“You have to eat something”. Everybody knows this sentence from his/her mother/grandmother. And it is actually true. Starvation is life-threatening. So no wonder that the human body takes this matter quite serious and responds with some emergency plans for energy conservation, like e.g. reduction of metabolism and body temperature. But starvation induced reduction in body temperature can not only be found in humans and other mammals but also in ectotherms, such as mosquitoes, cockroaches, and rainbow trout. What about Drosophila (fruit flies)? Yujiro Umezaki, et al. tested if Drosophila also shows starvation-induced body temperature reduction and if so, how they control it. Drosophila are so small, that their body temperature is mainly regulated by the ambient temperature. The small flies actively move to temperature regimes which suits their needs. Yujiro Umezaki, et al. showed, that starvation results in a lower preferred temperature in Drosophila. This process is like other starvation-induced behaviors controlled by the insulin/insulin-like growth factor (IGF) signaling pathway. (It is the same pathway we had in the last paper of the day, for the longevity and egg quality in C.elegans). To make a long story short: Starvation in Drosophila results in an increased expression of insulin-like peptide 6 (Ilp6) in the fat body (fly liver and adipose tissues). Ilp6 then alternates the “warm sensing” (TrpA1) channels of the temperature controlling neurons (anterior cells), so that the “too warm” threshold is decreased. Therefore, the preferred temperature is lower. What is most interesting, and the taking-home message for today is that the IGF signaling pathway is well conserved in vertebrates and invertebrates. It has been shown that starvation-induced decrease in body temperature in mice is controlled by IGF receptors, and Drosophila Ilp6 is functionally and structurally similar to IGFs. Therefore, it seems like the mechanism underlying the starvation-induced reduction in body temperature may be evolutionarily conserved between different species. So your body response to starving is not so different from the body response in Drosophila.
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I am really sorry that I didn’t write much in the last time. I am preparing my first paper, and that is a little bit time and energy consuming. Nevertheless, I have to share this jewel of a paper with you: “How animals follow stars” (James J. Foster, et al. 2018). When I read the paper I was immediately on fire: animal follow stars? I could not imagine that. So I had to read it. Some people debate if our destiny is written in the stars. However, I guess nobody questions that your current location and direction are hidden in the stars above you. In history, sailors used that fact to navigate their ships in the night. Fixed stars like the Polaris can help for directions, and experienced sailors can see the latitude of their location by watching the patterns of stars. If you have a good clock with you, you can even find out the longitude (you need the clock to calculate the earth rotation which produces the same shift in star patterns as a change in longitude). So all in all, humans are able to navigate by stars. The question is if there are also animals which use the stars for their navigation. Orientation by fix stars, for example, require learning to identify individual stars by their configuration. Therefore, animals which would be able to navigate by stars, need a certain “intelligence” and “eye quality”. However, that restriction does not exclude too many species. Therefore, many different scientists analyze the behavior of many different species under the artificial sky of a planetarium or after a geographical displacement (and therefore “different” natural sky). What should I say? There is evidence that some birds can use star clues for their migration. Moreover, night-flying moths seem to orient on both the moon and the star, even though they don’t do that perfectly. Moths show a drift over time, which could be a result of lacking time-compensation for celestial rotation. Of course, there are also non-flying animals which show a talent for star navigation. For example, you can train seals to identify specific star patterns, but the question is if they use that in their natural habitat. What I found most interesting in the review of James J. Foster, et al. (2017) is the story about the ball-rolling dung beetles. Such a dung beetle does not make large journeys which need precise navigation, but nocturnal species like the Scarabaeus satyrus seem to use celestial cues to maintain their initial heading when rolling their dung ball. That prevents them from returning to their point of origin. Planetarium experiments showed that Scarabaeus satyrus use the Milky Way as the primary stellar orientation cue. Of course, the little dung beetle does not see the Milky Way like we do. An experimental study which used an artificial ‘Milky Way’ band consisting of LED lights, showed that their orientation is based on a brightness comparison. It is suggested that the beetles may identify the angle of a bright sky region or the direction of a broad-field brightness gradient. Isn’t that amazing? A small beetle using the large sky to roll their dung home safely! Some animals can communicate via color patches on their skin. For example, everybody knows what is going on with you when you suddenly blush. Just kidding. Of course, I don’t talk about humans. The paper of the day is about the common chameleon. In color communication (which you also find in insects, birds,…) there are two different strategies: I) adapt your color to different situations, II) have a color pattern which you just show in specific situations and otherwise hide/conceal it. Chameleon colors belong to the first type: they change them according to the season, background and social signaling, instead of concealing them. But what about the lateral white stripes? (see figure) Tammy Keren-Rotem, et al. (2018) analyzed the appearance of white spots in chameleons in different situations (season and social context). They showed that male and female chameleons consistently display the white badges, while body colors and patterns change. However, while mating, the white badges are concealed. What is the meaning of this? It could be that the white badges are used to identify individuals, as they are stable in shape within individuals but vary between individuals. It could also be, that the fact, that the white badges are proportional to the total body size, allows conclusions about individual quality, fighting ability and/or dominance. The authors explain their findings by the multitasking hypothesis: The information transfer in one color pattern is constrained by the presence of another color pattern. That means, when I would be a chameleon, the white stripes may help to show