Today's paper gave me the chance to refresh my knowledge about ebb and flow (falling and rising tide). We remember: The water gets elevated by the gravitational force of the moon. This created the tidal bulge (~54cm) just underside the moon. As moon and earth both circulate around a point (barycenter) which is not in the earth center, the resulting “wobble” movement of the earth creates another tidal bulge on the opposite side (see figure). Because of the 24h rotation of the earth, any point on the earth crosses both tidal bulges over the day (~12h tidal rhythm). The tidal high varies over the month, because the gravitational force of sun also creates a water bulge (~25cm) which, depending on the moon-sun-location, either enhance the moon tidal bulge (spring tides at new moon and full moon) or counteract with the moon tidal bulge (neap tides at half moon). The standard calculation of the tidal bulge height is quite easy but it is based on some simplifications. First, the calculations are for a earth without land, which is completely covered with water. Second, only the earth and the moon contribute to the gravitational potential for points near the surface of the earth. However, the tidal bulge itself also produces a gravitational potential which should be considered. How to calculate this additional potential and how it change the end result, can be found in the paper of Travis Norsen et al. (2017). As mentioned by the authors, the idea of gravitational self-interaction of the tidal bulge is not new. The equation was already published in 1775 by d’Alamber. “But since it seems to have been— inappropriately, we think, due to the size of the effect— largely forgotten in pedagogical discussions of the tides, we thought it was worth sharing our approach with educators and students in its original format.” (Norsen et al. 2017) The gravitational self-interaction of the Earth's tidal bulge.
Norsen, T., Dreese, M., & West, C. (2017). American Journal of Physics, 85(9), 663-669.
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The today’s paper is an “Aha” paper: not an “I finally found the answer to an urgent question- Aha” but more a “There are papers about that? - Aha”. The paper from Shuying Wei et al. (2017) deals with the question how different cooking/baking methods change the chemical composition in sweet potatoes. Call me stubborn traditional German but I still favour normal potatoes over sweet potatoes, although the latter became more and more famous in Germany over the last year. However, I know many people who like the starchy, sweet-tasting, nutrient rich storage roots which are native to the tropical regions in America. So maybe these people always wondered how cooking change the starch and sugar content in the potato? If so, the paper today gives a detailed answer. Shuying Wei et al. tested four different sweet potato cultivates ( two yellow flesh and two purple flesh cultivars) with three different cooking methods (boiling, steaming, baking) and analyzed the change in dry weight, starch content, sugar composition, sweetness and α-amylase activity (α-amylase is an enzyme which transforms starch to sugar). In general, yellow fleh cultivars seem to contain more sugar that the purple flesh cultivars. The effect of the different cooking methods (boiling, steaming, baking) depend on the cultivate type, but all three cooking methods reduce starch content and create maltose (which can not be found in the raw potato). All in all, cooking increased total sugar content especially reducing sugars which explains why cooked sweet potatoes taste sweeter as raw ones. This is because in the begin of the cooking process the amylase activity is increased (and more starch is concerted to sugar) before the high temperatures stop any amylase activity in the end. “Aha”. "Effects of cooking methods on starch and sugar composition of sweetpotato storage roots."
S. Wei, G. Lu, H. Cao (2017) PLoS ONE 12(8): e0182604. Rooibus is a plant (shrub) which can be found in South Africa. It is great for making tea and contains chemical components (aspalathin) which has antimutagenic and antioxidant properties. When given to male rats (as drink in liquid form), Rooibus showed positive effects on sperm concentration, viability, and the percentage of motile sperm. In contrast, injected in the Leydig cells (for sperm production), Rooibus supressed male hormon production (anti-androgenic properties) and therefore lead to an deacrease in sperm quality. So what are the in vitro effects of rooibos extract on sperm function? José Luis Ros-Santaella and Eliana Pintus (2017) analyzed the effect of Rooibus extract on boar sperm quality. As in pig breeding industry more than 99% of artificial inseminations (AIs) in the are performed using extended semen in the liquid state and stored at 15–20°C, any admixture of chemical components which increase sperm survivability would be beneficial. They tested boar sperm velocity, membrane integrity and acrosomal (sperm”head”) status after admixture with fermented and unfermented rooibos extracts. Both, sperm velocity and acrosomal status was enhanced by (fermented) rooibus extract. This positive effect was detectable even after 96h of liquid semen storage. However, “too much of anything is bad for you” also holds for the interaction of rooibus extract and boar sperm: Too high concentration decrease sperm velocity and therefore decrease sperm quality. Taking home message: If you want to store liquid semen (of a boar) then add some rooibus extract. And if you don’t have rooibus tea at home, in that moment: Another study showed that rosemary also helps to increase the boar sperm quality. "Rooibos (Aspalathus linearis) extract enhances boar sperm velocity up to 96 hours of semen storage."
