Kequan Chen
“Mars mouse”, the new creature we just discovered on Mars recently, is being a very popular topic now. But we barely know anything about them. In this protocol, we will firstly deduce the basic features regarding this creature based on the limited information we collect from Mars. Secondly, we will discuss what kind of information we need to obtain and a nalyze for our further plan. Then, we can try to design a research facility depended on all the information we have and start to conduct some feeding trials to investigate their nutritional requirements and develop their artificial diet, eventually.
Current information we have
According to the basic information of Mars we got from NASA, few assumptions we can make regarding this new creature. Firstly, the atmosphere of Mars is very different from Earth, which contains almost 96% of carbon dioxide and rarely has oxygen. Thus, this creature should be an anaerobe, which uses electron acceptors, like nitrate, fumarate, sulphate, or ferric, rather than molecular oxygen. Besides, as we have already known that the “Red Planet” is named due to the effect of the iron oxide prevalent on Mars’ surface. Therefore, we assume this creature is an anaerobe via anaerobic ferric iron respiration. Although, the anaerobic respiration generates less energy than aerobic respiration, according to the low surface gravity of Mars (38% of Earth), they only spend 30% of energy against gravity compared to the creatures on Earth. What’s more, the days and seasons of Mars are comparable to Earth, due to the rotational period as well as the title of the rotational axis relative to the ecliptic plane are similar. However, because of the thin atmosphere which can’t store much solar heat, the low atmospheric pressure, and the low thermal inertia of Mars soil, the daily or seasonal temperature varies a lot, from lows of about - 143 degree centigrade at the winter polar caps to the highs of up to 35 degree centigrade in the equatorial summer. Therefore, this creature may have to hibernate or migrate during the winter to overcome the cold weather. In conclusion, this “Mars mouse” maybe an anaerobe using ferric iron as electron acceptor and need to hibernate or migrate during winter. According to these assumptions, I will suggest we should conduct the feeding study on Mars rather than bring them back to Earth.
Further information we need
To further establish the research base for “Mars mouse”, we need more details, such as their habitats, habits, food sources, and so on. Thus, we may need to use Mars rovers or satellites to track and collect some samples.
Home range
If you want to rise an animal in a research base, it’s very important to know their natural habitat. Thus, we need to collect the temperature, humidity, and size data, not only about their habitat, but also their caves. It will be better for us to know, if they will hibernate during the winter, or they will migrate to some warmer area like some birds on Earth. Furthermore, we need to check out if they are social or solitary animals. If they are social animals, we need to know if they have a hierarchy in their society and cannibalis m behavior in their group.
Food sources
We need to chase this “Mars mouse” and figure out what kind of natural foods they like. Next, we have to collect some of their food back to a nalyze the nutritional composition, if possible. According to the composition results from their food, we can infer the feeding habits of this “Mars mouse”. For example, if they are carnivorous, herbivorous, or omnivorous, and if they swallow or crew their food.
Anatomy
Anatomy is a very common method to study and understand the digestion system of a creature. For example, if we can’t find the natural food sources for this “Mars mouse” via chasing them, we can also roughly evaluate their nutritional habits by dissecting their digestion system. After a nalyzing their digestion system, there are several important information we can obtain. Firstly, if they have teeth or teeth similar structure has crewing or grinding function to reduce the size of their food. Secondly, if they have a stomach organ and what’s the structure of their stomach. They may have the stomach structure like most of the monogastric animals on Earth, or like ruminants have multiple stomachs with different functions, or maybe have no stomach like herbivorous fish. What’s more, the length and structure of the intestine are also very important for us to better understand the digestion system of this “Mars mouse”. Usually, the ratio between body length and intestine length can help us to tell if an animal is carnivorous or herbivorous. Additionally, the structure of the intestine will help us to know the development of this creature’s intestine. For instance, if their intestine likes poultry have different segments, or likes fish just be simply divided into anterior and proximal parts.
Chyme, digesta and fecal sample compositions
We can also estimate the food preference and the absorbability of nutrients of this “Mars mouse” by collecting and a nalyzing the compositions of their chyme, digesta, and fecal samples. The chyme sample from their stomach can help us to understand and determine their food sources. Furthermore, after comparing the nutritional composition results among chyme, digesta, and fecal samples, we can roughly infer their digestion process, like the digestibility and absorbability of some certain nutrients, which is very helpful for our further research.
After a nalyzing and summarizing all the data we collect from this “Mars mouse”, we can finally start designing the feeding trials to determine their nutritional requirements.
