Changing nitrogen availability impacts allocation to ornamentation and dynamics of sexual selection

Background/Question/Methods

The honesty of traits important in female choice or male-male competition is often enforced by costs or physical constraints during development.  Nutrient availability is commonly a limiting factor for such sexually selected traits.  While scientists have long appreciated the link between nutritional ecology and sexual selection, there is little research investigating whether drastic changes in nutrient input due to human activity may affect sexual selection.  This experiment focuses on sexually dimorphic traits in the cabbage white butterfly (Pieris rapae). This species uses nitrogen-rich pterin pigments as a sexual signal, which serves as an honest indicator of nutrient assimilation ability. We investigated how wing coloration correlates with spatial and temporal variation in fertilization rates across the upper midwest. 

Results/Conclusions

Preliminary results suggest that investment in wing ornamentation increases over time, concordant with increases in fertilizer use. Diet manipulations of populations that differ in long-term exposure to higher fertilizer levels suggest that the increases in ornamentation are due to evolutionary changes in how much nitrogen is allocated to ornamentation.  This research suggests that human-induced changes in nutrient availability may affect the evolution of life history allocation and sexual selection dynamics.