Question

Deer are hosts of ticks but are not reservoirs of \(B\). burgdorferitheir immune systems detect and kill the bacterium. But a tick with a prior bacterial infection can consume a blood meal from a deer and then bite and infect a human. The fitness effects of a deer on \(B\). burgdorferi can be summarized as: a. \(+\) because the deer supplies the bacterium with food. b. - because the deer kills the bacteria in its blood. c. \(+\) because the deer feeds and disperses the tick that can then infect a human with the bacterium. d. \(-\) or \(+\) depending on whether the deer is the tick's last host.

Short answer

In summary, the fitness effects of a deer on B. burgdorferi are: (a) positive (+) as the deer provides food for the tick; (b) negative (-) because the deer's immune system kills the bacterium; (c) positive (+) as the deer promotes tick dispersal and human infection; and (d) depending on whether the deer is the tick's last host, the effect could be negative (-) or positive (+).

Step-by-step solution

List out the different fitness effects.

The different fitness effects of a deer on B. burgdorferi are: a. + because the deer supplies the bacterium with food. b. - because the deer kills the bacteria in its blood. c. + because the deer feeds and disperses the tick that can then infect a human with the bacterium. d. - or + depending on whether the deer is the tick's last host.

Determine the fitness effect for each scenario.

Now, let's analyze each effect and evaluate if it's positive (+) or negative (-) for the bacterium B. burgdorferi. a. The fitness effect is positive (+) in this case because the deer supplies the tick (which can carry the bacterium) with blood as a food source. With this nourishment, the tick can continue spreading the bacterium to other hosts, such as humans. b. The fitness effect is negative (-) in this case because the deer's immune system can detect and kill the bacterium present in its blood, thereby preventing the transmission of B. burgdorferi to other organisms through the deer's bloodstream. c. The fitness effect in this scenario is positive (+), considering that the deer provides sustenance (blood meal) to the ticks, which, in turn, aids their dispersal and increases the chances of B. burgdorferi infection being passed to a human host. d. The fitness effect depends on whether the deer is the tick's last host in the life cycle. If the deer is the last host and the bacterium is unable to further infect a human host due to the deer's immune system, then the fitness effect is negative (-) considering that deer eliminated the bacterium. If the deer is not the tick's last host and the tick can still infect a human host, then the fitness effect is positive (+), as the deer indirectly helped spread the bacterium to a susceptible human.

Summary of fitness effects on B. burgdorferi.

Thus, we have deduced the fitness effects on B. burgdorferi from the four given scenarios: a. Positive effect (+) because deer provides food for the tick. b. Negative effect (-) because deer's immune system kills the bacterium. c. Positive effect (+) because deer promotes tick dispersal and human infection. d. Depends on whether the deer is the tick's last host, it could be negative (-) or positive (+).

Key concepts

Deer as Host

In the ecological web of life, deer play a critical role as hosts for ticks, which are vectors for various pathogens, including the bacterium Borrelia burgdorferi. However, deer are not reservoirs for B. burgdorferi because their immune system efficiently eradicates the bacterium from their bloodstream. Instead, deer serve as a feeding ground for ticks, providing a crucial blood meal. This feeding allows ticks to flourish, and move onto the next stage of their life cycle.

With ticks being well-nourished, they can continue to thrive and spread once they detach from their deer hosts. While deer cannot directly transmit B. burgdorferi to humans, they help in sustaining tick populations. This, in turn, facilitates ticks carrying the bacteria onto new hosts, potentially including humans.

Ticks as Vectors

Ticks function as the primary vectors in the transmission of B. burgdorferi. They acquire the bacterium usually during their larval or nymphal life stages, often from small mammals. Once infected, ticks carry the bacterium throughout their lifecycle stages.

Ticks are capable of transmitting the bacterium to new hosts as they feed. After feeding on a deer, ticks can detach and later attach to humans or other animals, potentially transmitting B. burgdorferi.

• Deer blood meals enable ticks to develop and expand their range.
• Upon subsequent host encounters, these ticks can pass on the bacterium.

In their role as vectors, ticks are essential in maintaining the circulation of B. burgdorferi in the ecosystem, highlighting the indirect role that deer play in this process through sustaining vector populations.

Bacterial Transmission

The process of bacterial transmission involves the movement of B. burgdorferi from ticks to other suitable hosts like humans. Ticks infected with the bacterium can pass it during the act of biting and feeding. As ticks feed, they release B. burgdorferi into the host's bloodstream, where it can cause Lyme disease.

Transmission does not happen immediately, which is why prompt tick removal can reduce the risk of infection. However, once established in a new host, the bacterium can proliferate and cause various symptoms.

• Hosts must be bitten by an infected tick for transmission to occur.
• Ticks must feed for a certain amount of time before the bacterium is passed.

In this way, the transmission of B. burgdorferi is a complex interaction between vector, host, and pathogen.

Fitness Effects on Bacteria

The interaction between deer, ticks, and B. burgdorferi can have varied fitness effects on the bacterium. The survival, reproduction, and dissemination of B. burgdorferi can be positively or negatively impacted, depending on the context:

- **Positive Effects:** When ticks feed on deer, they acquire necessary nutrients, supporting lifecycle completion. This can help B. burgdorferi persist in the ecosystem as ticks progress to stages that can infect humans.

• Providing food to ticks enhances their fitness and survival.
• Ticks then have more opportunities to spread the bacterium.

- **Negative Effects:** Deer kill the bacteria within their own systems, which cuts off one potential route of transmission. If the tick's last host is a deer, and it does not move onto another host, the bacterium might not reach a human or another suitable host.

Ultimately, while deer do not serve as reservoirs for B. burgdorferi, they contribute to the epidemiological cycle by supporting tick populations that continue to propagate the bacterium.