Influence of geographical locations on morphological and genetic structure of Tetranychus urticae Koch (Acari : Tetranychidae) populations
(2004)
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- Authors
- Supervisors
- Hance, Thierry
- Abstract
- The species distribution at the Earth surface is affected by environmental conditions such as climate and other ecological factors that vary in space and time. In this context, global change and, particularly, temperature can affect species abundance and distribution. For instance, different studies reported the risk of possible increases in abundance of herbivorous arthropods. In the same way, geographic distribution may be affected and Northern expansion of some species is observed or predicted in Europe. This thesis concerns the study of the population structure of a highly mobile species, Tetranychus urticae, a cosmopolite and phytophagous mite for which new infestation and damage to uncommon host plants were recorded in Europe. The new infestations showed a Northwards spreading suggesting a range expansion of some Southern mites towards Northern areas. The aim is to test this hypothesis of changes in geographical distribution by analysis the morphological and genetic structure of European populations. The first step was to analyse one morphological character, the shape of cuticular lobes, in relation with geographic locations of the samplings to obtain information on mite dispersal capacities and on mite origins in Europe. However, a great variability was found in the shape of lobes. Therefore, no link with mite sampling origins could be established. We concluded that the shape of lobes is not a reliable character in taxonomy even if it is still used in some studies. The aim of the second step was to analyse the genetic structure of mite populations using different molecular markers, to determine genetic distances between populations in relation with geographical distances. A South-North European transect revealed a differentiation linked with geographical distances, this pattern do not support the hypothesis of range expansion of mites from Southern areas except if during migration, barriers to gene flow have led to the observed differentiation. In the case of this South-North transect, temperature gradient could have influenced gene flow. To test this hypothesis, mites samples were analyzed along a second transect (West-East), more stable concerning mean annual temperature. The absence of differentiation with distance along this transect suggests a high migratory capacity of this mite. Gene flow influenced by global climatic conditions and local environment. In conclusion, the two-spotted spider mite Tetranychus urticae Koch is a very variable species with high dispersal abilities. Climate and environment probably affect gene flow between populations, increasing differentiation. These results should help in detailed analyses of the relation between expansions and global change and lead to monitor the future risk of outbreaks. ...
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Citations
Carbonnelle, S. (2004). Influence of geographical locations on morphological and genetic structure of Tetranychus urticae Koch (Acari : Tetranychidae) populations. https://hdl.handle.net/2078.5/97969