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.
0 Kommentare
Appel and Cocroft (2014) published a paper in which title they claimed that “plants respond to leaf vibrations caused by insect herbivore chewing”. In their study, the plant defence mechanism (production of toxins) which is normally activated by the feeding caterpillars, could also be activated by appropriate application of acoustic vibration directly to a leaf. That means that the acoustic vibrations are either directly transmitted through the leaf tissue or (even more interesting) are transmitted through the air and detected by plant “ears” (antenneas). If the latter is true, plants could “hear” if a neighbour plant is attacked, just by detecting the chewing sound waves of the caterpillars. Is that possible? “Yes it is possible” says the paper from Shaobao Liu et al. (2017). They analyzed if the Arabidopsis trichomes (hair cells) which has several mechanosensory functions, could additionally work as acoustic detectors. For that they analyzed geometry, mass and stiffness of the trichomes and showed theoretically that their primary modal frequencies would be able to resonate when exposed to acoustic waves with the frequencies similar to chewing caterpillar. In easy words: theoretically the trichomes could work like ears for the plant and detect chewing sounds. "Arabidopsis Leaf Trichomes as Acoustic Antennae."
Liu, Shaobao, et al. Biophysical Journal 113.9 (2017): 2068-2076. Welcome back from the fall vacation break. Did you ever wonder how a leaf becomes its leaf form? Jiyan Qi et al (2017) had this question and wrote a paper about it. We know that a leaf is constructed by different tissues/parts: because of differences in gene expression the upper side (adaxial domain) looks different from the lower side (abaxial domain). But which mechanism creates the flat leaf form with upper and lower side? The bud… ergo the start of a developing leaf… is round! Jiyan Qi et al (2017) showed that “relatively simple changes in mechanical properties can account for dynamic shape changes during asymmetric leaf development”. To make a long story short: In the developing (round) leaf the lower side has a higher auxin concentration as the upper side. Auxin is a plant hormone and can lead for example to cell wall loosening by de-methyl-esterification of pectins, a major component of the primary cell wall. The lower sider gets more elastic as the upper side. This difference in elasticity leads to the leaf asymmetry. With proceeding development, the rigid zone of the upper side moves to the middle. “From a physical perspective, the stiff cells receive stronger constraints from their neighbouring […] cells, such that they prefer to grow and divide by pressing on the soft inner cells“. The leaf stretches and gets flat. Just as side note: What I like about the paper is that they use computational models to test their hypothesis if differences in cell wall stiffness and epidermal restriction can lead to the leaf asymmetry. They model what would happen if the cell wall elasticity of the upper and lower region is changed/mixed up. Then they test the model predictions by manipulating the cell wall plasticity experimentally. 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. 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). Climate change does not only destroy the living environment of polar bears but also affects plants in future. That also affects the soybean… one of the important ingredients of the vegetarian diet (see for example: The Role of Soy in Vegetarian Diets by M. Messina and V.Messina (2010)). Therefore, Sailaja Koti et al. (2004) analysed the effect of carbon dioxide, temperature, and ultraviolet-B radiation on the soybean reproduction (Flower morphology, pollen production, pollen germination, pollen tube lengths and pollen morphology). All three factors are supposed to rise in future. Normally a higher concentration of carbon dioxide is better for plants. However, in combination with higher temperature the positive effect of carbon dioxide on soybean reproduction success is missing. Indeed, Sailaja Koti et al. showed that as soon as increased carbon dioxid concentration is combinated with an increase in temperature or ultraviolet-B radiation, it is producing stress in the soybean. “There were no beneficial interactions between the three important global change factors ([CO2], temperature, and UV-B radiation) on the reproductive processes of soybean.” The amount of stress induced by these factors depend on the soybean genotype. Among the six tested genotypes, the soybean DG 5630RR was the one with the lowest stress response. So in future… if the carbon dioxide concentration, temperature, and ultraviolet-B radiation increases, this is the soybean you should rely on (in comparison to the other 5 genotypes and just regarding the reproduction… not the value as ingredient of your diet). "Interactive effects of carbon dioxide, temperature, and ultraviolet-B radiation on soybean (Glycine max L.) flower and pollen morphology, pollen production, germination, and tube lengths."
