Extreme environmental variation sharpens selection that drives the evolution of a mutualism

Area of Science:

• Ecology
• Evolutionary Biology
• Plant-Animal Interactions

Background:

• The role of infrequent ecological events in adaptive evolution and species interaction dynamics remains understudied.
• Masting, the synchronized production of large seed crops by plants, is an infrequent event with potential evolutionary consequences.

Purpose of the Study:

• To investigate how whitebark pine (Pinus albicaulis) masting influences phenotypic selection by its primary seed predator-disperser, the Clark's nutcracker (Nucifraga columbiana).
• To determine the conditions under which infrequent events shape species interactions and evolutionary trajectories.

Main Methods:

• Observational study correlating whitebark pine seed production with Clark's nutcracker behavior and selection pressures.
• Analysis of phenotypic selection on whitebark pine traits during years of varying seed abundance.

Main Results:

• Phenotypic selection on whitebark pine was not detected in common years with low seed abundance.
• Replicated selection favoring traits for seed dispersal occurred during infrequent years of high seed abundance (masting).
• Clark's nutcrackers shifted from primarily seed predation to seed dispersal during masting events, intensifying mutualistic selection.

Conclusions:

• Infrequent events, such as masting, are critical drivers of adaptive evolution.
• The evolutionary dynamics of species interactions, particularly mutualisms, can be significantly shaped by infrequent, high-impact events.
• Understanding rare ecological phenomena is essential for comprehending evolutionary processes.