“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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Life is not fair: while men can reproduce until they die, for females their reproduction ability declines over their lifetime. This is because men continuously create new gametes (sperm), while females relay on the gametes (eggs) they have since their birth. Therefore, while sperms are always young and fresh, the eggs get old and get some damage over time. This is true not only for mammals but also for invertebrates. However, there may be a treatment against the decreasing egg quality. Nicole M. Templeman et al. analyzed the effect of the insulin/insulin-like growth factor (IGF)-1 signaling pathway on the egg (oocyte) quality. This growth factor is known to regulate longevity and that it slows down reproductive aging. Comparison between gene expression in oocytes from wildtype C.elegans (small roundworm) and IGF-1 mutants show that Cathepsin-B protease activity is reduced in the IGF-1 mutants. In the wildtype, Cathepsin-B protease activity rises with age, and it is assumed that this leads to the age-dependent deterioration in oocyte quality. Indeed, Templeman et al. were able to show that pharmacological inhibition of Cathepsin-B protease can slow down the age-related reproductive decline in C.elegans. Of course, there is a difference between C.elegans and humans, but nevertheless, this is a promising result. Maybe in some years, we can help aged women to increase their chance for healthy children with this treatment. Noses are great. Noses allow us to smell and they humidify, heat and clean the air for us. Although, it fulfills the same tasks in all vertebrates, nasal geometries vary highly among species. The question is, what determines the form of the nasal cavity. One answer to this question can be found in the paper from David Zwicker at al. They calculated the optimal nasal cavity structure regarding the air flow and the heating and humidifying of the air. While narrower geometry improves the efficiency of heating and humidification, the airflow resistance increases. So the optimum lies somewhere in the middle: narrow enough to guarantee the right heat and humidity and wide enough so that the lung power allows air to go through the structure. In their paper, David Zwicker at al. transformed all this in physical equations and calculated the optimal nasal cavity: a narrow tube with a constant diameter and a certain length. So why the most animals have a labyrinth shaped instead of a tube-shaped nose cavity? Is there something wrong with the equations? No. The problem is the length. The nose (and the skull) restrict the possible space, and a straight tube structure of the optimal length would just not fit in. Therefore, the nasal cavities have this labyrinth-like structure. It also has a constant narrow diameter, as calculated. And Zwicker et al. showed that the branching and bending, does not change the airflow resistance. So messages of the day: 1. There are people which calculate the optimal nasal cavity. 2. The nasal cavities found in nature are quite optimal. STOP. The last point is not true for humans. The paper shows that the nasal cavity gap width and surface area is smaller as assumed by the model. The authors assume that the resulting higher resistance in air flow is the reason why humans are obligate oral breathers: during heavy physical activity, we don’t get enough airflow through our nose and therefore we tend to breathe through our mouth. Remember that, the next time you take a deep breath :) The paper of the day, made me curious, because it is about theft in ant colonies and in the abstract you find a hint, that you could learn something about general “tricks” used by successful thieves… in ants and in humans. Thievery is quite common in the animal kingdom. The most common stolen “items” are food, nesting sites, nesting material and sometimes even the brood itself. The brood of somebody else can be used in different ways: you can eat them, adopt them or take them as slaves. All three strategies can be observed e.g. in different ant species. Army ants with their mass raids, tend to eat 75% of the brood of the victim colonies. Slave-making, can be observed in different ant species and most of them it is obligatory: The colony cannot survive without slaves. In their paper, Bishwarup Paul and Sumana Annagiri, checked under which conditions the risk for brood thievery increases, what tricks are used by the thieves and how they can be stopped. The ant of interest in this study was the primitively eusocial ponerine ant Diacamma indicum that inhabits the tropics. Interestingly, this ant species lacks a queen caste. A single mated worker maintains the reproductive monopoly. In the study, two ant colonies, are placed in the opposite corners of a rectangular box. Then both nests are disturbed and only one alternative nest is placed in the middle. As both colonies had to look for a new nest, this setup increased the inter-colony interaction, as both