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