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.
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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. Life as a female moth is hard. Sitting alone in the dark, you are listening to the ultrasonic sounds of the night. Is this the attractive call of a male moth? If so, go ahead and make some love. But be careful. Bats are out there. You can hear their ultrasonic sounds which they use for echolocation. So you should be sure that the singing male moth is worth the risk. Is it the Romeo of your dreams or just a little wimp? The answer lies in the song, the environment temperature and your perception. The lesser wax moth (Achroia grisella) belongs to the group of insects which choose their partner mainly by their acoustic performance, like you know it from crickets and grasshoppers. A healthy male moth is supposed to produce louder songs with higher frequencies, compared to his old/weak rivals. However, there is the problem of the environmental temperature which can make the process of finding a partner a little bit more tricky. As cold blooded animals, the muscle performance of the male (and so its song quality) is enhanced with increasing temperatures. Therefore, in grasshoppers, not only the male song changes with increasing temperature but also the preferred song of the female is temperature dependent. This temperature coupling of “producer” and “receiver” ensures that the female is able to identify the males of the right species at different temperatures. (Here I would like to refer to the great work of my former colleague F.A. Römschied https://elifesciences.org/articles/02078 ). But is this temperature coupling, which can be found in many different acoustic species, really the result of the evolutionary need to find the right partner or is it just a lucky coincidence, that the female perception changes with temperature? This is the question of a paper from Greefield and Medlock in 2007. They point out that temperature coupling just makes sense when you (1) have a narrow range of “attractive songs” for females which selects against faster and slower rates and you (2) have other acoustic species around, which you have to distinguish. Therefore, in their paper, they focus on the lesser wax moth, which does not fulfill these criteria. Female moth prefer any songs above a certain frequency and their habitat is lacking any other acoustic species (besides the bats with low frequency sounds). Moreover, the female acceptance threshold for acceptance is much lower than the male song rates. Therefore, temperature effects on male song rates does not conflict with the moth concept of “the fastest and loudest song is the most attractive one”. Nevertheless, male song rate and female acceptance threshold do exhibit parallel increases with elevated temperature. But why, when there is no evolutionary benefit? Greefield and Medlock show that male and female thermal effects are genetically correlated. Of course that genetic coupling could be there, because evolution selected for parallel temperature effects in female and male. However, as evolutionary benefit of thermal coupling is hard to explain in this case, it could also be, that the thermal coupling is just a coincidence because the same genes can control different properties in different tissues like the song production with the wings in the male and the song perception in the female. So the main message of the paper is, that when there is thermal coupling between the sexes, you should not automatically assume that it is based on an evolutionary need to adapt sound and sound preference but it could also just be that sound production and sound perception are two temperature dependent processes which are controlled by the same genes. 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. “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). Isn’t it great to know that at least half of your genome is a winner? This part of you won the race of the sperm to the egg cell. Regarding the genetic/epigenetic variation among the sperm of your father, this part of you was the fastest and robustest your father could produce. The question is, if this race between the haploid sperms of the same man, results in a sort of selection which is important for the Darwinian fitness. In other words: Does Darwin’s “The survival of the fittest” describe not only the selection among the diploid organisms but also the selection among the haploid sperm? And does this selection between the gamete phenotypes of the same man have a fitness consequence for the created offspring? Ghazal Alavioon et al. say “yes”. They selected zebrafish sperm for their longevity, and indeed, the offspring of this longevity sperm had a better survival rate and the sons which were created by longevity sperm produced significantly faster-swimming sperm compared to the sons of short living sperm. Also the fitness of the fertilized egg cell seems enhanced with longevity sperm compared to short living sperm. This fitness effect was still valid in the second generation. "Haploid selection within a single ejaculate increases offspring fitness."
Ghazal Alavioon, et al. Proceedings of the National Academy of Sciences(2017): 201705601. The word “cephalopod” has its origin in Greek and means as much as “head foot”. Consequently, the class cephalopods includes octopuses, squid, cuttlefish and nautiluses, which are all characterized by their arms/tentacles (“feet”) which are directly connected to their head. Since at least the movie “Finding Dory”, we all know again why cephalopods are such fascinating animals. Their ability to change their colors and body shape, “ink” production, three hearts,… . Moreover they are found “in all oceans of the world, from the tropics to the poles, the intertidal to the abyss.” (http://www.thecephalopodpage.org) So, of course, they also exist in the nort-western Mediterranean and Roger Villanueva published a paper in 1992 in which he looked at the distribution of cephalpalopods in the bathybenthic zone (700-2000m) of the nort-western Mediterranean. He mainly found the octopus Bathypolypus sponsalis and the squid Neorossia caroli. In both species, young and small individuals could be found in a wider range of depths as old and large individuals. The large individuals are nearer to the surface while the small individuals can also be found in larger depths. So if you are afraid of meeting large cephalopods while diving, you have to dive deeper. "Deep-sea cephalopods of the north-western Mediterranean: Indications of up-slope ontogenetic migration in two bathybenthic species."
Roger Villanueva Journal of Zoology 227.2 (1992): 267-276. 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. Collagenous tissues which have different passive mechanical properties in response to different environmental and mechanical stimuli are called mutable collagenous tissues (MCTs). The rapid changes of their mechanical properties are nervously mediated. It is assumed that the tissue properties are regulated by certain molecules which secretion is controlled by nerve terminals connected to the secretory cells. The secretory cells associated with MCTs are called juxtaligamental cells. They are characterized “by the presence in their cytoplasm of numerous electron-dense, membrane-bound granules.” There is no known MCT that lacks these cells, whereas they are absent from the few definitely non-mutable collagenous structures examined. It has always been suggested that the tube feet of sea urchin and sea star are MCTs, but proof was missing until 2005. In 2005, Romana Santos et al. published a paper in which they showed that the tube feet tissue indeed (I) contains juxtaligamental cells and (II) shows differences in stiffness/elasticity in response to environmental stimuli. The mechanical properties of the tube feet from both species were influenced by the environmental calcium concentration. They both became more flexible in an low calcium environment. However, stiffness response to cell-disrupting treatments was more prominent in the sea urchin compared to the sea star. This may be based on their different function (and structure). The feet of the sea urchin are flexible. Their task is mainly “pulling” the sea urchin to the ground and even movement is based on a pulling process. Therefore, cell stress (e.g. because of waves pushing the sea urchin) induces the secretion of molecules which increase the stiffness of the feet which may be helpful for an energy-sparing maintenance of position. Sea stars have a different method of movement, compared to the sea urchin. Instead of pulling, their feet are like little columns which lift the body up. Therefore, they are already quite stiff and cell stress can not significantly increase this stiffness further. "The tube feet of sea urchins and sea stars contain functionally different mutable collagenous tissues."
Romana Santos, et al. Journal of experimental biology 208.12 (2005): 2277-2288. |
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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