Browsing by Subject "Attini"
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Item Diversity and evolution of reproductive systems in Mycocepurus fungus-growing ants(2010-05) Rabeling, Christian; Mueller, Ulrich G.; Hillis, David M.; Bolnick, Daniel I.; Schultz, Theodore R.; Singer, Michael C.The general prevalence of sexual reproduction over asexual reproduction among metazoans testifies to the evolutionary, long-term benefits of genetic recombination. Despite the benefits of genetic recombination under sexual reproduction, asexual organisms sporadically occur throughout the tree of life, and a few asexual lineages persisted over significant evolutionary time without apparent recombination. The study of asexual organisms therefore may provide clues to answer why almost all eukaryotes reproduce via meiosis and syngamy and why asexual eukaryotes are almost always evolutionarily short-lived. Towards understanding the evolution of asexual lineages in the Hymenoptera, I first review the diversity of reproductive systems in the Hymenoptera, introduce the study organism, the fungus-gardening ant Mycocepurus smithii, and discuss my research objectives. Second, I integrate information from reproductive physiology, reproductive morphology, natural history and behavior, to document that that queens of M. smithii are capable of thelytokous parthenogenesis, workers are sterile, and males are absent from the surveyed population. These results suggest that M. smithii might be obligately asexual. To place the origin and maintenance of asexual reproduction in M. smithii in an evolutionary context, I use molecular phylogenetic and population-genetic methods to (i) test if M. smithii reproduces asexually throughout its distribution range; (ii) infer if asexuality evolved once or multiple times; (iii) date the origin of asexual reproduction in M. smithii; and (iv) elucidate the cytogenetic mechanism of thelytokous parthenogenesis. During field collecting for these studies throughout the Neotropics, I discovered a new species of obligate social parasite in the genus Mycocepurus. Social parasites are of great interest to evolutionary biology in order to elucidate mechanisms demonstrating how parasites gained reproductive isolation from their host species in sympatry. I describe this new parasite species, characterize its morphological and behavioral adaptations to the parasitic lifestyle, and discuss the parasite’s life history evolution in the context of social parasitism in fungus-growing ants. The dissertation research integrates population-genetic, phylogenetic, physiological and morphological approaches to advance our understanding of the evolution of reproductive systems and diversity of life-history traits in animals.Item Embryogenesis, trophic eggs, and early colony growth of myrmicine ants(2019-05-08) Fang, Chi-Chun; Mueller, Ulrich G.; Gilbert, Lawrence E; Hofmann, Johann A; Stein, David S; Wild, Alexander LMyrmicinae is the largest subfamily of ants (Formicidae, Hymenoptera) that encompass a great diversity of morphology, behavior, and life-histories. As model systems, ants have been used to address mainly questions of social cooperation, division of labor, and reproductive conflict, but little research has been accomplished to date on embryonic development of ants. In Chapter 1, I provide a brief summary of the current understanding of embryogenesis in insects, and specifically embryogenesis of ants. In Chapter 2, I use histology to characterize the embryonic development series of three myrmicine ant species, Atta texana and Mycocepurus smithii (both fungus-gardening ants), as well as Solenopsis invicta (red imported fire ant). These detailed developmental series of ant embryogenesis will be a foundation for future gene-regulatory studies of caste determination. I further study the gene expression patterns of two genes (wingless and engrailed) in A. texana, and I demonstrate that ants possess a mosaic embryogenesis combining features of both short and long germ-band development, which is different from the conventional long germ-band type development exhibited by the hymenopteran species Apis and Nasonia. In Chapter 3, I elucidate factors that optimize colony fitness during the early nest-founding stage of the fungus-gardening ant M. smithii, a species that typically founds nests by single queens (monogyny), but mature nests have multiple queens (polygyny). By varying the queen-to-worker ratio in small experimental colonies set up with a standardized fungus-garden biomass, I identify factors contributing to colony fitness and gyne reproduction in M. smithii. In Chapter 4, I describe the discovery of a third kind of egg laid by A. texana foundresses in addition to reproductive and trophic eggs, and I report the first observation of nanitic males in A. texana that were killed by the foundress queen shortly after the males' eclosion. This dissertation investigates embryogenesis of three myrmicine ant species, the survival strategies of M. smithii, and a so-far undescribed type of trophic egg laid by A. texana foundresses. Ants represent a unique lineage with independently evolved developmental patterns that will contribute to future comparative studies of embryogenesis among social insects.