Breakdown of dioecy: models where males acquire cosexual functions

Area of Science:

• Evolutionary Biology
• Population Genetics
• Plant Reproduction

Background:

• Dioecy, a reproductive system with separate male and female sexes, can break down into gynodioecy (females and hermaphrodites) or cosexuality.
• Modified males, capable of some female function, may invade dioecious populations under specific conditions.
• Previous models did not fully incorporate factors like pollen limitation, partial selfing, and inbreeding depression.

Purpose of the Study:

• To reanalyze models of dioecy breakdown involving modified males.
• To investigate the factors influencing female frequencies in gynodioecious populations.
• To identify empirically detectable advantages for modified males exhibiting cosexual traits.

Main Methods:

• Reanalysis of existing models of dioecy breakdown.
• Inclusion of biologically relevant factors: pollen limitation, partial selfing, and inbreeding depression.
• Mathematical modeling to determine conditions for invasion by modified males.

Main Results:

• Modified males gain advantages from selfing (transmission advantage) and reproductive assurance when pollen is limited.
• Cosexual phenotypes may require smaller pollen pool sizes for successful seed set compared to females under resource limitation.
• High female frequencies can result from poor competition of Y-chromosome-bearing pollen against X-chromosome-bearing pollen.

Conclusions:

• Modified males can invade dioecious populations, leading to either replacement by cosexuality or the maintenance of sexual polymorphism.
• The evolution of cosexuality is influenced by the interplay of selfing, pollen competition, and resource allocation.
• Understanding these dynamics is crucial for predicting the evolutionary trajectories of plant mating systems.