Outcrossing and Sex Function in Hermaphrodites: A Resource-Allocation Model

Area of Science:

• Population Genetics
• Plant Reproductive Biology
• Evolutionary Ecology

Background:

• Traditional outcrossing rate estimates in seed plants often neglect variations in pollen fertility.
• Evidence suggests pollen fertility can differ significantly from ovule fertility, impacting reproductive success.
• Hermaphroditic plants exhibit unequal male and female functioning due to fertility variations.

Purpose of the Study:

• To propose a novel combined ovule and pollen outcrossing rate based on successful gametes.
• To define and analyze 'functional sex' as a measure of female reproductive contribution.
• To investigate the frequency-dependent nature of these rates and their implications for population dynamics.

Main Methods:

• Development of a new combined outcrossing rate incorporating successful ovule and pollen gametes.
• Definition of 'functional sex' as the proportion of successful ovules among all successful gametes.
• Utilized a one-locus, two-allele genetic model with dominance to study male/female resource allocation and its impact on outcrossing rates and population dynamics.

Main Results:

• The combined outcrossing rate is influenced by pollen fertility, with higher pollen fertility leading to a greater rate.
• In polymorphic populations, genotypic combined outcrossing rates increase with the frequency of more ovule-fertile phenotypes.
• Functional sex increases, while fitness decreases, with the frequency of more pollen-fertile phenotypes when ovule selfing rate is less than 1.

Conclusions:

• The proposed combined outcrossing rate and functional sex provide a more accurate measure of reproductive success in plants with variable gamete fertility.
• Resource allocation strategies significantly influence population dynamics, potentially leading to polymorphism even with dominance.
• Mean population fitness can decrease with selection, and equilibrium populations show specific relationships between outcrossing rates, functional sex, and selfing rates.