Conduct feeding trials
Since the environment of Mars and Earth is so different, it will be better for us to conduct the research on Mars. Several artificial caves will be built, which support a similar environment as the creature’s natural caves. The capacity of each cave will depend on the creature’s living habits. The young creatures which can live independently will be chosen as our experimental targets. And, all the feeding trials will be at least triplicates.
If we are lucky to figure out the creature’s natural food sources and collect plenty of food, the first feeding trial can be designed to feed them with their natural food to saturation. Then, we can obtain the feeding ratio based on their body weight and calculate the apparent digestibility of protein, lipid, and carbohydrate (total amount of nutrient intake - total amount of nutrient in feces / total amount of nutrient intake ×100%). The precision of the apparent digestibility results will depend on if we can collect all their fecal samples. Another method can be applied to avoid this issue when we feed this creature our artificial diets.
Based on the results we get from our first feeding trial, we can start to design our experimental diets. First of all, we should decide on the form of our diet. The diet can be powder, crumbled, or pellet, based on the creature’s eating habit and their life stage. Then, the natural food will be used as our reference diet and its nutritional composition will be the dietary nutritional standard. The experimental diets will still use natural food as the main ingredient and mix with other ingredients from Earth which have similar nutritional composition. The trial duration will depend on the growth speed and life stage of this creature. At the end of this feeding trial, we will compare the growth performance results, like survival ratio, weight gain, feed efficiency. One-way ANOVA will be used as the statistical method. Thus, we can select several ingredients that this creature likes. If possible, we can also test the feeding trial with experimental diets compose with purified or semipurified ingredients, such as starch and casein. Purified or semipruified diets are commonly used to evaluate some nutritional requirements of animals, like amino acids, vitamins or minerals.
According to the apparent digestibility results from the first feeding trial and the best selected ingredients from the second feeding trial, we can plan our following nutritional requirements studies.
Protein and amino acids
Proteins are essential nutrients for the structure and function of all living organis ms on Earth. Since proteins are continually being used by the animal for growth, repair of tissues, and enzymes, a continuous supply of protein, especially the indispensable amino acids, is needed.
Firstly, we will design at least 5 experimental diets with a wide range of equally spaced protein levels, where the protein level of our reference diet will be in the middle. At the trial termination, we will calculate the growth performance index and a nalyze the whole-body composition, such as protein, lipid, ash, and energy. Regarding the digestibility part, there’re two common ways to investigate, depending on if it’s easy to fully collect the fecal samples. If it’s possible for us to entirely collect this creature’s feces, then we can simply use the equation, total amount of nutrient intake - total amount of nutrient in feces / total amount of nutrient intake × 100%, to directly calculate. If their fecal sample is not easy for us to collect, we have to add a marker, which is not absorbed by animals, to all diets and calculate the apparent digestibility based on the following formula: =100−(100×% indicator in feed / % indicator in feces)×(% nutrient in feces / % nutrient in feed). Broken-line, regression model, or one-way ANOVA is the common statistical methods we use to determine the optimal dietary protein level. Secondly, we will apply the same method but using a narrower interval of protein level, where the optimal protein level we found in the previous feeding trial is in the middle. Thus, we can achieve a preciser dietary protein level for this “Mars mouse”.
Since Earth animals can’t synthesize indispensable amino acids, the dietary requirement of these essential amino acids is usually more important than dietary protein level. In this case, the ideal experiment design will use purified or semipurified diet which doesn’t contain any of the certain amino acid as our reference diet, and experimental diets will use the same formulation as basal diet but containing graded levels of the certain amino acid. The process of feeding trial will be similar to our dietary protein requirement experiment. Check the whole-body amino acids composition may be the only extra a nalysis we need to run for calculating the minimum dietary requirement of certain amino acid. If this creature doesn’t like the purified or semipurified diet, we have to formulate our reference using the ingredients this creature likes and contain certain kind of amino acid as low as possible. Since we don’t know which amino acids are concerned as indispensable to this creature, we have to test all the amino acids we detect in their natural food or chyme. After we figure out the dietary requirement of all the essential amino acids, we can modify our dietary protein requirement experiment, to make sure all the treatments will meet the minimum amino acids requirement of this creature.
