Mismatched Mimics: Insights and Conundrums from the Evolutionary History of Colorful Ground Beetles

Abstract

A particular form of evolutionary convergence among species—known as mimicry—is a phenomenon that has stimulated great progress in the fields of ecology and evolutionary biology. In particular, the phenomenon of Müllerian mimicry (the phenotypic convergence between aposematic species driven by shared predators) has been studied for more than 100 years in butterflies from the genus Heliconius because the almost perfect matching of color morphs between species highlights the power of natural selection as a deterministic evolutionary force. Although many lessons have been learned from this study system, many questions still remain; for example, it is still unclear how general the principles learnt from this system are or what role it plays on generating diversity. Here, a new mimicry system—the ground beetle genus Ceroglossus—is uncovered and studied to test some of these important questions. First, although the evolution of color matching between some species was clearly supported by data and simulation-based analyses (Chapter 2), the most remarkable characteristic is that the strength or degree of mimicry varies across regions. This finding may provide exceptional opportunities to study aspects of mimicry that cannot be analyzed in systems where mimicry is more accurate. For example, understanding the factors causing the variation of the degree of mimicry across space might shed light on how mimicry evolves or under what scenarios mimicry can be facilitated or impeded. Second, the diversity of intraspecific forms in this system is quantified and analyzed using recently developed species delimitation methods to understand the taxonomic diversity of the Genus (chapter 2). The results of this chapter highlight important issues and challenges of species delimitation methods, particularly when combined with large amounts of molecular data. For example, it was found that although phenotypic diversity suggested the potential for multiple species, current delimitation methods were not able to distinguish whether lineage diversity corresponded to population or species structure. These results are important because appropriately distinguishing taxonomic limits not only affect estimations of diversity, but also our understanding of important evolutionary processes and their role on mimicry and evolution more generally. Finally, in chapter 3, the evolutionary history of co-distributed species was studied and quantified to test coevolution, a long standing question in Müllerian mimicry research. Because Müllerian mimicry is considered a mutualistic process, it has been argued that Müllerian mimicry provides particularly good conditions for coevolution. The results showed high levels of phylogenetic congruence in agreement with the hypothesis of coevolution. However, the results also showed that the varying degrees of mimicry across regions did not affect the phylogenetic congruence, failing to support an association between mimicry and coevolution. This is the first time that the degree of mimicry is accounted for to understand these processes at a regional scale and the results suggest that the role of mimicry on speciation and diversification is complex and requires further investigation. The study of this system provides a window to deepen our understanding about the role of mimicry on generating patterns of diversity, but most importantly, its uniqueness in regards to the spatial variation in the strength of mimicry also provides a natural experiment to investigate a completely new set of questions about factors favoring or disfavoring the evolution of phenotypic convergence