|Lysyk, Timothy - AGRI AGRI-FOODS CANADA|
Submitted to: Journal of Medical Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 18, 2008
Publication Date: May 20, 2008
Citation: Lysyk, T.J., Scoles, G.A. 2008. Reproductive Compatibility of Prairie and Montane Populations of Dermacentor andersoni. Journal of Medical Entomology. 45(6):1064-1070. Interpretive Summary: In British Columbia (BC) feeding of the Rocky Mountain Wood ticks on cattle can lead to tick paralysis, this has resulted in significant losses for the Canadian cattle industry. Ticks from populations in Alberta (AB) do not cause paralysis. Because the ability of ticks to cause paralysis is a genetically determined trait it has been suggested that introduction of AB ticks into BC could reduce the paralyzing ability of the BC ticks. Population genetic analysis shows that the BC and AB tick populations are genetically distinct from one another. The data suggests that there is limited migration between the two populations and there is more genetic variation between the populations than within them. The AB population also had significantly more genetic diversity than the BC population. As a preliminary to further studies it is necessary to see if crosses between BC and AB ticks could produce fertile offspring. Field collected ticks from the two different populations were crossed (heterogeneous crosses) and compared to crosses within the same population (homogenous crosses). In the next generation the offspring from the parental crosses were crossed to confirm their fertility (progeny crosses). There was not much difference in reproductive success between the different crosses in the parental generation and these differences were not evident in the progeny crosses, confirming that there is very little reproductive incompatibility between these two tick populations. Even though there is very little migration between these two tick populations they continue to be reproductively compatible.
Technical Abstract: Genetic analysis of a prairie and a montane population of Dermacentor andersoni (Stiles) indicated limited gene flow (Nm < 1) and a large amount of genetic differentiation (Fst = 0.49) between the populations. The prairie population also had a greater level of genetic diversity. Mating experiments indicated that females of geographically heterogeneous crosses had similar engorgement and oviposition failure as homogenous crosses in the parental generation, but that egg mass sterility was greatest for the AB female x BC male cross, intermediate for the homogenous crosses, and lowest for the BC female x AB male cross. The progeny of all crosses produced fertile eggs, and the only significant effect in the progeny generation was increased oviposition failure of the pure AB cross. Covariate analysis indicated that egg mass sterility was associated with BC males in the parental generation and that oviposition failure was associated with AB males and AB females in the progeny generation. The hazard of cumulative reproductive failure was increased with AB females in both generations, reduced for AB males in the parental generation, and increased with AB males in the progeny generation. Overall, heterogenous crosses had the greatest and least reproductive failure in the parental generation, but were intermediate to the homogenous crosses in the progeny generation. The limited gene flow between the populations appears to have been sufficient to maintain reproductive compatibility.