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Title:A snapshot of color: Exploring the ecological and genetic basis of color variation in the Neotropical tortoise beetle, Chelymorpha alternans (chrysomelidae:cassidinae)
Author(s):Strickland, Lynette Renae
Director of Research:Caceres, Carla E
Doctoral Committee Chair(s):Caceres, Carla E
Doctoral Committee Member(s):Fuller, Rebecca C; Catchen, Julian; Windsor, Donald
Department / Program:Evolution Ecology Behavior
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):color polymorphisms, intraspecific variation, tropical ecology
Abstract:In our pursuit to understand how life’s diversity is shaped and maintained, color polymorphisms serve as a powerful tool to connect phenotypic variation with the ecological processes that influence them and the genomic factors that maintain them. My dissertation focuses on a polymorphic species within a unique and striking subfamily, Cassidinae (tortoise beetles), found predominately in the Neotropics. For my dissertation, I addressed the following questions in the Panamanian tortoise beetle, 1) What is the geographic distribution of the Neotropical tortoise beetle, Chelymorpha alternans, across the Isthmus of Panama? 2) What is the inheritance hierarchy of alleles for color polymorphisms in Chelymorpha alternans? 3) Do mating preferences for particular color morphs influence the maintenance of color polymorphisms in C. alternans? 4) Do differences in fecundity or offspring survival differ as a function of parental color morph? 5) Does differential predation contribute to the maintenance of this polymorphism and do differences in cuticular hydrocarbon profiles (which might influence predator choice) contribute to the maintenance of these polymorphisms? To address these questions, I performed a series of crossing and fertility studies combined with sexual selection and predator bioassays. I performed more than 100 controlled crosses between all phenotypes, producing over 10,000 offspring, and tracked these offspring to adulthood to understand the relationship between parent phenotypes and offspring phenotypic ratios. These reveal that C. alternans consists of five genetically inherited color pattern variants which segregate by classic Mendelian ratios. A RAD-sequencing study of 30 individuals from a single population show that color morphs do not cluster separately based on population pairwise FST estimates of 4464 loci, suggesting that individuals have a high degree of admixture in natural populations. I then performed a series of mate-choice bioassays to assess whether phenotypes exhibit preferential mating and found that individuals show no preference and will mate randomly among all phenotypes. However, an analysis of offspring development revealed that offspring produced by parents with different phenotypes have higher survivorship compared with those produced from parents of the same phenotype. Predator bioassays reveal that phenotypes do experience different levels of predation and elicit learned avoidance patterns in some predators. This, along with their highly specialized herbivorous diet, suggests that the bright coloration (combinations of red coloration, metallic stripes, and black stripes) in this species serves as an aposematic signal to deter predation. Next, I performed a study to investigate the chemical profiles of different phenotypes using Gas Chromatography/ Mass-Spectroscopy. I found that different color morphs cluster separately based on cuticular hydrocarbon profiles, suggesting that they may differ in their ability to sequester plant secondary compounds, potentially explaining the observed differences in predator response toward different phenotypes.
Issue Date:2020-05-26
Rights Information:Copyright 2020 Lynette Strickland
Date Available in IDEALS:2020-10-07
Date Deposited:2020-08

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