Hybrid affinities between the green and the red forms of the two-spotted spider mite Tetranychus urticae (Acari: Tetranychidae) under laboratory and semi-natural conditions
2002
Sugasawa, J. (Ibaraki Univ., Ami (Japan). Faculty of Agriculture) | Kitashima, Y. | Gotoh, T.
The systematic status of the green and the red forms of Tetranychus urticae Koch is still unresolved because the ability of the two forms to interbreed varies considerably depending on the populations used. First, to investigate the hybrid fertility between the two forms in the laboratory, we interbred them for five generations. The hybrids produced showed relatively lower fitness (lower hatchability, lower proportion of female adults and lower production of fertile offspring) than their parents, and in some crossings, no female offspring emerged. Second, we used phosphoglucoisomerase (PGI) allozymes as genetic markers to analyze the temporal changes in hybridization of the two forms under semi-natural conditions. The temporal changes of hybridization were analyzed by the F-statistic. Intra-form mating was initially predominant, but as the number of damaged leaves increased, inter-form mating increased because the mites dispersed more frequently. However, as the fitness of hybrids from inter-form mating was much lower than that from intra-form mating, most hybrids were unable to produce offspring or had become extinct on the rose leaves. Thus, the gene flow between the two forms appears to be extremely restricted, indicating that a strong genetic differentiation is present between the two forms.
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