my quality. However, my lack of multitasking ability restricts my communication when I use stripes and color and I can not clearly transmit my mating intentions. Therefore, I get rid of the white stripes when I find a nice mate. That is the idea. Proof is still needed. Pigeons are normally a heterosexual and monogamous species (the exception proves the rule). But what happens if you skew the sex ratio to more female-biased or male-biased? Łukasz Jankowiak, et al. (2018) did such experiments and found out that same-sex pairs can occur in such situations. It is known that female-same-sex pairs have a higher likelihood in monogamous species compared to polygamous species. In contrast, male-same-sex pairs are more likely in polygamous species. Indeed, this trend is supported by the experiment, which showed that there are more female-female pairings in a female-biased sex ration as male-male pairings in male-biased sex ratios. Moreover, the female-female partnerships were longer lasting and resulted in successful breeding whereas the male-male partnerships where short and showed no egg adoption behavior. Unfortunately, it is hard to find driving force behind same-sex pairs: there are many different theories (from mistaken sex identity to intersexual conflicts). The authors guess, that in this pigeon experiments, the same-sex pairing in males can be explained by the "heterosexual deprivation" (meaning: there are just no females available, therefore they go for males), while the female-female pairs are more driven by "alloparenting" (you need two adults for successful breeding so you better "bind" a female to your nest as breeding alone). But of course, it is just a guess. So message of the day: female-female pairs more in monogamous species, male-male pairs more in polygamous species. According to the paper, it has something to do with parental care: when the male provides a lot of parental care in monogamous species, females tend to compensate missing males with females, while males show a smaller chance of male-male pairing. In contrast, in polygamous species, if the males care less, the females do not have to compensate the missing men (less female-female pairs) while the frequency of male-male pairs increases. There are people who fear robots taking over our lives. But it is not only human life in which robots will play a more and more prominent role. Also, lab animal life changes because of robotics. The field of "ethorobotics" grows: more and more experiments use robots to trigger and analyze certain behavioral responses of their study object. The paper of Kim et al. (2018) mentions robot studies which examine e.g. honeybee dance communication, bird courtship, fish schooling and the social behavior of rats. So the idea is to put a robot which simulates a certain behavior and look how living organisms are reacting to it. Many of these studies use “open-loop control”: the behavior of robot is pre-programmed and can not respond to the behavior of the live object. In contrast, “closed-loop control” systems allow the robot to interact in real-time with live subjects based on feedback from the animal behavior. Kim et al. developed a "closed-loop control" system in which a robotic arm moves a 3D printed zebra-fish replica in response to the behavior of a living zebrafish in its 3D water environment. They were able to show, that when replica and living original are in separate tanks which allow the zebrafish to watch the movement of the robot, the zebrafish seeks the closeness of the replica more often when its movement in one direction (y-axis) is closed-loop controlled compared to a complete open-loop controlled system. The increased shoaling time can be interpreted as an improved degree of biomimicry. Unfortunately, full 3D closed-loop control did not increase the replica performance. Kim et al. argue that this could be because of the increased probability of the replica to crash against the wall when all 3 axes are controlled by the living behavior. Maybe that wall crashing was interpreted as aggressive behavior and therefore induced avoidance behavior in the living fish. So the system is maybe not perfect yet, but it shows a new interactive robotics-based approach for zebrafish behavioural phenotyping in 3D . A large variety of life exists on earth. Biologists sort this biodiversity in a hierarchical system of taxonomic ranks: species, genus, family and so on. Interestingly, “at any taxonomical level, a very small number of units have a very large number of subunits, e.g., individuals per species, or genera per family, followed by a very rapid dropoff, resulting in what is commonly called a hollow curve distribution.” (Beres, et al. 2005). How does this unequal distribution evolve? Normally, when we talk about evolution and origin of biodiversity, we think about “survival of the fittest”, and mutations which help to adapt to different niches, … . However, in order to reproduce the hollow curve distribution (with mathematical models) you don’t need to assume differences in fitness and survival rate. The so called (Hubbell’s) “unified neutral theory of biodiversity” assumes that death and reproduction rates is independent from individual’s species and its neighbourhood. You fix the amount of individuals for an area (“zero-sum” assumption). The individuals can belong to different species. Every time step you pick randomly on of the individuals which has to die. At the same time you choose randomly on of the individuals who reproduces itself to fill the new gap. Moreover, there is a chance that the new individual evolves to a new species which balances random extinction and allows the number of species to stabilise. Of course there are different versions of that theory, more or less complicated, which were fitted to different datasets describing distributions e.g. of tree or coral species. But I want to point out (and what fascinates me about this topic) is that these simple assumptions/rules are all you do not need in order to reproduce the measured hollow curve distributions: No survival of the fittest but simple random events of death and reproduction and some mutations. Egbert G Leigh Jr. et al. (2010), Scholarpedia, 5(11):8822.
"The unified neutral theory of biodiversity and biogeography at age ten." James Rosindell, Stephen P. Hubbell, and Rampal S. Etienne. Trends in ecology & evolution 26.7 (2011): 340-348. "Rotifers and Hubbell's unified neutral theory of biodiversity and biogeography." Karl A. Beres, Robert L. Wallace, and Hendrik H. Segers. Natural Resource Modeling 18.3 (2005): 363-376. 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 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). |
IdeaI love to increase my general science knowledge by reading papers from different fields of science. Here I share some of them. Archiv
März 2018
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