Ros-Santaella JL, Pintus E (2017) PLoS ONE 12(8): e0183682. In 1973, D. Weihs modelled fish schools and predicetd that the diamond shape (shifted rows, so that the single fish is always in the middle between the two nearest neighbours in front of it) is the preferred organization structure. He could show by 2D modelling, that the diamond shape could improve swimming efficiency because of the hydrodynamic interactions with the vortices created by the fishes in front. Intesaaf Ashraf et al. (2017) challenge this widespread idea of prefered diamond shape organization. They studied fish schools of the red nose tetra fish (Hemigrammus bleheri) and showed that the organization structure depends on the swimming speed. Slow swiming fishgroups showed indeed a preference for diamond or T-shape organization. However, when forced to swim faster, so in a situation in which energy efficiency would be most beneficial (for example when escaping a predator), they prefer a “in line” (phalanx-shaped) organization. This phalanx pattern reduces the distance to to the nearest neighbour. Both configurations, diamond-shaped and phalanx-shaped, save energy (reducing tail-flapping frequency) compared to a single fish swimming alone. So why changing to a line when fast swimming is required? Ashraf et al. think this conformation change is connected to the change of swim-movement-synchronization. While slow swimming fishes show no correlation in their tail movement, fast swiming fishes were synchronized (in phase or out-of phase) with their nearest neighbour. Ashraf et al. predict that this synchronized swimming kinetics together with the “side by side” organization is a good strategy to optimize thrust (and therefore speed). Unfortunately, they didn’t modeled this configuration to proof this idea. However, this study shows that maybe Weihs model of energy-saving diamond-shaped fish schools maybe needs some improvement. “Simple phalanx pattern leads to energy saving in cohesive fish schooling“
I. Ashraf et al. (2017) PNAS, doi:10.1073/pnas.1706503114 “You are an island.” This poetical sentence is originally intended to highlight the character of a lone warrior. However, who claimed that this island is uninhabited? Just think of the large amount of microbial symbionts you are hosting on and in your body. You are a sort of island for them. You are the world for them. So even the loneliest warrior is not lonely at all. In fact, you will never be completely alone. This knowledge about the colonies of microorganisms for example on our skin or in our gut seduces us to think that this is sort of a rule for any larger organism. So it doesn’t make sense to study any animal alone, but you need to understand the animal as “holobiont”, as host plus its microbiome, because just the interplay between the commensal, pathogenic, and mutualistic microorganisms and their host make the host to what it seems to be… a rabbit, a dog, a human,… . The usage of antibiotics, which damage our gut microbiome, shows perfectly how much our health is connected to these little gut inhabitants. Many organisms show developmental disorders if there is something wrong with their gut microbiome. Many organisms… not all! Caterpillars doesn’t have a gut microbiome. This is the message of the paper from Tobin J. Hammer et al. (2017). Gut microbiome analyzation of 124 different species (15 different families) of wild leaf-feeding caterpillars in the United States and Costa Rica showed that Lepidoptera (butterflies) had gut bacterial densities multiple orders of magnitude lower than the microbiomes of other insects. Moreover, the majority of the small amount of gut bacteria which could be found in the guts of caterpillars, were leaf-associated bacteria. They didn’t live in the gut but were more transient visitors because their original home was eaten. So caterpillars seem not to depend on a gut microbiome which help them to digest the plant parts. Indeed, treatment with antibiotics didn’t affected the growth and development of the caterpillar. In contrast, in the laboratory, it actually increases growth because it kills pathogenic microorganisms. So we may should correct our idea that all organisms are like us: large hosts which life and health are connected to millions of small symbionts. Walking sticks, sawfly larvae and certain ants as well as a herbivorous goose (Branta bernicla) and a insectivorous bat (Myotis lucifugus) all these species are known for showing low fecal bacterial loads comparable to the caterpillars. They all seem to resign the additional digest help of gut bacteria in order to get more energy out of their food and instead focus on a sort of “more is more” strategy. They all have short guts with rapid digestive transit (so high feeding rate). So even if they don’t get much out of a single portion of food, they compensate this by eating a lot. This has the benefit that they can keep all nutrients for themselves, as the don’t have to “pay” the gut bacteria for their work, and they are maybe more flexibel what they can eat, as they just have to satisfy their own taste and not the taste of one million gut inhabitants. "Caterpillars lack a resident gut microbiome."
