Co-Director of Graduate Partners in Science Education
Heliconius mimicry rings in a new light
Brett Seymoure, W. Owen McMillan, Kevin McGraw, Ron Rutowski
Müllerian mimicry theory states that two or more aposematic individuals will converge on a similar signal to share the costs of predator education. However, this is not the case in many organisms that should exhibit Müllerian mimicry. We tested the hypothesis that different mimicry rings (differently colored groups of aposematic individuals) have evolved due to microhabitat segregation utilizing Heliconius butterflies. We predicted individuals in mimicry rings choose light environments that confer the strongest signals. In the tropical forest there are four light environments: small gap, large gap, woodland shade, and forest shade. We predicted individuals within the red and yellow mimicry ring would be found in well lit habitats (small gap and large gap), while individuals within the blue and black mimicry ring would be found in darker habitats (woodland shade and forest shade). We measured light environments (via irradiance and canopy cover) along transects where the mimicry rings are found. Behavioral trials were run to determine if butterflies had a preference for a light environment that granted a stronger signal and we employed visual models to verify that light environments would influence the perception of coloration of the different mimicry rings. We found light habitats differed among mimicry rings and butterflies preferred different light environments. We show the effects of disparate light environments on the signal strength of the mimicry rings. This study demonstrates that different mimicry rings could evolve due to signal efficacy in different microhabitats.