Does an achromatic border alter color discrimination of male <i> Speyeria mormonia </i> butterflies during mate searching?

Abstract

Larval food stress for the butterfly Speyeria mormonia causes less pigmentation in female butterflies. For this reason, males may approach females with higher pigmentation more often because it is a sign that they are healthier. Past studies have shown that this could be true, but they have not taken into account the markings on the butterflies’ wings. The achromatic black markings in contrast with the orange color stimulus of the wing could cause the male butterflies to perceive the color stimulus differently than they would without the markings. I added a black border to butterfly decoys made from three different colored Pantone papers, representing a super stimulus, high pigmentation, and low pigmentation, and observed approaches by males to see whether the achromatic border makes a difference in the way males perceive the color stimulus. I hypothesized that I would see a 1:1 ratio of approaches to butterfly decoy pairs with the border, and that the ratio for decoy pairs with the border would not differ from those without the border. Only the super stimulus and high pigment pair with borders did not deviate from a 1:1 ratio of approaches by males. Comparing results for decoy pairs with the border and without the border, only the high pigment and low pigment pairs differed, with more approaches to the low pigment decoy with the border than without the border. This suggests that while pigmentation does matter in the likelihood of approach by a male, so does the black border and markings. Females with low pigmentation will still be approached because of their achromatic markings causing the male butterflies to perceive the color stimulus differently.

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