HOST-PLANT ASSOCIATIONS IN THE SPIDER-MITE TETRANYCHUS-URTICAE (ACARI, TETRANYCHIDAE) - INSIGHTS FROM MOLECULAR PHYLOGEOGRAPHY

This article integrates studies on the genetic variation of T. urticae populations and the interspecific variation of several tetranychid sp ecies. It aims at obtaining insights into the roles of the historical, geographical and ecological factors in the partitioning of variation of species. Two types of molecular markers were used to determine whet her the patterns of genetic variation in mites inhabiting different ho st plants can shed light on the existence of host plant associations. The ribosomal sequences of the second internal transcribed spacer (ITS 2), which evolves through concerted evolution, are good indicators of long-term isolation between populations and reveal exceptional homogen eity in a worldwide sampling of T. urticae. The mitochondrial cytochro me oxidase I (COI) sequences do not disclose old divergences related t o host plant in this mite but rather suggest recent geographic coloniz ation patterns of the species. Allozyme variation on a fine scale give s some evidence of host associations in the case of citrus trees. Howe ver, if any divergence of mites related to this host plant exists, it probably prevails in local populations only and it should not be old e nough to be revealed by a phylogenetic analysis of mitochondrial COI s equences. The phyletic constraint in the evolution of feeding specific ity in the family Tetranychidae is investigated based on a phylogeneti c analysis of mitochondrial sequences. The results provide some suppor t for the hypothesis that an evolutionary trend towards polyphagy has occurred in the family. Overall, it seems that the major characteristi c of T. urticae is its high colonization potential. Polyphagy has enha nced its successful spread and may have led to connectivity between po pulations worldwide. (C) 1998 Chapman & Hall Ltd.