Experimental and Population Genetic Evidence of Host Race Formation in a Specialized Lycaenid Butterfly
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Host-associated differentiation in phytophagous insects is an important mechanism of speciation. The current study investigates whether adaptation to different hosts drives population genetic divergence in the juniper hairstreak butterfly, Mitoura gryneus. Mitoura exhibit host plant fidelity, in which males lek and mating occurs on host trees. Female oviposition preference for the natal host, and differential fitness of larvae when reared on natal vs. alternate hosts, was examined to assess specialization. While some evidence of specialization was found, populations varied in their patterns of preference and performance, possibly reflecting differences in the timing and direction of colonization of hosts by Mitoura. Molecular genetic data were also examined to test the hypothesis that specialization on three alternate hosts restricts gene flow among different host-associated populations of Mitoura. Combined with the previous experimental results, mitochondrial DNA sequence and AFLP data indicate varying levels of differentiation among host associations, and identify a role for both isolation in allopatry as well as ecological factors in limiting gene exchange. The experimental assessment of specialization and host fidelity, along with population genetics analyses, provides strong support for the hypothesis of ongoing host race formation in these butterflies. The Mitoura species complex within North America includes multiple, differentiated lineages at varying stages of divergence, providing an opportunity to examine the multifarious mechanisms that generate biodiversity in phytophagous insects.