A Study of the Effects of Parasites on Their Host, a Study Performed by Le Khoklova Etal and Giorgi Etal

Diseases can come from a variety of places - bacteria, viruses, and parasites to name a few, all which can affect metabolic rates in animals. Khokhlova etal, conducted an experiment where they infected indiviudal gerbils (Gerbillus dasyurus) with 50 fleas (Xenopsylla ramesis) per gerbil, and varied how much food they were given (85%, 100%, 115% of food needed for maintenance). Each day they took the body masses of the gerbils and calculated dry matter digestibility and metabolizable energy intake. At the end, the researchers calculated how much blood the fleas drank, and concluded that there was very little parasitic pressure because they only drank .17% of the gerbil's blood. They also concluded that parasitized gerbils have higher energy expenditures than non-parasitized because only the parasitized gerbils fed 115% of energy requirements maintained body weight, while the non-parasitized gerbils fed 115% and 100% of energy requirements maintained body weight. Lastly, the efficiency of utilization of metabolizable energy was the same in both groups, using the body mass change and food intake data. In alignment with this finding, an experiment was conducted by Giorgi etal to observe the effect of mites (Spinturnix myoti) on bats (Myotis myotis).

The researchers put bats in a solitary box without food or water for 24 hours 3 separate times, with varying numbers of mites (0, 20, or 40), and monitored their behavior (they were cleaned after each 24 hour period). They saw that with 40 mites bats increased the amount of time spent grooming, decreased the amount of time resting, and thus increased oxygen consumption when compared to individuals w/ 20 mites and no mites. With 20 mites, there was a similar trend when compared to no mites on the bat, sa but was not as strong a bat with 40 mites. In contrast to these, an experiment by Simon etal was run on Blue tit chicks, where some nested with parasites and others were protected from them. Despite increased motion and decreased rest with parasites, their CO2 consumption data showed no increase in metabolic rate.

When analyzing the findings of these articles, only 2 of the 3 came to the same conclusion, and through different means. The experiment with gerbils and fleas used blood consumed, food consumed, and body mass change to determine the effect, whereas the bat experiment used a combination of behavioral patterns and monitoring oxygen levels with an open-air respirometer. This method seems the most reliable because they used an actual respirometer, which gives the most accurate results for oxygen consumption and metabolism, as opposed to food intake and body mass change in the gerbil experiment. This is less accurate in that it is not a direct measurement of metabolism, whereas oxygen consumption is.

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This is why I find the bat experiment more convincing. The results of the last experiment disagreed with the prior two results in that they showed parasitism had no effect on the metabolism of the animal; however, for reasons unknown as it had very similar results to the bat experiment (increased movement and decreased rest). It may have been due to parasites affecting the growth of the chicks, or the parasites decreasing the body temperature of the chicks causing less oxygen consumption. This article was also dealing with a much different scenario - baby birds that are trying to grow at a furious rate, while the other experiments used sub adult bats and adult gerbils (individuals that are developing much more slowly). Furthermore, the data collected was not based on a specified individual; 2 chicks were taken at random to do tests everyday. In the other two experiments, data was collected from each individual, not at random.. I agree with all the authors' conclusions, although I believe that with changes to the blue tit experiment, such as adjusting the protected nesting, they will find results that are more similar to those of the other experiments.

The findings of Le Khoklova etal and Giorgi etal (Simon etal exsperiment was inconclusive and needed further testing) that showed that parasites have negative affects on the host have many ecological implications, such as decreasing a population's ability to fight off disease, deal with drought/food shortages, or other challenges that may arise. When challenges arise, an individual must allocate energy to properly face it; however, there are tradeoffs when this arises -- the principle of allocation. For example, if there was a disease going around a population, the individuals will allocate more energy to their immune system, but in doing so weaken themselves in other aspects. This is where parasites could have a major impact on the population because the individuals are now more susceptible to their affects. In bats, parasites could hurt their ability to hunt or have energy for activities by heightening loss of energy the parasites already cause.

This in turn lowers their survival rate- increased risk to predation, loss of body mass due to less food acquisition, and risk of dying from the disease. The last one is probably the biggest danger - there is just not enough energy to allocate to all the challenges an individual is facing and the disease gets the better of it. Also, the findings in this research imply that parasitism could have an impact on things such as the food chain and trophic levels. If the parasite's effects on the animals increase with infection, the host's survival rate will decrease based off being less fit after infection (decreased ability to avoid predation/obtain food for example), leading to a drop in population. Consequently this leads to change in the trophic levels, as the host's prey/vegetation increases rapidly with less predatory pressure, and the host's predators decrease or adjust their hunting habits to shift with the changing demographics, creating an entirely different ecosystem.

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