Reproductive tradeoffs of learning in a butterfly

The evolution of learning has long been hypothesized to be limited by fitness trade-offs such as delays in reproduction. We explored the relationship between host learning and reproduction in the cabbage white butterfly, Pieris rapae. The cabbage white female is innately biased to search for common green hosts but can learn to search for rare red hosts. Host learning was shown previously to vary among full-sibling families and to incur costs in terms of host search efficiency and brain size. In the present study, we show that butterflies from full-sib families with relatively better learning performance on red hosts tend to emerge as adults with relatively fewer and less-developed eggs. We also used methoprene, a juvenile hormone mimic, to advance reproduction in female cabbage whites. We found that methoprene-treated butterflies improved host-finding ability less with experience, relative to controls, providing independent evidence of a link between learning and timing of reproduction. Finally, we show that the learning experience itself is associated with additional decreases in lifetime fecundity. These results support a range of theoretical and comparative studies highlighting the importance of fitness tradeoffs in the evolution of learning and cognition.