Tobin J. Hammer, et al. (2017) PNAS, doi:10.1073/pnas.1707186114 Copper… on the one hand copper is an important trace element for life (for example as part of the red blood cells), on the other hand it is toxic. Water-soluble copper in inshore waters and soil is a danger for many microorganisms and plants. Therefore, it is important to understand the dispersion of water-soluble copper. When you add water-soluble copper (Cu) into soil, it instantly partitions between solid and solution phases. However, this state is not stable: with increasing “age”, its lability (bioavailability, toxicity, isotopic exchange-ability and extractability) decreases because of diffusion and reactions with the surrounding material. Theoretical models help to predict this time dependent change in lability, which depends on a lot of soil parameters like temperature, soil organic matter content and soil pH. Zeng, et al. (2017) published an improved model for copper lability which describes short and long term effect of water-soluble copper added to soil in one single model. In their model, copper lability depends on three processes:
The model showed good predicting ability when compared to experimental data of different soil samples with different chemical properties (like pH value, clay and organic carbon content and copper concentration), although other copper ageing processes like moisture, plant absorption, and microbial activities are not considered. "A new model integrating short- and long-term aging of copper added to soils"
Zeng S, Li J, Wei D, Ma Y (2017) PLOS ONE 12(8): e0182944. This smell! She didn't know where it came from or what it mean. Nevertheless, it did something to her. Suddenly making babies wasn't a great idea as it was before. Maybe she should move out? Aphids (plant louses) are a pain for any gardener: they devitalize plants by sucking their sap. But what we can do against these hordes of plant vampires? Ladybugs and aphid lions are known predators. But how many aphids a single bug should eat in order to produce serious damage to the aphid colony size? Actually the reduction of prey number is not only a cause of the hunting of the predator. It is the fear which the predator produces, which makes prey life hard and reduces the mood for producing offspring. Mohammad Shadi Khudr et al.(2017) explored the effect of predator clues on aphid reproduction rate. Of course, the living predator (aphid lion) was most successful but although dead aphid lion bodys and sprayed or earth-injected aphid lion smoothies (which transfer the predator smell) were able to reduce the number of aphid offspring. Of course, the fear-effect of the naïve aphids (which never saw an aphid lion before) variied between the individuals but all in all it is good to know that already the smell may reduce the number of the plant-vampires and that most aphids prefer plants with no predator clues. Unfortunately, the paper doesn't explain why reproduction success declines when predators seem to be around, although this is a prey response which was observed in different studies and different organisms. Maybe it is a sort of strategy, or it is just the result of the stress. Taking home message: If you have problems with aphids in your garden: buy aphid lions... dead or alive (but alive is preferred). "Fear of predation alters clone-specific performance in phloem-feeding prey."
Mouhammad Shadi Khudr, et al. Scientific Reports 7 (2017). The magic of a break. For a short time put your work aside and do something else. At least while struggling with verbal learning tasks, such breaks should be helpful and improve your memory. The “spacing effect” as it is called in memory literature, refers to the fact that spatial learning (with temporal lags between the learning session) results in greater retention accuracy and less forgetting compared to massed learning (no lags). There are many different theories why “spatial learning” works. Maybe it works because that the cues which are present in the different learning session variate (a different environment, a different mood) and improve learning. And/or it is just this cycle between forgetting (in the lags) and recall (during the session) which strength the memory. Whatever it is: does it work for any type of learning? Most experiments focus on verbal learning. For motor learning the studies show variating results. Melody Wiseheart (great name by the way) and colleagues analysed if there is a spacing effect while learning to play the piano. They asked students with varying music education to perform two tasks: One focuses on the “translation” from music sheets to the right finger movement on the piano keyboard, the other on the auditory feedback to reproduce a certain melody with right volume and rhythm. Interestingly, massed learning and spatial learning strategy showed both the same learning performance in both tests. Maybe the time lags (max 15min) were to short. But at least it shows, that the spacing effect may vary with the learning task. “Lack of spacing effects during piano learning”
Wiseheart M, D’Souza AA, Chae J (2017) PLoS ONE 12(8): e0182986. Imagine you are a god and you have to design the poisonous fangs of a snake. Which form is the best and should you put it In the front of the jaw or in the back? Fact is that there are three types of venomous snake fangs: Boomslangs for example have fixed grooved fangs in the end of the jaw (type I). Just imagine a fang with a slit/groove in which the venom is floating. This grooved structure was the base for the evolution of tunnel fangs which improve the poison injection. Evolutionary, the ends of the groove came together and a closed, and tunnel-like structure was born. There are snakes like the cobra where you can still see the “two ends” rolled together. These are the closed but non-fused fangs, which are located in the front of the jaw (type II). Even more advanced are the fangs of vipers etc. There the rolled ends are smoothed. Their closed fused tunnel fangs can be also found in the front of the jaw and they are mobile (foldaway) (type III). Chris Broeckhoven and Anton du Plessis (Biology Letters, 2017) wondered if the evolutionary change in location (back to front) is a result of the change in structure (grooved to tunnel). Maybe the change in structure changed the stress amount under load and therefore a different location was favourable? So they analysed the structure, length and location of fangs in 20 different snake species and used computer models to predict the stress under load. Interestingly, the structure (grooved or tunnel) didn’t changed the highest stress value (always near the fang tip). The stress just correlated with the length: longer fangs could break easier. However, curve form and more stable material can compensate for that. So change in location has nothing to do with the stability of the fang. Instead they assume that it has something to do with the hunting strategy. Snakes with grooved fangs in the end of the jaw focus on the bite-and-hold strategy while the vipers with the mobile tunnel fangs in the front of the jaw focus on the bite-and-release strategy. SO… IF you are god and have to design the poisonous fangs of a snake ask for her preferred hunting strategy. "Has snake fang evolution lost its bite? New insights from a structural mechanics viewpoint"
Broeckhoven and du Plessis A (2017) Biology Letters 13(8): 20170293. |
IdeaI love to increase my general science knowledge by reading papers from different fields of science. Here I share some of them. Archiv
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