Subtle variation in size and shape of the whole forewing and the red band among co‐mimics revealed by geometric morphometric analysis in Heliconius butterflies

Abstract

Heliconius are unpalatable butterflies that exhibit remarkable intra‐ and interspecific variation in wing color pattern, specifically warning coloration. Species that have converged on the same pattern are often clustered in Müllerian mimicry rings. Overall, wing color patterns are nearly identical among co‐mimics. However, fine‐scale differences exist, indicating that factors in addition to natural selection may underlie wing phenotype. Here, we investigate differences in shape and size of the forewing and the red band in the Heliconius postman mimicry ring (H. erato phyllis and the co‐mimics H. besckei, H. melpomene burchelli, and H. melpomene nanna) using a landmark‐based approach. If phenotypic evolution is driven entirely by predation pressure, we expect nonsignificant differences among co‐mimics in terms of wing shape. Also, a reinforcement of wing pattern (i.e., greater similarity) could occur when co‐mimics are in sympatry. We also examined variation in the red forewing band because this trait is critical for both mimicry and sexual communication. Morphometric results revealed significant but small differences among species, particularly in the shape of the forewing of co‐mimics. Although we did not observe greater similarity when co‐mimics were in sympatry, nearly identical patterns provided evidence of convergence for mimicry. In contrast, mimetic pairs could be distinguished based on the shape (but not the size) of the red band, suggesting an “advergence” process. In addition, sexual dimorphism in the red band shape (but not size) was found for all lineages. Thus, we infer that natural selection due to predation by birds might not be the only mechanism responsible for variation in color patterns, and sexual selection could be an important driver of wing phenotypic evolution in this mimicry ring.

Altitude and life-history shape the evolution ofHeliconiuswings

“…Differences in behavior between sexes have been identified as one of the main drivers of wing aspect ratio and size sexual dimorphism in insects (Rossato et al 2018a;Le Roy et al 2019). In butterflies, males tend to spend more time looking for mates and patrolling territories, while females focus their energy on searching for suitable host plants for oviposition (Rossato et al 2018b).…”

“…It represents a striking case of Müllerian mimicry, with co-occurring subspecies sharing warn-ing wing color patterns to avoid predators and leading to multispecies mimicry rings across South America (Merrill et al 2015). Wing aspect ratio and size are part of the mimetic signal (Jones et al 2013;Mérot et al 2016;Rossato et al 2018a). Wing morphology is involved in many aspects of Heliconius biology other than mimicry, such as mating or flight mode, but these have been less well studied (Rodrigues and Moreira 2004;Srygley 2004a;Mendoza-Cuenca and MacÍas-Ordóñez 2010).…”

Altitude and life‐history shape the evolution ofHeliconiuswings

“…), and in the Heliconius postman mimicry ring in Brazil significant across‐species wing aspect ratio differences were also found (Rossato et al. ). These studies highlight that while it is clear that color pattern and, to some extent, flight are important for mimicry in Heliconius , wing aspect ratio is also subject to other selection pressures (Mérot et al.…”

“…; Rossato et al. ). Wing morphology is involved in many aspects of Heliconius biology other than mimicry, such as mating or flight mode, but these have been less well studied (Rodrigues and Moreira ; Srygley ; Mendoza‐Cuenca and MacÍas‐Ordóñez ).…”

“…Differences in behavior between sexes have been identified as one of the main drivers of wing aspect ratio and size sexual dimorphism in insects (Rossato et al. ; Le Roy et al. ).…”