Revealing Evolutionary Mechanisms by Mapping Pigmentation Character States and Developmental Mechanisms onto a Resolved Fruit Phylogenetic Tree Jesse Hughes, Abigail Groszkiewicz, and Thomas M. Williams The Department of Biology at the University of Dayton; 300 College Park, Dayton, OH 45469

ABSTRACT Challenges with Infering Ancestral and Derived Phentypes Saltans and Lordiphosa Groups Include Dimorphic Species Since the origin of the 36 recognized phyla over 500 million years ago, subsequent evolu- A. Lordiphosa Species Group A. Phenotype 2 B. Phenotype 2 We found that dimorphic species reside tion can be largely summarized as the diversi cation of physiological, behavioral, and morpho- in the Saltans and Lordiphosa species logical characteristics among these original 36 body plans. Diversi cation continues to this day Phenotype 1 Phenotype 2 groups too. Thus dimorphic and can be seen in humans as dierences in coloration, lactose metabolism, and energy storage pigmentation is observed in several in fat tissue. As all animal characteristics are products of development, a key challenge for con- Phenotype 1 Phenotype 1 species groups among the major temporary research is to reveal the ways in which development evolves through changes in the lineages of . (A) In cases where few taxa are sampled, simple Phenotype 1 L. collinella L. claro nis uses of genes. To meet this challenge, investigations must prioritize characteristics: that have re- B. Saltans Sprecies Group cently evolved, the direction of character evolution is known, and for which the underlying genes inferences about the ancestral and derived states can be made. Phenotype 1 can be studied by modern genetic manipulations. One ideal trait is the diverse coloration patterns This raises uncertainty as to whether observed on the abdominal tergites of fruit y species from the Sophophora subgenus. Prior re- Phenotype 1 Here Phenotype 1 appears ancestral and 2 derived. dimorphism was ancestral and search has supported a scenario where melanic pigmentation limited to the male abdomen frequently lost, or alternatively evolved once within this clade through the evolution of a sexually dimorphic pattern of expres- Phenotype 1 whether dimorphic pigmentation sion for the bric-à-brac transcription factor genes. My research challenges this scenario by looking (B) When more taxa are considered, the interpretation D. emarginata D. sturtevanti evolved on multiple occasions. at the patterns of pigmentation on the abdomens of species representing the diverse Sophophora Phenotype 2 species groups and interrogating the patterns of bric-à-brac expression during the development of what is the ancestral state can become ambiguous. Using Gene Network Structure to Reveal Homology Phenotype 1 of the abdominal tergites. Success in this work will advance the fruit y pigmentation model as Was phenotype 2 ancestral and lost several times, or or Convergence exemplar of how diversity evolves through the re-working of developmental mechanisms. Phenotype 1 did phenotype 2 evolve more than once? Patterning Genes The melanogaster pigmentation gene Pigmentation Evolution in the Sophophora Subgenus regulatory network has been well studied. A. B. Abd-B dsx Novel TF What are the Genetic Differences Underlying Earth’s D. melanogaster lordiphosa A cornerstone feature of the network shaping

Diversity of Life? Sophophora male-limited expression of pigmentation melanogaster enzymes is the drastically reduced expression

Diversity can be seen at dierent taxonomic levels of comparison: D. obscura obscura of the Bab transcription factors in the male 1. Intraspeci c level bab1 and bab2 yellow tan ebony abdomen. 1 Pigmentation Genes 2. Order Level willistoni 3. Class Level D. willistoni saltans Bab1 Expression Hints to an Independent Origin of 4. Super-class level 2 Dimorphism

-How do novelties evolve? Z. ghesquierei D. pseudoobscura D. anis D. melanogaster 3 In a monomorphic and a dimorphic pigmented -Which genes have been functionally changed? species of the obscura group, we found nearly -How have gene functions been modi ed? equivalent expression of Bab1 in the male and -Are there trends in the types of genes changed (A) Working model, based on limited taxa sampling, is that monomorphic pigmentation is the female abdomens. and how are they modi ed? 4 ancestral state in Sophophora and dimorphic pigmentation is derived. This suggests that Bab expression diers in this To answer these questions requires knowing about (B) However, the Sophophora subgenus includes many dierent species groups and hundreds of species group, and that tergite pigmentation is the ancestral phenotypic and genetic makeup. extant species. We were curious whether a more thorough taxa sampling would support or contradict the working model. not repressed by the Bab transcription factors. This is a challenge for traits and genetic Hidden Dimorphism in Obscura Group

material that the ancestral states cannot be D. affinis obtained The Molecular Evolution of a Bab Regulatory Sequence

D. algonquin mel mel Dsx1 wil wil wil Dsx1 mel Conceptual Model for the Gene Network Basis of Evolution Female speci c Bab expression is controlled by a regulatory We identi ed that species exist in the obscura D. azteca element known as the dimorphic element which has binding sites for the Abd-B and Dsx transcription factors. A B C D group with sexually dimorphic pigmentation D Key D. persimilis Conserved Trait raising the possibility that dimorphism existed Gene 1 This element and binding sites are conserved in the D. melanogaster Gene 2 in the most recent common ancestor of the D. pseudoobscura Ancestral Novel monomorphic species D. willistoni, but a Dsx binding site’s State Trait Gene 3 melanogaster and obscura species X Gene 4 D. miranda groups. polarity is inverted that leads to spatially-limited D. willistoni Gene 5 regulatory activity. ? Gene 6 D.ambigua Diversied Trait No Gene Expression L. collinella KEY D. obscura We found that a Lordiphosa species has the inverted site Abd-B Gain of ABD-B Site 12a and b polarity too, supporting the conclusion that Bab regulation Dsx Dimer Dsx Site 1 polarity reversed Gain of Sites 12a and b Abd-B Site Dsx Site Polarity Flip Gain of ABD-B Site 13 D. bifasciata is a novel feature of dimorphic pigmentation for Dsx Site Loss of Abd-B Site 8 Gain of Site 13

D. melanogaster and closely related species. Near Dsx Site X Lost Site 8 Dsx Site 2 Enhancement At lower taxonomic levels gene gains Trait Loss Thus, it can be anticipated that D. guanche and losses have been infrequent evolution has largely been CONCLUSIONS AND FUTURE DIRECTIONS shaped by the formation, D. melanogaster compared to the number of Our data supports a scenario where sexually dimorphic pigmentation evolved on multiple occasions modi cation, and destruction of dierences in the expression of in the Sophophora subgenus and through unique inputs of transcriptional regulatory proteins. networks of co-expressed genes. conserved genes. D. saltans

D. willistoni Our future work will prioritize revealing how dimorphism evolved to be made at the levels of pigmentation enzyme genes and their upstream transcriptional regulators. REFERENCES ACKNOWLEDGEMENTS 1. Salomone JR, Rogers WA, Rebeiz M, Williams TM: The evolution of Bab paralog expression and abdominal pigmentation among Sophophora fruit y species. Jesse Hughes was supported by an NSF Research Experience for Undergraduates Species stocks were acquired from the San Diego Drosophila Stock Center [Internet]. Evol. Dev. 2013, 15:442–57. award

2. Williams TM, Selegue JE, Werner T, Gompel N, Kopp A, Carroll SB: The regulation and evolution of a genetic switch controlling sexually dimorphic traits in TMW was supported through funding from the American Heart Association Corresponding Author Contact Information: [email protected] Drosophila. [Internet]. Cell 2008, 134:610–23. (11BGIA7280000) and National Science Foundation (IOS-1146373).