OPTIMAL OUTCROSSING IN IPOMOPSIS AGGREGAT A: SEED SET AND OFFSPRING FITNEs.

Area of Science:

• Ecology
• Evolutionary Biology
• Plant Sciences

Background:

• Gene flow and local selection influence genetic similarity in plant populations.
• Inbreeding depression (crosses between close relatives) and outbreeding depression (crosses between distant relatives) can reduce fitness.
• Outbreeding depression is often linked to the disruption of locally adapted gene complexes.

Purpose of the Study:

• To investigate the existence and extent of an optimal outcrossing distance in the plant species Ipomopsis aggregata.
• To determine if seed set and offspring fitness are maximized at intermediate pollination distances.
• To explore potential mechanisms, such as local adaptation, contributing to outbreeding depression.

Main Methods:

• Conducted six replicate pollination experiments with Ipomopsis aggregata, varying outcrossing distances (selfing, 1-10m, >100m).
• Measured seed set per flower for different pollination treatments.
• Grew offspring from experimental crosses under natural conditions and monitored survival, flowering time, and lifetime fitness over seven years.
• Assessed offspring fitness in relation to planting distance from the seed parent (1-30m).
• Analyzed vegetation changes in the study population to understand spatial variation in selection regimes.

Main Results:

• Mean seed set per flower was significantly higher in crosses with an outcrossing distance of 1-10m compared to selfing or >100m crosses.
• Offspring from 10m crosses exhibited higher survival rates, a greater likelihood of flowering, and earlier flowering than offspring from 1m or 100m crosses.
• Lifetime fitness of offspring from 1m and 100m crosses was substantially lower (47% and 68%, respectively) than that of offspring from 10m crosses.
• Offspring fitness decreased with increasing planting distance from the seed parent (1-30m).

Conclusions:

• The study supports the prediction of an optimal outcrossing distance in Ipomopsis aggregata, with intermediate distances (1-10m) promoting the highest reproductive success and offspring fitness.
• Local adaptation to the maternal environment is a plausible contributing factor to outbreeding depression, as evidenced by reduced offspring fitness with increasing planting distance.
• Spatial variation in selection regimes, occurring at scales of meters to hundreds of meters, likely interacts with mating distance to influence population dynamics and fitness.