A 23-million-year record of morphological evolution within Neotropical grass pollen

Area of Science:

• Paleobotany
• Evolutionary Biology
• South American Flora

Background:

• Grass-dominated biomes in South America have a long history, but their evolutionary trajectory and drivers are not well understood.
• Understanding grass evolution is crucial for reconstructing past ecosystems and predicting future biome dynamics.

Purpose of the Study:

• To investigate the evolutionary history and drivers of grass (Poaceae) pollen micro-ornamentation in the Neotropics since the Early Miocene.
• To quantify the morphometric variation in grass pollen exine over geological timescales.

Main Methods:

• Utilized scanning electron microscopy (SEM) for high-resolution imaging of grass pollen.
• Applied computational analysis to quantify pollen exine morphometrics.
• Assembled three spatial-temporal pollen datasets spanning from the Early Miocene to the present.

Main Results:

• Identified three distinct spatial-temporal pollen groups with unique, partially overlapping exine morphospace regions.
• Observed a consistent directional shift in pollen micro-ornamentation over time, progressing towards less dense patterns.
• Found no significant variation in the extent of the occupied morphospace, despite directional changes in ornamentation.

Conclusions:

• The study provides the first comprehensive view of morphological variation in Poaceae pollen micro-ornamentation through time.
• Hypothesized that evolutionary drift, directional selection, and continental-scale migration drove changes in grass pollen exine since the Early Miocene.
• Concluded that high pollen micro-ornamentation diversity is linked to the evolutionary success of grasses in the Neogene.