CMS
McCauley DE & Bailey MF 2009 Recent advances in the study of gynodioecy: the interface of theory and empiricism. Ann Bot 104:611-620.
- five areas of active inquiry
- the cost of restoration
- the influence of population structure on spatial sex-ratio variation
- the influence of inbreeding on sex expression
- the signature of cyto-nuclear coevolution on the mitochondrial genome
- the consequences of mitochondrial paternal leakage
- theory has guided empiricism
- empiricism has guided theory
- future advances will require that some of the methods currently available only for model organisms be applied to a wider range of species
- it is to the evolutionary advantage of a CMS element, then, to cause a phenotype that produces more or better seeds
- it is a common observation in gynodioecious plant species that females produce more and/or higher quality seeds than hermaphrodites
- the greater number of seeds is most likely due to the diversion of energy, otherwise devoted to pollen production, to seed
- since the majority of gynodioecious species are self-compatible the hermaphrodite morph can often self-fertilize
- higher quality seed production by females can result from the inability of that morph to self, thereby limiting inbreeding depression in their offspring
- other observed female–hermaphrodite differences that could relate to fitness through seed include differences in flower number and fruit set
- there are also well-known cases of gynodioecy in which sex determination is under nuclear control
- Dufay et al. (2008) found that restoration appeared additive with many CMS individuals with intermediate anther phenotypes and pollen production levels
- cost of restoration seemed discrete, producing roughly two types of MF hermaphrodites with either high or low pollen viability
- gynodioecious systems are often characterized by considerable variation from locality to locality in the relative proportion of female and hermaphrodite individuals
- plant organellar genes show much greater population structure (as measured by Fst or its derivatives) than do nuclear genes
- with frequent population turnover, founding events could, by chance, limit associations between particular CMS elements and their restorers in some populations
- this kind of population structure can have interesting consequences for sex-ratio evolution, assuming local pollen limitation
- a new population cannot persist if founded only by seeds destined to be females
- this kind of population structure favours hermaphrodites over females and reduces the global frequency of females, relative to panmixia
- the cost of restoration could vary from locality to locality as a consequence of environmental variation
- differences in this cost influence the outcome of sex-ratio evolution
- the influence of context-dependent self-fertilization should be incorporated more fully into future models of the evolution of gynodioecy, especially those that consider meta-population dynamics