Geography and Genetics of Ecological Speciation in Pea Aphids

During ecological speciation, divergent natural selection drives evolution of ecological specialization and genetic differentiation of populations on alternate environments. Populations diverging onto the same alternate environments may be geographically widespread, so that divergence may occur at an array of locations simultaneously. Spatial variation in the process of divergence may produce a pattern of differences in divergence among locations called the Geographic Mosaic of Divergence. Diverging populations may vary in their degree of genetic differentiation and ecological specialization among locations. My dissertation examines the pattern and evolutionary processes of divergence in pea aphids (Acyrthosiphon pisum) on alfalfa (Medicago sativa) and clover (Trifolium pretense). In Chapter One, I examined differences among North American aphid populations in genetic differentiation at nuclear, sequence-based markers and in ecological specialization, measured as aphid fecundity on each host plant. In the East, aphids showed high host-plant associated ecological specialization and high genetic differentiation. In the West, aphids from clover were genetically indistinguishable from aphids on alfalfa, and aphids from clover were less specialized. Thus, the pattern of divergence differed among locations, suggesting a Geographic Mosaic of Divergence. In Chapter Two, I examined genomic heterogeneity in divergence in aphids on alfalfa and clover across North America using amplified fragment length polymorphisms (AFLPs). The degree of genetic differentiation varied greatly among markers, suggesting that divergent natural selection drives aphid divergence in all geographic locations. Three of the same genetic markers were identified as evolving under divergent selection in the eastern and western regions, and additional divergent markers were identified in the East. In Chapter Three, I investigated population structure of aphids in North America, France, and Sweden using AFLPs. Aphids on the same host plant were genetically similar across many parts of their range, so the evolution of host plant specialization does not appear to have occurred independently in every location. While aphids on alfalfa and clover were genetically differentiated in most locations, aphids from alfalfa and clover were genetically similar in both western North America and Sweden. High gene flow from alfalfa onto clover may constrain divergence in these locations.

PHILIPPE ROGIER (c.1561-1596): MISSA INCLITA STIRPS JESSE. A CRITICAL AND PERFORMING EDITION WITH PERFORMANCE COMMENTARY

The dissertation comprises two parts: (a) a musical edition and (b) a performance given on 3 July, 2008 of Philippe Rogier’s Missa Inclita stirps Jesse. The dissertation explores some of the editorial decisions required, how the demands of performers and musicologists differ, and whether they can be reconciled in one single edition. The commentary explains the preparation and realization of the edition. A video recording of the concert performance is attached to the dissertation. The Mass: The Missa Inclita stirps Jesse was published in Madrid in 1598 in a collection entitled Missae Sex. The mass setting is for four voices, except the Agnus Dei, which is for five, and is based on musical material in the motet Inclita stirps Jesse by Jacobus Clemens non Papa (c. 1510-15 – c.1556-6). Rogier’s choice and use of musical material from the motet (published in 1549) are discussed in the dissertation. The Edition: The edition is made from a microfilm copy of the Missae Sex held in the Biblioteca del Conservatorio de Musica “Giuseppe Verdi” in Milan. The Missae Sex was originally dedicated to King Philip II of Spain (1527-1598, reg. 1556-1598), whom Rogier had served as chorister and then maestro de capilla. Both Rogier and King Philip died before the volume was ready for publication. One of Rogier’s pupils, Géry de Ghersem, prepared the volume, which was printed in 1598, dedicated to King Philip III. The Performance: The mass was performed at a concert of Spanish Renaissance music in St. Matthew’s Cathedral, Washington, DC, on 3 July 2008, sung by the ensemble Orpheus directed by Philip Cave as part of the Chorworks summer workshop entitled Kings and Conquistadors: Music of Old and New Spain.