Length and duration,… these are important parameters for sexual success. That refers not only to the sexual act itself but also to the sperm traits. Longer and faster spermatozoa with longer life-duration are expected to have an advantage in competitive interactions between ejaculates. However, there is little evidence for this sperm competition theory. The sperm competition theory claims that (I) increasing sperm competition leads to faster spermatozoa and (II) this increase of speed is related to an increase in sperm length. However, both, that sperm competition promotes evolution of faster-swimming sperm across species, and link between sperm morphology and swimming speed, is weakly supported by just a handful of studies and even neglected by other studies. For example: the only clear evidence for the length-speed correlation of sperm within a species comes from the roundworm C.elegans and its sperm has, unlike the sperm of the most animals, an amoeboid form (lacking a flagellum). In order to prove that theory, species are needed which relatedness are well studied and which show a high diversity of mating behaviour, like the cichlid fishes of the Lake Tanganyika. Therefore, John L. Fitzpatrick et al. (2009) tested the sperm competition theory in 29 closely related species of cichlid fishes from Lake Tanganyika. They proved both hypotheses of the sperm competition theory by slitting fish testes and comparing sperm traits across the species (inside a species proof of the hypotheses mainly failed). They showed that:
"Female promiscuity promotes the evolution of faster sperm in cichlid fishes".
John L. Fitzpatrick, et al. Proceedings of the National Academy of Sciences 106.4 (2009): 1128-1132.
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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. The neotropic ecozone covers a small tropical part of North America and complete South America. The birds there are called neotropical birds and the flavescent warbler ( Basileuterus flaveolus) is one of them. It inhabits forests and forest edges as well as woody savanna and desert vegetation and eats mainly beetles. In 2005, Charles Duca and Miguel Â. Marini published a paper about the territory size of the flavescent warbler in South Brazil. Previous studies suggest a correlation between territory size and habitat structure. The ‘ecological trap hypothesis’ predicts that on the one hand more insects are accessible for the birds at the forrest edge. On the other hand the nest predator rate is higher at the forest edges. However, the study of Duca and Marini does not support this hypothesis. Neither the insect biomass nor the nest predation vary significant between forest interior and forest edge. The territory size also does not depend on the distance to the forest border and vary little during the season. Nevertheless, the flavescent warbler seems to prefer living on the edge. “Males defending territories closer to the forest edge were more successful in pairing than those in the forest interior.” Territory size of the Flavescent Warbler, Basileuterus flaveolus (Passeriformes, Emberizidae),
in a forest fragment in Southeastern Brazil Charles Duca and Miguel Â. Marini Lundiana, Belo Horizonte 6.1 (2005): 29-33 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. According to the challenge hypothesis, the testosterone level correlates with the mating related aggression in seasonal breeders. In the breeding season, the testosterone level baseline is higher compared to the non-breeding season. The high baseline in breeding season is said to be necessary for successful reproductive behavior. While this seasonal change is due to environmental clues, social clues from conspecifics can additional increase the testosterone level in the begin of breeding season leading to more aggressive behavior in defending territory or finding mating partners. But how is that in non-aggressive species like the tufted capuchin monkey? Jessica W. Lynch, Toni E. Ziegler and Karen B. Strier published 2002 a study were they analyzed the seasonal changes in fecal testosterone levels of wild male tufted capuchin monkeys. As expected, all male individuals had their highest testosterone level in the period when the adult females were fertile. However, despite the high testosterone level, the aggression level in the group was low. Interestingly, the highest aggression level could be seen in the non-breeding season when the testosterone level was low in all individuals, but these aggressions were not mating related but related to food competition. Moreover, the testosterone level of the top-ranked male, who is favored as mating partner by the females, did not differ from the other males. However, the alpha male just achieved the position three month before the begin of the study. Therefore, it is not sure if on long timescale the alpha male will produce more testosterone as the others. Sure is that there are exceptions to the challenge hypothesis and a high testosterone level does not have to lead to higher aggression levels... at least in tufted capuchin monkeys. Individual and Seasonal Variation in Fecal Testosterone and Cortisol Levels of Wild Male Tufted Capuchin Monkeys, Cebus apella nigritus
Jessica W. Lynch, Toni E. Ziegler and Karen B.Strier Hormones and Behavior 41, 275–287 (2002) doi:10.1006/hbeh.2002.1772 |
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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