Genetic evidence for host race formation in the leafmining fly, Phytomyza glabricola (Diptera: Agromyzidae)

Phytophagous insects are extremely diverse, and one major factor contributing to this diversity involves changes in host use. Host races, populations of a species found on different hosts with limited gene flow between them, are often studied to determine the underlying mechanisms for speciation, and therefore diversity in insect lineages. This study examines potential host race formation in Phytomyza glabricola, a leafmining fly native to eastern North America that feeds on two native species of holly, Ilex glabra and I. coriacea. In order to determine genetic divergence within and between populations, the conserved developmental gene elongation factor 1 alpha (EF1α) was sequenced in flies from available hosts in seven locations across their range. Significant genetic differences were found between populations of flies from different hosts at all locations where both hosts occurred. However there were several shared alleles, found only as heterozygotes, indicating limited gene flow. These results support the observation that P. glabricola consists of host races. The degree of genetic differences between host races also varied among populations from different locations. This suggests locations may differ in the rates of gene flow between races, indicating a geographic mosaic of genetic divergence in these flies.