Sailaja Koti, et al. (2005) Journal of Experimental Botany 56.412 (2005): 725-736. The todays paper reads a little bit like an ad for alternative medicine. It is about “the clinical practices and perceptions of professional herbalists providing patient care concurrently with conventional medical practice in Australia.” (Mavourneen Casey, et al. , 2007). Back then, in 2007, “a total of 1.9 million consultations for herbal medicine and naturopathy have been reported to occur annually in Australia.” I first thought that this isn’t much but this was due to a lack of my geographic knowledge. In the surprisingly small population of Australia of 23 million people (compared to Germany with 80million people), 1.9 million is around 8%. Herbal medicine comprises oral medication of strong pharmacologically active compounds. In a former "paper of the day" I wrote about the health supporting effect of the traditional Maori diet which included e.g. plants with cancer suppressing effects. Also “common pharmaceutical medications such as aspirin, morphine, codeine, atropine and digoxin were originally derived from herbal medicines.” So herbal medicine is interesting, especially its position to conventional medicine. Therefore, Casey et al. sent a postal survey “to all full members of the only national association of Western herbal medicine practitioners in Australia, the National Herbalists’ Association of Australia (NHAA).” The questions covered educational qualification and years of working experience of the herbalists as well as the methods/workflow of their therapy and the interaction with conventional medicine. Moreover, the herbalists were asked about their perceptions of their role in patient care, including medical diagnosis and the understanding of herbal therapy/pharmaceutical drug interactions. The results of the survey show a tight connection between herbal and conventional medicine. On the one hand, the number of herbalists with university qualifications increases which supports the trend of the integration of orthodox medical knowledge into herbal practices like blood test, lever function test and hormone profiles for treatment decision. On the other hand, the patients themselves tend to seek treatment in both medicines parallel. “Most patients who visit professional herbalists tend to seek care for chronic conditions, already have a medical diagnosis, and continue with concurrent conventional medical treatment.” This increases the risk of drug interactions. Therefore, in order to guarantee the safety of the patients, a study of the active compounds of the herbal medicine is important as well as a closer collaboration and cooperation between the medical communities. “An understanding of the ways in which herbalists practice and prescribe may be invaluable in the debate about the safety and efficacy of herbal medicines and may help the planning of reliable and valid research in the future.“ "An examination of the clinical practices and perceptions of professional herbalists providing patient care concurrently with conventional medical practice in Australia"
Mavourneen Casey, Jon Adams, and David Sibbritt Complementary therapies in medicine 16.4 (2008): 228-232 Which factors determine micro-arthropods (like mites and springtails) abundance and diversity in the soil? Stef Bokhorst et al. addressed this question in a paper which was published in 2014. They analyzed the effect of plant removals in pine forest sectors in Sweden which differ in their age (time scince last forest fire) on the micro-arthropod community living in the soil. With increasing forest age, the soil fertility and amount of fast growing plant species decreases while the humus layer and amount of slow growing plant species increases. The forest sectors in this experiments were between 44 and 364 years old. In each sector, Bokhorst et al. did the same two experiments: I) removal of feather mosses and dwarf shrubs as the two main understory functional groups (understory = plant life on the ground of the forest) and II) removal of specific dwarf shrub species. While feather mosses are thought to have a large effect on the soil ecosystem because of its temperature and humidity regulation effects, dwarf shrubs (something between herb and bush) influence the soil with their litter production. However, as leaves are also produced by trees, it doesn’t wonder that the removal of moss had larger influence on the abundance of micro-arthropods as the removal of dwarf shrubs (in experiment I). All in all, the dwarf shrubs species had just minor effects on the micro-arthropods abundance and diversity, independent of their litter quality (experiment II). So mites and springtails care mainly about moss. But what about the age of the forest which affects the properties of the soil? Interestingly, only a few groups of micro-arthropods were affected by the forrest age. The others don’t care. And this is already the summary of this article: Plant removal, forest age? If you don’t touch the moss, the micro-arthropods don’t care so much what you are doing there on the surface. "Impact of understory mosses and dwarf shrubs on soil micro-arthropods in a boreal forest chronosequence."
