Reproductive innovations and pulsed rise in plant complexity.

Area of Science:

• Evolutionary biology
• Paleobotany
• Developmental biology

Background:

• Morphological complexity is a hallmark of multicellular organisms, but its evolutionary trajectory remains debated.
• Vascular plant reproductive structures, like flowers, exemplify intricate biological design.

Purpose of the Study:

• To investigate the tempo and mode of evolutionary changes in morphological complexity within vascular plant reproductive structures.
• To determine if complexity increases occur gradually over time or in rapid bursts.

Main Methods:

• A quantitative approach was employed, focusing on the number of distinct part types within reproductive structures.
• Analysis of morphological changes across geological time, spanning from the Devonian to the Late Cretaceous.

Main Results:

• Reproductive complexity in vascular plants did not increase gradually but rather in two distinct pulses.
• An initial pulse of complexity arose during the Devonian period, coinciding with early vascular plant diversification.
• A second, more pronounced pulse occurred in the Late Cretaceous, driven by the diversification of flowering plants (angiosperms).

Conclusions:

• Evolutionary increases in morphological complexity are episodic, punctuated by long periods of stasis.
• These pulses of complexity are strongly associated with the emergence of novel functions and increased functional diversity.
• The link between functional innovation and complexity shifts holds true irrespective of their timing in vascular plant evolutionary history.