Shifts in the distributional ranges of <Emphasis Type="Italic">Boophilus</Emphasis> ticks in Tanzania: evidence that a parapatric boundary between <Emphasis Type="Italic">Boophilus microplus</Emphasis> and <Emphasis Type="Italic">B. decoloratus</Emphasis> follows climate gradients |
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Authors: | Godelieve Lynen Petr Zeman Christine Bakuname Giuseppe Di Giulio Paul Mtui Paul Sanka Frans Jongejan |
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Institution: | (1) Ministry of Water and Livestock Development, Veterinary Investigation Centre, P.O. Box 1068, Arusha, Tanzania;(2) Vetagro Tanzania Ltd., P.O. Box 13188, Arusha, Tanzania;(3) Crop Research Institute, Drnovska 507, Prague-6, Czech Republic;(4) Utrecht Centre for Tick-borne Diseases, Department of Infectious Diseases and Immunology, Faculty of Veterinary Medicine, Utrecht University, Yalelaan 1, 3584CL Utrecht, The Netherlands;(5) Department of Veterinary Tropical Diseases, Faculty of Veterinary Science, University of Pretoria, Private Bag X04, Onderstepoort, 0110, South Africa |
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Abstract: | Based on a national tick survey conducted in Tanzania between 1998 and 2001, predictive maps of tick distribution for B. microplus and B. decoloratus were computed and compared with historical maps that originated about 40 years ago. The new data collected showed that except
for extremely cold and dry areas B. microplus has extended its distribution range and is now present in all the northern regions of Tanzania, and that high suitability
is currently recorded for most of the previously non-occupied areas. In contrast, B. decoloratus, once abundant in Tanzania, has largely retreated to highlands in north and central Tanzania and several other high-altitude
refuges. Geostatistical analysis revealed a dissimilar character of distribution for the two species at a local and regional
scale, as well as an antagonistic relationship between them in a spatial context. The Tanzania data suggest that an equilibrium
phase with a stable parapatric boundary that follows a climate gradient has been achieved. The zone of overlap in the distribution ranges of B. microplus and B. decoloratus is characterized by a decreased infestation rate as well as mutual exclusion on infested cattle. This finding matches studies
on parapatry with hybrid zones, where the latter zones that separate species tend to rest in density troughs. Analysis of
the Tanzania data shows that the critical factor for the advance of B. microplus and the retreat of B. decoloratus is associated with the 58 mm isohyet and the 22–23°C isotherm and indicates a well developed higher-temperature tolerance
for B. microplus. It can be anticipated that climate changes may enhance the spread of B. microplus and consequently Babesia bovis into new areas of the African continent. |
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Keywords: | Boophilus decoloratus B microplus Cattle ticks Parapatry Predictive modeling Tanzania |
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