Creative Commons License

Creative Commons License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License.

Date of Graduation

Summer 5-2-2019

Document Type


Degree Name

Master of Science (MS)


Department of Biology


Idelle Cooper

Heather Griscom

David McLeod


An ongoing evolutionary question is how co-occurring species maintain reproductive barriers when they are morphologically, behaviorally, and ecologically similar. Without geographic isolation, traits involved in species recognition may be under selection to enhance reproductive barriers. Exaggerated trait differences between species in sympatric populations may reflect selection to reduce misdirected mating between species, or reproductive character displacement. While this phenomenon is widely recognized as an important stage in the speciation process, there is little direct evidence of this process in nature. In two North American damselfly species, Calopteryx aequabilis and C. maculata, wing pigmentation is sexually dimorphic and also shows exaggerated differences in sympatric populations, particularly in female wings. When these species occur together, they occupy the same mating territories and the potential for misdirected mating is high. I hypothesize that female wing pigmentation is under selection for species recognition. In this study, I conducted male mate choice experiments in which I altered female wings by switching them within and between species. I measured male mating preference of both species in allopatric and sympatric populations by giving males a choice of two female types in a natural setting. Results supported the hypothesis that male preferences in sympatry diverge corresponding to female wing pigmentation. Sympatric C. aequabilis males preferred lighter-winged females, which significantly differed from the dark wing preferences of C. maculata males and allopatric C. aequabilis males. By manipulating the female wing pigmentation directly, I identified that this is the specific trait under selection. These findings indicate that male mating preferences and female wing pigmentation diverged in sympatry to reduce misdirected mating of two closely related species.



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