P3.124 Friday, Jan. 6 Size matters, but so does shape: Quantifying complex shape changes in a sexually selected trait in stalk-eyed flies WORTHINGTON, Amy/M; BERNS, Chelsea/M; SWALLOW, John/G*; Iowa State University, Ames; Iowa State University, Ames; University of South Dakota, Vermillion email@example.com
The elaborate morphologies of sexually selected ornaments are predicted to be costly. Ornament size is frequently used as a measure of fitness, yet shape plays an important role and, surprisingly, is often overlooked. Shape often exhibits allometry with size, which can occur due to biomechanical, developmental, or performance constraints. Therefore, shape can provide additional insights into the morphological differences between individuals and the potential limits on sexual trait exaggeration. Here, we used landmark-based geometric methods to quantify head shape in a sexually dimorphic species of stalk-eyed fly (Teleopsis dalmanni) to examine patterns of sexual shape dimorphism. Our analyses revealed a significant difference in head shape between the sexes, with males exhibiting smaller eye bulbs, thinner stalks, and smaller heads than females. Additionally, as eyestalk length increased within each sex, a similar pattern of shape change was observed as that between sexes. We discuss how shape variation may be the result of constraints acting against further ornament exaggeration and how changes in shape may significantly impact whole-organism performance in stalk-eyed flies.