Stef Bokhorst, et al. Plant and soil 379.1-2 (2014): 121-133. When you look at a leaf you may think about photosynthesis, seasons, plant diseases,…, but have you ever thought about what is living on and in the leaf? The term phyllosphere describes leaves as habitat for different microorganisms. Fungi, yeasts, bacteria and bacteriophages can be found in and on leaves. Their interplay with the plant can be beneficial or pathological, dependend on plant and bacterial genetics and physical aspects like the weather. Leaves as habitat are no difficult habitat if you compare the temperature maximum and minimum or radiation with other environments at which you find microorganisms (e.g. hot springs). The difficulties of this habitat are the (rapid) day-night changes of temperature, radiation, rain and wind, and the short existence of the habitat of several weeks in annual plants because of seasons. Nevertheless, many different bacteria can be found on leaves and the dominant species may change with plant age or with environmental conditions. One example of leaf-living bacteria is Pseudomonas syringae and it has a real paradoxial way of rewarding its own success. In 2000, Susan S. Hirano and Christen D. Upper published a review about P.syringae with the focus on its role in the leaf ecosystem. P.syringae is a known pathogen which creates lesions. Besides the lesions, P. syringae is known for its ability to nucleate supercooled water to form ice which damages the plant. The probabilty of both, the lesion formation and ice-nucleation, increases with increasing population size. That means that if the leaf offers good conditions for successful reproduction for P.syringae, it destroys its own habitat by lesion formation and ice-nucleation. That is paradoxial! Therefore, the paper claims that these overpopulations are just accidents. “The real function of P.syringae is to live on healthy leaves.” So maybe there is just a sensitive interplay between the host plant and the bacteria which normally restricts the population size. “Only when conditions become unusually favorable and population sizes of the bacteria become too large does the entire system crash, to the detriment of both host and bacteria.” The question is why this happens. Why the plant can't prohibit this process and creates a favorable habitat for its enemy. And why has P.syringae no feedback mechanism, which prevents the destruction of its own habitat? Maybe P.syringae just doesn’t care as it immigrates by the plant seeds and by the wind… Bacteria in the Leaf Ecosystem with Emphasis onPseudomonas syringae—a Pathogen, Ice Nucleus, and Epiphyte.
Susan S. Hirano, and Christen D. Upper Microbiology and molecular biology reviews 64.3 (2000): 624-653. Maori were the first settler of New Zealand. Richard C. Cambie and Lynnette R. Ferguson published a paper in 2003 in which they discuss if the rise of diabetes, cancer and vascular related diseases in Maori people lately may be related to change in the diet. Were there any protective chemical constituents in the food plants of the traditional Maori diet which are now missing? In the survey they listed the chemical components of food plants which were part of the traditional Maori diet. Indeed they found a lot of different chemical constituents with anti-inflammatory, anti-cancer, anti-coagulation, anti-ulcer, anti-hepatoxin and anti-viral activity and positive effects on capillary walls and eye sight. This medical properties of the traditional Maori diet may suppressed diseases like diabetes, cancer and vascular related diseases but more details about the changed diet would be needed for a more detailed discussion. However, the survey shows the medical potential of some native plants in New Zealand. Potential functional foods in the traditional Maori diet.
Richard C. Cambie and Lynnette R. Ferguson Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis 523, 109-117 (2003) PMID: 12628508 |
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
Kategorien
Alle
|