Evolutionary Origin of Prolonged Delayed Fertilization in the Fagaceae.

Area of Science:

• Evolutionary biology
• Plant reproductive strategies
• Angiosperm life-history evolution

Background:

• Angiosperms exhibit diverse life-history strategies, with temporal organization of flowering, fertilization, and fruiting being crucial.
• Most angiosperms complete fruit development within one growing season (1-year fruiting).
• However, many Fagaceae species display a 2-year fruiting strategy, delaying fruit maturation until the year after flowering, a strategy whose evolutionary origins are poorly understood.

Purpose of the Study:

• To investigate the evolutionary origins of the 2-year fruiting strategy in Fagaceae.
• To determine if pollination mode and leaf habit influence the evolution of 2-year fruiting.
• To test for evolutionary constraints between fruiting strategy, pollination mode, and leaf habit.

Main Methods:

• Reconstructed ancestral states on a phylogeny of 88 Fagaceae species.
• Employed phylogenetic comparative analyses to assess trait correlations.
• Analyzed pollination mode (animal vs. wind) and leaf habit (evergreen vs. deciduous).

Main Results:

• A single origin of the 2-year fruiting strategy was inferred in the common ancestor of a major Fagaceae clade.
• Multiple independent reversions to 1-year fruiting occurred in lineages such as Castanea, Quercus, and Castanopsis.
• Entomophily (animal pollination) and evergreen habit were ancestral in Quercoideae, predating the 2-year fruiting strategy, but did not correlate with fruiting strategy transitions.

Conclusions:

• The 2-year fruiting strategy in Fagaceae has a single evolutionary origin and is subject to multiple reversions.
• Extreme extensions in the interval between pollination and fertilization can be evolutionarily stable.
• Once lost, the 2-year fruiting strategy rarely re-evolves, indicating long-term evolutionary constraints or selection pressures.