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Geography and genetics of ecological speciation in pea aphids.

機譯：豌豆蚜蟲生態(tài)形成的地理和遺傳學(xué)。

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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.
機譯：在生態(tài)物種形成過程中，不同的自然選擇驅(qū)動著生態(tài)專業(yè)化的發(fā)展以及不同環(huán)境下種群的遺傳分化。散布到相同替代環(huán)境上的種群可能在地理上分布廣泛，因此散布可能同時發(fā)生在一系列位置上。發(fā)散過程中的空間變化可能會在稱為“發(fā)散地理馬賽克”的位置之間產(chǎn)生發(fā)散差異的模式。不同地區(qū)之間的種群遺傳分化程度和生態(tài)專業(yè)化程度可能有所不同。本論文研究了苜蓿（苜蓿）和三葉草（Trifolium pretense）上豌豆蚜蟲（Acyrthosiphon pisum）發(fā)散的格局和進化過程。標(biāo)記和生態(tài)專業(yè)化程度，以每種寄主植物上的蚜蟲繁殖力來衡量。在東部，蚜蟲表現(xiàn)出高度的寄主植物相關(guān)生態(tài)專業(yè)性和高度的遺傳分化。在西方，三葉草的蚜蟲與苜蓿的蚜蟲在遺傳上沒有區(qū)別，三葉草的蚜蟲的專業(yè)性較差。因此，不同地區(qū)之間的發(fā)散模式不同，這暗示了地理上的發(fā)散。在第二章中，我使用擴增片段長度多態(tài)性（AFLP）研究了苜蓿和三葉草上北美蚜蟲發(fā)散的基因組異質(zhì)性。標(biāo)記之間的遺傳分化程度差異很大，表明不同的自然選擇推動了所有地理位置的蚜蟲分化。在東部和西部地區(qū)，三個相同的遺傳標(biāo)記被確定為在進化選擇下進化，而在東部則確定了其他的遺傳標(biāo)記。在第三章中，我使用以下方法調(diào)查了北美，法國和瑞典的蚜蟲種群結(jié)構(gòu)。 AFLP。同一寄主植物上的蚜蟲在其范圍的許多部分在遺傳上相似，因此寄主植物專化的發(fā)展似乎并非在每個位置都獨立發(fā)生。苜蓿和三葉草上的蚜蟲在大多數(shù)地方都有遺傳分化，而北美西部和瑞典的苜蓿和三葉草上的蚜蟲在遺傳上相似。從苜蓿到三葉草的高基因流量可能會限制這些位置的差異。

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