Answer
option (d) is the correct answer, i.e. – or + depending on whether the deer is the tick’s last host. The fitness effect of deer on B. burgdorferi depends on whether the deer is its last host. The fitness effect can be –, resulting in the lower fitness of ticks, or +, in which the relationship of ticks with deer provides benefit to the ticks for survival and growth.
Work Step by Step
The deer are hosts of ticks, which are the carriers of B. burgdorferi bacterium which causes Lyme disease. The immune system of deer detects B. burgdorferi and kills it. Thus, the deer are not the reservoirs of B. burgdorferi. Therefore, the fitness effect of deer on B. burgdorferi, in this case, is –, as the interaction of B. burgdorferi with deer results in the cost of B. burgdorferi’s life.
When the tick is infected with B. burgdorferi prior to living as a parasite on the deer, B. burgdorferi survives and is not killed by the deer’s immune system. In this case, as the deer is not the first host of the ticks, the fitness effect of a deer on B. burgdorferi is +. So, option (d) is correct.
