Genetic Variation in Two Populations of the Brown Ear Tick, Rhipicephalus Appendiculatus, in Kenya

Abstract

Several studies have shown that Rhipicephalus appendiculatus from geographically isolated areas differ in their susceptibilities to Theileria parva, the haemoprotozoan causative agent of East Coast Fever. In Kenya, R appendiculatus from Muguga have been reported to be less susceptible to T. parva infection than those from Rusinga Islands. As the same tick species from different areas shows variation in vector competence, it was considered to be of epidemiological interest to determine whether these tick populations are genetically different. Most population genetic studies have been done by comparing protein electrophoretic patterns, and more recently by DNA analysis However, all available techniques have limitations. It is therefore not advisable to rely on only one technique. In this study, two-dimensional protein electrophoresis and random amplified polymorphic DNA Polymerase chain reaction were used to compare two R appendiculatus populations from Muguga and Rusinga, in Kenya. Most proteins were common to both populations. However, some proteins were population-specific. Two proteins (M-14.4-19,000), one protein (M-26,000) and two proteins (M-47-50,000), were specific to the Muguga population. On the other hand, three proteins (M-14,000), one protein (M-22,000), one protein (M-29,000), one protein (M-41,000), and three proteins (M-45-48,000), were specific to the Rusinga population. Homologous proteins are probably species-specific. In the RAPD technique, both pooled and individual tick DNA samples were analysed. Five different primers were used. In the pooled DNA, each primer gave some population-specific bands. However, individual DNA samples showed considerable band variation among individuals within each population. The genetic distance between the two populations averaged 0.047. This implies that these populations are closely related, sharing about 95% of their genes. The presence of population-specific proteins and DNA fragments, together with a genetic distance greater than zero suggests that genetic differences exist between the two populations. The observed differences may not be directly linked to a particular phenotype. Nevertheless, it is possible that the differences in the vectorial capacities of these populations may be accounted for by genetic factors. However, further studies will be required to confirm this.