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A Self-Incompatibility System Explains High Male Frequencies in an Androdioecious Plant

Science  26 Mar 2010:
Vol. 327, Issue 5973, pp. 1648-1650
DOI: 10.1126/science.1186687

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The Making of the Males

Most plants have a hermaphroditic mating system with flowers with both male and female function. However, in some cases, species are invaded by a sex-specific sterility factor. When female sterility factors invade a population, it results in a mating system called androdioecy. Theoretically, these female sterile (male) individuals should occur at low frequencies because of their reduced reproductive capacity. However, some species in the olive family have a greater than expected frequency of males. Saumitou-Laprade et al. (p. 1648) show that, for one species, males were able to reach high frequencies because of the retention of a self-incompatibility factor within hermaphroditic individuals. In this case, hermaphroditic individuals can only mate with individuals outside of their incompatibility type, reducing their available mating partners, whereas males are able to mate with all hermaphrodites. This explains how, contrary to theory, high frequencies of males can exist within populations.

Abstract

Androdioecy is a sexual system in which males co-occur with hermaphrodites, which have both male and female function. Stable androdioecy is rare in nature, and theory suggests that it requires that males sire more than twice as many offspring as hermaphrodites. In several members of the olive family (Oleaceae), androdioecy occurs with higher frequencies of males than predicted by theory. In Phillyrea angustifolia L., we found that high male frequencies can be maintained in natural populations because hermaphrodites belong exclusively to one of two self-incompatibility groups, and thus, each can fertilize only half of all pollen recipients. In contrast, males can pollinate all hermaphrodites. Thus, in this species, the reproductive disadvantage that males face due to the loss of female function is offset by the fact that all males are fully compatible with all pollen recipients.

  • * Present address: Laboratoire d'Ecologie, systématique et évolution (ESE), Département Génétique et Ecologie Evolutives, UMR 8079, Bâtiment 360 and 362, Université Paris–Sud, 91405 Orsay CEDEX, France.

  • Present address: 22 rue des Orangers, 30000 NÎmes, France.

  • Present address: University of Maryland Institute for Advanced Computer Studies (UMIACS), 296 Biomolecular Sciences Building, Room 3104H, College Park, MD 20742, USA.

  • § Present address: 294 chemin des Baumes, 34980 Montferrier-sur-Lez, France.

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