colonies have to look for a new nest. As just one of them can actually move, all experiments end with one colony moving and building up their new nest in the middle of the arena, while the other has to stay in their destroyed nest. Color dots on the single ants and cameras observe while this process: who steals what, when and with which strategy and how and if the thieves are blocked by guards. The results of the study show that thievery in ants is not so different from thievery in humans: (I) Nest damage increases the colonies’ vulnerability to brood theft. The ants suddenly have to look for a new home, a perturbed and cannot guard their entrance as usually. If your family house suddenly has broken windows and doors, you also have other problems and a thief can sneak in more easily. (II) Thieves were successful when they acted quickly, and hidden (defensive) and just stole unguarded brood. I guess that are the same rules as for human thieves. As promised, today there will be no paper of the day. Instead, I will first write something about the amazing pattern&development workshop, I attended last week. When you read my profile, you know that I work on temperature effect on neural systems. Unfortunately, many people are not aware, that temperature is a strong and general parameter in nearly any biological process. Temperature is defined as the kinetic energy of molecules. So if you heat up your apartment (at the moment it is so freezing cold in Berlin!), you actually make the molecules in the air (oxygen and Co) speed up. The same happens if you heat up a biological cell. All molecules get higher kinetic energy. That results for example in changes of ion channel gating and metabolism rates. So the question is: if everything is changing with temperature, how can it be that "living" works at different temperatures? One organism which experiences quite large temperature changes is the fruit fly (Drosophila). It has a small body size and is cold-blooded. Therefore, it is crucial for the fruit fly to find mechanisms to deal with different temperatures. This temperature adaptation starts already in the development. It is known that environmental temperature during development affects, for example, body size, pigmentation, immunology, behavior, and fecundity of the fly. Nevertheless, I was quite amazed when Christian Schlötterer told us, that when they analyzed gene expression at different temperatures, only 53% of the genes were expressed at all different temperatures, and only 16 of them showed no temperature dependence of their expression level. So the first message of the day: the fruit fly which developed in my cold kitchen, has a different gene expression as the fruit fly in my warm living room. Temperature changes (nearly) everything! But is that true? Maybe gene expression patterns changes and the two flies differ in body size and pigmentation, but you will nevertheless identify both as fruit flies. Both have the same amount of legs for example. That means, that there are steps in development, which are independent of the environmental temperature. One example for that is the body segmentation. Alexander Aulehla gave a great talk about the stability of the body segmentation process with the focus on the development of the somite segments (somite = a division of the embryo in different parts) in mice. Independent of the embryo size and the environmental temperature, there is always the same number of somites, and in the embryo, all somites have a regular shape with a fixed width. How can that happen? Alulehla told us, that this regular segmentation is the result of the oscillatory activity of different signaling pathways in segment precursor cells. All cells in a certain region, produce that oscillatory signal: synchronous with their neighbors but phase shifted. That results in a wave pattern in the segment creation zone. The phase span between "begin and end" of the segment creation zone, is the base for the regular segmentation. Therefore, temperature changes, which affect the wave velocity but not the phase range, has no effect on the size and number of segments. Just the segment creation time changes. So one could say: even if temperature changes everything, for some processes/outcomes it changes nothing at all. Interested, or my description was too confusing? Please read for example:
"Temperature-related reaction norms of gene expression: Regulatory architecture and functional implications." Jun Chen, Viola Nolte, and Christian Schlötterer. Molecular biology and evolution 32.9 (2015): 2393-2402. "Scaling of embryonic patterning based on phase-gradient encoding." Volker M. Lauschke, et al. Nature 493.7430 (2013): 101. My dear reader, 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.
journals.plos.org/plosone/article?id=10.1371/journal.pone.0191456"Revisiting facial resemblance in couples."
Yetta Kwailing Wong, et al. PloS one 13.1 (2018): e0191456. |
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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