Lipid and fatty acid
Lipid is the source of essential fatty acids, digestible energy, vehicle for absorption of fat-soluble vitamins, and carrier for other fat-soluble compounds. The dietary lipid requirement experiment will be similar to how we determine the dietary protein level. The dietary protein and amino acids levels will be modified of our reference diet, based on the results we obtained from previous feeding trial. And at least 4 experimental diets with a wide range of equally spaced lipid level on both side of our reference diet will be formulated to conduct this feeding trial. After we achieve the optimal dietary lipid level, a second feeding trial with at least 5 treatments using a narrower interval of lipid level will be designed to determine the more accurate dietary lipid requirement of this creature.
On Earth, vertebrate and crustacean species need a dietary requirement for certain specific n-3 and n-6 PUFA, because they can’t synthesize these fatty acids from monounsaturated fatty acids. However, unlike the dietary amino acids requirement research, we can’t just simply remove one fatty acid without affecting other important aspects of diet, such as attraction and palatability. Additionally, we don’t know if this creature has the ability to synthesize other fatty acids. Thus, currently, we may just use the mixed lipid source which has similar fatty acid composition as the natural food of this creature. In the future, after we have more information regarding the lipid digestion pathway of this creature, we can design the dietary fatty acid requirement experiment better.
Carbohydrate
Carbohydrates make up the bulk of a poultry diet on a weight basis to provide energy, which mainly used for energy supply, but not that popular in fish diet. In addition, although diets devoid of carbohydrates result in very slow growth of poultry, the carbohydrate is not a dietary essential nutrient. However, since this creature may be anaerobe, which uses glucose as fuel, the dietary carbohydrate concentration should be important. Thus, the same feeding trials design like evaluating dietary protein and lipid requirement will be used to determine the dietary carbohydrate requirement. We may have to pay attention to the dietary non-starch polysaccharide (NSP) concentration. Most of the Earth animals can’t digest and utilize the NSP, expect the ruminants. Therefore, according to the structure of their stomach, we may have to limit the dietary NSP level.
Vitamins
Vitamins are organic compounds which are generally not synthesized by animals on Earth, and usually responsible for specific deficiency disease if not present in the diet. Vitamins can be divided into fat-soluble and water-soluble. Usually, fat-soluble vitamins can be stored in appreciable quantities in Earth animal body, which can’t be excreted in urine and will be toxic if in high dietary level. On the other hand, water-soluble vitamins are not stored in animal body in large quantities, which will be excreted rapidly in the urine. However, since we haven’t found liquid water on Mars yet, maybe both of the fat-soluble and water-soluble vitamins will be stored in this creature’s body in a large quantity. Thus, high dietary vitamins level may be toxic to this creature, only if they have an unknown method to excrete the exceeded vitamins. We can use the same method we used to investigate the dietary amino acids requirement to determine the dietary vitamins requirement. At the end of the feeding trial, growth performance index, whole body composition will be calculated and a nalyzed. We also need to a nalyze the vitamins concentration in organs to determine their distribution which can help us to study the pathway of different vitamins in the further.
Minerals
Minerals are inorganic elements essential for normal body functions of Earth animals, which can associate with the energy nutrients, be structural elements, and homeostatic elements. To most animals on Earth, we usually use purified or semipurified diet to determine their dietary mineral requirement, except for the aquatic animals. Because aquatic animals can absorb some minerals from the aquatic medium in which they live, in addition to from their diet. To this creature, the same method we used to evaluate the dietary amino acids can be applied to study the dietary minerals requirement. Only one mineral we may have to pay attention to, which is iron. Iron is concerned as a trace mineral to Earth animals. However, since there’s lots of iron oxide on Mars’ surface and this creature may use iron respiration to generate energy, they may have a high demand for dietary iron level. Also, we need to a nalyze the minerals concentration in their bone or exoskeleton or endoskeleton and organs to investigate the minerals distribution which can be used for our future research.
Water
Since there’s barely liquid water on Mars, we assume that water is not one of this creature’s essential nutrients.
If we can’t find their natural food or we can’t collect enough food samples to conduct our feeding trials, we have to design the artificial diet for this “Mars mouse” based on the nutritional composition of their natural food or the chyme sample we collect from their stomach. In this case, we can only roughly estimate what kind of nutrients are highly digestible and absorbable by this creature via comparing the difference of nutrient ratio among chyme, digesta and fecal samples. Then, based on the nutritional composition of chyme sample and the estimated digestibility results, we can try to formulate the diet for this creature by mixing the ingredients we can find on Earth which have close nutritional composition.
After we successfully select the ingredients this creature likes and figure out the formulation of diet which won’t impact the growth performance and health of this creature, compared to the wild captured, we can start our next step. We will use this formulation as our basal diet and apply the method we mentioned above to conduct our nutritional requirement research.
