Evolution of Ultraviolet Reflectance Patterns in Sulphur Butterflies Mary Mendoza and Ronald L. Rutowski Department of Biology Arizona State University, Tempe AZ 85287-1501 Abstract In sulphur butterflies, males often exhibit an intense ultraviolet reflectance pattern on their wing surface. This reflectance varies greatly in terms of intensity, the angle at which it is visible, and overall pattern among individuals. The purpose of this experiment is to examine the phylogenetic history of UV reflectance among the North Amercian Sulphur butterflies. According to the hypothesis of sexual selection, it is expected that UV patterns will vary greatly among sister species, or closely related species. In other words, closely related species should vary in terms of sexual traits but are similar in nonsexual traits (Brunton 1998). Alternative hypotheses suggest that species should have similar patterns of UV reflectance. We classified male sulphurs (Coliadinae) from 25 species in terms of whether or not they displayed UV reflectance and if they did, the pattern of UV reflection from the wings. This was done from literature accounts and first-hand observation. The UV pattern was then mapped onto a phylogeny for Coliadinae that we derived from published molecular analyses and the taxonomy of the groups. This phylogeny for UV reflectance supports the sexual selection hypothesis.

Results The phylogenetic relationships among the 27 Introduction sennae species of North American sulphurs are shown in the phylogeny. The species fall into 8 sister The function of butterfly coloration has been of groups (Grps. 1-8) each consisting of two to great interest to biologists for years. This interest agarithe five closely related species. We are still became even greater when it was discovered that collecting data on UV reflectance patterns and many butterflies have elements of UV color argante Group 1 Group currently have data for 23 species and 7 of the pattern which are not visible to humans. This is sister groups. especially true for the sulphur butterflies (Family philea Pieridae; Subfamily Coliadinae) in which males Presence of UV reflectance: In 16 of the often have a brilliant UV reflectance produced by Phoebis 22 species, males have an iridescent UV the structural features of special scales on their reflectance. In four of the sister groups all or dorsal wing surface (Silberglied & Taylor, 1973, statira most species (>75 %) males were UV 1978). reflectant (Grps. 1-2, 4 and 7). Two groups The most common functional explanation for contained more non-reflectant than reflectant brilliant UV signals in males is that they evolved Zerene eurydice species (Grps. 5 -6). We lacked sufficient data in response to female preferences for males with to assess the distribution of UV reflectance bright coloration. Brightness may be an indicator cesonia within the other two clades (Grps. 3 and 8). of several aspects of male quality including their 2 Group ability to produce a spermatophore (Rutowski Patterns of UV reflectance: The data we 1985) and their species identity (Silberglied and croceus currently have on the UV patterns suggest that Taylor 1973, 1978). Support for this sexual Colias the pattern of UV reflectance varies selection hypothesis comes from experimental and dramatically within some groups. comparative studies. erate 3 Group For example, Brunton (1998) mapped the Conclusions presence or absence of male UV reflectance onto a phylogeny for European sulphurs to test the sexual alexandra 1. Closely related species can vary greatly selection hypothesis. This hypothesis states that not only in the presence or absence of UV is a trait under inter and/or intra-specific UV reflectance but also in the pattern as selection and predicts highly variable UV signals meadii 4 Group well. Therefore, the results for North among males in terms of presence or absence and American Coliadinae support the pattern. Furthermore, frequent loss or hecla hypothesis of sexual selection. Whether maintenance of UV is expected to occur over time. paleano the UV signals are most important in the Therefore, the presence and pattern of UV among context of female choice or male-male males will vary greatly regardless of ecological or interactions has yet to be determined. nastes 5 Group environmental factors. Even species that are 2. The prevalence of male UV reflectance closely related, are expected to vary in UV in this subfamily and its phylogenetic patterns. Brunton’s analysis yielded results in scudderi distribution suggest that male UV support of these predictions supporting the presence is the ancestral state. hypothesis that UV is an ancestral state that has philodice 3. We are currently borrowing specimens evolved via sexual selection. of the other species to complete the data The study reported here has two goals. The first set and will reevaluate these conclusions is to repeat Brunton’s analysis using the North 6 Group when that is done. American sulphurs to provide another test of the eurytheme References sexual selection hypothesis for the evolution of male UV reflectance. The second is to extend this behri Brunton CFA 1998. The evolution of ultraviolet patterns in European Colias butterflies (Lepidoptera: analysis to consider also the evolution of the daira Pieridae): a phylogeny using mitochondrial DNA. distribution or pattern of UV reflectance on the Heredity, 611-616. male’s wings. boisduvaliana Knuttel H, Fiedler K. 2000. On the use of ultraviolet photography and ultraviolet wing patterns in butterfly Methods morphology and taxonomy. Journal of the mexicana Lepidopterists’ Society. 54(4) 137-144. Group 7 Group We examined 27 species of sulphurs that are Miller LD, Brown FM. 1981. A Catalogue/checklist of found north of the US-Mexico border. A nicipe the Butterflies of America North of Mexico. The phylogeny for the clade was developed using Lepidopterists’ Society. existing molecular phylogenies (Pollack et.al. 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Silberglied RE, Taylor OR Jr. 1978. Ultra-violet Acknowledgments reflection and its behavioural role in the courtship of the sulphur butterflies Colias eurytheme and C. I would like to thank Dr. Darrel Kemp, Dr. David Pearson, and Kendra Greenlee for all their philodice. Behav. Ecol. Sociobiol., 3, 203-243. help, guidance and support.