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Title:Hiding in plain sight: unveiling cryptic diversity and patterns in bumble bees
Author(s):Duennes, Michelle A.
Director of Research:Cameron, Sydney A
Doctoral Committee Chair(s):Cameron, Sydney A
Doctoral Committee Member(s):Cheviron, Zachary; Johnson, Kevin; Malhi, Ripan; Rapti, Zoi
Department / Program:Entomology
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):bumble bees
population genetics
color pattern
Abstract:Bumble bee research has a rich history that spans more than three centuries. The distributions and the vibrant color patterns of nearly all species of bumble bees are well mapped and described. In addition, the natural history, colony structure and social behavior of bumble bees are well documented and a well-supported phylogeny of the ~250 species currently recognized within the genus has been constructed. Yet despite the breadth of research that has been conducted on bumble bees, there is still much that is unknown about this charismatic group of social insects. My dissertation focuses on three areas: phylogenetics, population genetics and evolutionary development. In Chapter One I explore the population genetics of the Bombus ephippiatus-Bombus wilmattae species group. The color pattern diversity within this group across a variety of habitats in Mexico and Central America has brought their taxonomic status into question for over 150 years. To resolve the uncertain species status of this group, I collected extensive genetic data from twelve microsatellite loci and a fragment of the cytochrome oxidase I gene to conduct an in-depth population genetic and phylogenetic study of the group across its widespread distribution. I also explore the use of wing geometric morphometrics to delineate species within this taxon. This group exhibits extensive genetic structure across its range, with major barriers to gene flow at the Isthmus of Tehuantepec in southern Mexico and the Nicaraguan Depression in southern Nicaragua. Wing morphometric data support these genetic divisions within the species complex. The differences in wing shape are not sufficiently divergent to be useful as species diagnostic characters, but they provide another line of evidence to support species boundaries. These extensive genetic and morphometric data provide a wealth of evidence for revising the taxonomic status of the B. ephippiatus-B. wilmattae complex. In Chapter Two, I describe two genetically distinct, sympatric species with limited gene flow in Mexico south of the Isthmus of Tehuantepec through Honduras. I revise the species B. wilmattae within this region to include previously unknown queen and worker polymorphisms and describe a new species sympatric with B. wilmattae, B. maya sp. nov. I recognize a single species in Mexico north of the Isthmus of Tehuantepec, with extensive population structure corresponding to the four main mountain ranges of the Mexican highlands. I consider the species B. ephippiatus to extend only from northwest Mexico to the southern state of Oaxaca, just north of the Isthmus of Tehuantepec. There is also a distinct species in Costa Rica, to which I assign the resurrected name B. schneideri. In Chapter Three, I explore trends in variation among the color patterns of Bombus worldwide. The white, yellow, orange, and black contrasting stripes of color on bumble bees have long served as classic examples of aposematic coloration and their convergence upon common patterns across their extensive distribution has served as a classic example of Müllerian mimicry. Yet nothing is known about the developmental regulation of these color patterns. As a first step in exploring the developmental regulation of color, I mapped the color patterns across the body of individual species with high resolution using a grid map. My collaborators and I use this system to look for common elements of pattern across ~95% of the known species of bumble bees. This novel method revealed twelve primary pattern elements across the dorsal thorax and abdomen, with six on the thorax and six on the abdomen. It also revealed five smaller secondary pattern elements that lie medially and laterally on the abdomen. With the exception of three elements on the scutum, these primary elements correspond to segmental boundaries across the body, which suggests that the developmental regulation of color pattern might involve Hox genes, the same genes that control the development of segmental boundaries early in development. This meticulous exploration of color pattern also revealed common trends in the occurrence of certain colors across the body. Black hairs occur in the center of the thorax in up to 77% of the species included in the analysis, and yellow hairs are found predominantly anteriorly and posteriorly along the edges of the thorax and the first two segments of the abdomen. Orange hairs predominate throughout the last segments of the abdomen. The differential patterns of color expression across species suggest that certain colors occur in specific positions on the body to maximize contrast and aposematic signal to predators. My study of the genotypic and phenotypic diversity of the B. ephippiatus-B. wilmattae species group and investigation of the core elements of pattern responsible for generating the diversity of color patterns across Bombus worldwide explore historically well-characterized systems, providing novel insights into long-standing questions within each system using new methods and approaches.
Issue Date:2015-11-30
Rights Information:Copyright 2015 Michelle Duennes
Date Available in IDEALS:2016-03-02
Date Deposited:2015-12

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