat (ISSR) based analysis of genetic diversity ofLobelia rhynchopetalum(Campanulaceae)

“…The results obtained in this study suggest that the highest genetic diversity of L. rhynchopetalum is found around the mid altitude of its distributional range, and thus can be considered as diversity hotspot and should get priority from a conservation point of view. Many natural ecosystems are subject to habitat fragmentation, which results in smaller and more isolated populations (Byers et al 2005). Plant species remaining in fragmented habitats are of conservation concern.…”

Sex ratio variation in gynodioecious Lobelia siphilitica: effects of population size and geographic location

“…This will increase female frequency regardless of whether inbreeding depression is exposed. Genetic drift can either increase (Byers et al. , 2005) or decrease (Murayama et al.…”