Population, Phylogenetic, and Coalescent Analyses of Character Evolution in Gossamer-Winged Butterflies (Lepidoptera: Lycaenidae)

Abstract

To understand the processes responsible for the diversity of life, one must consider evolutionary history. By incorporating a phylogenetic approach to studies of character evolution and species interactions, we may better understand the mechanisms governing this tangled bank. This work addresses fundamental questions regarding morphological and behavioral evolution, using gossamer-winged butterflies (Lepidoptera: Lycaenidae) as model systems.By investigating the pattern of genetic variation in a group of closely related species of copper butterflies (Lycaena), I show morphological divergence occurred in the absence of gene flow between Lycaena xanthoides and L. editha. Additionally, genetic divergence between populations of L. xanthoides has occurred without considerable morphological divergence. These findings highlight the utility of genetic data for inferring species boundaries and identification of cryptic lineages.Inferring evolutionary relationships among closely related species should benefit from multiple sources of information, e.g., unlinked genetic markers. Here I extend a method of reconstructing species relationships based on multiple reconstructed gene trees, using the number of incomplete lineage sorting events ('deep coalescences') as the objective function. This approach provides a more complete understanding of species' histories by accommodating population-level processes which may lead to discordance between gene genealogies and species phylogenies. The approach is evaluated with simulated and empirical data, and I discuss conditions which may result in misleading inferences.Finally, incorporating data from multiple gene trees, I investigate the evolution of association in a lycaenid-ant interaction. Lycaenid butterfly caterpillars are often involved in mutualisms with ant hosts: these larvae use volatile signals and provide carbohydrate rewards from the dorsal nectary organ (DNO) to associated ants to gain protection from natural enemies. However, larvae of some lycaenid species, such as L. xanthoides, do not possess the reward-producing organ, yet are still found in association with ants. Evaluating the relationship in a phylogenetic framework, I show that L. xanthoides likely evolved from a non-ant-associated ancestor. This suggests that L. xanthoides has 'cracked the code' that other, honest-signaling lycaenid larvae use to communicate to ants. Evolution of mutualisms between honest-signaling larvae and ants will likely be affected by the impact of illicit-signaling larvae.