Trade-off between fecundity and survival generates stabilizing selection on gall size

Area of Science:

• Ecology
• Evolutionary Biology
• Animal Behavior

Background:

• Multitrophic interactions drive species evolution.
• Fitness trade-offs, where traits are adaptive in some contexts and maladaptive in others, are common outcomes of species interactions.
• The cynipid wasp Callirhytis quercusbatatoides induces galls on Quercus virginiana, exhibiting complex ecological dynamics.

Purpose of the Study:

• To identify and quantify a fitness trade-off between fecundity and survival in Callirhytis quercusbatatoides.
• To investigate the impact of opposing selection pressures on gall size evolution.
• To assess the rapid evolutionary response of gall size to altered environmental conditions.

Main Methods:

• Quantified trade-offs in natural populations by documenting relationships between gall size, fecundity, and bird predation rates.
• Conducted a five-year field experiment excluding avian predators from host trees.
• Monitored changes in gall size in response to predator exclusion.

Main Results:

• Larger galls were positively associated with higher fecundity (more offspring).
• Larger galls were negatively associated with survival due to increased bird predation.
• Excluding birds for five years resulted in a significant shift towards larger gall sizes per tree.

Conclusions:

• Opposing selection pressures (fecundity vs. predation) can generate stabilizing selection on phenotypic traits like gall size.
• Callirhytis quercusbatatoides exhibits rapid evolution in gall size when predator-induced selection is removed.
• This study highlights the dynamic interplay between species interactions and evolutionary adaptation in ecological communities.